1 /*
2 * Copyright (c) 2001, 2014, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderData.hpp"
27 #include "classfile/stringTable.hpp"
28 #include "classfile/systemDictionary.hpp"
29 #include "code/codeCache.hpp"
30 #include "gc_implementation/shared/adaptiveSizePolicy.hpp"
31 #include "gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.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.inline.hpp"
52 #include "memory/padded.hpp"
53 #include "memory/referencePolicy.hpp"
54 #include "memory/resourceArea.hpp"
55 #include "memory/tenuredGeneration.hpp"
56 #include "oops/oop.inline.hpp"
57 #include "prims/jvmtiExport.hpp"
58 #include "runtime/atomic.inline.hpp"
59 #include "runtime/globals_extension.hpp"
60 #include "runtime/handles.inline.hpp"
61 #include "runtime/java.hpp"
62 #include "runtime/orderAccess.inline.hpp"
63 #include "runtime/vmThread.hpp"
64 #include "services/memoryService.hpp"
65 #include "services/runtimeService.hpp"
66
67 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
68
69 // statics
70 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
71 bool CMSCollector::_full_gc_requested = false;
72 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
73
74 //////////////////////////////////////////////////////////////////
75 // In support of CMS/VM thread synchronization
76 //////////////////////////////////////////////////////////////////
77 // We split use of the CGC_lock into 2 "levels".
78 // The low-level locking is of the usual CGC_lock monitor. We introduce
79 // a higher level "token" (hereafter "CMS token") built on top of the
80 // low level monitor (hereafter "CGC lock").
81 // The token-passing protocol gives priority to the VM thread. The
82 // CMS-lock doesn't provide any fairness guarantees, but clients
83 // should ensure that it is only held for very short, bounded
84 // durations.
85 //
86 // When either of the CMS thread or the VM thread is involved in
87 // collection operations during which it does not want the other
88 // thread to interfere, it obtains the CMS token.
89 //
90 // If either thread tries to get the token while the other has
91 // it, that thread waits. However, if the VM thread and CMS thread
92 // both want the token, then the VM thread gets priority while the
93 // CMS thread waits. This ensures, for instance, that the "concurrent"
94 // phases of the CMS thread's work do not block out the VM thread
95 // for long periods of time as the CMS thread continues to hog
96 // the token. (See bug 4616232).
97 //
98 // The baton-passing functions are, however, controlled by the
99 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
100 // and here the low-level CMS lock, not the high level token,
101 // ensures mutual exclusion.
102 //
103 // Two important conditions that we have to satisfy:
104 // 1. if a thread does a low-level wait on the CMS lock, then it
105 // relinquishes the CMS token if it were holding that token
106 // when it acquired the low-level CMS lock.
107 // 2. any low-level notifications on the low-level lock
108 // should only be sent when a thread has relinquished the token.
109 //
110 // In the absence of either property, we'd have potential deadlock.
111 //
112 // We protect each of the CMS (concurrent and sequential) phases
113 // with the CMS _token_, not the CMS _lock_.
114 //
115 // The only code protected by CMS lock is the token acquisition code
116 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
117 // baton-passing code.
118 //
119 // Unfortunately, i couldn't come up with a good abstraction to factor and
120 // hide the naked CGC_lock manipulation in the baton-passing code
121 // further below. That's something we should try to do. Also, the proof
122 // of correctness of this 2-level locking scheme is far from obvious,
123 // and potentially quite slippery. We have an uneasy suspicion, for instance,
124 // that there may be a theoretical possibility of delay/starvation in the
125 // low-level lock/wait/notify scheme used for the baton-passing because of
126 // potential interference with the priority scheme embodied in the
127 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
128 // invocation further below and marked with "XXX 20011219YSR".
129 // Indeed, as we note elsewhere, this may become yet more slippery
130 // in the presence of multiple CMS and/or multiple VM threads. XXX
131
132 class CMSTokenSync: public StackObj {
133 private:
134 bool _is_cms_thread;
135 public:
136 CMSTokenSync(bool is_cms_thread):
137 _is_cms_thread(is_cms_thread) {
138 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
139 "Incorrect argument to constructor");
140 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
141 }
142
143 ~CMSTokenSync() {
144 assert(_is_cms_thread ?
145 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
146 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
147 "Incorrect state");
148 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
149 }
150 };
151
152 // Convenience class that does a CMSTokenSync, and then acquires
153 // upto three locks.
154 class CMSTokenSyncWithLocks: public CMSTokenSync {
155 private:
156 // Note: locks are acquired in textual declaration order
157 // and released in the opposite order
158 MutexLockerEx _locker1, _locker2, _locker3;
159 public:
160 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
161 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
162 CMSTokenSync(is_cms_thread),
163 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
164 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
165 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
166 { }
167 };
168
169
170 // Wrapper class to temporarily disable icms during a foreground cms collection.
171 class ICMSDisabler: public StackObj {
172 public:
173 // The ctor disables icms and wakes up the thread so it notices the change;
174 // the dtor re-enables icms. Note that the CMSCollector methods will check
175 // CMSIncrementalMode.
176 ICMSDisabler() { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
177 ~ICMSDisabler() { CMSCollector::enable_icms(); }
178 };
179
180 //////////////////////////////////////////////////////////////////
181 // Concurrent Mark-Sweep Generation /////////////////////////////
182 //////////////////////////////////////////////////////////////////
183
184 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
185
186 // This struct contains per-thread things necessary to support parallel
187 // young-gen collection.
188 class CMSParGCThreadState: public CHeapObj<mtGC> {
189 public:
190 CFLS_LAB lab;
191 PromotionInfo promo;
192
193 // Constructor.
194 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
195 promo.setSpace(cfls);
196 }
197 };
198
199 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
200 ReservedSpace rs, size_t initial_byte_size, int level,
201 CardTableRS* ct, bool use_adaptive_freelists,
202 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
203 CardGeneration(rs, initial_byte_size, level, ct),
204 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
205 _debug_collection_type(Concurrent_collection_type),
206 _did_compact(false)
207 {
208 HeapWord* bottom = (HeapWord*) _virtual_space.low();
209 HeapWord* end = (HeapWord*) _virtual_space.high();
210
211 _direct_allocated_words = 0;
212 NOT_PRODUCT(
213 _numObjectsPromoted = 0;
214 _numWordsPromoted = 0;
215 _numObjectsAllocated = 0;
216 _numWordsAllocated = 0;
217 )
218
219 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
220 use_adaptive_freelists,
221 dictionaryChoice);
222 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
223 if (_cmsSpace == NULL) {
224 vm_exit_during_initialization(
225 "CompactibleFreeListSpace allocation failure");
226 }
227 _cmsSpace->_gen = this;
228
229 _gc_stats = new CMSGCStats();
230
231 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
232 // offsets match. The ability to tell free chunks from objects
233 // depends on this property.
234 debug_only(
235 FreeChunk* junk = NULL;
236 assert(UseCompressedClassPointers ||
237 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
238 "Offset of FreeChunk::_prev within FreeChunk must match"
239 " that of OopDesc::_klass within OopDesc");
240 )
241 if (CollectedHeap::use_parallel_gc_threads()) {
242 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
243 _par_gc_thread_states =
244 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
245 if (_par_gc_thread_states == NULL) {
246 vm_exit_during_initialization("Could not allocate par gc structs");
247 }
248 for (uint i = 0; i < ParallelGCThreads; i++) {
249 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
250 if (_par_gc_thread_states[i] == NULL) {
251 vm_exit_during_initialization("Could not allocate par gc structs");
252 }
253 }
254 } else {
255 _par_gc_thread_states = NULL;
256 }
257 _incremental_collection_failed = false;
258 // The "dilatation_factor" is the expansion that can occur on
259 // account of the fact that the minimum object size in the CMS
260 // generation may be larger than that in, say, a contiguous young
261 // generation.
262 // Ideally, in the calculation below, we'd compute the dilatation
263 // factor as: MinChunkSize/(promoting_gen's min object size)
264 // Since we do not have such a general query interface for the
265 // promoting generation, we'll instead just use the minimum
266 // object size (which today is a header's worth of space);
267 // note that all arithmetic is in units of HeapWords.
268 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
269 assert(_dilatation_factor >= 1.0, "from previous assert");
270 }
271
272
273 // The field "_initiating_occupancy" represents the occupancy percentage
274 // at which we trigger a new collection cycle. Unless explicitly specified
275 // via CMSInitiatingOccupancyFraction (argument "io" below), it
276 // is calculated by:
277 //
278 // Let "f" be MinHeapFreeRatio in
279 //
280 // _initiating_occupancy = 100-f +
281 // f * (CMSTriggerRatio/100)
282 // where CMSTriggerRatio is the argument "tr" below.
283 //
284 // That is, if we assume the heap is at its desired maximum occupancy at the
285 // end of a collection, we let CMSTriggerRatio of the (purported) free
286 // space be allocated before initiating a new collection cycle.
287 //
288 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
289 assert(io <= 100 && tr <= 100, "Check the arguments");
290 if (io >= 0) {
291 _initiating_occupancy = (double)io / 100.0;
292 } else {
293 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
294 (double)(tr * MinHeapFreeRatio) / 100.0)
295 / 100.0;
296 }
297 }
298
299 void ConcurrentMarkSweepGeneration::ref_processor_init() {
300 assert(collector() != NULL, "no collector");
301 collector()->ref_processor_init();
302 }
303
304 void CMSCollector::ref_processor_init() {
305 if (_ref_processor == NULL) {
306 // Allocate and initialize a reference processor
307 _ref_processor =
308 new ReferenceProcessor(_span, // span
309 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
310 (int) ParallelGCThreads, // mt processing degree
311 _cmsGen->refs_discovery_is_mt(), // mt discovery
312 (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
313 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
314 &_is_alive_closure); // closure for liveness info
315 // Initialize the _ref_processor field of CMSGen
316 _cmsGen->set_ref_processor(_ref_processor);
317
318 }
319 }
320
321 AdaptiveSizePolicy* CMSCollector::size_policy() {
322 GenCollectedHeap* gch = GenCollectedHeap::heap();
323 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
324 "Wrong type of heap");
325 return gch->gen_policy()->size_policy();
326 }
327
328 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
329
330 const char* gen_name = "old";
331 GenCollectorPolicy* gcp = (GenCollectorPolicy*) GenCollectedHeap::heap()->collector_policy();
332
333 // Generation Counters - generation 1, 1 subspace
334 _gen_counters = new GenerationCounters(gen_name, 1, 1,
335 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
336
337 _space_counters = new GSpaceCounters(gen_name, 0,
338 _virtual_space.reserved_size(),
339 this, _gen_counters);
340 }
341
342 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
343 _cms_gen(cms_gen)
344 {
345 assert(alpha <= 100, "bad value");
346 _saved_alpha = alpha;
347
348 // Initialize the alphas to the bootstrap value of 100.
349 _gc0_alpha = _cms_alpha = 100;
350
351 _cms_begin_time.update();
352 _cms_end_time.update();
353
354 _gc0_duration = 0.0;
355 _gc0_period = 0.0;
356 _gc0_promoted = 0;
357
358 _cms_duration = 0.0;
359 _cms_period = 0.0;
360 _cms_allocated = 0;
361
362 _cms_used_at_gc0_begin = 0;
363 _cms_used_at_gc0_end = 0;
364 _allow_duty_cycle_reduction = false;
365 _valid_bits = 0;
366 _icms_duty_cycle = CMSIncrementalDutyCycle;
367 }
368
369 double CMSStats::cms_free_adjustment_factor(size_t free) const {
370 // TBD: CR 6909490
371 return 1.0;
372 }
373
374 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
375 }
376
377 // If promotion failure handling is on use
378 // the padded average size of the promotion for each
379 // young generation collection.
380 double CMSStats::time_until_cms_gen_full() const {
381 size_t cms_free = _cms_gen->cmsSpace()->free();
382 GenCollectedHeap* gch = GenCollectedHeap::heap();
383 size_t expected_promotion = MIN2(gch->get_gen(0)->capacity(),
384 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
385 if (cms_free > expected_promotion) {
386 // Start a cms collection if there isn't enough space to promote
387 // for the next minor collection. Use the padded average as
388 // a safety factor.
389 cms_free -= expected_promotion;
390
391 // Adjust by the safety factor.
392 double cms_free_dbl = (double)cms_free;
393 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
394 // Apply a further correction factor which tries to adjust
395 // for recent occurance of concurrent mode failures.
396 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
397 cms_free_dbl = cms_free_dbl * cms_adjustment;
398
399 if (PrintGCDetails && Verbose) {
400 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
401 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
402 cms_free, expected_promotion);
403 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
404 cms_free_dbl, cms_consumption_rate() + 1.0);
405 }
406 // Add 1 in case the consumption rate goes to zero.
407 return cms_free_dbl / (cms_consumption_rate() + 1.0);
408 }
409 return 0.0;
410 }
411
412 // Compare the duration of the cms collection to the
413 // time remaining before the cms generation is empty.
414 // Note that the time from the start of the cms collection
415 // to the start of the cms sweep (less than the total
416 // duration of the cms collection) can be used. This
417 // has been tried and some applications experienced
418 // promotion failures early in execution. This was
419 // possibly because the averages were not accurate
420 // enough at the beginning.
421 double CMSStats::time_until_cms_start() const {
422 // We add "gc0_period" to the "work" calculation
423 // below because this query is done (mostly) at the
424 // end of a scavenge, so we need to conservatively
425 // account for that much possible delay
426 // in the query so as to avoid concurrent mode failures
427 // due to starting the collection just a wee bit too
428 // late.
429 double work = cms_duration() + gc0_period();
430 double deadline = time_until_cms_gen_full();
431 // If a concurrent mode failure occurred recently, we want to be
432 // more conservative and halve our expected time_until_cms_gen_full()
433 if (work > deadline) {
434 if (Verbose && PrintGCDetails) {
435 gclog_or_tty->print(
436 " CMSCollector: collect because of anticipated promotion "
437 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
438 gc0_period(), time_until_cms_gen_full());
439 }
440 return 0.0;
441 }
442 return work - deadline;
443 }
444
445 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
446 // amount of change to prevent wild oscillation.
447 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
448 unsigned int new_duty_cycle) {
449 assert(old_duty_cycle <= 100, "bad input value");
450 assert(new_duty_cycle <= 100, "bad input value");
451
452 // Note: use subtraction with caution since it may underflow (values are
453 // unsigned). Addition is safe since we're in the range 0-100.
454 unsigned int damped_duty_cycle = new_duty_cycle;
455 if (new_duty_cycle < old_duty_cycle) {
456 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
457 if (new_duty_cycle + largest_delta < old_duty_cycle) {
458 damped_duty_cycle = old_duty_cycle - largest_delta;
459 }
460 } else if (new_duty_cycle > old_duty_cycle) {
461 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
462 if (new_duty_cycle > old_duty_cycle + largest_delta) {
463 damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
464 }
465 }
466 assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
467
468 if (CMSTraceIncrementalPacing) {
469 gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
470 old_duty_cycle, new_duty_cycle, damped_duty_cycle);
471 }
472 return damped_duty_cycle;
473 }
474
475 unsigned int CMSStats::icms_update_duty_cycle_impl() {
476 assert(CMSIncrementalPacing && valid(),
477 "should be handled in icms_update_duty_cycle()");
478
479 double cms_time_so_far = cms_timer().seconds();
480 double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
481 double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
482
483 // Avoid division by 0.
484 double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
485 double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
486
487 unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
488 if (new_duty_cycle > _icms_duty_cycle) {
489 // Avoid very small duty cycles (1 or 2); 0 is allowed.
490 if (new_duty_cycle > 2) {
491 _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
492 new_duty_cycle);
493 }
494 } else if (_allow_duty_cycle_reduction) {
495 // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
496 new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
497 // Respect the minimum duty cycle.
498 unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
499 _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
500 }
501
502 if (PrintGCDetails || CMSTraceIncrementalPacing) {
503 gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
504 }
505
506 _allow_duty_cycle_reduction = false;
507 return _icms_duty_cycle;
508 }
509
510 #ifndef PRODUCT
511 void CMSStats::print_on(outputStream *st) const {
512 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
513 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
514 gc0_duration(), gc0_period(), gc0_promoted());
515 st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
516 cms_duration(), cms_duration_per_mb(),
517 cms_period(), cms_allocated());
518 st->print(",cms_since_beg=%g,cms_since_end=%g",
519 cms_time_since_begin(), cms_time_since_end());
520 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
521 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
522 if (CMSIncrementalMode) {
523 st->print(",dc=%d", icms_duty_cycle());
524 }
525
526 if (valid()) {
527 st->print(",promo_rate=%g,cms_alloc_rate=%g",
528 promotion_rate(), cms_allocation_rate());
529 st->print(",cms_consumption_rate=%g,time_until_full=%g",
530 cms_consumption_rate(), time_until_cms_gen_full());
531 }
532 st->print(" ");
533 }
534 #endif // #ifndef PRODUCT
535
536 CMSCollector::CollectorState CMSCollector::_collectorState =
537 CMSCollector::Idling;
538 bool CMSCollector::_foregroundGCIsActive = false;
539 bool CMSCollector::_foregroundGCShouldWait = false;
540
541 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
542 CardTableRS* ct,
543 ConcurrentMarkSweepPolicy* cp):
544 _cmsGen(cmsGen),
545 _ct(ct),
546 _ref_processor(NULL), // will be set later
547 _conc_workers(NULL), // may be set later
548 _abort_preclean(false),
549 _start_sampling(false),
550 _between_prologue_and_epilogue(false),
551 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
552 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
553 -1 /* lock-free */, "No_lock" /* dummy */),
554 _modUnionClosure(&_modUnionTable),
555 _modUnionClosurePar(&_modUnionTable),
556 // Adjust my span to cover old (cms) gen
557 _span(cmsGen->reserved()),
558 // Construct the is_alive_closure with _span & markBitMap
559 _is_alive_closure(_span, &_markBitMap),
560 _restart_addr(NULL),
561 _overflow_list(NULL),
562 _stats(cmsGen),
563 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true)),
564 _eden_chunk_array(NULL), // may be set in ctor body
565 _eden_chunk_capacity(0), // -- ditto --
566 _eden_chunk_index(0), // -- ditto --
567 _survivor_plab_array(NULL), // -- ditto --
568 _survivor_chunk_array(NULL), // -- ditto --
569 _survivor_chunk_capacity(0), // -- ditto --
570 _survivor_chunk_index(0), // -- ditto --
571 _ser_pmc_preclean_ovflw(0),
572 _ser_kac_preclean_ovflw(0),
573 _ser_pmc_remark_ovflw(0),
574 _par_pmc_remark_ovflw(0),
575 _ser_kac_ovflw(0),
576 _par_kac_ovflw(0),
577 #ifndef PRODUCT
578 _num_par_pushes(0),
579 #endif
580 _collection_count_start(0),
581 _verifying(false),
582 _icms_start_limit(NULL),
583 _icms_stop_limit(NULL),
584 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
585 _completed_initialization(false),
586 _collector_policy(cp),
587 _should_unload_classes(CMSClassUnloadingEnabled),
588 _concurrent_cycles_since_last_unload(0),
589 _roots_scanning_options(SharedHeap::SO_None),
590 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
591 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
592 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
593 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
594 _cms_start_registered(false)
595 {
596 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
597 ExplicitGCInvokesConcurrent = true;
598 }
599 // Now expand the span and allocate the collection support structures
600 // (MUT, marking bit map etc.) to cover both generations subject to
601 // collection.
602
603 // For use by dirty card to oop closures.
604 _cmsGen->cmsSpace()->set_collector(this);
605
606 // Allocate MUT and marking bit map
607 {
608 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
609 if (!_markBitMap.allocate(_span)) {
610 warning("Failed to allocate CMS Bit Map");
611 return;
612 }
613 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
614 }
615 {
616 _modUnionTable.allocate(_span);
617 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
618 }
619
620 if (!_markStack.allocate(MarkStackSize)) {
621 warning("Failed to allocate CMS Marking Stack");
622 return;
623 }
624
625 // Support for multi-threaded concurrent phases
626 if (CMSConcurrentMTEnabled) {
627 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
628 // just for now
629 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
630 }
631 if (ConcGCThreads > 1) {
632 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
633 ConcGCThreads, true);
634 if (_conc_workers == NULL) {
635 warning("GC/CMS: _conc_workers allocation failure: "
636 "forcing -CMSConcurrentMTEnabled");
637 CMSConcurrentMTEnabled = false;
638 } else {
639 _conc_workers->initialize_workers();
640 }
641 } else {
642 CMSConcurrentMTEnabled = false;
643 }
644 }
645 if (!CMSConcurrentMTEnabled) {
646 ConcGCThreads = 0;
647 } else {
648 // Turn off CMSCleanOnEnter optimization temporarily for
649 // the MT case where it's not fixed yet; see 6178663.
650 CMSCleanOnEnter = false;
651 }
652 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
653 "Inconsistency");
654
655 // Parallel task queues; these are shared for the
656 // concurrent and stop-world phases of CMS, but
657 // are not shared with parallel scavenge (ParNew).
658 {
659 uint i;
660 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
661
662 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
663 || ParallelRefProcEnabled)
664 && num_queues > 0) {
665 _task_queues = new OopTaskQueueSet(num_queues);
666 if (_task_queues == NULL) {
667 warning("task_queues allocation failure.");
668 return;
669 }
670 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
671 if (_hash_seed == NULL) {
672 warning("_hash_seed array allocation failure");
673 return;
674 }
675
676 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
677 for (i = 0; i < num_queues; i++) {
678 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
679 if (q == NULL) {
680 warning("work_queue allocation failure.");
681 return;
682 }
683 _task_queues->register_queue(i, q);
684 }
685 for (i = 0; i < num_queues; i++) {
686 _task_queues->queue(i)->initialize();
687 _hash_seed[i] = 17; // copied from ParNew
688 }
689 }
690 }
691
692 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
693
694 // Clip CMSBootstrapOccupancy between 0 and 100.
695 _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100;
696
697 _full_gcs_since_conc_gc = 0;
698
699 // Now tell CMS generations the identity of their collector
700 ConcurrentMarkSweepGeneration::set_collector(this);
701
702 // Create & start a CMS thread for this CMS collector
703 _cmsThread = ConcurrentMarkSweepThread::start(this);
704 assert(cmsThread() != NULL, "CMS Thread should have been created");
705 assert(cmsThread()->collector() == this,
706 "CMS Thread should refer to this gen");
707 assert(CGC_lock != NULL, "Where's the CGC_lock?");
708
709 // Support for parallelizing young gen rescan
710 GenCollectedHeap* gch = GenCollectedHeap::heap();
711 _young_gen = gch->prev_gen(_cmsGen);
712 if (gch->supports_inline_contig_alloc()) {
713 _top_addr = gch->top_addr();
714 _end_addr = gch->end_addr();
715 assert(_young_gen != NULL, "no _young_gen");
716 _eden_chunk_index = 0;
717 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
718 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
719 if (_eden_chunk_array == NULL) {
720 _eden_chunk_capacity = 0;
721 warning("GC/CMS: _eden_chunk_array allocation failure");
722 }
723 }
724 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
725
726 // Support for parallelizing survivor space rescan
727 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
728 const size_t max_plab_samples =
729 ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
730
731 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
732 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
733 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
734 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
735 || _cursor == NULL) {
736 warning("Failed to allocate survivor plab/chunk array");
737 if (_survivor_plab_array != NULL) {
738 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
739 _survivor_plab_array = NULL;
740 }
741 if (_survivor_chunk_array != NULL) {
742 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
743 _survivor_chunk_array = NULL;
744 }
745 if (_cursor != NULL) {
746 FREE_C_HEAP_ARRAY(size_t, _cursor, mtGC);
747 _cursor = NULL;
748 }
749 } else {
750 _survivor_chunk_capacity = 2*max_plab_samples;
751 for (uint i = 0; i < ParallelGCThreads; i++) {
752 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
753 if (vec == NULL) {
754 warning("Failed to allocate survivor plab array");
755 for (int j = i; j > 0; j--) {
756 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array(), mtGC);
757 }
758 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
759 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
760 _survivor_plab_array = NULL;
761 _survivor_chunk_array = NULL;
762 _survivor_chunk_capacity = 0;
763 break;
764 } else {
765 ChunkArray* cur =
766 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
767 max_plab_samples);
768 assert(cur->end() == 0, "Should be 0");
769 assert(cur->array() == vec, "Should be vec");
770 assert(cur->capacity() == max_plab_samples, "Error");
771 }
772 }
773 }
774 }
775 assert( ( _survivor_plab_array != NULL
776 && _survivor_chunk_array != NULL)
777 || ( _survivor_chunk_capacity == 0
778 && _survivor_chunk_index == 0),
779 "Error");
780
781 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
782 _gc_counters = new CollectorCounters("CMS", 1);
783 _completed_initialization = true;
784 _inter_sweep_timer.start(); // start of time
785 }
786
787 const char* ConcurrentMarkSweepGeneration::name() const {
788 return "concurrent mark-sweep generation";
789 }
790 void ConcurrentMarkSweepGeneration::update_counters() {
791 if (UsePerfData) {
792 _space_counters->update_all();
793 _gen_counters->update_all();
794 }
795 }
796
797 // this is an optimized version of update_counters(). it takes the
798 // used value as a parameter rather than computing it.
799 //
800 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
801 if (UsePerfData) {
802 _space_counters->update_used(used);
803 _space_counters->update_capacity();
804 _gen_counters->update_all();
805 }
806 }
807
808 void ConcurrentMarkSweepGeneration::print() const {
809 Generation::print();
810 cmsSpace()->print();
811 }
812
813 #ifndef PRODUCT
814 void ConcurrentMarkSweepGeneration::print_statistics() {
815 cmsSpace()->printFLCensus(0);
816 }
817 #endif
818
819 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
820 GenCollectedHeap* gch = GenCollectedHeap::heap();
821 if (PrintGCDetails) {
822 if (Verbose) {
823 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
824 level(), short_name(), s, used(), capacity());
825 } else {
826 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
827 level(), short_name(), s, used() / K, capacity() / K);
828 }
829 }
830 if (Verbose) {
831 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
832 gch->used(), gch->capacity());
833 } else {
834 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
835 gch->used() / K, gch->capacity() / K);
836 }
837 }
838
839 size_t
840 ConcurrentMarkSweepGeneration::contiguous_available() const {
841 // dld proposes an improvement in precision here. If the committed
842 // part of the space ends in a free block we should add that to
843 // uncommitted size in the calculation below. Will make this
844 // change later, staying with the approximation below for the
845 // time being. -- ysr.
846 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
847 }
848
849 size_t
850 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
851 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
852 }
853
854 size_t ConcurrentMarkSweepGeneration::max_available() const {
855 return free() + _virtual_space.uncommitted_size();
856 }
857
858 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
859 size_t available = max_available();
860 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
861 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
862 if (Verbose && PrintGCDetails) {
863 gclog_or_tty->print_cr(
864 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
865 "max_promo("SIZE_FORMAT")",
866 res? "":" not", available, res? ">=":"<",
867 av_promo, max_promotion_in_bytes);
868 }
869 return res;
870 }
871
872 // At a promotion failure dump information on block layout in heap
873 // (cms old generation).
874 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
875 if (CMSDumpAtPromotionFailure) {
876 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
877 }
878 }
879
880 CompactibleSpace*
881 ConcurrentMarkSweepGeneration::first_compaction_space() const {
882 return _cmsSpace;
883 }
884
885 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
886 // Clear the promotion information. These pointers can be adjusted
887 // along with all the other pointers into the heap but
888 // compaction is expected to be a rare event with
889 // a heap using cms so don't do it without seeing the need.
890 for (uint i = 0; i < ParallelGCThreads; i++) {
891 _par_gc_thread_states[i]->promo.reset();
892 }
893 }
894
895 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
896 blk->do_space(_cmsSpace);
897 }
898
899 void ConcurrentMarkSweepGeneration::compute_new_size() {
900 assert_locked_or_safepoint(Heap_lock);
901
902 // If incremental collection failed, we just want to expand
903 // to the limit.
904 if (incremental_collection_failed()) {
905 clear_incremental_collection_failed();
906 grow_to_reserved();
907 return;
908 }
909
910 // The heap has been compacted but not reset yet.
911 // Any metric such as free() or used() will be incorrect.
912
913 CardGeneration::compute_new_size();
914
915 // Reset again after a possible resizing
916 if (did_compact()) {
917 cmsSpace()->reset_after_compaction();
918 }
919 }
920
921 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
922 assert_locked_or_safepoint(Heap_lock);
923
924 // If incremental collection failed, we just want to expand
925 // to the limit.
926 if (incremental_collection_failed()) {
927 clear_incremental_collection_failed();
928 grow_to_reserved();
929 return;
930 }
931
932 double free_percentage = ((double) free()) / capacity();
933 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
934 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
935
936 // compute expansion delta needed for reaching desired free percentage
937 if (free_percentage < desired_free_percentage) {
938 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
939 assert(desired_capacity >= capacity(), "invalid expansion size");
940 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
941 if (PrintGCDetails && Verbose) {
942 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
943 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
944 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
945 gclog_or_tty->print_cr(" Desired free fraction %f",
946 desired_free_percentage);
947 gclog_or_tty->print_cr(" Maximum free fraction %f",
948 maximum_free_percentage);
949 gclog_or_tty->print_cr(" Capacity "SIZE_FORMAT, capacity()/1000);
950 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
951 desired_capacity/1000);
952 int prev_level = level() - 1;
953 if (prev_level >= 0) {
954 size_t prev_size = 0;
955 GenCollectedHeap* gch = GenCollectedHeap::heap();
956 Generation* prev_gen = gch->_gens[prev_level];
957 prev_size = prev_gen->capacity();
958 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
959 prev_size/1000);
960 }
961 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
962 unsafe_max_alloc_nogc()/1000);
963 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
964 contiguous_available()/1000);
965 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
966 expand_bytes);
967 }
968 // safe if expansion fails
969 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
970 if (PrintGCDetails && Verbose) {
971 gclog_or_tty->print_cr(" Expanded free fraction %f",
972 ((double) free()) / capacity());
973 }
974 } else {
975 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
976 assert(desired_capacity <= capacity(), "invalid expansion size");
977 size_t shrink_bytes = capacity() - desired_capacity;
978 // Don't shrink unless the delta is greater than the minimum shrink we want
979 if (shrink_bytes >= MinHeapDeltaBytes) {
980 shrink_free_list_by(shrink_bytes);
981 }
982 }
983 }
984
985 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
986 return cmsSpace()->freelistLock();
987 }
988
989 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
990 bool tlab) {
991 CMSSynchronousYieldRequest yr;
992 MutexLockerEx x(freelistLock(),
993 Mutex::_no_safepoint_check_flag);
994 return have_lock_and_allocate(size, tlab);
995 }
996
997 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
998 bool tlab /* ignored */) {
999 assert_lock_strong(freelistLock());
1000 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
1001 HeapWord* res = cmsSpace()->allocate(adjustedSize);
1002 // Allocate the object live (grey) if the background collector has
1003 // started marking. This is necessary because the marker may
1004 // have passed this address and consequently this object will
1005 // not otherwise be greyed and would be incorrectly swept up.
1006 // Note that if this object contains references, the writing
1007 // of those references will dirty the card containing this object
1008 // allowing the object to be blackened (and its references scanned)
1009 // either during a preclean phase or at the final checkpoint.
1010 if (res != NULL) {
1011 // We may block here with an uninitialized object with
1012 // its mark-bit or P-bits not yet set. Such objects need
1013 // to be safely navigable by block_start().
1014 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
1015 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
1016 collector()->direct_allocated(res, adjustedSize);
1017 _direct_allocated_words += adjustedSize;
1018 // allocation counters
1019 NOT_PRODUCT(
1020 _numObjectsAllocated++;
1021 _numWordsAllocated += (int)adjustedSize;
1022 )
1023 }
1024 return res;
1025 }
1026
1027 // In the case of direct allocation by mutators in a generation that
1028 // is being concurrently collected, the object must be allocated
1029 // live (grey) if the background collector has started marking.
1030 // This is necessary because the marker may
1031 // have passed this address and consequently this object will
1032 // not otherwise be greyed and would be incorrectly swept up.
1033 // Note that if this object contains references, the writing
1034 // of those references will dirty the card containing this object
1035 // allowing the object to be blackened (and its references scanned)
1036 // either during a preclean phase or at the final checkpoint.
1037 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1038 assert(_markBitMap.covers(start, size), "Out of bounds");
1039 if (_collectorState >= Marking) {
1040 MutexLockerEx y(_markBitMap.lock(),
1041 Mutex::_no_safepoint_check_flag);
1042 // [see comments preceding SweepClosure::do_blk() below for details]
1043 //
1044 // Can the P-bits be deleted now? JJJ
1045 //
1046 // 1. need to mark the object as live so it isn't collected
1047 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1048 // 3. need to mark the end of the object so marking, precleaning or sweeping
1049 // can skip over uninitialized or unparsable objects. An allocated
1050 // object is considered uninitialized for our purposes as long as
1051 // its klass word is NULL. All old gen objects are parsable
1052 // as soon as they are initialized.)
1053 _markBitMap.mark(start); // object is live
1054 _markBitMap.mark(start + 1); // object is potentially uninitialized?
1055 _markBitMap.mark(start + size - 1);
1056 // mark end of object
1057 }
1058 // check that oop looks uninitialized
1059 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
1060 }
1061
1062 void CMSCollector::promoted(bool par, HeapWord* start,
1063 bool is_obj_array, size_t obj_size) {
1064 assert(_markBitMap.covers(start), "Out of bounds");
1065 // See comment in direct_allocated() about when objects should
1066 // be allocated live.
1067 if (_collectorState >= Marking) {
1068 // we already hold the marking bit map lock, taken in
1069 // the prologue
1070 if (par) {
1071 _markBitMap.par_mark(start);
1072 } else {
1073 _markBitMap.mark(start);
1074 }
1075 // We don't need to mark the object as uninitialized (as
1076 // in direct_allocated above) because this is being done with the
1077 // world stopped and the object will be initialized by the
1078 // time the marking, precleaning or sweeping get to look at it.
1079 // But see the code for copying objects into the CMS generation,
1080 // where we need to ensure that concurrent readers of the
1081 // block offset table are able to safely navigate a block that
1082 // is in flux from being free to being allocated (and in
1083 // transition while being copied into) and subsequently
1084 // becoming a bona-fide object when the copy/promotion is complete.
1085 assert(SafepointSynchronize::is_at_safepoint(),
1086 "expect promotion only at safepoints");
1087
1088 if (_collectorState < Sweeping) {
1089 // Mark the appropriate cards in the modUnionTable, so that
1090 // this object gets scanned before the sweep. If this is
1091 // not done, CMS generation references in the object might
1092 // not get marked.
1093 // For the case of arrays, which are otherwise precisely
1094 // marked, we need to dirty the entire array, not just its head.
1095 if (is_obj_array) {
1096 // The [par_]mark_range() method expects mr.end() below to
1097 // be aligned to the granularity of a bit's representation
1098 // in the heap. In the case of the MUT below, that's a
1099 // card size.
1100 MemRegion mr(start,
1101 (HeapWord*)round_to((intptr_t)(start + obj_size),
1102 CardTableModRefBS::card_size /* bytes */));
1103 if (par) {
1104 _modUnionTable.par_mark_range(mr);
1105 } else {
1106 _modUnionTable.mark_range(mr);
1107 }
1108 } else { // not an obj array; we can just mark the head
1109 if (par) {
1110 _modUnionTable.par_mark(start);
1111 } else {
1112 _modUnionTable.mark(start);
1113 }
1114 }
1115 }
1116 }
1117 }
1118
1119 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1120 {
1121 size_t delta = pointer_delta(addr, space->bottom());
1122 return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1123 }
1124
1125 void CMSCollector::icms_update_allocation_limits()
1126 {
1127 Generation* young = GenCollectedHeap::heap()->get_gen(0);
1128 EdenSpace* eden = young->as_DefNewGeneration()->eden();
1129
1130 const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1131 if (CMSTraceIncrementalPacing) {
1132 stats().print();
1133 }
1134
1135 assert(duty_cycle <= 100, "invalid duty cycle");
1136 if (duty_cycle != 0) {
1137 // The duty_cycle is a percentage between 0 and 100; convert to words and
1138 // then compute the offset from the endpoints of the space.
1139 size_t free_words = eden->free() / HeapWordSize;
1140 double free_words_dbl = (double)free_words;
1141 size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1142 size_t offset_words = (free_words - duty_cycle_words) / 2;
1143
1144 _icms_start_limit = eden->top() + offset_words;
1145 _icms_stop_limit = eden->end() - offset_words;
1146
1147 // The limits may be adjusted (shifted to the right) by
1148 // CMSIncrementalOffset, to allow the application more mutator time after a
1149 // young gen gc (when all mutators were stopped) and before CMS starts and
1150 // takes away one or more cpus.
1151 if (CMSIncrementalOffset != 0) {
1152 double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1153 size_t adjustment = (size_t)adjustment_dbl;
1154 HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1155 if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1156 _icms_start_limit += adjustment;
1157 _icms_stop_limit = tmp_stop;
1158 }
1159 }
1160 }
1161 if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1162 _icms_start_limit = _icms_stop_limit = eden->end();
1163 }
1164
1165 // Install the new start limit.
1166 eden->set_soft_end(_icms_start_limit);
1167
1168 if (CMSTraceIncrementalMode) {
1169 gclog_or_tty->print(" icms alloc limits: "
1170 PTR_FORMAT "," PTR_FORMAT
1171 " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1172 p2i(_icms_start_limit), p2i(_icms_stop_limit),
1173 percent_of_space(eden, _icms_start_limit),
1174 percent_of_space(eden, _icms_stop_limit));
1175 if (Verbose) {
1176 gclog_or_tty->print("eden: ");
1177 eden->print_on(gclog_or_tty);
1178 }
1179 }
1180 }
1181
1182 // Any changes here should try to maintain the invariant
1183 // that if this method is called with _icms_start_limit
1184 // and _icms_stop_limit both NULL, then it should return NULL
1185 // and not notify the icms thread.
1186 HeapWord*
1187 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1188 size_t word_size)
1189 {
1190 // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1191 // nop.
1192 if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1193 if (top <= _icms_start_limit) {
1194 if (CMSTraceIncrementalMode) {
1195 space->print_on(gclog_or_tty);
1196 gclog_or_tty->stamp();
1197 gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1198 ", new limit=" PTR_FORMAT
1199 " (" SIZE_FORMAT "%%)",
1200 p2i(top), p2i(_icms_stop_limit),
1201 percent_of_space(space, _icms_stop_limit));
1202 }
1203 ConcurrentMarkSweepThread::start_icms();
1204 assert(top < _icms_stop_limit, "Tautology");
1205 if (word_size < pointer_delta(_icms_stop_limit, top)) {
1206 return _icms_stop_limit;
1207 }
1208
1209 // The allocation will cross both the _start and _stop limits, so do the
1210 // stop notification also and return end().
1211 if (CMSTraceIncrementalMode) {
1212 space->print_on(gclog_or_tty);
1213 gclog_or_tty->stamp();
1214 gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1215 ", new limit=" PTR_FORMAT
1216 " (" SIZE_FORMAT "%%)",
1217 p2i(top), p2i(space->end()),
1218 percent_of_space(space, space->end()));
1219 }
1220 ConcurrentMarkSweepThread::stop_icms();
1221 return space->end();
1222 }
1223
1224 if (top <= _icms_stop_limit) {
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 (CMSTraceIncrementalMode) {
1239 space->print_on(gclog_or_tty);
1240 gclog_or_tty->stamp();
1241 gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1242 ", new limit=" PTR_FORMAT,
1243 top, NULL);
1244 }
1245 }
1246
1247 return NULL;
1248 }
1249
1250 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1251 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1252 // allocate, copy and if necessary update promoinfo --
1253 // delegate to underlying space.
1254 assert_lock_strong(freelistLock());
1255
1256 #ifndef PRODUCT
1257 if (Universe::heap()->promotion_should_fail()) {
1258 return NULL;
1259 }
1260 #endif // #ifndef PRODUCT
1261
1262 oop res = _cmsSpace->promote(obj, obj_size);
1263 if (res == NULL) {
1264 // expand and retry
1265 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1266 expand(s*HeapWordSize, MinHeapDeltaBytes,
1267 CMSExpansionCause::_satisfy_promotion);
1268 // Since there's currently no next generation, we don't try to promote
1269 // into a more senior generation.
1270 assert(next_gen() == NULL, "assumption, based upon which no attempt "
1271 "is made to pass on a possibly failing "
1272 "promotion to next generation");
1273 res = _cmsSpace->promote(obj, obj_size);
1274 }
1275 if (res != NULL) {
1276 // See comment in allocate() about when objects should
1277 // be allocated live.
1278 assert(obj->is_oop(), "Will dereference klass pointer below");
1279 collector()->promoted(false, // Not parallel
1280 (HeapWord*)res, obj->is_objArray(), obj_size);
1281 // promotion counters
1282 NOT_PRODUCT(
1283 _numObjectsPromoted++;
1284 _numWordsPromoted +=
1285 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1286 )
1287 }
1288 return res;
1289 }
1290
1291
1292 HeapWord*
1293 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1294 HeapWord* top,
1295 size_t word_sz)
1296 {
1297 return collector()->allocation_limit_reached(space, top, word_sz);
1298 }
1299
1300 // IMPORTANT: Notes on object size recognition in CMS.
1301 // ---------------------------------------------------
1302 // A block of storage in the CMS generation is always in
1303 // one of three states. A free block (FREE), an allocated
1304 // object (OBJECT) whose size() method reports the correct size,
1305 // and an intermediate state (TRANSIENT) in which its size cannot
1306 // be accurately determined.
1307 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1308 // -----------------------------------------------------
1309 // FREE: klass_word & 1 == 1; mark_word holds block size
1310 //
1311 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1312 // obj->size() computes correct size
1313 //
1314 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1315 //
1316 // STATE IDENTIFICATION: (64 bit+COOPS)
1317 // ------------------------------------
1318 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1319 //
1320 // OBJECT: klass_word installed; klass_word != 0;
1321 // obj->size() computes correct size
1322 //
1323 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1324 //
1325 //
1326 // STATE TRANSITION DIAGRAM
1327 //
1328 // mut / parnew mut / parnew
1329 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1330 // ^ |
1331 // |------------------------ DEAD <------------------------------------|
1332 // sweep mut
1333 //
1334 // While a block is in TRANSIENT state its size cannot be determined
1335 // so readers will either need to come back later or stall until
1336 // the size can be determined. Note that for the case of direct
1337 // allocation, P-bits, when available, may be used to determine the
1338 // size of an object that may not yet have been initialized.
1339
1340 // Things to support parallel young-gen collection.
1341 oop
1342 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1343 oop old, markOop m,
1344 size_t word_sz) {
1345 #ifndef PRODUCT
1346 if (Universe::heap()->promotion_should_fail()) {
1347 return NULL;
1348 }
1349 #endif // #ifndef PRODUCT
1350
1351 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1352 PromotionInfo* promoInfo = &ps->promo;
1353 // if we are tracking promotions, then first ensure space for
1354 // promotion (including spooling space for saving header if necessary).
1355 // then allocate and copy, then track promoted info if needed.
1356 // When tracking (see PromotionInfo::track()), the mark word may
1357 // be displaced and in this case restoration of the mark word
1358 // occurs in the (oop_since_save_marks_)iterate phase.
1359 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1360 // Out of space for allocating spooling buffers;
1361 // try expanding and allocating spooling buffers.
1362 if (!expand_and_ensure_spooling_space(promoInfo)) {
1363 return NULL;
1364 }
1365 }
1366 assert(promoInfo->has_spooling_space(), "Control point invariant");
1367 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1368 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1369 if (obj_ptr == NULL) {
1370 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1371 if (obj_ptr == NULL) {
1372 return NULL;
1373 }
1374 }
1375 oop obj = oop(obj_ptr);
1376 OrderAccess::storestore();
1377 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1378 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1379 // IMPORTANT: See note on object initialization for CMS above.
1380 // Otherwise, copy the object. Here we must be careful to insert the
1381 // klass pointer last, since this marks the block as an allocated object.
1382 // Except with compressed oops it's the mark word.
1383 HeapWord* old_ptr = (HeapWord*)old;
1384 // Restore the mark word copied above.
1385 obj->set_mark(m);
1386 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1387 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1388 OrderAccess::storestore();
1389
1390 if (UseCompressedClassPointers) {
1391 // Copy gap missed by (aligned) header size calculation below
1392 obj->set_klass_gap(old->klass_gap());
1393 }
1394 if (word_sz > (size_t)oopDesc::header_size()) {
1395 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1396 obj_ptr + oopDesc::header_size(),
1397 word_sz - oopDesc::header_size());
1398 }
1399
1400 // Now we can track the promoted object, if necessary. We take care
1401 // to delay the transition from uninitialized to full object
1402 // (i.e., insertion of klass pointer) until after, so that it
1403 // atomically becomes a promoted object.
1404 if (promoInfo->tracking()) {
1405 promoInfo->track((PromotedObject*)obj, old->klass());
1406 }
1407 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1408 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1409 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1410
1411 // Finally, install the klass pointer (this should be volatile).
1412 OrderAccess::storestore();
1413 obj->set_klass(old->klass());
1414 // We should now be able to calculate the right size for this object
1415 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1416
1417 collector()->promoted(true, // parallel
1418 obj_ptr, old->is_objArray(), word_sz);
1419
1420 NOT_PRODUCT(
1421 Atomic::inc_ptr(&_numObjectsPromoted);
1422 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1423 )
1424
1425 return obj;
1426 }
1427
1428 void
1429 ConcurrentMarkSweepGeneration::
1430 par_promote_alloc_undo(int thread_num,
1431 HeapWord* obj, size_t word_sz) {
1432 // CMS does not support promotion undo.
1433 ShouldNotReachHere();
1434 }
1435
1436 void
1437 ConcurrentMarkSweepGeneration::
1438 par_promote_alloc_done(int thread_num) {
1439 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1440 ps->lab.retire(thread_num);
1441 }
1442
1443 void
1444 ConcurrentMarkSweepGeneration::
1445 par_oop_since_save_marks_iterate_done(int thread_num) {
1446 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1447 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1448 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1449 }
1450
1451 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1452 size_t size,
1453 bool tlab)
1454 {
1455 // We allow a STW collection only if a full
1456 // collection was requested.
1457 return full || should_allocate(size, tlab); // FIX ME !!!
1458 // This and promotion failure handling are connected at the
1459 // hip and should be fixed by untying them.
1460 }
1461
1462 bool CMSCollector::shouldConcurrentCollect() {
1463 if (_full_gc_requested) {
1464 if (Verbose && PrintGCDetails) {
1465 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1466 " gc request (or gc_locker)");
1467 }
1468 return true;
1469 }
1470
1471 // For debugging purposes, change the type of collection.
1472 // If the rotation is not on the concurrent collection
1473 // type, don't start a concurrent collection.
1474 NOT_PRODUCT(
1475 if (RotateCMSCollectionTypes &&
1476 (_cmsGen->debug_collection_type() !=
1477 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1478 assert(_cmsGen->debug_collection_type() !=
1479 ConcurrentMarkSweepGeneration::Unknown_collection_type,
1480 "Bad cms collection type");
1481 return false;
1482 }
1483 )
1484
1485 FreelistLocker x(this);
1486 // ------------------------------------------------------------------
1487 // Print out lots of information which affects the initiation of
1488 // a collection.
1489 if (PrintCMSInitiationStatistics && stats().valid()) {
1490 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1491 gclog_or_tty->stamp();
1492 gclog_or_tty->cr();
1493 stats().print_on(gclog_or_tty);
1494 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1495 stats().time_until_cms_gen_full());
1496 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1497 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1498 _cmsGen->contiguous_available());
1499 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1500 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1501 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1502 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1503 gclog_or_tty->print_cr("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1504 gclog_or_tty->print_cr("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1505 gclog_or_tty->print_cr("metadata initialized %d",
1506 MetaspaceGC::should_concurrent_collect());
1507 }
1508 // ------------------------------------------------------------------
1509
1510 // If the estimated time to complete a cms collection (cms_duration())
1511 // is less than the estimated time remaining until the cms generation
1512 // is full, start a collection.
1513 if (!UseCMSInitiatingOccupancyOnly) {
1514 if (stats().valid()) {
1515 if (stats().time_until_cms_start() == 0.0) {
1516 return true;
1517 }
1518 } else {
1519 // We want to conservatively collect somewhat early in order
1520 // to try and "bootstrap" our CMS/promotion statistics;
1521 // this branch will not fire after the first successful CMS
1522 // collection because the stats should then be valid.
1523 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1524 if (Verbose && PrintGCDetails) {
1525 gclog_or_tty->print_cr(
1526 " CMSCollector: collect for bootstrapping statistics:"
1527 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1528 _bootstrap_occupancy);
1529 }
1530 return true;
1531 }
1532 }
1533 }
1534
1535 // Otherwise, we start a collection cycle if
1536 // old gen want a collection cycle started. Each may use
1537 // an appropriate criterion for making this decision.
1538 // XXX We need to make sure that the gen expansion
1539 // criterion dovetails well with this. XXX NEED TO FIX THIS
1540 if (_cmsGen->should_concurrent_collect()) {
1541 if (Verbose && PrintGCDetails) {
1542 gclog_or_tty->print_cr("CMS old gen initiated");
1543 }
1544 return true;
1545 }
1546
1547 // We start a collection if we believe an incremental collection may fail;
1548 // this is not likely to be productive in practice because it's probably too
1549 // late anyway.
1550 GenCollectedHeap* gch = GenCollectedHeap::heap();
1551 assert(gch->collector_policy()->is_generation_policy(),
1552 "You may want to check the correctness of the following");
1553 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1554 if (Verbose && PrintGCDetails) {
1555 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1556 }
1557 return true;
1558 }
1559
1560 if (MetaspaceGC::should_concurrent_collect()) {
1561 if (Verbose && PrintGCDetails) {
1562 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1563 }
1564 return true;
1565 }
1566
1567 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1568 if (CMSTriggerInterval >= 0) {
1569 if (CMSTriggerInterval == 0) {
1570 // Trigger always
1571 return true;
1572 }
1573
1574 // Check the CMS time since begin (we do not check the stats validity
1575 // as we want to be able to trigger the first CMS cycle as well)
1576 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1577 if (Verbose && PrintGCDetails) {
1578 if (stats().valid()) {
1579 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1580 stats().cms_time_since_begin());
1581 } else {
1582 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (first collection)");
1583 }
1584 }
1585 return true;
1586 }
1587 }
1588
1589 return false;
1590 }
1591
1592 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1593
1594 // Clear _expansion_cause fields of constituent generations
1595 void CMSCollector::clear_expansion_cause() {
1596 _cmsGen->clear_expansion_cause();
1597 }
1598
1599 // We should be conservative in starting a collection cycle. To
1600 // start too eagerly runs the risk of collecting too often in the
1601 // extreme. To collect too rarely falls back on full collections,
1602 // which works, even if not optimum in terms of concurrent work.
1603 // As a work around for too eagerly collecting, use the flag
1604 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1605 // giving the user an easily understandable way of controlling the
1606 // collections.
1607 // We want to start a new collection cycle if any of the following
1608 // conditions hold:
1609 // . our current occupancy exceeds the configured initiating occupancy
1610 // for this generation, or
1611 // . we recently needed to expand this space and have not, since that
1612 // expansion, done a collection of this generation, or
1613 // . the underlying space believes that it may be a good idea to initiate
1614 // a concurrent collection (this may be based on criteria such as the
1615 // following: the space uses linear allocation and linear allocation is
1616 // going to fail, or there is believed to be excessive fragmentation in
1617 // the generation, etc... or ...
1618 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1619 // the case of the old generation; see CR 6543076):
1620 // we may be approaching a point at which allocation requests may fail because
1621 // we will be out of sufficient free space given allocation rate estimates.]
1622 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1623
1624 assert_lock_strong(freelistLock());
1625 if (occupancy() > initiating_occupancy()) {
1626 if (PrintGCDetails && Verbose) {
1627 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1628 short_name(), occupancy(), initiating_occupancy());
1629 }
1630 return true;
1631 }
1632 if (UseCMSInitiatingOccupancyOnly) {
1633 return false;
1634 }
1635 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1636 if (PrintGCDetails && Verbose) {
1637 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1638 short_name());
1639 }
1640 return true;
1641 }
1642 if (_cmsSpace->should_concurrent_collect()) {
1643 if (PrintGCDetails && Verbose) {
1644 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1645 short_name());
1646 }
1647 return true;
1648 }
1649 return false;
1650 }
1651
1652 void ConcurrentMarkSweepGeneration::collect(bool full,
1653 bool clear_all_soft_refs,
1654 size_t size,
1655 bool tlab)
1656 {
1657 collector()->collect(full, clear_all_soft_refs, size, tlab);
1658 }
1659
1660 void CMSCollector::collect(bool full,
1661 bool clear_all_soft_refs,
1662 size_t size,
1663 bool tlab)
1664 {
1665 if (!UseCMSCollectionPassing && _collectorState > Idling) {
1666 // For debugging purposes skip the collection if the state
1667 // is not currently idle
1668 if (TraceCMSState) {
1669 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1670 Thread::current(), full, _collectorState);
1671 }
1672 return;
1673 }
1674
1675 // The following "if" branch is present for defensive reasons.
1676 // In the current uses of this interface, it can be replaced with:
1677 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1678 // But I am not placing that assert here to allow future
1679 // generality in invoking this interface.
1680 if (GC_locker::is_active()) {
1681 // A consistency test for GC_locker
1682 assert(GC_locker::needs_gc(), "Should have been set already");
1683 // Skip this foreground collection, instead
1684 // expanding the heap if necessary.
1685 // Need the free list locks for the call to free() in compute_new_size()
1686 compute_new_size();
1687 return;
1688 }
1689 acquire_control_and_collect(full, clear_all_soft_refs);
1690 _full_gcs_since_conc_gc++;
1691 }
1692
1693 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1694 GenCollectedHeap* gch = GenCollectedHeap::heap();
1695 unsigned int gc_count = gch->total_full_collections();
1696 if (gc_count == full_gc_count) {
1697 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1698 _full_gc_requested = true;
1699 _full_gc_cause = cause;
1700 CGC_lock->notify(); // nudge CMS thread
1701 } else {
1702 assert(gc_count > full_gc_count, "Error: causal loop");
1703 }
1704 }
1705
1706 bool CMSCollector::is_external_interruption() {
1707 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1708 return GCCause::is_user_requested_gc(cause) ||
1709 GCCause::is_serviceability_requested_gc(cause);
1710 }
1711
1712 void CMSCollector::report_concurrent_mode_interruption() {
1713 if (is_external_interruption()) {
1714 if (PrintGCDetails) {
1715 gclog_or_tty->print(" (concurrent mode interrupted)");
1716 }
1717 } else {
1718 if (PrintGCDetails) {
1719 gclog_or_tty->print(" (concurrent mode failure)");
1720 }
1721 _gc_tracer_cm->report_concurrent_mode_failure();
1722 }
1723 }
1724
1725
1726 // The foreground and background collectors need to coordinate in order
1727 // to make sure that they do not mutually interfere with CMS collections.
1728 // When a background collection is active,
1729 // the foreground collector may need to take over (preempt) and
1730 // synchronously complete an ongoing collection. Depending on the
1731 // frequency of the background collections and the heap usage
1732 // of the application, this preemption can be seldom or frequent.
1733 // There are only certain
1734 // points in the background collection that the "collection-baton"
1735 // can be passed to the foreground collector.
1736 //
1737 // The foreground collector will wait for the baton before
1738 // starting any part of the collection. The foreground collector
1739 // will only wait at one location.
1740 //
1741 // The background collector will yield the baton before starting a new
1742 // phase of the collection (e.g., before initial marking, marking from roots,
1743 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1744 // of the loop which switches the phases. The background collector does some
1745 // of the phases (initial mark, final re-mark) with the world stopped.
1746 // Because of locking involved in stopping the world,
1747 // the foreground collector should not block waiting for the background
1748 // collector when it is doing a stop-the-world phase. The background
1749 // collector will yield the baton at an additional point just before
1750 // it enters a stop-the-world phase. Once the world is stopped, the
1751 // background collector checks the phase of the collection. If the
1752 // phase has not changed, it proceeds with the collection. If the
1753 // phase has changed, it skips that phase of the collection. See
1754 // the comments on the use of the Heap_lock in collect_in_background().
1755 //
1756 // Variable used in baton passing.
1757 // _foregroundGCIsActive - Set to true by the foreground collector when
1758 // it wants the baton. The foreground clears it when it has finished
1759 // the collection.
1760 // _foregroundGCShouldWait - Set to true by the background collector
1761 // when it is running. The foreground collector waits while
1762 // _foregroundGCShouldWait is true.
1763 // CGC_lock - monitor used to protect access to the above variables
1764 // and to notify the foreground and background collectors.
1765 // _collectorState - current state of the CMS collection.
1766 //
1767 // The foreground collector
1768 // acquires the CGC_lock
1769 // sets _foregroundGCIsActive
1770 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1771 // various locks acquired in preparation for the collection
1772 // are released so as not to block the background collector
1773 // that is in the midst of a collection
1774 // proceeds with the collection
1775 // clears _foregroundGCIsActive
1776 // returns
1777 //
1778 // The background collector in a loop iterating on the phases of the
1779 // collection
1780 // acquires the CGC_lock
1781 // sets _foregroundGCShouldWait
1782 // if _foregroundGCIsActive is set
1783 // clears _foregroundGCShouldWait, notifies _CGC_lock
1784 // waits on _CGC_lock for _foregroundGCIsActive to become false
1785 // and exits the loop.
1786 // otherwise
1787 // proceed with that phase of the collection
1788 // if the phase is a stop-the-world phase,
1789 // yield the baton once more just before enqueueing
1790 // the stop-world CMS operation (executed by the VM thread).
1791 // returns after all phases of the collection are done
1792 //
1793
1794 void CMSCollector::acquire_control_and_collect(bool full,
1795 bool clear_all_soft_refs) {
1796 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1797 assert(!Thread::current()->is_ConcurrentGC_thread(),
1798 "shouldn't try to acquire control from self!");
1799
1800 // Start the protocol for acquiring control of the
1801 // collection from the background collector (aka CMS thread).
1802 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1803 "VM thread should have CMS token");
1804 // Remember the possibly interrupted state of an ongoing
1805 // concurrent collection
1806 CollectorState first_state = _collectorState;
1807
1808 // Signal to a possibly ongoing concurrent collection that
1809 // we want to do a foreground collection.
1810 _foregroundGCIsActive = true;
1811
1812 // Disable incremental mode during a foreground collection.
1813 ICMSDisabler icms_disabler;
1814
1815 // release locks and wait for a notify from the background collector
1816 // releasing the locks in only necessary for phases which
1817 // do yields to improve the granularity of the collection.
1818 assert_lock_strong(bitMapLock());
1819 // We need to lock the Free list lock for the space that we are
1820 // currently collecting.
1821 assert(haveFreelistLocks(), "Must be holding free list locks");
1822 bitMapLock()->unlock();
1823 releaseFreelistLocks();
1824 {
1825 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1826 if (_foregroundGCShouldWait) {
1827 // We are going to be waiting for action for the CMS thread;
1828 // it had better not be gone (for instance at shutdown)!
1829 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1830 "CMS thread must be running");
1831 // Wait here until the background collector gives us the go-ahead
1832 ConcurrentMarkSweepThread::clear_CMS_flag(
1833 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1834 // Get a possibly blocked CMS thread going:
1835 // Note that we set _foregroundGCIsActive true above,
1836 // without protection of the CGC_lock.
1837 CGC_lock->notify();
1838 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1839 "Possible deadlock");
1840 while (_foregroundGCShouldWait) {
1841 // wait for notification
1842 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1843 // Possibility of delay/starvation here, since CMS token does
1844 // not know to give priority to VM thread? Actually, i think
1845 // there wouldn't be any delay/starvation, but the proof of
1846 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1847 }
1848 ConcurrentMarkSweepThread::set_CMS_flag(
1849 ConcurrentMarkSweepThread::CMS_vm_has_token);
1850 }
1851 }
1852 // The CMS_token is already held. Get back the other locks.
1853 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1854 "VM thread should have CMS token");
1855 getFreelistLocks();
1856 bitMapLock()->lock_without_safepoint_check();
1857 if (TraceCMSState) {
1858 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1859 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1860 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1861 }
1862
1863 // Check if we need to do a compaction, or if not, whether
1864 // we need to start the mark-sweep from scratch.
1865 bool should_compact = false;
1866 bool should_start_over = false;
1867 decide_foreground_collection_type(clear_all_soft_refs,
1868 &should_compact, &should_start_over);
1869
1870 NOT_PRODUCT(
1871 if (RotateCMSCollectionTypes) {
1872 if (_cmsGen->debug_collection_type() ==
1873 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1874 should_compact = true;
1875 } else if (_cmsGen->debug_collection_type() ==
1876 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1877 should_compact = false;
1878 }
1879 }
1880 )
1881
1882 if (first_state > Idling) {
1883 report_concurrent_mode_interruption();
1884 }
1885
1886 set_did_compact(should_compact);
1887 if (should_compact) {
1888 // If the collection is being acquired from the background
1889 // collector, there may be references on the discovered
1890 // references lists that have NULL referents (being those
1891 // that were concurrently cleared by a mutator) or
1892 // that are no longer active (having been enqueued concurrently
1893 // by the mutator).
1894 // Scrub the list of those references because Mark-Sweep-Compact
1895 // code assumes referents are not NULL and that all discovered
1896 // Reference objects are active.
1897 ref_processor()->clean_up_discovered_references();
1898
1899 if (first_state > Idling) {
1900 save_heap_summary();
1901 }
1902
1903 do_compaction_work(clear_all_soft_refs);
1904
1905 // Has the GC time limit been exceeded?
1906 DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1907 size_t max_eden_size = young_gen->max_capacity() -
1908 young_gen->to()->capacity() -
1909 young_gen->from()->capacity();
1910 GenCollectedHeap* gch = GenCollectedHeap::heap();
1911 GCCause::Cause gc_cause = gch->gc_cause();
1912 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1913 young_gen->eden()->used(),
1914 _cmsGen->max_capacity(),
1915 max_eden_size,
1916 full,
1917 gc_cause,
1918 gch->collector_policy());
1919 } else {
1920 do_mark_sweep_work(clear_all_soft_refs, first_state,
1921 should_start_over);
1922 }
1923 // Reset the expansion cause, now that we just completed
1924 // a collection cycle.
1925 clear_expansion_cause();
1926 _foregroundGCIsActive = false;
1927 return;
1928 }
1929
1930 // Resize the tenured generation
1931 // after obtaining the free list locks for the
1932 // two generations.
1933 void CMSCollector::compute_new_size() {
1934 assert_locked_or_safepoint(Heap_lock);
1935 FreelistLocker z(this);
1936 MetaspaceGC::compute_new_size();
1937 _cmsGen->compute_new_size_free_list();
1938 }
1939
1940 // A work method used by foreground collection to determine
1941 // what type of collection (compacting or not, continuing or fresh)
1942 // it should do.
1943 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1944 // and CMSCompactWhenClearAllSoftRefs the default in the future
1945 // and do away with the flags after a suitable period.
1946 void CMSCollector::decide_foreground_collection_type(
1947 bool clear_all_soft_refs, bool* should_compact,
1948 bool* should_start_over) {
1949 // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1950 // flag is set, and we have either requested a System.gc() or
1951 // the number of full gc's since the last concurrent cycle
1952 // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1953 // or if an incremental collection has failed
1954 GenCollectedHeap* gch = GenCollectedHeap::heap();
1955 assert(gch->collector_policy()->is_generation_policy(),
1956 "You may want to check the correctness of the following");
1957 // Inform cms gen if this was due to partial collection failing.
1958 // The CMS gen may use this fact to determine its expansion policy.
1959 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1960 assert(!_cmsGen->incremental_collection_failed(),
1961 "Should have been noticed, reacted to and cleared");
1962 _cmsGen->set_incremental_collection_failed();
1963 }
1964 *should_compact =
1965 UseCMSCompactAtFullCollection &&
1966 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1967 GCCause::is_user_requested_gc(gch->gc_cause()) ||
1968 gch->incremental_collection_will_fail(true /* consult_young */));
1969 *should_start_over = false;
1970 if (clear_all_soft_refs && !*should_compact) {
1971 // We are about to do a last ditch collection attempt
1972 // so it would normally make sense to do a compaction
1973 // to reclaim as much space as possible.
1974 if (CMSCompactWhenClearAllSoftRefs) {
1975 // Default: The rationale is that in this case either
1976 // we are past the final marking phase, in which case
1977 // we'd have to start over, or so little has been done
1978 // that there's little point in saving that work. Compaction
1979 // appears to be the sensible choice in either case.
1980 *should_compact = true;
1981 } else {
1982 // We have been asked to clear all soft refs, but not to
1983 // compact. Make sure that we aren't past the final checkpoint
1984 // phase, for that is where we process soft refs. If we are already
1985 // past that phase, we'll need to redo the refs discovery phase and
1986 // if necessary clear soft refs that weren't previously
1987 // cleared. We do so by remembering the phase in which
1988 // we came in, and if we are past the refs processing
1989 // phase, we'll choose to just redo the mark-sweep
1990 // collection from scratch.
1991 if (_collectorState > FinalMarking) {
1992 // We are past the refs processing phase;
1993 // start over and do a fresh synchronous CMS cycle
1994 _collectorState = Resetting; // skip to reset to start new cycle
1995 reset(false /* == !asynch */);
1996 *should_start_over = true;
1997 } // else we can continue a possibly ongoing current cycle
1998 }
1999 }
2000 }
2001
2002 // A work method used by the foreground collector to do
2003 // a mark-sweep-compact.
2004 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
2005 GenCollectedHeap* gch = GenCollectedHeap::heap();
2006
2007 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
2008 gc_timer->register_gc_start();
2009
2010 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
2011 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
2012
2013 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL, gc_tracer->gc_id());
2014 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
2015 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
2016 "collections passed to foreground collector", _full_gcs_since_conc_gc);
2017 }
2018
2019 // Temporarily widen the span of the weak reference processing to
2020 // the entire heap.
2021 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
2022 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
2023 // Temporarily, clear the "is_alive_non_header" field of the
2024 // reference processor.
2025 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
2026 // Temporarily make reference _processing_ single threaded (non-MT).
2027 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
2028 // Temporarily make refs discovery atomic
2029 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
2030 // Temporarily make reference _discovery_ single threaded (non-MT)
2031 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
2032
2033 ref_processor()->set_enqueuing_is_done(false);
2034 ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/);
2035 ref_processor()->setup_policy(clear_all_soft_refs);
2036 // If an asynchronous collection finishes, the _modUnionTable is
2037 // all clear. If we are assuming the collection from an asynchronous
2038 // collection, clear the _modUnionTable.
2039 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
2040 "_modUnionTable should be clear if the baton was not passed");
2041 _modUnionTable.clear_all();
2042 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
2043 "mod union for klasses should be clear if the baton was passed");
2044 _ct->klass_rem_set()->clear_mod_union();
2045
2046 // We must adjust the allocation statistics being maintained
2047 // in the free list space. We do so by reading and clearing
2048 // the sweep timer and updating the block flux rate estimates below.
2049 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
2050 if (_inter_sweep_timer.is_active()) {
2051 _inter_sweep_timer.stop();
2052 // Note that we do not use this sample to update the _inter_sweep_estimate.
2053 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
2054 _inter_sweep_estimate.padded_average(),
2055 _intra_sweep_estimate.padded_average());
2056 }
2057
2058 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
2059 ref_processor(), clear_all_soft_refs);
2060 #ifdef ASSERT
2061 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
2062 size_t free_size = cms_space->free();
2063 assert(free_size ==
2064 pointer_delta(cms_space->end(), cms_space->compaction_top())
2065 * HeapWordSize,
2066 "All the free space should be compacted into one chunk at top");
2067 assert(cms_space->dictionary()->total_chunk_size(
2068 debug_only(cms_space->freelistLock())) == 0 ||
2069 cms_space->totalSizeInIndexedFreeLists() == 0,
2070 "All the free space should be in a single chunk");
2071 size_t num = cms_space->totalCount();
2072 assert((free_size == 0 && num == 0) ||
2073 (free_size > 0 && (num == 1 || num == 2)),
2074 "There should be at most 2 free chunks after compaction");
2075 #endif // ASSERT
2076 _collectorState = Resetting;
2077 assert(_restart_addr == NULL,
2078 "Should have been NULL'd before baton was passed");
2079 reset(false /* == !asynch */);
2080 _cmsGen->reset_after_compaction();
2081 _concurrent_cycles_since_last_unload = 0;
2082
2083 // Clear any data recorded in the PLAB chunk arrays.
2084 if (_survivor_plab_array != NULL) {
2085 reset_survivor_plab_arrays();
2086 }
2087
2088 // Adjust the per-size allocation stats for the next epoch.
2089 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
2090 // Restart the "inter sweep timer" for the next epoch.
2091 _inter_sweep_timer.reset();
2092 _inter_sweep_timer.start();
2093
2094 gc_timer->register_gc_end();
2095
2096 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
2097
2098 // For a mark-sweep-compact, compute_new_size() will be called
2099 // in the heap's do_collection() method.
2100 }
2101
2102 // A work method used by the foreground collector to do
2103 // a mark-sweep, after taking over from a possibly on-going
2104 // concurrent mark-sweep collection.
2105 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2106 CollectorState first_state, bool should_start_over) {
2107 if (PrintGC && Verbose) {
2108 gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2109 "collector with count %d",
2110 _full_gcs_since_conc_gc);
2111 }
2112 switch (_collectorState) {
2113 case Idling:
2114 if (first_state == Idling || should_start_over) {
2115 // The background GC was not active, or should
2116 // restarted from scratch; start the cycle.
2117 _collectorState = InitialMarking;
2118 }
2119 // If first_state was not Idling, then a background GC
2120 // was in progress and has now finished. No need to do it
2121 // again. Leave the state as Idling.
2122 break;
2123 case Precleaning:
2124 // In the foreground case don't do the precleaning since
2125 // it is not done concurrently and there is extra work
2126 // required.
2127 _collectorState = FinalMarking;
2128 }
2129 collect_in_foreground(clear_all_soft_refs, GenCollectedHeap::heap()->gc_cause());
2130
2131 // For a mark-sweep, compute_new_size() will be called
2132 // in the heap's do_collection() method.
2133 }
2134
2135
2136 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
2137 DefNewGeneration* dng = _young_gen->as_DefNewGeneration();
2138 EdenSpace* eden_space = dng->eden();
2139 ContiguousSpace* from_space = dng->from();
2140 ContiguousSpace* to_space = dng->to();
2141 // Eden
2142 if (_eden_chunk_array != NULL) {
2143 gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
2144 eden_space->bottom(), eden_space->top(),
2145 eden_space->end(), eden_space->capacity());
2146 gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
2147 "_eden_chunk_capacity=" SIZE_FORMAT,
2148 _eden_chunk_index, _eden_chunk_capacity);
2149 for (size_t i = 0; i < _eden_chunk_index; i++) {
2150 gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
2151 i, _eden_chunk_array[i]);
2152 }
2153 }
2154 // Survivor
2155 if (_survivor_chunk_array != NULL) {
2156 gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
2157 from_space->bottom(), from_space->top(),
2158 from_space->end(), from_space->capacity());
2159 gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
2160 "_survivor_chunk_capacity=" SIZE_FORMAT,
2161 _survivor_chunk_index, _survivor_chunk_capacity);
2162 for (size_t i = 0; i < _survivor_chunk_index; i++) {
2163 gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
2164 i, _survivor_chunk_array[i]);
2165 }
2166 }
2167 }
2168
2169 void CMSCollector::getFreelistLocks() const {
2170 // Get locks for all free lists in all generations that this
2171 // collector is responsible for
2172 _cmsGen->freelistLock()->lock_without_safepoint_check();
2173 }
2174
2175 void CMSCollector::releaseFreelistLocks() const {
2176 // Release locks for all free lists in all generations that this
2177 // collector is responsible for
2178 _cmsGen->freelistLock()->unlock();
2179 }
2180
2181 bool CMSCollector::haveFreelistLocks() const {
2182 // Check locks for all free lists in all generations that this
2183 // collector is responsible for
2184 assert_lock_strong(_cmsGen->freelistLock());
2185 PRODUCT_ONLY(ShouldNotReachHere());
2186 return true;
2187 }
2188
2189 // A utility class that is used by the CMS collector to
2190 // temporarily "release" the foreground collector from its
2191 // usual obligation to wait for the background collector to
2192 // complete an ongoing phase before proceeding.
2193 class ReleaseForegroundGC: public StackObj {
2194 private:
2195 CMSCollector* _c;
2196 public:
2197 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2198 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2199 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2200 // allow a potentially blocked foreground collector to proceed
2201 _c->_foregroundGCShouldWait = false;
2202 if (_c->_foregroundGCIsActive) {
2203 CGC_lock->notify();
2204 }
2205 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2206 "Possible deadlock");
2207 }
2208
2209 ~ReleaseForegroundGC() {
2210 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2211 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2212 _c->_foregroundGCShouldWait = true;
2213 }
2214 };
2215
2216 // There are separate collect_in_background and collect_in_foreground because of
2217 // the different locking requirements of the background collector and the
2218 // foreground collector. There was originally an attempt to share
2219 // one "collect" method between the background collector and the foreground
2220 // collector but the if-then-else required made it cleaner to have
2221 // separate methods.
2222 void CMSCollector::collect_in_background(bool clear_all_soft_refs, GCCause::Cause cause) {
2223 assert(Thread::current()->is_ConcurrentGC_thread(),
2224 "A CMS asynchronous collection is only allowed on a CMS thread.");
2225
2226 GenCollectedHeap* gch = GenCollectedHeap::heap();
2227 {
2228 bool safepoint_check = Mutex::_no_safepoint_check_flag;
2229 MutexLockerEx hl(Heap_lock, safepoint_check);
2230 FreelistLocker fll(this);
2231 MutexLockerEx x(CGC_lock, safepoint_check);
2232 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2233 // The foreground collector is active or we're
2234 // not using asynchronous collections. Skip this
2235 // background collection.
2236 assert(!_foregroundGCShouldWait, "Should be clear");
2237 return;
2238 } else {
2239 assert(_collectorState == Idling, "Should be idling before start.");
2240 _collectorState = InitialMarking;
2241 register_gc_start(cause);
2242 // Reset the expansion cause, now that we are about to begin
2243 // a new cycle.
2244 clear_expansion_cause();
2245
2246 // Clear the MetaspaceGC flag since a concurrent collection
2247 // is starting but also clear it after the collection.
2248 MetaspaceGC::set_should_concurrent_collect(false);
2249 }
2250 // Decide if we want to enable class unloading as part of the
2251 // ensuing concurrent GC cycle.
2252 update_should_unload_classes();
2253 _full_gc_requested = false; // acks all outstanding full gc requests
2254 _full_gc_cause = GCCause::_no_gc;
2255 // Signal that we are about to start a collection
2256 gch->increment_total_full_collections(); // ... starting a collection cycle
2257 _collection_count_start = gch->total_full_collections();
2258 }
2259
2260 // Used for PrintGC
2261 size_t prev_used;
2262 if (PrintGC && Verbose) {
2263 prev_used = _cmsGen->used(); // XXXPERM
2264 }
2265
2266 // The change of the collection state is normally done at this level;
2267 // the exceptions are phases that are executed while the world is
2268 // stopped. For those phases the change of state is done while the
2269 // world is stopped. For baton passing purposes this allows the
2270 // background collector to finish the phase and change state atomically.
2271 // The foreground collector cannot wait on a phase that is done
2272 // while the world is stopped because the foreground collector already
2273 // has the world stopped and would deadlock.
2274 while (_collectorState != Idling) {
2275 if (TraceCMSState) {
2276 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2277 Thread::current(), _collectorState);
2278 }
2279 // The foreground collector
2280 // holds the Heap_lock throughout its collection.
2281 // holds the CMS token (but not the lock)
2282 // except while it is waiting for the background collector to yield.
2283 //
2284 // The foreground collector should be blocked (not for long)
2285 // if the background collector is about to start a phase
2286 // executed with world stopped. If the background
2287 // collector has already started such a phase, the
2288 // foreground collector is blocked waiting for the
2289 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
2290 // are executed in the VM thread.
2291 //
2292 // The locking order is
2293 // PendingListLock (PLL) -- if applicable (FinalMarking)
2294 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
2295 // CMS token (claimed in
2296 // stop_world_and_do() -->
2297 // safepoint_synchronize() -->
2298 // CMSThread::synchronize())
2299
2300 {
2301 // Check if the FG collector wants us to yield.
2302 CMSTokenSync x(true); // is cms thread
2303 if (waitForForegroundGC()) {
2304 // We yielded to a foreground GC, nothing more to be
2305 // done this round.
2306 assert(_foregroundGCShouldWait == false, "We set it to false in "
2307 "waitForForegroundGC()");
2308 if (TraceCMSState) {
2309 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2310 " exiting collection CMS state %d",
2311 Thread::current(), _collectorState);
2312 }
2313 return;
2314 } else {
2315 // The background collector can run but check to see if the
2316 // foreground collector has done a collection while the
2317 // background collector was waiting to get the CGC_lock
2318 // above. If yes, break so that _foregroundGCShouldWait
2319 // is cleared before returning.
2320 if (_collectorState == Idling) {
2321 break;
2322 }
2323 }
2324 }
2325
2326 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2327 "should be waiting");
2328
2329 switch (_collectorState) {
2330 case InitialMarking:
2331 {
2332 ReleaseForegroundGC x(this);
2333 stats().record_cms_begin();
2334 VM_CMS_Initial_Mark initial_mark_op(this);
2335 VMThread::execute(&initial_mark_op);
2336 }
2337 // The collector state may be any legal state at this point
2338 // since the background collector may have yielded to the
2339 // foreground collector.
2340 break;
2341 case Marking:
2342 // initial marking in checkpointRootsInitialWork has been completed
2343 if (markFromRoots(true)) { // we were successful
2344 assert(_collectorState == Precleaning, "Collector state should "
2345 "have changed");
2346 } else {
2347 assert(_foregroundGCIsActive, "Internal state inconsistency");
2348 }
2349 break;
2350 case Precleaning:
2351 // marking from roots in markFromRoots has been completed
2352 preclean();
2353 assert(_collectorState == AbortablePreclean ||
2354 _collectorState == FinalMarking,
2355 "Collector state should have changed");
2356 break;
2357 case AbortablePreclean:
2358 abortable_preclean();
2359 assert(_collectorState == FinalMarking, "Collector state should "
2360 "have changed");
2361 break;
2362 case FinalMarking:
2363 {
2364 ReleaseForegroundGC x(this);
2365
2366 VM_CMS_Final_Remark final_remark_op(this);
2367 VMThread::execute(&final_remark_op);
2368 }
2369 assert(_foregroundGCShouldWait, "block post-condition");
2370 break;
2371 case Sweeping:
2372 // final marking in checkpointRootsFinal has been completed
2373 sweep(true);
2374 assert(_collectorState == Resizing, "Collector state change "
2375 "to Resizing must be done under the free_list_lock");
2376 _full_gcs_since_conc_gc = 0;
2377
2378 case Resizing: {
2379 // Sweeping has been completed...
2380 // At this point the background collection has completed.
2381 // Don't move the call to compute_new_size() down
2382 // into code that might be executed if the background
2383 // collection was preempted.
2384 {
2385 ReleaseForegroundGC x(this); // unblock FG collection
2386 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2387 CMSTokenSync z(true); // not strictly needed.
2388 if (_collectorState == Resizing) {
2389 compute_new_size();
2390 save_heap_summary();
2391 _collectorState = Resetting;
2392 } else {
2393 assert(_collectorState == Idling, "The state should only change"
2394 " because the foreground collector has finished the collection");
2395 }
2396 }
2397 break;
2398 }
2399 case Resetting:
2400 // CMS heap resizing has been completed
2401 reset(true);
2402 assert(_collectorState == Idling, "Collector state should "
2403 "have changed");
2404
2405 MetaspaceGC::set_should_concurrent_collect(false);
2406
2407 stats().record_cms_end();
2408 // Don't move the concurrent_phases_end() and compute_new_size()
2409 // calls to here because a preempted background collection
2410 // has it's state set to "Resetting".
2411 break;
2412 case Idling:
2413 default:
2414 ShouldNotReachHere();
2415 break;
2416 }
2417 if (TraceCMSState) {
2418 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2419 Thread::current(), _collectorState);
2420 }
2421 assert(_foregroundGCShouldWait, "block post-condition");
2422 }
2423
2424 // Should this be in gc_epilogue?
2425 collector_policy()->counters()->update_counters();
2426
2427 {
2428 // Clear _foregroundGCShouldWait and, in the event that the
2429 // foreground collector is waiting, notify it, before
2430 // returning.
2431 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2432 _foregroundGCShouldWait = false;
2433 if (_foregroundGCIsActive) {
2434 CGC_lock->notify();
2435 }
2436 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2437 "Possible deadlock");
2438 }
2439 if (TraceCMSState) {
2440 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2441 " exiting collection CMS state %d",
2442 Thread::current(), _collectorState);
2443 }
2444 if (PrintGC && Verbose) {
2445 _cmsGen->print_heap_change(prev_used);
2446 }
2447 }
2448
2449 void CMSCollector::register_foreground_gc_start(GCCause::Cause cause) {
2450 if (!_cms_start_registered) {
2451 register_gc_start(cause);
2452 }
2453 }
2454
2455 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2456 _cms_start_registered = true;
2457 _gc_timer_cm->register_gc_start();
2458 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2459 }
2460
2461 void CMSCollector::register_gc_end() {
2462 if (_cms_start_registered) {
2463 report_heap_summary(GCWhen::AfterGC);
2464
2465 _gc_timer_cm->register_gc_end();
2466 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2467 _cms_start_registered = false;
2468 }
2469 }
2470
2471 void CMSCollector::save_heap_summary() {
2472 GenCollectedHeap* gch = GenCollectedHeap::heap();
2473 _last_heap_summary = gch->create_heap_summary();
2474 _last_metaspace_summary = gch->create_metaspace_summary();
2475 }
2476
2477 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2478 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2479 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2480 }
2481
2482 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs, GCCause::Cause cause) {
2483 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2484 "Foreground collector should be waiting, not executing");
2485 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2486 "may only be done by the VM Thread with the world stopped");
2487 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2488 "VM thread should have CMS token");
2489
2490 // The gc id is created in register_foreground_gc_start if this collection is synchronous
2491 const GCId gc_id = _collectorState == InitialMarking ? GCId::peek() : _gc_tracer_cm->gc_id();
2492 NOT_PRODUCT(GCTraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2493 true, NULL, gc_id);)
2494 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2495
2496 HandleMark hm; // Discard invalid handles created during verification
2497
2498 if (VerifyBeforeGC &&
2499 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2500 Universe::verify();
2501 }
2502
2503 // Snapshot the soft reference policy to be used in this collection cycle.
2504 ref_processor()->setup_policy(clear_all_soft_refs);
2505
2506 // Decide if class unloading should be done
2507 update_should_unload_classes();
2508
2509 bool init_mark_was_synchronous = false; // until proven otherwise
2510 while (_collectorState != Idling) {
2511 if (TraceCMSState) {
2512 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2513 Thread::current(), _collectorState);
2514 }
2515 switch (_collectorState) {
2516 case InitialMarking:
2517 register_foreground_gc_start(cause);
2518 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2519 checkpointRootsInitial(false);
2520 assert(_collectorState == Marking, "Collector state should have changed"
2521 " within checkpointRootsInitial()");
2522 break;
2523 case Marking:
2524 // initial marking in checkpointRootsInitialWork has been completed
2525 if (VerifyDuringGC &&
2526 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2527 Universe::verify("Verify before initial mark: ");
2528 }
2529 {
2530 bool res = markFromRoots(false);
2531 assert(res && _collectorState == FinalMarking, "Collector state should "
2532 "have changed");
2533 break;
2534 }
2535 case FinalMarking:
2536 if (VerifyDuringGC &&
2537 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2538 Universe::verify("Verify before re-mark: ");
2539 }
2540 checkpointRootsFinal(false, clear_all_soft_refs,
2541 init_mark_was_synchronous);
2542 assert(_collectorState == Sweeping, "Collector state should not "
2543 "have changed within checkpointRootsFinal()");
2544 break;
2545 case Sweeping:
2546 // final marking in checkpointRootsFinal has been completed
2547 if (VerifyDuringGC &&
2548 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2549 Universe::verify("Verify before sweep: ");
2550 }
2551 sweep(false);
2552 assert(_collectorState == Resizing, "Incorrect state");
2553 break;
2554 case Resizing: {
2555 // Sweeping has been completed; the actual resize in this case
2556 // is done separately; nothing to be done in this state.
2557 _collectorState = Resetting;
2558 break;
2559 }
2560 case Resetting:
2561 // The heap has been resized.
2562 if (VerifyDuringGC &&
2563 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2564 Universe::verify("Verify before reset: ");
2565 }
2566 save_heap_summary();
2567 reset(false);
2568 assert(_collectorState == Idling, "Collector state should "
2569 "have changed");
2570 break;
2571 case Precleaning:
2572 case AbortablePreclean:
2573 // Elide the preclean phase
2574 _collectorState = FinalMarking;
2575 break;
2576 default:
2577 ShouldNotReachHere();
2578 }
2579 if (TraceCMSState) {
2580 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2581 Thread::current(), _collectorState);
2582 }
2583 }
2584
2585 if (VerifyAfterGC &&
2586 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2587 Universe::verify();
2588 }
2589 if (TraceCMSState) {
2590 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2591 " exiting collection CMS state %d",
2592 Thread::current(), _collectorState);
2593 }
2594 }
2595
2596 bool CMSCollector::waitForForegroundGC() {
2597 bool res = false;
2598 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2599 "CMS thread should have CMS token");
2600 // Block the foreground collector until the
2601 // background collectors decides whether to
2602 // yield.
2603 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2604 _foregroundGCShouldWait = true;
2605 if (_foregroundGCIsActive) {
2606 // The background collector yields to the
2607 // foreground collector and returns a value
2608 // indicating that it has yielded. The foreground
2609 // collector can proceed.
2610 res = true;
2611 _foregroundGCShouldWait = false;
2612 ConcurrentMarkSweepThread::clear_CMS_flag(
2613 ConcurrentMarkSweepThread::CMS_cms_has_token);
2614 ConcurrentMarkSweepThread::set_CMS_flag(
2615 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2616 // Get a possibly blocked foreground thread going
2617 CGC_lock->notify();
2618 if (TraceCMSState) {
2619 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2620 Thread::current(), _collectorState);
2621 }
2622 while (_foregroundGCIsActive) {
2623 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2624 }
2625 ConcurrentMarkSweepThread::set_CMS_flag(
2626 ConcurrentMarkSweepThread::CMS_cms_has_token);
2627 ConcurrentMarkSweepThread::clear_CMS_flag(
2628 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2629 }
2630 if (TraceCMSState) {
2631 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2632 Thread::current(), _collectorState);
2633 }
2634 return res;
2635 }
2636
2637 // Because of the need to lock the free lists and other structures in
2638 // the collector, common to all the generations that the collector is
2639 // collecting, we need the gc_prologues of individual CMS generations
2640 // delegate to their collector. It may have been simpler had the
2641 // current infrastructure allowed one to call a prologue on a
2642 // collector. In the absence of that we have the generation's
2643 // prologue delegate to the collector, which delegates back
2644 // some "local" work to a worker method in the individual generations
2645 // that it's responsible for collecting, while itself doing any
2646 // work common to all generations it's responsible for. A similar
2647 // comment applies to the gc_epilogue()'s.
2648 // The role of the variable _between_prologue_and_epilogue is to
2649 // enforce the invocation protocol.
2650 void CMSCollector::gc_prologue(bool full) {
2651 // Call gc_prologue_work() for the CMSGen
2652 // we are responsible for.
2653
2654 // The following locking discipline assumes that we are only called
2655 // when the world is stopped.
2656 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2657
2658 // The CMSCollector prologue must call the gc_prologues for the
2659 // "generations" that it's responsible
2660 // for.
2661
2662 assert( Thread::current()->is_VM_thread()
2663 || ( CMSScavengeBeforeRemark
2664 && Thread::current()->is_ConcurrentGC_thread()),
2665 "Incorrect thread type for prologue execution");
2666
2667 if (_between_prologue_and_epilogue) {
2668 // We have already been invoked; this is a gc_prologue delegation
2669 // from yet another CMS generation that we are responsible for, just
2670 // ignore it since all relevant work has already been done.
2671 return;
2672 }
2673
2674 // set a bit saying prologue has been called; cleared in epilogue
2675 _between_prologue_and_epilogue = true;
2676 // Claim locks for common data structures, then call gc_prologue_work()
2677 // for each CMSGen.
2678
2679 getFreelistLocks(); // gets free list locks on constituent spaces
2680 bitMapLock()->lock_without_safepoint_check();
2681
2682 // Should call gc_prologue_work() for all cms gens we are responsible for
2683 bool duringMarking = _collectorState >= Marking
2684 && _collectorState < Sweeping;
2685
2686 // The young collections clear the modified oops state, which tells if
2687 // there are any modified oops in the class. The remark phase also needs
2688 // that information. Tell the young collection to save the union of all
2689 // modified klasses.
2690 if (duringMarking) {
2691 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2692 }
2693
2694 bool registerClosure = duringMarking;
2695
2696 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2697 &_modUnionClosurePar
2698 : &_modUnionClosure;
2699 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2700
2701 if (!full) {
2702 stats().record_gc0_begin();
2703 }
2704 }
2705
2706 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2707
2708 _capacity_at_prologue = capacity();
2709 _used_at_prologue = used();
2710
2711 // Delegate to CMScollector which knows how to coordinate between
2712 // this and any other CMS generations that it is responsible for
2713 // collecting.
2714 collector()->gc_prologue(full);
2715 }
2716
2717 // This is a "private" interface for use by this generation's CMSCollector.
2718 // Not to be called directly by any other entity (for instance,
2719 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2720 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2721 bool registerClosure, ModUnionClosure* modUnionClosure) {
2722 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2723 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2724 "Should be NULL");
2725 if (registerClosure) {
2726 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2727 }
2728 cmsSpace()->gc_prologue();
2729 // Clear stat counters
2730 NOT_PRODUCT(
2731 assert(_numObjectsPromoted == 0, "check");
2732 assert(_numWordsPromoted == 0, "check");
2733 if (Verbose && PrintGC) {
2734 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2735 SIZE_FORMAT" bytes concurrently",
2736 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2737 }
2738 _numObjectsAllocated = 0;
2739 _numWordsAllocated = 0;
2740 )
2741 }
2742
2743 void CMSCollector::gc_epilogue(bool full) {
2744 // The following locking discipline assumes that we are only called
2745 // when the world is stopped.
2746 assert(SafepointSynchronize::is_at_safepoint(),
2747 "world is stopped assumption");
2748
2749 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2750 // if linear allocation blocks need to be appropriately marked to allow the
2751 // the blocks to be parsable. We also check here whether we need to nudge the
2752 // CMS collector thread to start a new cycle (if it's not already active).
2753 assert( Thread::current()->is_VM_thread()
2754 || ( CMSScavengeBeforeRemark
2755 && Thread::current()->is_ConcurrentGC_thread()),
2756 "Incorrect thread type for epilogue execution");
2757
2758 if (!_between_prologue_and_epilogue) {
2759 // We have already been invoked; this is a gc_epilogue delegation
2760 // from yet another CMS generation that we are responsible for, just
2761 // ignore it since all relevant work has already been done.
2762 return;
2763 }
2764 assert(haveFreelistLocks(), "must have freelist locks");
2765 assert_lock_strong(bitMapLock());
2766
2767 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2768
2769 _cmsGen->gc_epilogue_work(full);
2770
2771 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2772 // in case sampling was not already enabled, enable it
2773 _start_sampling = true;
2774 }
2775 // reset _eden_chunk_array so sampling starts afresh
2776 _eden_chunk_index = 0;
2777
2778 size_t cms_used = _cmsGen->cmsSpace()->used();
2779
2780 // update performance counters - this uses a special version of
2781 // update_counters() that allows the utilization to be passed as a
2782 // parameter, avoiding multiple calls to used().
2783 //
2784 _cmsGen->update_counters(cms_used);
2785
2786 if (CMSIncrementalMode) {
2787 icms_update_allocation_limits();
2788 }
2789
2790 bitMapLock()->unlock();
2791 releaseFreelistLocks();
2792
2793 if (!CleanChunkPoolAsync) {
2794 Chunk::clean_chunk_pool();
2795 }
2796
2797 set_did_compact(false);
2798 _between_prologue_and_epilogue = false; // ready for next cycle
2799 }
2800
2801 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2802 collector()->gc_epilogue(full);
2803
2804 // Also reset promotion tracking in par gc thread states.
2805 for (uint i = 0; i < ParallelGCThreads; i++) {
2806 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2807 }
2808 }
2809
2810 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2811 assert(!incremental_collection_failed(), "Should have been cleared");
2812 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2813 cmsSpace()->gc_epilogue();
2814 // Print stat counters
2815 NOT_PRODUCT(
2816 assert(_numObjectsAllocated == 0, "check");
2817 assert(_numWordsAllocated == 0, "check");
2818 if (Verbose && PrintGC) {
2819 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2820 SIZE_FORMAT" bytes",
2821 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2822 }
2823 _numObjectsPromoted = 0;
2824 _numWordsPromoted = 0;
2825 )
2826
2827 if (PrintGC && Verbose) {
2828 // Call down the chain in contiguous_available needs the freelistLock
2829 // so print this out before releasing the freeListLock.
2830 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2831 contiguous_available());
2832 }
2833 }
2834
2835 #ifndef PRODUCT
2836 bool CMSCollector::have_cms_token() {
2837 Thread* thr = Thread::current();
2838 if (thr->is_VM_thread()) {
2839 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2840 } else if (thr->is_ConcurrentGC_thread()) {
2841 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2842 } else if (thr->is_GC_task_thread()) {
2843 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2844 ParGCRareEvent_lock->owned_by_self();
2845 }
2846 return false;
2847 }
2848 #endif
2849
2850 // Check reachability of the given heap address in CMS generation,
2851 // treating all other generations as roots.
2852 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2853 // We could "guarantee" below, rather than assert, but I'll
2854 // leave these as "asserts" so that an adventurous debugger
2855 // could try this in the product build provided some subset of
2856 // the conditions were met, provided they were interested in the
2857 // results and knew that the computation below wouldn't interfere
2858 // with other concurrent computations mutating the structures
2859 // being read or written.
2860 assert(SafepointSynchronize::is_at_safepoint(),
2861 "Else mutations in object graph will make answer suspect");
2862 assert(have_cms_token(), "Should hold cms token");
2863 assert(haveFreelistLocks(), "must hold free list locks");
2864 assert_lock_strong(bitMapLock());
2865
2866 // Clear the marking bit map array before starting, but, just
2867 // for kicks, first report if the given address is already marked
2868 gclog_or_tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", addr,
2869 _markBitMap.isMarked(addr) ? "" : " not");
2870
2871 if (verify_after_remark()) {
2872 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2873 bool result = verification_mark_bm()->isMarked(addr);
2874 gclog_or_tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", addr,
2875 result ? "IS" : "is NOT");
2876 return result;
2877 } else {
2878 gclog_or_tty->print_cr("Could not compute result");
2879 return false;
2880 }
2881 }
2882
2883
2884 void
2885 CMSCollector::print_on_error(outputStream* st) {
2886 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2887 if (collector != NULL) {
2888 CMSBitMap* bitmap = &collector->_markBitMap;
2889 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, bitmap);
2890 bitmap->print_on_error(st, " Bits: ");
2891
2892 st->cr();
2893
2894 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2895 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, mut_bitmap);
2896 mut_bitmap->print_on_error(st, " Bits: ");
2897 }
2898 }
2899
2900 ////////////////////////////////////////////////////////
2901 // CMS Verification Support
2902 ////////////////////////////////////////////////////////
2903 // Following the remark phase, the following invariant
2904 // should hold -- each object in the CMS heap which is
2905 // marked in markBitMap() should be marked in the verification_mark_bm().
2906
2907 class VerifyMarkedClosure: public BitMapClosure {
2908 CMSBitMap* _marks;
2909 bool _failed;
2910
2911 public:
2912 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2913
2914 bool do_bit(size_t offset) {
2915 HeapWord* addr = _marks->offsetToHeapWord(offset);
2916 if (!_marks->isMarked(addr)) {
2917 oop(addr)->print_on(gclog_or_tty);
2918 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2919 _failed = true;
2920 }
2921 return true;
2922 }
2923
2924 bool failed() { return _failed; }
2925 };
2926
2927 bool CMSCollector::verify_after_remark(bool silent) {
2928 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2929 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2930 static bool init = false;
2931
2932 assert(SafepointSynchronize::is_at_safepoint(),
2933 "Else mutations in object graph will make answer suspect");
2934 assert(have_cms_token(),
2935 "Else there may be mutual interference in use of "
2936 " verification data structures");
2937 assert(_collectorState > Marking && _collectorState <= Sweeping,
2938 "Else marking info checked here may be obsolete");
2939 assert(haveFreelistLocks(), "must hold free list locks");
2940 assert_lock_strong(bitMapLock());
2941
2942
2943 // Allocate marking bit map if not already allocated
2944 if (!init) { // first time
2945 if (!verification_mark_bm()->allocate(_span)) {
2946 return false;
2947 }
2948 init = true;
2949 }
2950
2951 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2952
2953 // Turn off refs discovery -- so we will be tracing through refs.
2954 // This is as intended, because by this time
2955 // GC must already have cleared any refs that need to be cleared,
2956 // and traced those that need to be marked; moreover,
2957 // the marking done here is not going to interfere in any
2958 // way with the marking information used by GC.
2959 NoRefDiscovery no_discovery(ref_processor());
2960
2961 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2962
2963 // Clear any marks from a previous round
2964 verification_mark_bm()->clear_all();
2965 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2966 verify_work_stacks_empty();
2967
2968 GenCollectedHeap* gch = GenCollectedHeap::heap();
2969 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2970 // Update the saved marks which may affect the root scans.
2971 gch->save_marks();
2972
2973 if (CMSRemarkVerifyVariant == 1) {
2974 // In this first variant of verification, we complete
2975 // all marking, then check if the new marks-vector is
2976 // a subset of the CMS marks-vector.
2977 verify_after_remark_work_1();
2978 } else if (CMSRemarkVerifyVariant == 2) {
2979 // In this second variant of verification, we flag an error
2980 // (i.e. an object reachable in the new marks-vector not reachable
2981 // in the CMS marks-vector) immediately, also indicating the
2982 // identify of an object (A) that references the unmarked object (B) --
2983 // presumably, a mutation to A failed to be picked up by preclean/remark?
2984 verify_after_remark_work_2();
2985 } else {
2986 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2987 CMSRemarkVerifyVariant);
2988 }
2989 if (!silent) gclog_or_tty->print(" done] ");
2990 return true;
2991 }
2992
2993 void CMSCollector::verify_after_remark_work_1() {
2994 ResourceMark rm;
2995 HandleMark hm;
2996 GenCollectedHeap* gch = GenCollectedHeap::heap();
2997
2998 // Get a clear set of claim bits for the roots processing to work with.
2999 ClassLoaderDataGraph::clear_claimed_marks();
3000
3001 // Mark from roots one level into CMS
3002 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
3003 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3004
3005 gch->gen_process_roots(_cmsGen->level(),
3006 true, // younger gens are roots
3007 true, // activate StrongRootsScope
3008 SharedHeap::ScanningOption(roots_scanning_options()),
3009 should_unload_classes(),
3010 ¬Older,
3011 NULL,
3012 NULL); // SSS: Provide correct closure
3013
3014 // Now mark from the roots
3015 MarkFromRootsClosure markFromRootsClosure(this, _span,
3016 verification_mark_bm(), verification_mark_stack(),
3017 false /* don't yield */, true /* verifying */);
3018 assert(_restart_addr == NULL, "Expected pre-condition");
3019 verification_mark_bm()->iterate(&markFromRootsClosure);
3020 while (_restart_addr != NULL) {
3021 // Deal with stack overflow: by restarting at the indicated
3022 // address.
3023 HeapWord* ra = _restart_addr;
3024 markFromRootsClosure.reset(ra);
3025 _restart_addr = NULL;
3026 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3027 }
3028 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3029 verify_work_stacks_empty();
3030
3031 // Marking completed -- now verify that each bit marked in
3032 // verification_mark_bm() is also marked in markBitMap(); flag all
3033 // errors by printing corresponding objects.
3034 VerifyMarkedClosure vcl(markBitMap());
3035 verification_mark_bm()->iterate(&vcl);
3036 if (vcl.failed()) {
3037 gclog_or_tty->print("Verification failed");
3038 Universe::heap()->print_on(gclog_or_tty);
3039 fatal("CMS: failed marking verification after remark");
3040 }
3041 }
3042
3043 class VerifyKlassOopsKlassClosure : public KlassClosure {
3044 class VerifyKlassOopsClosure : public OopClosure {
3045 CMSBitMap* _bitmap;
3046 public:
3047 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
3048 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
3049 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
3050 } _oop_closure;
3051 public:
3052 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
3053 void do_klass(Klass* k) {
3054 k->oops_do(&_oop_closure);
3055 }
3056 };
3057
3058 void CMSCollector::verify_after_remark_work_2() {
3059 ResourceMark rm;
3060 HandleMark hm;
3061 GenCollectedHeap* gch = GenCollectedHeap::heap();
3062
3063 // Get a clear set of claim bits for the roots processing to work with.
3064 ClassLoaderDataGraph::clear_claimed_marks();
3065
3066 // Mark from roots one level into CMS
3067 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
3068 markBitMap());
3069 CLDToOopClosure cld_closure(¬Older, true);
3070
3071 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3072
3073 gch->gen_process_roots(_cmsGen->level(),
3074 true, // younger gens are roots
3075 true, // activate StrongRootsScope
3076 SharedHeap::ScanningOption(roots_scanning_options()),
3077 should_unload_classes(),
3078 ¬Older,
3079 NULL,
3080 &cld_closure);
3081
3082 // Now mark from the roots
3083 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
3084 verification_mark_bm(), markBitMap(), verification_mark_stack());
3085 assert(_restart_addr == NULL, "Expected pre-condition");
3086 verification_mark_bm()->iterate(&markFromRootsClosure);
3087 while (_restart_addr != NULL) {
3088 // Deal with stack overflow: by restarting at the indicated
3089 // address.
3090 HeapWord* ra = _restart_addr;
3091 markFromRootsClosure.reset(ra);
3092 _restart_addr = NULL;
3093 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3094 }
3095 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3096 verify_work_stacks_empty();
3097
3098 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
3099 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
3100
3101 // Marking completed -- now verify that each bit marked in
3102 // verification_mark_bm() is also marked in markBitMap(); flag all
3103 // errors by printing corresponding objects.
3104 VerifyMarkedClosure vcl(markBitMap());
3105 verification_mark_bm()->iterate(&vcl);
3106 assert(!vcl.failed(), "Else verification above should not have succeeded");
3107 }
3108
3109 void ConcurrentMarkSweepGeneration::save_marks() {
3110 // delegate to CMS space
3111 cmsSpace()->save_marks();
3112 for (uint i = 0; i < ParallelGCThreads; i++) {
3113 _par_gc_thread_states[i]->promo.startTrackingPromotions();
3114 }
3115 }
3116
3117 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
3118 return cmsSpace()->no_allocs_since_save_marks();
3119 }
3120
3121 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
3122 \
3123 void ConcurrentMarkSweepGeneration:: \
3124 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
3125 cl->set_generation(this); \
3126 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
3127 cl->reset_generation(); \
3128 save_marks(); \
3129 }
3130
3131 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
3132
3133 void
3134 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
3135 cl->set_generation(this);
3136 younger_refs_in_space_iterate(_cmsSpace, cl);
3137 cl->reset_generation();
3138 }
3139
3140 void
3141 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
3142 if (freelistLock()->owned_by_self()) {
3143 Generation::oop_iterate(cl);
3144 } else {
3145 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3146 Generation::oop_iterate(cl);
3147 }
3148 }
3149
3150 void
3151 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3152 if (freelistLock()->owned_by_self()) {
3153 Generation::object_iterate(cl);
3154 } else {
3155 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3156 Generation::object_iterate(cl);
3157 }
3158 }
3159
3160 void
3161 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3162 if (freelistLock()->owned_by_self()) {
3163 Generation::safe_object_iterate(cl);
3164 } else {
3165 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3166 Generation::safe_object_iterate(cl);
3167 }
3168 }
3169
3170 void
3171 ConcurrentMarkSweepGeneration::post_compact() {
3172 }
3173
3174 void
3175 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3176 // Fix the linear allocation blocks to look like free blocks.
3177
3178 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3179 // are not called when the heap is verified during universe initialization and
3180 // at vm shutdown.
3181 if (freelistLock()->owned_by_self()) {
3182 cmsSpace()->prepare_for_verify();
3183 } else {
3184 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3185 cmsSpace()->prepare_for_verify();
3186 }
3187 }
3188
3189 void
3190 ConcurrentMarkSweepGeneration::verify() {
3191 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3192 // are not called when the heap is verified during universe initialization and
3193 // at vm shutdown.
3194 if (freelistLock()->owned_by_self()) {
3195 cmsSpace()->verify();
3196 } else {
3197 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3198 cmsSpace()->verify();
3199 }
3200 }
3201
3202 void CMSCollector::verify() {
3203 _cmsGen->verify();
3204 }
3205
3206 #ifndef PRODUCT
3207 bool CMSCollector::overflow_list_is_empty() const {
3208 assert(_num_par_pushes >= 0, "Inconsistency");
3209 if (_overflow_list == NULL) {
3210 assert(_num_par_pushes == 0, "Inconsistency");
3211 }
3212 return _overflow_list == NULL;
3213 }
3214
3215 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3216 // merely consolidate assertion checks that appear to occur together frequently.
3217 void CMSCollector::verify_work_stacks_empty() const {
3218 assert(_markStack.isEmpty(), "Marking stack should be empty");
3219 assert(overflow_list_is_empty(), "Overflow list should be empty");
3220 }
3221
3222 void CMSCollector::verify_overflow_empty() const {
3223 assert(overflow_list_is_empty(), "Overflow list should be empty");
3224 assert(no_preserved_marks(), "No preserved marks");
3225 }
3226 #endif // PRODUCT
3227
3228 // Decide if we want to enable class unloading as part of the
3229 // ensuing concurrent GC cycle. We will collect and
3230 // unload classes if it's the case that:
3231 // (1) an explicit gc request has been made and the flag
3232 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3233 // (2) (a) class unloading is enabled at the command line, and
3234 // (b) old gen is getting really full
3235 // NOTE: Provided there is no change in the state of the heap between
3236 // calls to this method, it should have idempotent results. Moreover,
3237 // its results should be monotonically increasing (i.e. going from 0 to 1,
3238 // but not 1 to 0) between successive calls between which the heap was
3239 // not collected. For the implementation below, it must thus rely on
3240 // the property that concurrent_cycles_since_last_unload()
3241 // will not decrease unless a collection cycle happened and that
3242 // _cmsGen->is_too_full() are
3243 // themselves also monotonic in that sense. See check_monotonicity()
3244 // below.
3245 void CMSCollector::update_should_unload_classes() {
3246 _should_unload_classes = false;
3247 // Condition 1 above
3248 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3249 _should_unload_classes = true;
3250 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3251 // Disjuncts 2.b.(i,ii,iii) above
3252 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3253 CMSClassUnloadingMaxInterval)
3254 || _cmsGen->is_too_full();
3255 }
3256 }
3257
3258 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3259 bool res = should_concurrent_collect();
3260 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3261 return res;
3262 }
3263
3264 void CMSCollector::setup_cms_unloading_and_verification_state() {
3265 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3266 || VerifyBeforeExit;
3267 const int rso = SharedHeap::SO_AllCodeCache;
3268
3269 // We set the proper root for this CMS cycle here.
3270 if (should_unload_classes()) { // Should unload classes this cycle
3271 remove_root_scanning_option(rso); // Shrink the root set appropriately
3272 set_verifying(should_verify); // Set verification state for this cycle
3273 return; // Nothing else needs to be done at this time
3274 }
3275
3276 // Not unloading classes this cycle
3277 assert(!should_unload_classes(), "Inconsistency!");
3278
3279 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3280 // Include symbols, strings and code cache elements to prevent their resurrection.
3281 add_root_scanning_option(rso);
3282 set_verifying(true);
3283 } else if (verifying() && !should_verify) {
3284 // We were verifying, but some verification flags got disabled.
3285 set_verifying(false);
3286 // Exclude symbols, strings and code cache elements from root scanning to
3287 // reduce IM and RM pauses.
3288 remove_root_scanning_option(rso);
3289 }
3290 }
3291
3292
3293 #ifndef PRODUCT
3294 HeapWord* CMSCollector::block_start(const void* p) const {
3295 const HeapWord* addr = (HeapWord*)p;
3296 if (_span.contains(p)) {
3297 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3298 return _cmsGen->cmsSpace()->block_start(p);
3299 }
3300 }
3301 return NULL;
3302 }
3303 #endif
3304
3305 HeapWord*
3306 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3307 bool tlab,
3308 bool parallel) {
3309 CMSSynchronousYieldRequest yr;
3310 assert(!tlab, "Can't deal with TLAB allocation");
3311 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3312 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3313 CMSExpansionCause::_satisfy_allocation);
3314 if (GCExpandToAllocateDelayMillis > 0) {
3315 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3316 }
3317 return have_lock_and_allocate(word_size, tlab);
3318 }
3319
3320 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3321 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3322 // to CardGeneration and share it...
3323 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3324 return CardGeneration::expand(bytes, expand_bytes);
3325 }
3326
3327 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3328 CMSExpansionCause::Cause cause)
3329 {
3330
3331 bool success = expand(bytes, expand_bytes);
3332
3333 // remember why we expanded; this information is used
3334 // by shouldConcurrentCollect() when making decisions on whether to start
3335 // a new CMS cycle.
3336 if (success) {
3337 set_expansion_cause(cause);
3338 if (PrintGCDetails && Verbose) {
3339 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3340 CMSExpansionCause::to_string(cause));
3341 }
3342 }
3343 }
3344
3345 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3346 HeapWord* res = NULL;
3347 MutexLocker x(ParGCRareEvent_lock);
3348 while (true) {
3349 // Expansion by some other thread might make alloc OK now:
3350 res = ps->lab.alloc(word_sz);
3351 if (res != NULL) return res;
3352 // If there's not enough expansion space available, give up.
3353 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3354 return NULL;
3355 }
3356 // Otherwise, we try expansion.
3357 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3358 CMSExpansionCause::_allocate_par_lab);
3359 // Now go around the loop and try alloc again;
3360 // A competing par_promote might beat us to the expansion space,
3361 // so we may go around the loop again if promotion fails again.
3362 if (GCExpandToAllocateDelayMillis > 0) {
3363 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3364 }
3365 }
3366 }
3367
3368
3369 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3370 PromotionInfo* promo) {
3371 MutexLocker x(ParGCRareEvent_lock);
3372 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3373 while (true) {
3374 // Expansion by some other thread might make alloc OK now:
3375 if (promo->ensure_spooling_space()) {
3376 assert(promo->has_spooling_space(),
3377 "Post-condition of successful ensure_spooling_space()");
3378 return true;
3379 }
3380 // If there's not enough expansion space available, give up.
3381 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3382 return false;
3383 }
3384 // Otherwise, we try expansion.
3385 expand(refill_size_bytes, MinHeapDeltaBytes,
3386 CMSExpansionCause::_allocate_par_spooling_space);
3387 // Now go around the loop and try alloc again;
3388 // A competing allocation might beat us to the expansion space,
3389 // so we may go around the loop again if allocation fails again.
3390 if (GCExpandToAllocateDelayMillis > 0) {
3391 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3392 }
3393 }
3394 }
3395
3396
3397 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3398 assert_locked_or_safepoint(ExpandHeap_lock);
3399 // Shrink committed space
3400 _virtual_space.shrink_by(bytes);
3401 // Shrink space; this also shrinks the space's BOT
3402 _cmsSpace->set_end((HeapWord*) _virtual_space.high());
3403 size_t new_word_size = heap_word_size(_cmsSpace->capacity());
3404 // Shrink the shared block offset array
3405 _bts->resize(new_word_size);
3406 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3407 // Shrink the card table
3408 Universe::heap()->barrier_set()->resize_covered_region(mr);
3409
3410 if (Verbose && PrintGC) {
3411 size_t new_mem_size = _virtual_space.committed_size();
3412 size_t old_mem_size = new_mem_size + bytes;
3413 gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3414 name(), old_mem_size/K, new_mem_size/K);
3415 }
3416 }
3417
3418 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3419 assert_locked_or_safepoint(Heap_lock);
3420 size_t size = ReservedSpace::page_align_size_down(bytes);
3421 // Only shrink if a compaction was done so that all the free space
3422 // in the generation is in a contiguous block at the end.
3423 if (size > 0 && did_compact()) {
3424 shrink_by(size);
3425 }
3426 }
3427
3428 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3429 assert_locked_or_safepoint(Heap_lock);
3430 bool result = _virtual_space.expand_by(bytes);
3431 if (result) {
3432 size_t new_word_size =
3433 heap_word_size(_virtual_space.committed_size());
3434 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3435 _bts->resize(new_word_size); // resize the block offset shared array
3436 Universe::heap()->barrier_set()->resize_covered_region(mr);
3437 // Hmmmm... why doesn't CFLS::set_end verify locking?
3438 // This is quite ugly; FIX ME XXX
3439 _cmsSpace->assert_locked(freelistLock());
3440 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3441
3442 // update the space and generation capacity counters
3443 if (UsePerfData) {
3444 _space_counters->update_capacity();
3445 _gen_counters->update_all();
3446 }
3447
3448 if (Verbose && PrintGC) {
3449 size_t new_mem_size = _virtual_space.committed_size();
3450 size_t old_mem_size = new_mem_size - bytes;
3451 gclog_or_tty->print_cr("Expanding %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3452 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3453 }
3454 }
3455 return result;
3456 }
3457
3458 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3459 assert_locked_or_safepoint(Heap_lock);
3460 bool success = true;
3461 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3462 if (remaining_bytes > 0) {
3463 success = grow_by(remaining_bytes);
3464 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3465 }
3466 return success;
3467 }
3468
3469 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
3470 assert_locked_or_safepoint(Heap_lock);
3471 assert_lock_strong(freelistLock());
3472 if (PrintGCDetails && Verbose) {
3473 warning("Shrinking of CMS not yet implemented");
3474 }
3475 return;
3476 }
3477
3478
3479 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3480 // phases.
3481 class CMSPhaseAccounting: public StackObj {
3482 public:
3483 CMSPhaseAccounting(CMSCollector *collector,
3484 const char *phase,
3485 const GCId gc_id,
3486 bool print_cr = true);
3487 ~CMSPhaseAccounting();
3488
3489 private:
3490 CMSCollector *_collector;
3491 const char *_phase;
3492 elapsedTimer _wallclock;
3493 bool _print_cr;
3494 const GCId _gc_id;
3495
3496 public:
3497 // Not MT-safe; so do not pass around these StackObj's
3498 // where they may be accessed by other threads.
3499 jlong wallclock_millis() {
3500 assert(_wallclock.is_active(), "Wall clock should not stop");
3501 _wallclock.stop(); // to record time
3502 jlong ret = _wallclock.milliseconds();
3503 _wallclock.start(); // restart
3504 return ret;
3505 }
3506 };
3507
3508 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3509 const char *phase,
3510 const GCId gc_id,
3511 bool print_cr) :
3512 _collector(collector), _phase(phase), _print_cr(print_cr), _gc_id(gc_id) {
3513
3514 if (PrintCMSStatistics != 0) {
3515 _collector->resetYields();
3516 }
3517 if (PrintGCDetails) {
3518 gclog_or_tty->gclog_stamp(_gc_id);
3519 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
3520 _collector->cmsGen()->short_name(), _phase);
3521 }
3522 _collector->resetTimer();
3523 _wallclock.start();
3524 _collector->startTimer();
3525 }
3526
3527 CMSPhaseAccounting::~CMSPhaseAccounting() {
3528 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3529 _collector->stopTimer();
3530 _wallclock.stop();
3531 if (PrintGCDetails) {
3532 gclog_or_tty->gclog_stamp(_gc_id);
3533 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3534 _collector->cmsGen()->short_name(),
3535 _phase, _collector->timerValue(), _wallclock.seconds());
3536 if (_print_cr) {
3537 gclog_or_tty->cr();
3538 }
3539 if (PrintCMSStatistics != 0) {
3540 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3541 _collector->yields());
3542 }
3543 }
3544 }
3545
3546 // CMS work
3547
3548 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
3549 class CMSParMarkTask : public AbstractGangTask {
3550 protected:
3551 CMSCollector* _collector;
3552 int _n_workers;
3553 CMSParMarkTask(const char* name, CMSCollector* collector, int n_workers) :
3554 AbstractGangTask(name),
3555 _collector(collector),
3556 _n_workers(n_workers) {}
3557 // Work method in support of parallel rescan ... of young gen spaces
3558 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
3559 ContiguousSpace* space,
3560 HeapWord** chunk_array, size_t chunk_top);
3561 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
3562 };
3563
3564 // Parallel initial mark task
3565 class CMSParInitialMarkTask: public CMSParMarkTask {
3566 public:
3567 CMSParInitialMarkTask(CMSCollector* collector, int n_workers) :
3568 CMSParMarkTask("Scan roots and young gen for initial mark in parallel",
3569 collector, n_workers) {}
3570 void work(uint worker_id);
3571 };
3572
3573 // Checkpoint the roots into this generation from outside
3574 // this generation. [Note this initial checkpoint need only
3575 // be approximate -- we'll do a catch up phase subsequently.]
3576 void CMSCollector::checkpointRootsInitial(bool asynch) {
3577 assert(_collectorState == InitialMarking, "Wrong collector state");
3578 check_correct_thread_executing();
3579 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3580
3581 save_heap_summary();
3582 report_heap_summary(GCWhen::BeforeGC);
3583
3584 ReferenceProcessor* rp = ref_processor();
3585 SpecializationStats::clear();
3586 assert(_restart_addr == NULL, "Control point invariant");
3587 if (asynch) {
3588 // acquire locks for subsequent manipulations
3589 MutexLockerEx x(bitMapLock(),
3590 Mutex::_no_safepoint_check_flag);
3591 checkpointRootsInitialWork(asynch);
3592 // enable ("weak") refs discovery
3593 rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3594 _collectorState = Marking;
3595 } else {
3596 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3597 // which recognizes if we are a CMS generation, and doesn't try to turn on
3598 // discovery; verify that they aren't meddling.
3599 assert(!rp->discovery_is_atomic(),
3600 "incorrect setting of discovery predicate");
3601 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3602 "ref discovery for this generation kind");
3603 // already have locks
3604 checkpointRootsInitialWork(asynch);
3605 // now enable ("weak") refs discovery
3606 rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/);
3607 _collectorState = Marking;
3608 }
3609 SpecializationStats::print();
3610 }
3611
3612 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3613 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3614 assert(_collectorState == InitialMarking, "just checking");
3615
3616 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3617 // precede our marking with a collection of all
3618 // younger generations to keep floating garbage to a minimum.
3619 // XXX: we won't do this for now -- it's an optimization to be done later.
3620
3621 // already have locks
3622 assert_lock_strong(bitMapLock());
3623 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3624
3625 // Setup the verification and class unloading state for this
3626 // CMS collection cycle.
3627 setup_cms_unloading_and_verification_state();
3628
3629 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
3630 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
3631
3632 // Reset all the PLAB chunk arrays if necessary.
3633 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3634 reset_survivor_plab_arrays();
3635 }
3636
3637 ResourceMark rm;
3638 HandleMark hm;
3639
3640 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3641 GenCollectedHeap* gch = GenCollectedHeap::heap();
3642
3643 verify_work_stacks_empty();
3644 verify_overflow_empty();
3645
3646 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3647 // Update the saved marks which may affect the root scans.
3648 gch->save_marks();
3649
3650 // weak reference processing has not started yet.
3651 ref_processor()->set_enqueuing_is_done(false);
3652
3653 // Need to remember all newly created CLDs,
3654 // so that we can guarantee that the remark finds them.
3655 ClassLoaderDataGraph::remember_new_clds(true);
3656
3657 // Whenever a CLD is found, it will be claimed before proceeding to mark
3658 // the klasses. The claimed marks need to be cleared before marking starts.
3659 ClassLoaderDataGraph::clear_claimed_marks();
3660
3661 if (CMSPrintEdenSurvivorChunks) {
3662 print_eden_and_survivor_chunk_arrays();
3663 }
3664
3665 {
3666 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3667 if (CMSParallelInitialMarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
3668 // The parallel version.
3669 FlexibleWorkGang* workers = gch->workers();
3670 assert(workers != NULL, "Need parallel worker threads.");
3671 int n_workers = workers->active_workers();
3672 CMSParInitialMarkTask tsk(this, n_workers);
3673 gch->set_par_threads(n_workers);
3674 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3675 if (n_workers > 1) {
3676 GenCollectedHeap::StrongRootsScope srs(gch);
3677 workers->run_task(&tsk);
3678 } else {
3679 GenCollectedHeap::StrongRootsScope srs(gch);
3680 tsk.work(0);
3681 }
3682 gch->set_par_threads(0);
3683 } else {
3684 // The serial version.
3685 CLDToOopClosure cld_closure(¬Older, true);
3686 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3687 gch->gen_process_roots(_cmsGen->level(),
3688 true, // younger gens are roots
3689 true, // activate StrongRootsScope
3690 SharedHeap::ScanningOption(roots_scanning_options()),
3691 should_unload_classes(),
3692 ¬Older,
3693 NULL,
3694 &cld_closure);
3695 }
3696 }
3697
3698 // Clear mod-union table; it will be dirtied in the prologue of
3699 // CMS generation per each younger generation collection.
3700
3701 assert(_modUnionTable.isAllClear(),
3702 "Was cleared in most recent final checkpoint phase"
3703 " or no bits are set in the gc_prologue before the start of the next "
3704 "subsequent marking phase.");
3705
3706 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3707
3708 // Save the end of the used_region of the constituent generations
3709 // to be used to limit the extent of sweep in each generation.
3710 save_sweep_limits();
3711 verify_overflow_empty();
3712 }
3713
3714 bool CMSCollector::markFromRoots(bool asynch) {
3715 // we might be tempted to assert that:
3716 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3717 // "inconsistent argument?");
3718 // However that wouldn't be right, because it's possible that
3719 // a safepoint is indeed in progress as a younger generation
3720 // stop-the-world GC happens even as we mark in this generation.
3721 assert(_collectorState == Marking, "inconsistent state?");
3722 check_correct_thread_executing();
3723 verify_overflow_empty();
3724
3725 bool res;
3726 if (asynch) {
3727 // Weak ref discovery note: We may be discovering weak
3728 // refs in this generation concurrent (but interleaved) with
3729 // weak ref discovery by a younger generation collector.
3730
3731 CMSTokenSyncWithLocks ts(true, bitMapLock());
3732 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3733 CMSPhaseAccounting pa(this, "mark", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3734 res = markFromRootsWork(asynch);
3735 if (res) {
3736 _collectorState = Precleaning;
3737 } else { // We failed and a foreground collection wants to take over
3738 assert(_foregroundGCIsActive, "internal state inconsistency");
3739 assert(_restart_addr == NULL, "foreground will restart from scratch");
3740 if (PrintGCDetails) {
3741 gclog_or_tty->print_cr("bailing out to foreground collection");
3742 }
3743 }
3744 } else {
3745 assert(SafepointSynchronize::is_at_safepoint(),
3746 "inconsistent with asynch == false");
3747 // already have locks
3748 res = markFromRootsWork(asynch);
3749 _collectorState = FinalMarking;
3750 }
3751 verify_overflow_empty();
3752 return res;
3753 }
3754
3755 bool CMSCollector::markFromRootsWork(bool asynch) {
3756 // iterate over marked bits in bit map, doing a full scan and mark
3757 // from these roots using the following algorithm:
3758 // . if oop is to the right of the current scan pointer,
3759 // mark corresponding bit (we'll process it later)
3760 // . else (oop is to left of current scan pointer)
3761 // push oop on marking stack
3762 // . drain the marking stack
3763
3764 // Note that when we do a marking step we need to hold the
3765 // bit map lock -- recall that direct allocation (by mutators)
3766 // and promotion (by younger generation collectors) is also
3767 // marking the bit map. [the so-called allocate live policy.]
3768 // Because the implementation of bit map marking is not
3769 // robust wrt simultaneous marking of bits in the same word,
3770 // we need to make sure that there is no such interference
3771 // between concurrent such updates.
3772
3773 // already have locks
3774 assert_lock_strong(bitMapLock());
3775
3776 verify_work_stacks_empty();
3777 verify_overflow_empty();
3778 bool result = false;
3779 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3780 result = do_marking_mt(asynch);
3781 } else {
3782 result = do_marking_st(asynch);
3783 }
3784 return result;
3785 }
3786
3787 // Forward decl
3788 class CMSConcMarkingTask;
3789
3790 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3791 CMSCollector* _collector;
3792 CMSConcMarkingTask* _task;
3793 public:
3794 virtual void yield();
3795
3796 // "n_threads" is the number of threads to be terminated.
3797 // "queue_set" is a set of work queues of other threads.
3798 // "collector" is the CMS collector associated with this task terminator.
3799 // "yield" indicates whether we need the gang as a whole to yield.
3800 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3801 ParallelTaskTerminator(n_threads, queue_set),
3802 _collector(collector) { }
3803
3804 void set_task(CMSConcMarkingTask* task) {
3805 _task = task;
3806 }
3807 };
3808
3809 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3810 CMSConcMarkingTask* _task;
3811 public:
3812 bool should_exit_termination();
3813 void set_task(CMSConcMarkingTask* task) {
3814 _task = task;
3815 }
3816 };
3817
3818 // MT Concurrent Marking Task
3819 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3820 CMSCollector* _collector;
3821 int _n_workers; // requested/desired # workers
3822 bool _asynch;
3823 bool _result;
3824 CompactibleFreeListSpace* _cms_space;
3825 char _pad_front[64]; // padding to ...
3826 HeapWord* _global_finger; // ... avoid sharing cache line
3827 char _pad_back[64];
3828 HeapWord* _restart_addr;
3829
3830 // Exposed here for yielding support
3831 Mutex* const _bit_map_lock;
3832
3833 // The per thread work queues, available here for stealing
3834 OopTaskQueueSet* _task_queues;
3835
3836 // Termination (and yielding) support
3837 CMSConcMarkingTerminator _term;
3838 CMSConcMarkingTerminatorTerminator _term_term;
3839
3840 public:
3841 CMSConcMarkingTask(CMSCollector* collector,
3842 CompactibleFreeListSpace* cms_space,
3843 bool asynch,
3844 YieldingFlexibleWorkGang* workers,
3845 OopTaskQueueSet* task_queues):
3846 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3847 _collector(collector),
3848 _cms_space(cms_space),
3849 _asynch(asynch), _n_workers(0), _result(true),
3850 _task_queues(task_queues),
3851 _term(_n_workers, task_queues, _collector),
3852 _bit_map_lock(collector->bitMapLock())
3853 {
3854 _requested_size = _n_workers;
3855 _term.set_task(this);
3856 _term_term.set_task(this);
3857 _restart_addr = _global_finger = _cms_space->bottom();
3858 }
3859
3860
3861 OopTaskQueueSet* task_queues() { return _task_queues; }
3862
3863 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3864
3865 HeapWord** global_finger_addr() { return &_global_finger; }
3866
3867 CMSConcMarkingTerminator* terminator() { return &_term; }
3868
3869 virtual void set_for_termination(int active_workers) {
3870 terminator()->reset_for_reuse(active_workers);
3871 }
3872
3873 void work(uint worker_id);
3874 bool should_yield() {
3875 return ConcurrentMarkSweepThread::should_yield()
3876 && !_collector->foregroundGCIsActive()
3877 && _asynch;
3878 }
3879
3880 virtual void coordinator_yield(); // stuff done by coordinator
3881 bool result() { return _result; }
3882
3883 void reset(HeapWord* ra) {
3884 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3885 _restart_addr = _global_finger = ra;
3886 _term.reset_for_reuse();
3887 }
3888
3889 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3890 OopTaskQueue* work_q);
3891
3892 private:
3893 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3894 void do_work_steal(int i);
3895 void bump_global_finger(HeapWord* f);
3896 };
3897
3898 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3899 assert(_task != NULL, "Error");
3900 return _task->yielding();
3901 // Note that we do not need the disjunct || _task->should_yield() above
3902 // because we want terminating threads to yield only if the task
3903 // is already in the midst of yielding, which happens only after at least one
3904 // thread has yielded.
3905 }
3906
3907 void CMSConcMarkingTerminator::yield() {
3908 if (_task->should_yield()) {
3909 _task->yield();
3910 } else {
3911 ParallelTaskTerminator::yield();
3912 }
3913 }
3914
3915 ////////////////////////////////////////////////////////////////
3916 // Concurrent Marking Algorithm Sketch
3917 ////////////////////////////////////////////////////////////////
3918 // Until all tasks exhausted (both spaces):
3919 // -- claim next available chunk
3920 // -- bump global finger via CAS
3921 // -- find first object that starts in this chunk
3922 // and start scanning bitmap from that position
3923 // -- scan marked objects for oops
3924 // -- CAS-mark target, and if successful:
3925 // . if target oop is above global finger (volatile read)
3926 // nothing to do
3927 // . if target oop is in chunk and above local finger
3928 // then nothing to do
3929 // . else push on work-queue
3930 // -- Deal with possible overflow issues:
3931 // . local work-queue overflow causes stuff to be pushed on
3932 // global (common) overflow queue
3933 // . always first empty local work queue
3934 // . then get a batch of oops from global work queue if any
3935 // . then do work stealing
3936 // -- When all tasks claimed (both spaces)
3937 // and local work queue empty,
3938 // then in a loop do:
3939 // . check global overflow stack; steal a batch of oops and trace
3940 // . try to steal from other threads oif GOS is empty
3941 // . if neither is available, offer termination
3942 // -- Terminate and return result
3943 //
3944 void CMSConcMarkingTask::work(uint worker_id) {
3945 elapsedTimer _timer;
3946 ResourceMark rm;
3947 HandleMark hm;
3948
3949 DEBUG_ONLY(_collector->verify_overflow_empty();)
3950
3951 // Before we begin work, our work queue should be empty
3952 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3953 // Scan the bitmap covering _cms_space, tracing through grey objects.
3954 _timer.start();
3955 do_scan_and_mark(worker_id, _cms_space);
3956 _timer.stop();
3957 if (PrintCMSStatistics != 0) {
3958 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3959 worker_id, _timer.seconds());
3960 // XXX: need xxx/xxx type of notation, two timers
3961 }
3962
3963 // ... do work stealing
3964 _timer.reset();
3965 _timer.start();
3966 do_work_steal(worker_id);
3967 _timer.stop();
3968 if (PrintCMSStatistics != 0) {
3969 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3970 worker_id, _timer.seconds());
3971 // XXX: need xxx/xxx type of notation, two timers
3972 }
3973 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3974 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3975 // Note that under the current task protocol, the
3976 // following assertion is true even of the spaces
3977 // expanded since the completion of the concurrent
3978 // marking. XXX This will likely change under a strict
3979 // ABORT semantics.
3980 // After perm removal the comparison was changed to
3981 // greater than or equal to from strictly greater than.
3982 // Before perm removal the highest address sweep would
3983 // have been at the end of perm gen but now is at the
3984 // end of the tenured gen.
3985 assert(_global_finger >= _cms_space->end(),
3986 "All tasks have been completed");
3987 DEBUG_ONLY(_collector->verify_overflow_empty();)
3988 }
3989
3990 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3991 HeapWord* read = _global_finger;
3992 HeapWord* cur = read;
3993 while (f > read) {
3994 cur = read;
3995 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3996 if (cur == read) {
3997 // our cas succeeded
3998 assert(_global_finger >= f, "protocol consistency");
3999 break;
4000 }
4001 }
4002 }
4003
4004 // This is really inefficient, and should be redone by
4005 // using (not yet available) block-read and -write interfaces to the
4006 // stack and the work_queue. XXX FIX ME !!!
4007 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
4008 OopTaskQueue* work_q) {
4009 // Fast lock-free check
4010 if (ovflw_stk->length() == 0) {
4011 return false;
4012 }
4013 assert(work_q->size() == 0, "Shouldn't steal");
4014 MutexLockerEx ml(ovflw_stk->par_lock(),
4015 Mutex::_no_safepoint_check_flag);
4016 // Grab up to 1/4 the size of the work queue
4017 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4018 (size_t)ParGCDesiredObjsFromOverflowList);
4019 num = MIN2(num, ovflw_stk->length());
4020 for (int i = (int) num; i > 0; i--) {
4021 oop cur = ovflw_stk->pop();
4022 assert(cur != NULL, "Counted wrong?");
4023 work_q->push(cur);
4024 }
4025 return num > 0;
4026 }
4027
4028 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
4029 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4030 int n_tasks = pst->n_tasks();
4031 // We allow that there may be no tasks to do here because
4032 // we are restarting after a stack overflow.
4033 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
4034 uint nth_task = 0;
4035
4036 HeapWord* aligned_start = sp->bottom();
4037 if (sp->used_region().contains(_restart_addr)) {
4038 // Align down to a card boundary for the start of 0th task
4039 // for this space.
4040 aligned_start =
4041 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
4042 CardTableModRefBS::card_size);
4043 }
4044
4045 size_t chunk_size = sp->marking_task_size();
4046 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4047 // Having claimed the nth task in this space,
4048 // compute the chunk that it corresponds to:
4049 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
4050 aligned_start + (nth_task+1)*chunk_size);
4051 // Try and bump the global finger via a CAS;
4052 // note that we need to do the global finger bump
4053 // _before_ taking the intersection below, because
4054 // the task corresponding to that region will be
4055 // deemed done even if the used_region() expands
4056 // because of allocation -- as it almost certainly will
4057 // during start-up while the threads yield in the
4058 // closure below.
4059 HeapWord* finger = span.end();
4060 bump_global_finger(finger); // atomically
4061 // There are null tasks here corresponding to chunks
4062 // beyond the "top" address of the space.
4063 span = span.intersection(sp->used_region());
4064 if (!span.is_empty()) { // Non-null task
4065 HeapWord* prev_obj;
4066 assert(!span.contains(_restart_addr) || nth_task == 0,
4067 "Inconsistency");
4068 if (nth_task == 0) {
4069 // For the 0th task, we'll not need to compute a block_start.
4070 if (span.contains(_restart_addr)) {
4071 // In the case of a restart because of stack overflow,
4072 // we might additionally skip a chunk prefix.
4073 prev_obj = _restart_addr;
4074 } else {
4075 prev_obj = span.start();
4076 }
4077 } else {
4078 // We want to skip the first object because
4079 // the protocol is to scan any object in its entirety
4080 // that _starts_ in this span; a fortiori, any
4081 // object starting in an earlier span is scanned
4082 // as part of an earlier claimed task.
4083 // Below we use the "careful" version of block_start
4084 // so we do not try to navigate uninitialized objects.
4085 prev_obj = sp->block_start_careful(span.start());
4086 // Below we use a variant of block_size that uses the
4087 // Printezis bits to avoid waiting for allocated
4088 // objects to become initialized/parsable.
4089 while (prev_obj < span.start()) {
4090 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
4091 if (sz > 0) {
4092 prev_obj += sz;
4093 } else {
4094 // In this case we may end up doing a bit of redundant
4095 // scanning, but that appears unavoidable, short of
4096 // locking the free list locks; see bug 6324141.
4097 break;
4098 }
4099 }
4100 }
4101 if (prev_obj < span.end()) {
4102 MemRegion my_span = MemRegion(prev_obj, span.end());
4103 // Do the marking work within a non-empty span --
4104 // the last argument to the constructor indicates whether the
4105 // iteration should be incremental with periodic yields.
4106 Par_MarkFromRootsClosure cl(this, _collector, my_span,
4107 &_collector->_markBitMap,
4108 work_queue(i),
4109 &_collector->_markStack,
4110 _asynch);
4111 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
4112 } // else nothing to do for this task
4113 } // else nothing to do for this task
4114 }
4115 // We'd be tempted to assert here that since there are no
4116 // more tasks left to claim in this space, the global_finger
4117 // must exceed space->top() and a fortiori space->end(). However,
4118 // that would not quite be correct because the bumping of
4119 // global_finger occurs strictly after the claiming of a task,
4120 // so by the time we reach here the global finger may not yet
4121 // have been bumped up by the thread that claimed the last
4122 // task.
4123 pst->all_tasks_completed();
4124 }
4125
4126 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
4127 private:
4128 CMSCollector* _collector;
4129 CMSConcMarkingTask* _task;
4130 MemRegion _span;
4131 CMSBitMap* _bit_map;
4132 CMSMarkStack* _overflow_stack;
4133 OopTaskQueue* _work_queue;
4134 protected:
4135 DO_OOP_WORK_DEFN
4136 public:
4137 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
4138 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
4139 MetadataAwareOopClosure(collector->ref_processor()),
4140 _collector(collector),
4141 _task(task),
4142 _span(collector->_span),
4143 _work_queue(work_queue),
4144 _bit_map(bit_map),
4145 _overflow_stack(overflow_stack)
4146 { }
4147 virtual void do_oop(oop* p);
4148 virtual void do_oop(narrowOop* p);
4149
4150 void trim_queue(size_t max);
4151 void handle_stack_overflow(HeapWord* lost);
4152 void do_yield_check() {
4153 if (_task->should_yield()) {
4154 _task->yield();
4155 }
4156 }
4157 };
4158
4159 // Grey object scanning during work stealing phase --
4160 // the salient assumption here is that any references
4161 // that are in these stolen objects being scanned must
4162 // already have been initialized (else they would not have
4163 // been published), so we do not need to check for
4164 // uninitialized objects before pushing here.
4165 void Par_ConcMarkingClosure::do_oop(oop obj) {
4166 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
4167 HeapWord* addr = (HeapWord*)obj;
4168 // Check if oop points into the CMS generation
4169 // and is not marked
4170 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4171 // a white object ...
4172 // If we manage to "claim" the object, by being the
4173 // first thread to mark it, then we push it on our
4174 // marking stack
4175 if (_bit_map->par_mark(addr)) { // ... now grey
4176 // push on work queue (grey set)
4177 bool simulate_overflow = false;
4178 NOT_PRODUCT(
4179 if (CMSMarkStackOverflowALot &&
4180 _collector->simulate_overflow()) {
4181 // simulate a stack overflow
4182 simulate_overflow = true;
4183 }
4184 )
4185 if (simulate_overflow ||
4186 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4187 // stack overflow
4188 if (PrintCMSStatistics != 0) {
4189 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4190 SIZE_FORMAT, _overflow_stack->capacity());
4191 }
4192 // We cannot assert that the overflow stack is full because
4193 // it may have been emptied since.
4194 assert(simulate_overflow ||
4195 _work_queue->size() == _work_queue->max_elems(),
4196 "Else push should have succeeded");
4197 handle_stack_overflow(addr);
4198 }
4199 } // Else, some other thread got there first
4200 do_yield_check();
4201 }
4202 }
4203
4204 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4205 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4206
4207 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4208 while (_work_queue->size() > max) {
4209 oop new_oop;
4210 if (_work_queue->pop_local(new_oop)) {
4211 assert(new_oop->is_oop(), "Should be an oop");
4212 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4213 assert(_span.contains((HeapWord*)new_oop), "Not in span");
4214 new_oop->oop_iterate(this); // do_oop() above
4215 do_yield_check();
4216 }
4217 }
4218 }
4219
4220 // Upon stack overflow, we discard (part of) the stack,
4221 // remembering the least address amongst those discarded
4222 // in CMSCollector's _restart_address.
4223 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4224 // We need to do this under a mutex to prevent other
4225 // workers from interfering with the work done below.
4226 MutexLockerEx ml(_overflow_stack->par_lock(),
4227 Mutex::_no_safepoint_check_flag);
4228 // Remember the least grey address discarded
4229 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4230 _collector->lower_restart_addr(ra);
4231 _overflow_stack->reset(); // discard stack contents
4232 _overflow_stack->expand(); // expand the stack if possible
4233 }
4234
4235
4236 void CMSConcMarkingTask::do_work_steal(int i) {
4237 OopTaskQueue* work_q = work_queue(i);
4238 oop obj_to_scan;
4239 CMSBitMap* bm = &(_collector->_markBitMap);
4240 CMSMarkStack* ovflw = &(_collector->_markStack);
4241 int* seed = _collector->hash_seed(i);
4242 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
4243 while (true) {
4244 cl.trim_queue(0);
4245 assert(work_q->size() == 0, "Should have been emptied above");
4246 if (get_work_from_overflow_stack(ovflw, work_q)) {
4247 // Can't assert below because the work obtained from the
4248 // overflow stack may already have been stolen from us.
4249 // assert(work_q->size() > 0, "Work from overflow stack");
4250 continue;
4251 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4252 assert(obj_to_scan->is_oop(), "Should be an oop");
4253 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4254 obj_to_scan->oop_iterate(&cl);
4255 } else if (terminator()->offer_termination(&_term_term)) {
4256 assert(work_q->size() == 0, "Impossible!");
4257 break;
4258 } else if (yielding() || should_yield()) {
4259 yield();
4260 }
4261 }
4262 }
4263
4264 // This is run by the CMS (coordinator) thread.
4265 void CMSConcMarkingTask::coordinator_yield() {
4266 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4267 "CMS thread should hold CMS token");
4268 // First give up the locks, then yield, then re-lock
4269 // We should probably use a constructor/destructor idiom to
4270 // do this unlock/lock or modify the MutexUnlocker class to
4271 // serve our purpose. XXX
4272 assert_lock_strong(_bit_map_lock);
4273 _bit_map_lock->unlock();
4274 ConcurrentMarkSweepThread::desynchronize(true);
4275 ConcurrentMarkSweepThread::acknowledge_yield_request();
4276 _collector->stopTimer();
4277 if (PrintCMSStatistics != 0) {
4278 _collector->incrementYields();
4279 }
4280 _collector->icms_wait();
4281
4282 // It is possible for whichever thread initiated the yield request
4283 // not to get a chance to wake up and take the bitmap lock between
4284 // this thread releasing it and reacquiring it. So, while the
4285 // should_yield() flag is on, let's sleep for a bit to give the
4286 // other thread a chance to wake up. The limit imposed on the number
4287 // of iterations is defensive, to avoid any unforseen circumstances
4288 // putting us into an infinite loop. Since it's always been this
4289 // (coordinator_yield()) method that was observed to cause the
4290 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4291 // which is by default non-zero. For the other seven methods that
4292 // also perform the yield operation, as are using a different
4293 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4294 // can enable the sleeping for those methods too, if necessary.
4295 // See 6442774.
4296 //
4297 // We really need to reconsider the synchronization between the GC
4298 // thread and the yield-requesting threads in the future and we
4299 // should really use wait/notify, which is the recommended
4300 // way of doing this type of interaction. Additionally, we should
4301 // consolidate the eight methods that do the yield operation and they
4302 // are almost identical into one for better maintainability and
4303 // readability. See 6445193.
4304 //
4305 // Tony 2006.06.29
4306 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4307 ConcurrentMarkSweepThread::should_yield() &&
4308 !CMSCollector::foregroundGCIsActive(); ++i) {
4309 os::sleep(Thread::current(), 1, false);
4310 ConcurrentMarkSweepThread::acknowledge_yield_request();
4311 }
4312
4313 ConcurrentMarkSweepThread::synchronize(true);
4314 _bit_map_lock->lock_without_safepoint_check();
4315 _collector->startTimer();
4316 }
4317
4318 bool CMSCollector::do_marking_mt(bool asynch) {
4319 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4320 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
4321 conc_workers()->total_workers(),
4322 conc_workers()->active_workers(),
4323 Threads::number_of_non_daemon_threads());
4324 conc_workers()->set_active_workers(num_workers);
4325
4326 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4327
4328 CMSConcMarkingTask tsk(this,
4329 cms_space,
4330 asynch,
4331 conc_workers(),
4332 task_queues());
4333
4334 // Since the actual number of workers we get may be different
4335 // from the number we requested above, do we need to do anything different
4336 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4337 // class?? XXX
4338 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4339
4340 // Refs discovery is already non-atomic.
4341 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4342 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
4343 conc_workers()->start_task(&tsk);
4344 while (tsk.yielded()) {
4345 tsk.coordinator_yield();
4346 conc_workers()->continue_task(&tsk);
4347 }
4348 // If the task was aborted, _restart_addr will be non-NULL
4349 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4350 while (_restart_addr != NULL) {
4351 // XXX For now we do not make use of ABORTED state and have not
4352 // yet implemented the right abort semantics (even in the original
4353 // single-threaded CMS case). That needs some more investigation
4354 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4355 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4356 // If _restart_addr is non-NULL, a marking stack overflow
4357 // occurred; we need to do a fresh marking iteration from the
4358 // indicated restart address.
4359 if (_foregroundGCIsActive && asynch) {
4360 // We may be running into repeated stack overflows, having
4361 // reached the limit of the stack size, while making very
4362 // slow forward progress. It may be best to bail out and
4363 // let the foreground collector do its job.
4364 // Clear _restart_addr, so that foreground GC
4365 // works from scratch. This avoids the headache of
4366 // a "rescan" which would otherwise be needed because
4367 // of the dirty mod union table & card table.
4368 _restart_addr = NULL;
4369 return false;
4370 }
4371 // Adjust the task to restart from _restart_addr
4372 tsk.reset(_restart_addr);
4373 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4374 _restart_addr);
4375 _restart_addr = NULL;
4376 // Get the workers going again
4377 conc_workers()->start_task(&tsk);
4378 while (tsk.yielded()) {
4379 tsk.coordinator_yield();
4380 conc_workers()->continue_task(&tsk);
4381 }
4382 }
4383 assert(tsk.completed(), "Inconsistency");
4384 assert(tsk.result() == true, "Inconsistency");
4385 return true;
4386 }
4387
4388 bool CMSCollector::do_marking_st(bool asynch) {
4389 ResourceMark rm;
4390 HandleMark hm;
4391
4392 // Temporarily make refs discovery single threaded (non-MT)
4393 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
4394 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4395 &_markStack, CMSYield && asynch);
4396 // the last argument to iterate indicates whether the iteration
4397 // should be incremental with periodic yields.
4398 _markBitMap.iterate(&markFromRootsClosure);
4399 // If _restart_addr is non-NULL, a marking stack overflow
4400 // occurred; we need to do a fresh iteration from the
4401 // indicated restart address.
4402 while (_restart_addr != NULL) {
4403 if (_foregroundGCIsActive && asynch) {
4404 // We may be running into repeated stack overflows, having
4405 // reached the limit of the stack size, while making very
4406 // slow forward progress. It may be best to bail out and
4407 // let the foreground collector do its job.
4408 // Clear _restart_addr, so that foreground GC
4409 // works from scratch. This avoids the headache of
4410 // a "rescan" which would otherwise be needed because
4411 // of the dirty mod union table & card table.
4412 _restart_addr = NULL;
4413 return false; // indicating failure to complete marking
4414 }
4415 // Deal with stack overflow:
4416 // we restart marking from _restart_addr
4417 HeapWord* ra = _restart_addr;
4418 markFromRootsClosure.reset(ra);
4419 _restart_addr = NULL;
4420 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4421 }
4422 return true;
4423 }
4424
4425 void CMSCollector::preclean() {
4426 check_correct_thread_executing();
4427 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4428 verify_work_stacks_empty();
4429 verify_overflow_empty();
4430 _abort_preclean = false;
4431 if (CMSPrecleaningEnabled) {
4432 if (!CMSEdenChunksRecordAlways) {
4433 _eden_chunk_index = 0;
4434 }
4435 size_t used = get_eden_used();
4436 size_t capacity = get_eden_capacity();
4437 // Don't start sampling unless we will get sufficiently
4438 // many samples.
4439 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4440 * CMSScheduleRemarkEdenPenetration)) {
4441 _start_sampling = true;
4442 } else {
4443 _start_sampling = false;
4444 }
4445 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4446 CMSPhaseAccounting pa(this, "preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
4447 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4448 }
4449 CMSTokenSync x(true); // is cms thread
4450 if (CMSPrecleaningEnabled) {
4451 sample_eden();
4452 _collectorState = AbortablePreclean;
4453 } else {
4454 _collectorState = FinalMarking;
4455 }
4456 verify_work_stacks_empty();
4457 verify_overflow_empty();
4458 }
4459
4460 // Try and schedule the remark such that young gen
4461 // occupancy is CMSScheduleRemarkEdenPenetration %.
4462 void CMSCollector::abortable_preclean() {
4463 check_correct_thread_executing();
4464 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4465 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4466
4467 // If Eden's current occupancy is below this threshold,
4468 // immediately schedule the remark; else preclean
4469 // past the next scavenge in an effort to
4470 // schedule the pause as described above. By choosing
4471 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4472 // we will never do an actual abortable preclean cycle.
4473 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4474 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4475 CMSPhaseAccounting pa(this, "abortable-preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
4476 // We need more smarts in the abortable preclean
4477 // loop below to deal with cases where allocation
4478 // in young gen is very very slow, and our precleaning
4479 // is running a losing race against a horde of
4480 // mutators intent on flooding us with CMS updates
4481 // (dirty cards).
4482 // One, admittedly dumb, strategy is to give up
4483 // after a certain number of abortable precleaning loops
4484 // or after a certain maximum time. We want to make
4485 // this smarter in the next iteration.
4486 // XXX FIX ME!!! YSR
4487 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4488 while (!(should_abort_preclean() ||
4489 ConcurrentMarkSweepThread::should_terminate())) {
4490 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4491 cumworkdone += workdone;
4492 loops++;
4493 // Voluntarily terminate abortable preclean phase if we have
4494 // been at it for too long.
4495 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4496 loops >= CMSMaxAbortablePrecleanLoops) {
4497 if (PrintGCDetails) {
4498 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4499 }
4500 break;
4501 }
4502 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4503 if (PrintGCDetails) {
4504 gclog_or_tty->print(" CMS: abort preclean due to time ");
4505 }
4506 break;
4507 }
4508 // If we are doing little work each iteration, we should
4509 // take a short break.
4510 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4511 // Sleep for some time, waiting for work to accumulate
4512 stopTimer();
4513 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4514 startTimer();
4515 waited++;
4516 }
4517 }
4518 if (PrintCMSStatistics > 0) {
4519 gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
4520 loops, waited, cumworkdone);
4521 }
4522 }
4523 CMSTokenSync x(true); // is cms thread
4524 if (_collectorState != Idling) {
4525 assert(_collectorState == AbortablePreclean,
4526 "Spontaneous state transition?");
4527 _collectorState = FinalMarking;
4528 } // Else, a foreground collection completed this CMS cycle.
4529 return;
4530 }
4531
4532 // Respond to an Eden sampling opportunity
4533 void CMSCollector::sample_eden() {
4534 // Make sure a young gc cannot sneak in between our
4535 // reading and recording of a sample.
4536 assert(Thread::current()->is_ConcurrentGC_thread(),
4537 "Only the cms thread may collect Eden samples");
4538 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4539 "Should collect samples while holding CMS token");
4540 if (!_start_sampling) {
4541 return;
4542 }
4543 // When CMSEdenChunksRecordAlways is true, the eden chunk array
4544 // is populated by the young generation.
4545 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
4546 if (_eden_chunk_index < _eden_chunk_capacity) {
4547 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4548 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4549 "Unexpected state of Eden");
4550 // We'd like to check that what we just sampled is an oop-start address;
4551 // however, we cannot do that here since the object may not yet have been
4552 // initialized. So we'll instead do the check when we _use_ this sample
4553 // later.
4554 if (_eden_chunk_index == 0 ||
4555 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4556 _eden_chunk_array[_eden_chunk_index-1])
4557 >= CMSSamplingGrain)) {
4558 _eden_chunk_index++; // commit sample
4559 }
4560 }
4561 }
4562 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4563 size_t used = get_eden_used();
4564 size_t capacity = get_eden_capacity();
4565 assert(used <= capacity, "Unexpected state of Eden");
4566 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4567 _abort_preclean = true;
4568 }
4569 }
4570 }
4571
4572
4573 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4574 assert(_collectorState == Precleaning ||
4575 _collectorState == AbortablePreclean, "incorrect state");
4576 ResourceMark rm;
4577 HandleMark hm;
4578
4579 // Precleaning is currently not MT but the reference processor
4580 // may be set for MT. Disable it temporarily here.
4581 ReferenceProcessor* rp = ref_processor();
4582 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4583
4584 // Do one pass of scrubbing the discovered reference lists
4585 // to remove any reference objects with strongly-reachable
4586 // referents.
4587 if (clean_refs) {
4588 CMSPrecleanRefsYieldClosure yield_cl(this);
4589 assert(rp->span().equals(_span), "Spans should be equal");
4590 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4591 &_markStack, true /* preclean */);
4592 CMSDrainMarkingStackClosure complete_trace(this,
4593 _span, &_markBitMap, &_markStack,
4594 &keep_alive, true /* preclean */);
4595
4596 // We don't want this step to interfere with a young
4597 // collection because we don't want to take CPU
4598 // or memory bandwidth away from the young GC threads
4599 // (which may be as many as there are CPUs).
4600 // Note that we don't need to protect ourselves from
4601 // interference with mutators because they can't
4602 // manipulate the discovered reference lists nor affect
4603 // the computed reachability of the referents, the
4604 // only properties manipulated by the precleaning
4605 // of these reference lists.
4606 stopTimer();
4607 CMSTokenSyncWithLocks x(true /* is cms thread */,
4608 bitMapLock());
4609 startTimer();
4610 sample_eden();
4611
4612 // The following will yield to allow foreground
4613 // collection to proceed promptly. XXX YSR:
4614 // The code in this method may need further
4615 // tweaking for better performance and some restructuring
4616 // for cleaner interfaces.
4617 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
4618 rp->preclean_discovered_references(
4619 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
4620 gc_timer, _gc_tracer_cm->gc_id());
4621 }
4622
4623 if (clean_survivor) { // preclean the active survivor space(s)
4624 assert(_young_gen->kind() == Generation::DefNew ||
4625 _young_gen->kind() == Generation::ParNew,
4626 "incorrect type for cast");
4627 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4628 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4629 &_markBitMap, &_modUnionTable,
4630 &_markStack, true /* precleaning phase */);
4631 stopTimer();
4632 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4633 bitMapLock());
4634 startTimer();
4635 unsigned int before_count =
4636 GenCollectedHeap::heap()->total_collections();
4637 SurvivorSpacePrecleanClosure
4638 sss_cl(this, _span, &_markBitMap, &_markStack,
4639 &pam_cl, before_count, CMSYield);
4640 dng->from()->object_iterate_careful(&sss_cl);
4641 dng->to()->object_iterate_careful(&sss_cl);
4642 }
4643 MarkRefsIntoAndScanClosure
4644 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4645 &_markStack, this, CMSYield,
4646 true /* precleaning phase */);
4647 // CAUTION: The following closure has persistent state that may need to
4648 // be reset upon a decrease in the sequence of addresses it
4649 // processes.
4650 ScanMarkedObjectsAgainCarefullyClosure
4651 smoac_cl(this, _span,
4652 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
4653
4654 // Preclean dirty cards in ModUnionTable and CardTable using
4655 // appropriate convergence criterion;
4656 // repeat CMSPrecleanIter times unless we find that
4657 // we are losing.
4658 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4659 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4660 "Bad convergence multiplier");
4661 assert(CMSPrecleanThreshold >= 100,
4662 "Unreasonably low CMSPrecleanThreshold");
4663
4664 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4665 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4666 numIter < CMSPrecleanIter;
4667 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4668 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4669 if (Verbose && PrintGCDetails) {
4670 gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
4671 }
4672 // Either there are very few dirty cards, so re-mark
4673 // pause will be small anyway, or our pre-cleaning isn't
4674 // that much faster than the rate at which cards are being
4675 // dirtied, so we might as well stop and re-mark since
4676 // precleaning won't improve our re-mark time by much.
4677 if (curNumCards <= CMSPrecleanThreshold ||
4678 (numIter > 0 &&
4679 (curNumCards * CMSPrecleanDenominator >
4680 lastNumCards * CMSPrecleanNumerator))) {
4681 numIter++;
4682 cumNumCards += curNumCards;
4683 break;
4684 }
4685 }
4686
4687 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4688
4689 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4690 cumNumCards += curNumCards;
4691 if (PrintGCDetails && PrintCMSStatistics != 0) {
4692 gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
4693 curNumCards, cumNumCards, numIter);
4694 }
4695 return cumNumCards; // as a measure of useful work done
4696 }
4697
4698 // PRECLEANING NOTES:
4699 // Precleaning involves:
4700 // . reading the bits of the modUnionTable and clearing the set bits.
4701 // . For the cards corresponding to the set bits, we scan the
4702 // objects on those cards. This means we need the free_list_lock
4703 // so that we can safely iterate over the CMS space when scanning
4704 // for oops.
4705 // . When we scan the objects, we'll be both reading and setting
4706 // marks in the marking bit map, so we'll need the marking bit map.
4707 // . For protecting _collector_state transitions, we take the CGC_lock.
4708 // Note that any races in the reading of of card table entries by the
4709 // CMS thread on the one hand and the clearing of those entries by the
4710 // VM thread or the setting of those entries by the mutator threads on the
4711 // other are quite benign. However, for efficiency it makes sense to keep
4712 // the VM thread from racing with the CMS thread while the latter is
4713 // dirty card info to the modUnionTable. We therefore also use the
4714 // CGC_lock to protect the reading of the card table and the mod union
4715 // table by the CM thread.
4716 // . We run concurrently with mutator updates, so scanning
4717 // needs to be done carefully -- we should not try to scan
4718 // potentially uninitialized objects.
4719 //
4720 // Locking strategy: While holding the CGC_lock, we scan over and
4721 // reset a maximal dirty range of the mod union / card tables, then lock
4722 // the free_list_lock and bitmap lock to do a full marking, then
4723 // release these locks; and repeat the cycle. This allows for a
4724 // certain amount of fairness in the sharing of these locks between
4725 // the CMS collector on the one hand, and the VM thread and the
4726 // mutators on the other.
4727
4728 // NOTE: preclean_mod_union_table() and preclean_card_table()
4729 // further below are largely identical; if you need to modify
4730 // one of these methods, please check the other method too.
4731
4732 size_t CMSCollector::preclean_mod_union_table(
4733 ConcurrentMarkSweepGeneration* gen,
4734 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4735 verify_work_stacks_empty();
4736 verify_overflow_empty();
4737
4738 // strategy: starting with the first card, accumulate contiguous
4739 // ranges of dirty cards; clear these cards, then scan the region
4740 // covered by these cards.
4741
4742 // Since all of the MUT is committed ahead, we can just use
4743 // that, in case the generations expand while we are precleaning.
4744 // It might also be fine to just use the committed part of the
4745 // generation, but we might potentially miss cards when the
4746 // generation is rapidly expanding while we are in the midst
4747 // of precleaning.
4748 HeapWord* startAddr = gen->reserved().start();
4749 HeapWord* endAddr = gen->reserved().end();
4750
4751 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4752
4753 size_t numDirtyCards, cumNumDirtyCards;
4754 HeapWord *nextAddr, *lastAddr;
4755 for (cumNumDirtyCards = numDirtyCards = 0,
4756 nextAddr = lastAddr = startAddr;
4757 nextAddr < endAddr;
4758 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4759
4760 ResourceMark rm;
4761 HandleMark hm;
4762
4763 MemRegion dirtyRegion;
4764 {
4765 stopTimer();
4766 // Potential yield point
4767 CMSTokenSync ts(true);
4768 startTimer();
4769 sample_eden();
4770 // Get dirty region starting at nextOffset (inclusive),
4771 // simultaneously clearing it.
4772 dirtyRegion =
4773 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4774 assert(dirtyRegion.start() >= nextAddr,
4775 "returned region inconsistent?");
4776 }
4777 // Remember where the next search should begin.
4778 // The returned region (if non-empty) is a right open interval,
4779 // so lastOffset is obtained from the right end of that
4780 // interval.
4781 lastAddr = dirtyRegion.end();
4782 // Should do something more transparent and less hacky XXX
4783 numDirtyCards =
4784 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4785
4786 // We'll scan the cards in the dirty region (with periodic
4787 // yields for foreground GC as needed).
4788 if (!dirtyRegion.is_empty()) {
4789 assert(numDirtyCards > 0, "consistency check");
4790 HeapWord* stop_point = NULL;
4791 stopTimer();
4792 // Potential yield point
4793 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4794 bitMapLock());
4795 startTimer();
4796 {
4797 verify_work_stacks_empty();
4798 verify_overflow_empty();
4799 sample_eden();
4800 stop_point =
4801 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4802 }
4803 if (stop_point != NULL) {
4804 // The careful iteration stopped early either because it found an
4805 // uninitialized object, or because we were in the midst of an
4806 // "abortable preclean", which should now be aborted. Redirty
4807 // the bits corresponding to the partially-scanned or unscanned
4808 // cards. We'll either restart at the next block boundary or
4809 // abort the preclean.
4810 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4811 "Should only be AbortablePreclean.");
4812 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4813 if (should_abort_preclean()) {
4814 break; // out of preclean loop
4815 } else {
4816 // Compute the next address at which preclean should pick up;
4817 // might need bitMapLock in order to read P-bits.
4818 lastAddr = next_card_start_after_block(stop_point);
4819 }
4820 }
4821 } else {
4822 assert(lastAddr == endAddr, "consistency check");
4823 assert(numDirtyCards == 0, "consistency check");
4824 break;
4825 }
4826 }
4827 verify_work_stacks_empty();
4828 verify_overflow_empty();
4829 return cumNumDirtyCards;
4830 }
4831
4832 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4833 // below are largely identical; if you need to modify
4834 // one of these methods, please check the other method too.
4835
4836 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4837 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4838 // strategy: it's similar to precleamModUnionTable above, in that
4839 // we accumulate contiguous ranges of dirty cards, mark these cards
4840 // precleaned, then scan the region covered by these cards.
4841 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4842 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4843
4844 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4845
4846 size_t numDirtyCards, cumNumDirtyCards;
4847 HeapWord *lastAddr, *nextAddr;
4848
4849 for (cumNumDirtyCards = numDirtyCards = 0,
4850 nextAddr = lastAddr = startAddr;
4851 nextAddr < endAddr;
4852 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4853
4854 ResourceMark rm;
4855 HandleMark hm;
4856
4857 MemRegion dirtyRegion;
4858 {
4859 // See comments in "Precleaning notes" above on why we
4860 // do this locking. XXX Could the locking overheads be
4861 // too high when dirty cards are sparse? [I don't think so.]
4862 stopTimer();
4863 CMSTokenSync x(true); // is cms thread
4864 startTimer();
4865 sample_eden();
4866 // Get and clear dirty region from card table
4867 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4868 MemRegion(nextAddr, endAddr),
4869 true,
4870 CardTableModRefBS::precleaned_card_val());
4871
4872 assert(dirtyRegion.start() >= nextAddr,
4873 "returned region inconsistent?");
4874 }
4875 lastAddr = dirtyRegion.end();
4876 numDirtyCards =
4877 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4878
4879 if (!dirtyRegion.is_empty()) {
4880 stopTimer();
4881 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4882 startTimer();
4883 sample_eden();
4884 verify_work_stacks_empty();
4885 verify_overflow_empty();
4886 HeapWord* stop_point =
4887 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4888 if (stop_point != NULL) {
4889 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4890 "Should only be AbortablePreclean.");
4891 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4892 if (should_abort_preclean()) {
4893 break; // out of preclean loop
4894 } else {
4895 // Compute the next address at which preclean should pick up.
4896 lastAddr = next_card_start_after_block(stop_point);
4897 }
4898 }
4899 } else {
4900 break;
4901 }
4902 }
4903 verify_work_stacks_empty();
4904 verify_overflow_empty();
4905 return cumNumDirtyCards;
4906 }
4907
4908 class PrecleanKlassClosure : public KlassClosure {
4909 KlassToOopClosure _cm_klass_closure;
4910 public:
4911 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4912 void do_klass(Klass* k) {
4913 if (k->has_accumulated_modified_oops()) {
4914 k->clear_accumulated_modified_oops();
4915
4916 _cm_klass_closure.do_klass(k);
4917 }
4918 }
4919 };
4920
4921 // The freelist lock is needed to prevent asserts, is it really needed?
4922 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4923
4924 cl->set_freelistLock(freelistLock);
4925
4926 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4927
4928 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4929 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4930 PrecleanKlassClosure preclean_klass_closure(cl);
4931 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4932
4933 verify_work_stacks_empty();
4934 verify_overflow_empty();
4935 }
4936
4937 void CMSCollector::checkpointRootsFinal(bool asynch,
4938 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4939 assert(_collectorState == FinalMarking, "incorrect state transition?");
4940 check_correct_thread_executing();
4941 // world is stopped at this checkpoint
4942 assert(SafepointSynchronize::is_at_safepoint(),
4943 "world should be stopped");
4944 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4945
4946 verify_work_stacks_empty();
4947 verify_overflow_empty();
4948
4949 SpecializationStats::clear();
4950 if (PrintGCDetails) {
4951 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4952 _young_gen->used() / K,
4953 _young_gen->capacity() / K);
4954 }
4955 if (asynch) {
4956 if (CMSScavengeBeforeRemark) {
4957 GenCollectedHeap* gch = GenCollectedHeap::heap();
4958 // Temporarily set flag to false, GCH->do_collection will
4959 // expect it to be false and set to true
4960 FlagSetting fl(gch->_is_gc_active, false);
4961 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4962 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4963 int level = _cmsGen->level() - 1;
4964 if (level >= 0) {
4965 gch->do_collection(true, // full (i.e. force, see below)
4966 false, // !clear_all_soft_refs
4967 0, // size
4968 false, // is_tlab
4969 level // max_level
4970 );
4971 }
4972 }
4973 FreelistLocker x(this);
4974 MutexLockerEx y(bitMapLock(),
4975 Mutex::_no_safepoint_check_flag);
4976 assert(!init_mark_was_synchronous, "but that's impossible!");
4977 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4978 } else {
4979 // already have all the locks
4980 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4981 init_mark_was_synchronous);
4982 }
4983 verify_work_stacks_empty();
4984 verify_overflow_empty();
4985 SpecializationStats::print();
4986 }
4987
4988 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4989 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4990
4991 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4992
4993 assert(haveFreelistLocks(), "must have free list locks");
4994 assert_lock_strong(bitMapLock());
4995
4996 ResourceMark rm;
4997 HandleMark hm;
4998
4999 GenCollectedHeap* gch = GenCollectedHeap::heap();
5000
5001 if (should_unload_classes()) {
5002 CodeCache::gc_prologue();
5003 }
5004 assert(haveFreelistLocks(), "must have free list locks");
5005 assert_lock_strong(bitMapLock());
5006
5007 if (!init_mark_was_synchronous) {
5008 // We might assume that we need not fill TLAB's when
5009 // CMSScavengeBeforeRemark is set, because we may have just done
5010 // a scavenge which would have filled all TLAB's -- and besides
5011 // Eden would be empty. This however may not always be the case --
5012 // for instance although we asked for a scavenge, it may not have
5013 // happened because of a JNI critical section. We probably need
5014 // a policy for deciding whether we can in that case wait until
5015 // the critical section releases and then do the remark following
5016 // the scavenge, and skip it here. In the absence of that policy,
5017 // or of an indication of whether the scavenge did indeed occur,
5018 // we cannot rely on TLAB's having been filled and must do
5019 // so here just in case a scavenge did not happen.
5020 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
5021 // Update the saved marks which may affect the root scans.
5022 gch->save_marks();
5023
5024 if (CMSPrintEdenSurvivorChunks) {
5025 print_eden_and_survivor_chunk_arrays();
5026 }
5027
5028 {
5029 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
5030
5031 // Note on the role of the mod union table:
5032 // Since the marker in "markFromRoots" marks concurrently with
5033 // mutators, it is possible for some reachable objects not to have been
5034 // scanned. For instance, an only reference to an object A was
5035 // placed in object B after the marker scanned B. Unless B is rescanned,
5036 // A would be collected. Such updates to references in marked objects
5037 // are detected via the mod union table which is the set of all cards
5038 // dirtied since the first checkpoint in this GC cycle and prior to
5039 // the most recent young generation GC, minus those cleaned up by the
5040 // concurrent precleaning.
5041 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
5042 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5043 do_remark_parallel();
5044 } else {
5045 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
5046 _gc_timer_cm, _gc_tracer_cm->gc_id());
5047 do_remark_non_parallel();
5048 }
5049 }
5050 } else {
5051 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
5052 // The initial mark was stop-world, so there's no rescanning to
5053 // do; go straight on to the next step below.
5054 }
5055 verify_work_stacks_empty();
5056 verify_overflow_empty();
5057
5058 {
5059 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
5060 refProcessingWork(asynch, clear_all_soft_refs);
5061 }
5062 verify_work_stacks_empty();
5063 verify_overflow_empty();
5064
5065 if (should_unload_classes()) {
5066 CodeCache::gc_epilogue();
5067 }
5068 JvmtiExport::gc_epilogue();
5069
5070 // If we encountered any (marking stack / work queue) overflow
5071 // events during the current CMS cycle, take appropriate
5072 // remedial measures, where possible, so as to try and avoid
5073 // recurrence of that condition.
5074 assert(_markStack.isEmpty(), "No grey objects");
5075 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
5076 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
5077 if (ser_ovflw > 0) {
5078 if (PrintCMSStatistics != 0) {
5079 gclog_or_tty->print_cr("Marking stack overflow (benign) "
5080 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
5081 ", kac_preclean="SIZE_FORMAT")",
5082 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
5083 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
5084 }
5085 _markStack.expand();
5086 _ser_pmc_remark_ovflw = 0;
5087 _ser_pmc_preclean_ovflw = 0;
5088 _ser_kac_preclean_ovflw = 0;
5089 _ser_kac_ovflw = 0;
5090 }
5091 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
5092 if (PrintCMSStatistics != 0) {
5093 gclog_or_tty->print_cr("Work queue overflow (benign) "
5094 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
5095 _par_pmc_remark_ovflw, _par_kac_ovflw);
5096 }
5097 _par_pmc_remark_ovflw = 0;
5098 _par_kac_ovflw = 0;
5099 }
5100 if (PrintCMSStatistics != 0) {
5101 if (_markStack._hit_limit > 0) {
5102 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
5103 _markStack._hit_limit);
5104 }
5105 if (_markStack._failed_double > 0) {
5106 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
5107 " current capacity "SIZE_FORMAT,
5108 _markStack._failed_double,
5109 _markStack.capacity());
5110 }
5111 }
5112 _markStack._hit_limit = 0;
5113 _markStack._failed_double = 0;
5114
5115 if ((VerifyAfterGC || VerifyDuringGC) &&
5116 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5117 verify_after_remark();
5118 }
5119
5120 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
5121
5122 // Change under the freelistLocks.
5123 _collectorState = Sweeping;
5124 // Call isAllClear() under bitMapLock
5125 assert(_modUnionTable.isAllClear(),
5126 "Should be clear by end of the final marking");
5127 assert(_ct->klass_rem_set()->mod_union_is_clear(),
5128 "Should be clear by end of the final marking");
5129 }
5130
5131 void CMSParInitialMarkTask::work(uint worker_id) {
5132 elapsedTimer _timer;
5133 ResourceMark rm;
5134 HandleMark hm;
5135
5136 // ---------- scan from roots --------------
5137 _timer.start();
5138 GenCollectedHeap* gch = GenCollectedHeap::heap();
5139 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
5140
5141 // ---------- young gen roots --------------
5142 {
5143 work_on_young_gen_roots(worker_id, &par_mri_cl);
5144 _timer.stop();
5145 if (PrintCMSStatistics != 0) {
5146 gclog_or_tty->print_cr(
5147 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
5148 worker_id, _timer.seconds());
5149 }
5150 }
5151
5152 // ---------- remaining roots --------------
5153 _timer.reset();
5154 _timer.start();
5155
5156 CLDToOopClosure cld_closure(&par_mri_cl, true);
5157
5158 gch->gen_process_roots(_collector->_cmsGen->level(),
5159 false, // yg was scanned above
5160 false, // this is parallel code
5161 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5162 _collector->should_unload_classes(),
5163 &par_mri_cl,
5164 NULL,
5165 &cld_closure);
5166 assert(_collector->should_unload_classes()
5167 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5168 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5169 _timer.stop();
5170 if (PrintCMSStatistics != 0) {
5171 gclog_or_tty->print_cr(
5172 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
5173 worker_id, _timer.seconds());
5174 }
5175 }
5176
5177 // Parallel remark task
5178 class CMSParRemarkTask: public CMSParMarkTask {
5179 CompactibleFreeListSpace* _cms_space;
5180
5181 // The per-thread work queues, available here for stealing.
5182 OopTaskQueueSet* _task_queues;
5183 ParallelTaskTerminator _term;
5184
5185 public:
5186 // A value of 0 passed to n_workers will cause the number of
5187 // workers to be taken from the active workers in the work gang.
5188 CMSParRemarkTask(CMSCollector* collector,
5189 CompactibleFreeListSpace* cms_space,
5190 int n_workers, FlexibleWorkGang* workers,
5191 OopTaskQueueSet* task_queues):
5192 CMSParMarkTask("Rescan roots and grey objects in parallel",
5193 collector, n_workers),
5194 _cms_space(cms_space),
5195 _task_queues(task_queues),
5196 _term(n_workers, task_queues) { }
5197
5198 OopTaskQueueSet* task_queues() { return _task_queues; }
5199
5200 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5201
5202 ParallelTaskTerminator* terminator() { return &_term; }
5203 int n_workers() { return _n_workers; }
5204
5205 void work(uint worker_id);
5206
5207 private:
5208 // ... of dirty cards in old space
5209 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
5210 Par_MarkRefsIntoAndScanClosure* cl);
5211
5212 // ... work stealing for the above
5213 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
5214 };
5215
5216 class RemarkKlassClosure : public KlassClosure {
5217 KlassToOopClosure _cm_klass_closure;
5218 public:
5219 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
5220 void do_klass(Klass* k) {
5221 // Check if we have modified any oops in the Klass during the concurrent marking.
5222 if (k->has_accumulated_modified_oops()) {
5223 k->clear_accumulated_modified_oops();
5224
5225 // We could have transfered the current modified marks to the accumulated marks,
5226 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
5227 } else if (k->has_modified_oops()) {
5228 // Don't clear anything, this info is needed by the next young collection.
5229 } else {
5230 // No modified oops in the Klass.
5231 return;
5232 }
5233
5234 // The klass has modified fields, need to scan the klass.
5235 _cm_klass_closure.do_klass(k);
5236 }
5237 };
5238
5239 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
5240 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5241 EdenSpace* eden_space = dng->eden();
5242 ContiguousSpace* from_space = dng->from();
5243 ContiguousSpace* to_space = dng->to();
5244
5245 HeapWord** eca = _collector->_eden_chunk_array;
5246 size_t ect = _collector->_eden_chunk_index;
5247 HeapWord** sca = _collector->_survivor_chunk_array;
5248 size_t sct = _collector->_survivor_chunk_index;
5249
5250 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5251 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5252
5253 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
5254 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
5255 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
5256 }
5257
5258 // work_queue(i) is passed to the closure
5259 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
5260 // also is passed to do_dirty_card_rescan_tasks() and to
5261 // do_work_steal() to select the i-th task_queue.
5262
5263 void CMSParRemarkTask::work(uint worker_id) {
5264 elapsedTimer _timer;
5265 ResourceMark rm;
5266 HandleMark hm;
5267
5268 // ---------- rescan from roots --------------
5269 _timer.start();
5270 GenCollectedHeap* gch = GenCollectedHeap::heap();
5271 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5272 _collector->_span, _collector->ref_processor(),
5273 &(_collector->_markBitMap),
5274 work_queue(worker_id));
5275
5276 // Rescan young gen roots first since these are likely
5277 // coarsely partitioned and may, on that account, constitute
5278 // the critical path; thus, it's best to start off that
5279 // work first.
5280 // ---------- young gen roots --------------
5281 {
5282 work_on_young_gen_roots(worker_id, &par_mrias_cl);
5283 _timer.stop();
5284 if (PrintCMSStatistics != 0) {
5285 gclog_or_tty->print_cr(
5286 "Finished young gen rescan work in %dth thread: %3.3f sec",
5287 worker_id, _timer.seconds());
5288 }
5289 }
5290
5291 // ---------- remaining roots --------------
5292 _timer.reset();
5293 _timer.start();
5294 gch->gen_process_roots(_collector->_cmsGen->level(),
5295 false, // yg was scanned above
5296 false, // this is parallel code
5297 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5298 _collector->should_unload_classes(),
5299 &par_mrias_cl,
5300 NULL,
5301 NULL); // The dirty klasses will be handled below
5302
5303 assert(_collector->should_unload_classes()
5304 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5305 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5306 _timer.stop();
5307 if (PrintCMSStatistics != 0) {
5308 gclog_or_tty->print_cr(
5309 "Finished remaining root rescan work in %dth thread: %3.3f sec",
5310 worker_id, _timer.seconds());
5311 }
5312
5313 // ---------- unhandled CLD scanning ----------
5314 if (worker_id == 0) { // Single threaded at the moment.
5315 _timer.reset();
5316 _timer.start();
5317
5318 // Scan all new class loader data objects and new dependencies that were
5319 // introduced during concurrent marking.
5320 ResourceMark rm;
5321 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5322 for (int i = 0; i < array->length(); i++) {
5323 par_mrias_cl.do_class_loader_data(array->at(i));
5324 }
5325
5326 // We don't need to keep track of new CLDs anymore.
5327 ClassLoaderDataGraph::remember_new_clds(false);
5328
5329 _timer.stop();
5330 if (PrintCMSStatistics != 0) {
5331 gclog_or_tty->print_cr(
5332 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
5333 worker_id, _timer.seconds());
5334 }
5335 }
5336
5337 // ---------- dirty klass scanning ----------
5338 if (worker_id == 0) { // Single threaded at the moment.
5339 _timer.reset();
5340 _timer.start();
5341
5342 // Scan all classes that was dirtied during the concurrent marking phase.
5343 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
5344 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5345
5346 _timer.stop();
5347 if (PrintCMSStatistics != 0) {
5348 gclog_or_tty->print_cr(
5349 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
5350 worker_id, _timer.seconds());
5351 }
5352 }
5353
5354 // We might have added oops to ClassLoaderData::_handles during the
5355 // concurrent marking phase. These oops point to newly allocated objects
5356 // that are guaranteed to be kept alive. Either by the direct allocation
5357 // code, or when the young collector processes the roots. Hence,
5358 // we don't have to revisit the _handles block during the remark phase.
5359
5360 // ---------- rescan dirty cards ------------
5361 _timer.reset();
5362 _timer.start();
5363
5364 // Do the rescan tasks for each of the two spaces
5365 // (cms_space) in turn.
5366 // "worker_id" is passed to select the task_queue for "worker_id"
5367 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
5368 _timer.stop();
5369 if (PrintCMSStatistics != 0) {
5370 gclog_or_tty->print_cr(
5371 "Finished dirty card rescan work in %dth thread: %3.3f sec",
5372 worker_id, _timer.seconds());
5373 }
5374
5375 // ---------- steal work from other threads ...
5376 // ---------- ... and drain overflow list.
5377 _timer.reset();
5378 _timer.start();
5379 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
5380 _timer.stop();
5381 if (PrintCMSStatistics != 0) {
5382 gclog_or_tty->print_cr(
5383 "Finished work stealing in %dth thread: %3.3f sec",
5384 worker_id, _timer.seconds());
5385 }
5386 }
5387
5388 // Note that parameter "i" is not used.
5389 void
5390 CMSParMarkTask::do_young_space_rescan(uint worker_id,
5391 OopsInGenClosure* cl, ContiguousSpace* space,
5392 HeapWord** chunk_array, size_t chunk_top) {
5393 // Until all tasks completed:
5394 // . claim an unclaimed task
5395 // . compute region boundaries corresponding to task claimed
5396 // using chunk_array
5397 // . par_oop_iterate(cl) over that region
5398
5399 ResourceMark rm;
5400 HandleMark hm;
5401
5402 SequentialSubTasksDone* pst = space->par_seq_tasks();
5403
5404 uint nth_task = 0;
5405 uint n_tasks = pst->n_tasks();
5406
5407 if (n_tasks > 0) {
5408 assert(pst->valid(), "Uninitialized use?");
5409 HeapWord *start, *end;
5410 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5411 // We claimed task # nth_task; compute its boundaries.
5412 if (chunk_top == 0) { // no samples were taken
5413 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5414 start = space->bottom();
5415 end = space->top();
5416 } else if (nth_task == 0) {
5417 start = space->bottom();
5418 end = chunk_array[nth_task];
5419 } else if (nth_task < (uint)chunk_top) {
5420 assert(nth_task >= 1, "Control point invariant");
5421 start = chunk_array[nth_task - 1];
5422 end = chunk_array[nth_task];
5423 } else {
5424 assert(nth_task == (uint)chunk_top, "Control point invariant");
5425 start = chunk_array[chunk_top - 1];
5426 end = space->top();
5427 }
5428 MemRegion mr(start, end);
5429 // Verify that mr is in space
5430 assert(mr.is_empty() || space->used_region().contains(mr),
5431 "Should be in space");
5432 // Verify that "start" is an object boundary
5433 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5434 "Should be an oop");
5435 space->par_oop_iterate(mr, cl);
5436 }
5437 pst->all_tasks_completed();
5438 }
5439 }
5440
5441 void
5442 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5443 CompactibleFreeListSpace* sp, int i,
5444 Par_MarkRefsIntoAndScanClosure* cl) {
5445 // Until all tasks completed:
5446 // . claim an unclaimed task
5447 // . compute region boundaries corresponding to task claimed
5448 // . transfer dirty bits ct->mut for that region
5449 // . apply rescanclosure to dirty mut bits for that region
5450
5451 ResourceMark rm;
5452 HandleMark hm;
5453
5454 OopTaskQueue* work_q = work_queue(i);
5455 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5456 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5457 // CAUTION: This closure has state that persists across calls to
5458 // the work method dirty_range_iterate_clear() in that it has
5459 // embedded in it a (subtype of) UpwardsObjectClosure. The
5460 // use of that state in the embedded UpwardsObjectClosure instance
5461 // assumes that the cards are always iterated (even if in parallel
5462 // by several threads) in monotonically increasing order per each
5463 // thread. This is true of the implementation below which picks
5464 // card ranges (chunks) in monotonically increasing order globally
5465 // and, a-fortiori, in monotonically increasing order per thread
5466 // (the latter order being a subsequence of the former).
5467 // If the work code below is ever reorganized into a more chaotic
5468 // work-partitioning form than the current "sequential tasks"
5469 // paradigm, the use of that persistent state will have to be
5470 // revisited and modified appropriately. See also related
5471 // bug 4756801 work on which should examine this code to make
5472 // sure that the changes there do not run counter to the
5473 // assumptions made here and necessary for correctness and
5474 // efficiency. Note also that this code might yield inefficient
5475 // behavior in the case of very large objects that span one or
5476 // more work chunks. Such objects would potentially be scanned
5477 // several times redundantly. Work on 4756801 should try and
5478 // address that performance anomaly if at all possible. XXX
5479 MemRegion full_span = _collector->_span;
5480 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5481 MarkFromDirtyCardsClosure
5482 greyRescanClosure(_collector, full_span, // entire span of interest
5483 sp, bm, work_q, cl);
5484
5485 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5486 assert(pst->valid(), "Uninitialized use?");
5487 uint nth_task = 0;
5488 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5489 MemRegion span = sp->used_region();
5490 HeapWord* start_addr = span.start();
5491 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5492 alignment);
5493 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5494 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5495 start_addr, "Check alignment");
5496 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5497 chunk_size, "Check alignment");
5498
5499 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5500 // Having claimed the nth_task, compute corresponding mem-region,
5501 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
5502 // The alignment restriction ensures that we do not need any
5503 // synchronization with other gang-workers while setting or
5504 // clearing bits in thus chunk of the MUT.
5505 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5506 start_addr + (nth_task+1)*chunk_size);
5507 // The last chunk's end might be way beyond end of the
5508 // used region. In that case pull back appropriately.
5509 if (this_span.end() > end_addr) {
5510 this_span.set_end(end_addr);
5511 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5512 }
5513 // Iterate over the dirty cards covering this chunk, marking them
5514 // precleaned, and setting the corresponding bits in the mod union
5515 // table. Since we have been careful to partition at Card and MUT-word
5516 // boundaries no synchronization is needed between parallel threads.
5517 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5518 &modUnionClosure);
5519
5520 // Having transferred these marks into the modUnionTable,
5521 // rescan the marked objects on the dirty cards in the modUnionTable.
5522 // Even if this is at a synchronous collection, the initial marking
5523 // may have been done during an asynchronous collection so there
5524 // may be dirty bits in the mod-union table.
5525 _collector->_modUnionTable.dirty_range_iterate_clear(
5526 this_span, &greyRescanClosure);
5527 _collector->_modUnionTable.verifyNoOneBitsInRange(
5528 this_span.start(),
5529 this_span.end());
5530 }
5531 pst->all_tasks_completed(); // declare that i am done
5532 }
5533
5534 // . see if we can share work_queues with ParNew? XXX
5535 void
5536 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5537 int* seed) {
5538 OopTaskQueue* work_q = work_queue(i);
5539 NOT_PRODUCT(int num_steals = 0;)
5540 oop obj_to_scan;
5541 CMSBitMap* bm = &(_collector->_markBitMap);
5542
5543 while (true) {
5544 // Completely finish any left over work from (an) earlier round(s)
5545 cl->trim_queue(0);
5546 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5547 (size_t)ParGCDesiredObjsFromOverflowList);
5548 // Now check if there's any work in the overflow list
5549 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5550 // only affects the number of attempts made to get work from the
5551 // overflow list and does not affect the number of workers. Just
5552 // pass ParallelGCThreads so this behavior is unchanged.
5553 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5554 work_q,
5555 ParallelGCThreads)) {
5556 // found something in global overflow list;
5557 // not yet ready to go stealing work from others.
5558 // We'd like to assert(work_q->size() != 0, ...)
5559 // because we just took work from the overflow list,
5560 // but of course we can't since all of that could have
5561 // been already stolen from us.
5562 // "He giveth and He taketh away."
5563 continue;
5564 }
5565 // Verify that we have no work before we resort to stealing
5566 assert(work_q->size() == 0, "Have work, shouldn't steal");
5567 // Try to steal from other queues that have work
5568 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5569 NOT_PRODUCT(num_steals++;)
5570 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5571 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5572 // Do scanning work
5573 obj_to_scan->oop_iterate(cl);
5574 // Loop around, finish this work, and try to steal some more
5575 } else if (terminator()->offer_termination()) {
5576 break; // nirvana from the infinite cycle
5577 }
5578 }
5579 NOT_PRODUCT(
5580 if (PrintCMSStatistics != 0) {
5581 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5582 }
5583 )
5584 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5585 "Else our work is not yet done");
5586 }
5587
5588 // Record object boundaries in _eden_chunk_array by sampling the eden
5589 // top in the slow-path eden object allocation code path and record
5590 // the boundaries, if CMSEdenChunksRecordAlways is true. If
5591 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
5592 // sampling in sample_eden() that activates during the part of the
5593 // preclean phase.
5594 void CMSCollector::sample_eden_chunk() {
5595 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
5596 if (_eden_chunk_lock->try_lock()) {
5597 // Record a sample. This is the critical section. The contents
5598 // of the _eden_chunk_array have to be non-decreasing in the
5599 // address order.
5600 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
5601 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
5602 "Unexpected state of Eden");
5603 if (_eden_chunk_index == 0 ||
5604 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
5605 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
5606 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
5607 _eden_chunk_index++; // commit sample
5608 }
5609 _eden_chunk_lock->unlock();
5610 }
5611 }
5612 }
5613
5614 // Return a thread-local PLAB recording array, as appropriate.
5615 void* CMSCollector::get_data_recorder(int thr_num) {
5616 if (_survivor_plab_array != NULL &&
5617 (CMSPLABRecordAlways ||
5618 (_collectorState > Marking && _collectorState < FinalMarking))) {
5619 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5620 ChunkArray* ca = &_survivor_plab_array[thr_num];
5621 ca->reset(); // clear it so that fresh data is recorded
5622 return (void*) ca;
5623 } else {
5624 return NULL;
5625 }
5626 }
5627
5628 // Reset all the thread-local PLAB recording arrays
5629 void CMSCollector::reset_survivor_plab_arrays() {
5630 for (uint i = 0; i < ParallelGCThreads; i++) {
5631 _survivor_plab_array[i].reset();
5632 }
5633 }
5634
5635 // Merge the per-thread plab arrays into the global survivor chunk
5636 // array which will provide the partitioning of the survivor space
5637 // for CMS initial scan and rescan.
5638 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5639 int no_of_gc_threads) {
5640 assert(_survivor_plab_array != NULL, "Error");
5641 assert(_survivor_chunk_array != NULL, "Error");
5642 assert(_collectorState == FinalMarking ||
5643 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
5644 for (int j = 0; j < no_of_gc_threads; j++) {
5645 _cursor[j] = 0;
5646 }
5647 HeapWord* top = surv->top();
5648 size_t i;
5649 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5650 HeapWord* min_val = top; // Higher than any PLAB address
5651 uint min_tid = 0; // position of min_val this round
5652 for (int j = 0; j < no_of_gc_threads; j++) {
5653 ChunkArray* cur_sca = &_survivor_plab_array[j];
5654 if (_cursor[j] == cur_sca->end()) {
5655 continue;
5656 }
5657 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5658 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5659 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5660 if (cur_val < min_val) {
5661 min_tid = j;
5662 min_val = cur_val;
5663 } else {
5664 assert(cur_val < top, "All recorded addresses should be less");
5665 }
5666 }
5667 // At this point min_val and min_tid are respectively
5668 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5669 // and the thread (j) that witnesses that address.
5670 // We record this address in the _survivor_chunk_array[i]
5671 // and increment _cursor[min_tid] prior to the next round i.
5672 if (min_val == top) {
5673 break;
5674 }
5675 _survivor_chunk_array[i] = min_val;
5676 _cursor[min_tid]++;
5677 }
5678 // We are all done; record the size of the _survivor_chunk_array
5679 _survivor_chunk_index = i; // exclusive: [0, i)
5680 if (PrintCMSStatistics > 0) {
5681 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5682 }
5683 // Verify that we used up all the recorded entries
5684 #ifdef ASSERT
5685 size_t total = 0;
5686 for (int j = 0; j < no_of_gc_threads; j++) {
5687 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5688 total += _cursor[j];
5689 }
5690 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5691 // Check that the merged array is in sorted order
5692 if (total > 0) {
5693 for (size_t i = 0; i < total - 1; i++) {
5694 if (PrintCMSStatistics > 0) {
5695 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5696 i, _survivor_chunk_array[i]);
5697 }
5698 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5699 "Not sorted");
5700 }
5701 }
5702 #endif // ASSERT
5703 }
5704
5705 // Set up the space's par_seq_tasks structure for work claiming
5706 // for parallel initial scan and rescan of young gen.
5707 // See ParRescanTask where this is currently used.
5708 void
5709 CMSCollector::
5710 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5711 assert(n_threads > 0, "Unexpected n_threads argument");
5712 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5713
5714 // Eden space
5715 if (!dng->eden()->is_empty()) {
5716 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5717 assert(!pst->valid(), "Clobbering existing data?");
5718 // Each valid entry in [0, _eden_chunk_index) represents a task.
5719 size_t n_tasks = _eden_chunk_index + 1;
5720 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5721 // Sets the condition for completion of the subtask (how many threads
5722 // need to finish in order to be done).
5723 pst->set_n_threads(n_threads);
5724 pst->set_n_tasks((int)n_tasks);
5725 }
5726
5727 // Merge the survivor plab arrays into _survivor_chunk_array
5728 if (_survivor_plab_array != NULL) {
5729 merge_survivor_plab_arrays(dng->from(), n_threads);
5730 } else {
5731 assert(_survivor_chunk_index == 0, "Error");
5732 }
5733
5734 // To space
5735 {
5736 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5737 assert(!pst->valid(), "Clobbering existing data?");
5738 // Sets the condition for completion of the subtask (how many threads
5739 // need to finish in order to be done).
5740 pst->set_n_threads(n_threads);
5741 pst->set_n_tasks(1);
5742 assert(pst->valid(), "Error");
5743 }
5744
5745 // From space
5746 {
5747 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5748 assert(!pst->valid(), "Clobbering existing data?");
5749 size_t n_tasks = _survivor_chunk_index + 1;
5750 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5751 // Sets the condition for completion of the subtask (how many threads
5752 // need to finish in order to be done).
5753 pst->set_n_threads(n_threads);
5754 pst->set_n_tasks((int)n_tasks);
5755 assert(pst->valid(), "Error");
5756 }
5757 }
5758
5759 // Parallel version of remark
5760 void CMSCollector::do_remark_parallel() {
5761 GenCollectedHeap* gch = GenCollectedHeap::heap();
5762 FlexibleWorkGang* workers = gch->workers();
5763 assert(workers != NULL, "Need parallel worker threads.");
5764 // Choose to use the number of GC workers most recently set
5765 // into "active_workers". If active_workers is not set, set it
5766 // to ParallelGCThreads.
5767 int n_workers = workers->active_workers();
5768 if (n_workers == 0) {
5769 assert(n_workers > 0, "Should have been set during scavenge");
5770 n_workers = ParallelGCThreads;
5771 workers->set_active_workers(n_workers);
5772 }
5773 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5774
5775 CMSParRemarkTask tsk(this,
5776 cms_space,
5777 n_workers, workers, task_queues());
5778
5779 // Set up for parallel process_roots work.
5780 gch->set_par_threads(n_workers);
5781 // We won't be iterating over the cards in the card table updating
5782 // the younger_gen cards, so we shouldn't call the following else
5783 // the verification code as well as subsequent younger_refs_iterate
5784 // code would get confused. XXX
5785 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5786
5787 // The young gen rescan work will not be done as part of
5788 // process_roots (which currently doesn't know how to
5789 // parallelize such a scan), but rather will be broken up into
5790 // a set of parallel tasks (via the sampling that the [abortable]
5791 // preclean phase did of EdenSpace, plus the [two] tasks of
5792 // scanning the [two] survivor spaces. Further fine-grain
5793 // parallelization of the scanning of the survivor spaces
5794 // themselves, and of precleaning of the younger gen itself
5795 // is deferred to the future.
5796 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5797
5798 // The dirty card rescan work is broken up into a "sequence"
5799 // of parallel tasks (per constituent space) that are dynamically
5800 // claimed by the parallel threads.
5801 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5802
5803 // It turns out that even when we're using 1 thread, doing the work in a
5804 // separate thread causes wide variance in run times. We can't help this
5805 // in the multi-threaded case, but we special-case n=1 here to get
5806 // repeatable measurements of the 1-thread overhead of the parallel code.
5807 if (n_workers > 1) {
5808 // Make refs discovery MT-safe, if it isn't already: it may not
5809 // necessarily be so, since it's possible that we are doing
5810 // ST marking.
5811 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5812 GenCollectedHeap::StrongRootsScope srs(gch);
5813 workers->run_task(&tsk);
5814 } else {
5815 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5816 GenCollectedHeap::StrongRootsScope srs(gch);
5817 tsk.work(0);
5818 }
5819
5820 gch->set_par_threads(0); // 0 ==> non-parallel.
5821 // restore, single-threaded for now, any preserved marks
5822 // as a result of work_q overflow
5823 restore_preserved_marks_if_any();
5824 }
5825
5826 // Non-parallel version of remark
5827 void CMSCollector::do_remark_non_parallel() {
5828 ResourceMark rm;
5829 HandleMark hm;
5830 GenCollectedHeap* gch = GenCollectedHeap::heap();
5831 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5832
5833 MarkRefsIntoAndScanClosure
5834 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5835 &_markStack, this,
5836 false /* should_yield */, false /* not precleaning */);
5837 MarkFromDirtyCardsClosure
5838 markFromDirtyCardsClosure(this, _span,
5839 NULL, // space is set further below
5840 &_markBitMap, &_markStack, &mrias_cl);
5841 {
5842 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5843 // Iterate over the dirty cards, setting the corresponding bits in the
5844 // mod union table.
5845 {
5846 ModUnionClosure modUnionClosure(&_modUnionTable);
5847 _ct->ct_bs()->dirty_card_iterate(
5848 _cmsGen->used_region(),
5849 &modUnionClosure);
5850 }
5851 // Having transferred these marks into the modUnionTable, we just need
5852 // to rescan the marked objects on the dirty cards in the modUnionTable.
5853 // The initial marking may have been done during an asynchronous
5854 // collection so there may be dirty bits in the mod-union table.
5855 const int alignment =
5856 CardTableModRefBS::card_size * BitsPerWord;
5857 {
5858 // ... First handle dirty cards in CMS gen
5859 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5860 MemRegion ur = _cmsGen->used_region();
5861 HeapWord* lb = ur.start();
5862 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5863 MemRegion cms_span(lb, ub);
5864 _modUnionTable.dirty_range_iterate_clear(cms_span,
5865 &markFromDirtyCardsClosure);
5866 verify_work_stacks_empty();
5867 if (PrintCMSStatistics != 0) {
5868 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5869 markFromDirtyCardsClosure.num_dirty_cards());
5870 }
5871 }
5872 }
5873 if (VerifyDuringGC &&
5874 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5875 HandleMark hm; // Discard invalid handles created during verification
5876 Universe::verify();
5877 }
5878 {
5879 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5880
5881 verify_work_stacks_empty();
5882
5883 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5884 GenCollectedHeap::StrongRootsScope srs(gch);
5885
5886 gch->gen_process_roots(_cmsGen->level(),
5887 true, // younger gens as roots
5888 false, // use the local StrongRootsScope
5889 SharedHeap::ScanningOption(roots_scanning_options()),
5890 should_unload_classes(),
5891 &mrias_cl,
5892 NULL,
5893 NULL); // The dirty klasses will be handled below
5894
5895 assert(should_unload_classes()
5896 || (roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5897 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5898 }
5899
5900 {
5901 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5902
5903 verify_work_stacks_empty();
5904
5905 // Scan all class loader data objects that might have been introduced
5906 // during concurrent marking.
5907 ResourceMark rm;
5908 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5909 for (int i = 0; i < array->length(); i++) {
5910 mrias_cl.do_class_loader_data(array->at(i));
5911 }
5912
5913 // We don't need to keep track of new CLDs anymore.
5914 ClassLoaderDataGraph::remember_new_clds(false);
5915
5916 verify_work_stacks_empty();
5917 }
5918
5919 {
5920 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5921
5922 verify_work_stacks_empty();
5923
5924 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5925 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5926
5927 verify_work_stacks_empty();
5928 }
5929
5930 // We might have added oops to ClassLoaderData::_handles during the
5931 // concurrent marking phase. These oops point to newly allocated objects
5932 // that are guaranteed to be kept alive. Either by the direct allocation
5933 // code, or when the young collector processes the roots. Hence,
5934 // we don't have to revisit the _handles block during the remark phase.
5935
5936 verify_work_stacks_empty();
5937 // Restore evacuated mark words, if any, used for overflow list links
5938 if (!CMSOverflowEarlyRestoration) {
5939 restore_preserved_marks_if_any();
5940 }
5941 verify_overflow_empty();
5942 }
5943
5944 ////////////////////////////////////////////////////////
5945 // Parallel Reference Processing Task Proxy Class
5946 ////////////////////////////////////////////////////////
5947 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5948 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5949 CMSCollector* _collector;
5950 CMSBitMap* _mark_bit_map;
5951 const MemRegion _span;
5952 ProcessTask& _task;
5953
5954 public:
5955 CMSRefProcTaskProxy(ProcessTask& task,
5956 CMSCollector* collector,
5957 const MemRegion& span,
5958 CMSBitMap* mark_bit_map,
5959 AbstractWorkGang* workers,
5960 OopTaskQueueSet* task_queues):
5961 // XXX Should superclass AGTWOQ also know about AWG since it knows
5962 // about the task_queues used by the AWG? Then it could initialize
5963 // the terminator() object. See 6984287. The set_for_termination()
5964 // below is a temporary band-aid for the regression in 6984287.
5965 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5966 task_queues),
5967 _task(task),
5968 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5969 {
5970 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5971 "Inconsistency in _span");
5972 set_for_termination(workers->active_workers());
5973 }
5974
5975 OopTaskQueueSet* task_queues() { return queues(); }
5976
5977 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5978
5979 void do_work_steal(int i,
5980 CMSParDrainMarkingStackClosure* drain,
5981 CMSParKeepAliveClosure* keep_alive,
5982 int* seed);
5983
5984 virtual void work(uint worker_id);
5985 };
5986
5987 void CMSRefProcTaskProxy::work(uint worker_id) {
5988 ResourceMark rm;
5989 HandleMark hm;
5990 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5991 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5992 _mark_bit_map,
5993 work_queue(worker_id));
5994 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5995 _mark_bit_map,
5996 work_queue(worker_id));
5997 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5998 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5999 if (_task.marks_oops_alive()) {
6000 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
6001 _collector->hash_seed(worker_id));
6002 }
6003 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
6004 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
6005 }
6006
6007 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
6008 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
6009 EnqueueTask& _task;
6010
6011 public:
6012 CMSRefEnqueueTaskProxy(EnqueueTask& task)
6013 : AbstractGangTask("Enqueue reference objects in parallel"),
6014 _task(task)
6015 { }
6016
6017 virtual void work(uint worker_id)
6018 {
6019 _task.work(worker_id);
6020 }
6021 };
6022
6023 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
6024 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
6025 _span(span),
6026 _bit_map(bit_map),
6027 _work_queue(work_queue),
6028 _mark_and_push(collector, span, bit_map, work_queue),
6029 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6030 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
6031 { }
6032
6033 // . see if we can share work_queues with ParNew? XXX
6034 void CMSRefProcTaskProxy::do_work_steal(int i,
6035 CMSParDrainMarkingStackClosure* drain,
6036 CMSParKeepAliveClosure* keep_alive,
6037 int* seed) {
6038 OopTaskQueue* work_q = work_queue(i);
6039 NOT_PRODUCT(int num_steals = 0;)
6040 oop obj_to_scan;
6041
6042 while (true) {
6043 // Completely finish any left over work from (an) earlier round(s)
6044 drain->trim_queue(0);
6045 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
6046 (size_t)ParGCDesiredObjsFromOverflowList);
6047 // Now check if there's any work in the overflow list
6048 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
6049 // only affects the number of attempts made to get work from the
6050 // overflow list and does not affect the number of workers. Just
6051 // pass ParallelGCThreads so this behavior is unchanged.
6052 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
6053 work_q,
6054 ParallelGCThreads)) {
6055 // Found something in global overflow list;
6056 // not yet ready to go stealing work from others.
6057 // We'd like to assert(work_q->size() != 0, ...)
6058 // because we just took work from the overflow list,
6059 // but of course we can't, since all of that might have
6060 // been already stolen from us.
6061 continue;
6062 }
6063 // Verify that we have no work before we resort to stealing
6064 assert(work_q->size() == 0, "Have work, shouldn't steal");
6065 // Try to steal from other queues that have work
6066 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
6067 NOT_PRODUCT(num_steals++;)
6068 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
6069 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
6070 // Do scanning work
6071 obj_to_scan->oop_iterate(keep_alive);
6072 // Loop around, finish this work, and try to steal some more
6073 } else if (terminator()->offer_termination()) {
6074 break; // nirvana from the infinite cycle
6075 }
6076 }
6077 NOT_PRODUCT(
6078 if (PrintCMSStatistics != 0) {
6079 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
6080 }
6081 )
6082 }
6083
6084 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
6085 {
6086 GenCollectedHeap* gch = GenCollectedHeap::heap();
6087 FlexibleWorkGang* workers = gch->workers();
6088 assert(workers != NULL, "Need parallel worker threads.");
6089 CMSRefProcTaskProxy rp_task(task, &_collector,
6090 _collector.ref_processor()->span(),
6091 _collector.markBitMap(),
6092 workers, _collector.task_queues());
6093 workers->run_task(&rp_task);
6094 }
6095
6096 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
6097 {
6098
6099 GenCollectedHeap* gch = GenCollectedHeap::heap();
6100 FlexibleWorkGang* workers = gch->workers();
6101 assert(workers != NULL, "Need parallel worker threads.");
6102 CMSRefEnqueueTaskProxy enq_task(task);
6103 workers->run_task(&enq_task);
6104 }
6105
6106 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
6107
6108 ResourceMark rm;
6109 HandleMark hm;
6110
6111 ReferenceProcessor* rp = ref_processor();
6112 assert(rp->span().equals(_span), "Spans should be equal");
6113 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
6114 // Process weak references.
6115 rp->setup_policy(clear_all_soft_refs);
6116 verify_work_stacks_empty();
6117
6118 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
6119 &_markStack, false /* !preclean */);
6120 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
6121 _span, &_markBitMap, &_markStack,
6122 &cmsKeepAliveClosure, false /* !preclean */);
6123 {
6124 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6125
6126 ReferenceProcessorStats stats;
6127 if (rp->processing_is_mt()) {
6128 // Set the degree of MT here. If the discovery is done MT, there
6129 // may have been a different number of threads doing the discovery
6130 // and a different number of discovered lists may have Ref objects.
6131 // That is OK as long as the Reference lists are balanced (see
6132 // balance_all_queues() and balance_queues()).
6133 GenCollectedHeap* gch = GenCollectedHeap::heap();
6134 int active_workers = ParallelGCThreads;
6135 FlexibleWorkGang* workers = gch->workers();
6136 if (workers != NULL) {
6137 active_workers = workers->active_workers();
6138 // The expectation is that active_workers will have already
6139 // been set to a reasonable value. If it has not been set,
6140 // investigate.
6141 assert(active_workers > 0, "Should have been set during scavenge");
6142 }
6143 rp->set_active_mt_degree(active_workers);
6144 CMSRefProcTaskExecutor task_executor(*this);
6145 stats = rp->process_discovered_references(&_is_alive_closure,
6146 &cmsKeepAliveClosure,
6147 &cmsDrainMarkingStackClosure,
6148 &task_executor,
6149 _gc_timer_cm,
6150 _gc_tracer_cm->gc_id());
6151 } else {
6152 stats = rp->process_discovered_references(&_is_alive_closure,
6153 &cmsKeepAliveClosure,
6154 &cmsDrainMarkingStackClosure,
6155 NULL,
6156 _gc_timer_cm,
6157 _gc_tracer_cm->gc_id());
6158 }
6159 _gc_tracer_cm->report_gc_reference_stats(stats);
6160
6161 }
6162
6163 // This is the point where the entire marking should have completed.
6164 verify_work_stacks_empty();
6165
6166 if (should_unload_classes()) {
6167 {
6168 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6169
6170 // Unload classes and purge the SystemDictionary.
6171 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
6172
6173 // Unload nmethods.
6174 CodeCache::do_unloading(&_is_alive_closure, purged_class);
6175
6176 // Prune dead klasses from subklass/sibling/implementor lists.
6177 Klass::clean_weak_klass_links(&_is_alive_closure);
6178 }
6179
6180 {
6181 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6182 // Clean up unreferenced symbols in symbol table.
6183 SymbolTable::unlink();
6184 }
6185
6186 {
6187 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6188 // Delete entries for dead interned strings.
6189 StringTable::unlink(&_is_alive_closure);
6190 }
6191 }
6192
6193
6194 // Restore any preserved marks as a result of mark stack or
6195 // work queue overflow
6196 restore_preserved_marks_if_any(); // done single-threaded for now
6197
6198 rp->set_enqueuing_is_done(true);
6199 if (rp->processing_is_mt()) {
6200 rp->balance_all_queues();
6201 CMSRefProcTaskExecutor task_executor(*this);
6202 rp->enqueue_discovered_references(&task_executor);
6203 } else {
6204 rp->enqueue_discovered_references(NULL);
6205 }
6206 rp->verify_no_references_recorded();
6207 assert(!rp->discovery_enabled(), "should have been disabled");
6208 }
6209
6210 #ifndef PRODUCT
6211 void CMSCollector::check_correct_thread_executing() {
6212 Thread* t = Thread::current();
6213 // Only the VM thread or the CMS thread should be here.
6214 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
6215 "Unexpected thread type");
6216 // If this is the vm thread, the foreground process
6217 // should not be waiting. Note that _foregroundGCIsActive is
6218 // true while the foreground collector is waiting.
6219 if (_foregroundGCShouldWait) {
6220 // We cannot be the VM thread
6221 assert(t->is_ConcurrentGC_thread(),
6222 "Should be CMS thread");
6223 } else {
6224 // We can be the CMS thread only if we are in a stop-world
6225 // phase of CMS collection.
6226 if (t->is_ConcurrentGC_thread()) {
6227 assert(_collectorState == InitialMarking ||
6228 _collectorState == FinalMarking,
6229 "Should be a stop-world phase");
6230 // The CMS thread should be holding the CMS_token.
6231 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6232 "Potential interference with concurrently "
6233 "executing VM thread");
6234 }
6235 }
6236 }
6237 #endif
6238
6239 void CMSCollector::sweep(bool asynch) {
6240 assert(_collectorState == Sweeping, "just checking");
6241 check_correct_thread_executing();
6242 verify_work_stacks_empty();
6243 verify_overflow_empty();
6244 increment_sweep_count();
6245 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
6246
6247 _inter_sweep_timer.stop();
6248 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6249
6250 assert(!_intra_sweep_timer.is_active(), "Should not be active");
6251 _intra_sweep_timer.reset();
6252 _intra_sweep_timer.start();
6253 if (asynch) {
6254 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6255 CMSPhaseAccounting pa(this, "sweep", _gc_tracer_cm->gc_id(), !PrintGCDetails);
6256 // First sweep the old gen
6257 {
6258 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6259 bitMapLock());
6260 sweepWork(_cmsGen, asynch);
6261 }
6262
6263 // Update Universe::_heap_*_at_gc figures.
6264 // We need all the free list locks to make the abstract state
6265 // transition from Sweeping to Resetting. See detailed note
6266 // further below.
6267 {
6268 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
6269 // Update heap occupancy information which is used as
6270 // input to soft ref clearing policy at the next gc.
6271 Universe::update_heap_info_at_gc();
6272 _collectorState = Resizing;
6273 }
6274 } else {
6275 // already have needed locks
6276 sweepWork(_cmsGen, asynch);
6277 // Update heap occupancy information which is used as
6278 // input to soft ref clearing policy at the next gc.
6279 Universe::update_heap_info_at_gc();
6280 _collectorState = Resizing;
6281 }
6282 verify_work_stacks_empty();
6283 verify_overflow_empty();
6284
6285 if (should_unload_classes()) {
6286 // Delay purge to the beginning of the next safepoint. Metaspace::contains
6287 // requires that the virtual spaces are stable and not deleted.
6288 ClassLoaderDataGraph::set_should_purge(true);
6289 }
6290
6291 _intra_sweep_timer.stop();
6292 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6293
6294 _inter_sweep_timer.reset();
6295 _inter_sweep_timer.start();
6296
6297 // We need to use a monotonically non-decreasing time in ms
6298 // or we will see time-warp warnings and os::javaTimeMillis()
6299 // does not guarantee monotonicity.
6300 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
6301 update_time_of_last_gc(now);
6302
6303 // NOTE on abstract state transitions:
6304 // Mutators allocate-live and/or mark the mod-union table dirty
6305 // based on the state of the collection. The former is done in
6306 // the interval [Marking, Sweeping] and the latter in the interval
6307 // [Marking, Sweeping). Thus the transitions into the Marking state
6308 // and out of the Sweeping state must be synchronously visible
6309 // globally to the mutators.
6310 // The transition into the Marking state happens with the world
6311 // stopped so the mutators will globally see it. Sweeping is
6312 // done asynchronously by the background collector so the transition
6313 // from the Sweeping state to the Resizing state must be done
6314 // under the freelistLock (as is the check for whether to
6315 // allocate-live and whether to dirty the mod-union table).
6316 assert(_collectorState == Resizing, "Change of collector state to"
6317 " Resizing must be done under the freelistLocks (plural)");
6318
6319 // Now that sweeping has been completed, we clear
6320 // the incremental_collection_failed flag,
6321 // thus inviting a younger gen collection to promote into
6322 // this generation. If such a promotion may still fail,
6323 // the flag will be set again when a young collection is
6324 // attempted.
6325 GenCollectedHeap* gch = GenCollectedHeap::heap();
6326 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
6327 gch->update_full_collections_completed(_collection_count_start);
6328 }
6329
6330 // FIX ME!!! Looks like this belongs in CFLSpace, with
6331 // CMSGen merely delegating to it.
6332 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6333 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6334 HeapWord* minAddr = _cmsSpace->bottom();
6335 HeapWord* largestAddr =
6336 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
6337 if (largestAddr == NULL) {
6338 // The dictionary appears to be empty. In this case
6339 // try to coalesce at the end of the heap.
6340 largestAddr = _cmsSpace->end();
6341 }
6342 size_t largestOffset = pointer_delta(largestAddr, minAddr);
6343 size_t nearLargestOffset =
6344 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6345 if (PrintFLSStatistics != 0) {
6346 gclog_or_tty->print_cr(
6347 "CMS: Large Block: " PTR_FORMAT ";"
6348 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6349 largestAddr,
6350 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6351 }
6352 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6353 }
6354
6355 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6356 return addr >= _cmsSpace->nearLargestChunk();
6357 }
6358
6359 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6360 return _cmsSpace->find_chunk_at_end();
6361 }
6362
6363 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6364 bool full) {
6365 // The next lower level has been collected. Gather any statistics
6366 // that are of interest at this point.
6367 if (!full && (current_level + 1) == level()) {
6368 // Gather statistics on the young generation collection.
6369 collector()->stats().record_gc0_end(used());
6370 }
6371 }
6372
6373 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6374 if (PrintGCDetails && Verbose) {
6375 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6376 }
6377 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6378 _debug_collection_type =
6379 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6380 if (PrintGCDetails && Verbose) {
6381 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6382 }
6383 }
6384
6385 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6386 bool asynch) {
6387 // We iterate over the space(s) underlying this generation,
6388 // checking the mark bit map to see if the bits corresponding
6389 // to specific blocks are marked or not. Blocks that are
6390 // marked are live and are not swept up. All remaining blocks
6391 // are swept up, with coalescing on-the-fly as we sweep up
6392 // contiguous free and/or garbage blocks:
6393 // We need to ensure that the sweeper synchronizes with allocators
6394 // and stop-the-world collectors. In particular, the following
6395 // locks are used:
6396 // . CMS token: if this is held, a stop the world collection cannot occur
6397 // . freelistLock: if this is held no allocation can occur from this
6398 // generation by another thread
6399 // . bitMapLock: if this is held, no other thread can access or update
6400 //
6401
6402 // Note that we need to hold the freelistLock if we use
6403 // block iterate below; else the iterator might go awry if
6404 // a mutator (or promotion) causes block contents to change
6405 // (for instance if the allocator divvies up a block).
6406 // If we hold the free list lock, for all practical purposes
6407 // young generation GC's can't occur (they'll usually need to
6408 // promote), so we might as well prevent all young generation
6409 // GC's while we do a sweeping step. For the same reason, we might
6410 // as well take the bit map lock for the entire duration
6411
6412 // check that we hold the requisite locks
6413 assert(have_cms_token(), "Should hold cms token");
6414 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6415 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6416 "Should possess CMS token to sweep");
6417 assert_lock_strong(gen->freelistLock());
6418 assert_lock_strong(bitMapLock());
6419
6420 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6421 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
6422 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6423 _inter_sweep_estimate.padded_average(),
6424 _intra_sweep_estimate.padded_average());
6425 gen->setNearLargestChunk();
6426
6427 {
6428 SweepClosure sweepClosure(this, gen, &_markBitMap,
6429 CMSYield && asynch);
6430 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6431 // We need to free-up/coalesce garbage/blocks from a
6432 // co-terminal free run. This is done in the SweepClosure
6433 // destructor; so, do not remove this scope, else the
6434 // end-of-sweep-census below will be off by a little bit.
6435 }
6436 gen->cmsSpace()->sweep_completed();
6437 gen->cmsSpace()->endSweepFLCensus(sweep_count());
6438 if (should_unload_classes()) { // unloaded classes this cycle,
6439 _concurrent_cycles_since_last_unload = 0; // ... reset count
6440 } else { // did not unload classes,
6441 _concurrent_cycles_since_last_unload++; // ... increment count
6442 }
6443 }
6444
6445 // Reset CMS data structures (for now just the marking bit map)
6446 // preparatory for the next cycle.
6447 void CMSCollector::reset(bool asynch) {
6448 if (asynch) {
6449 CMSTokenSyncWithLocks ts(true, bitMapLock());
6450
6451 // If the state is not "Resetting", the foreground thread
6452 // has done a collection and the resetting.
6453 if (_collectorState != Resetting) {
6454 assert(_collectorState == Idling, "The state should only change"
6455 " because the foreground collector has finished the collection");
6456 return;
6457 }
6458
6459 // Clear the mark bitmap (no grey objects to start with)
6460 // for the next cycle.
6461 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6462 CMSPhaseAccounting cmspa(this, "reset", _gc_tracer_cm->gc_id(), !PrintGCDetails);
6463
6464 HeapWord* curAddr = _markBitMap.startWord();
6465 while (curAddr < _markBitMap.endWord()) {
6466 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6467 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6468 _markBitMap.clear_large_range(chunk);
6469 if (ConcurrentMarkSweepThread::should_yield() &&
6470 !foregroundGCIsActive() &&
6471 CMSYield) {
6472 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6473 "CMS thread should hold CMS token");
6474 assert_lock_strong(bitMapLock());
6475 bitMapLock()->unlock();
6476 ConcurrentMarkSweepThread::desynchronize(true);
6477 ConcurrentMarkSweepThread::acknowledge_yield_request();
6478 stopTimer();
6479 if (PrintCMSStatistics != 0) {
6480 incrementYields();
6481 }
6482 icms_wait();
6483
6484 // See the comment in coordinator_yield()
6485 for (unsigned i = 0; i < CMSYieldSleepCount &&
6486 ConcurrentMarkSweepThread::should_yield() &&
6487 !CMSCollector::foregroundGCIsActive(); ++i) {
6488 os::sleep(Thread::current(), 1, false);
6489 ConcurrentMarkSweepThread::acknowledge_yield_request();
6490 }
6491
6492 ConcurrentMarkSweepThread::synchronize(true);
6493 bitMapLock()->lock_without_safepoint_check();
6494 startTimer();
6495 }
6496 curAddr = chunk.end();
6497 }
6498 // A successful mostly concurrent collection has been done.
6499 // Because only the full (i.e., concurrent mode failure) collections
6500 // are being measured for gc overhead limits, clean the "near" flag
6501 // and count.
6502 size_policy()->reset_gc_overhead_limit_count();
6503 _collectorState = Idling;
6504 } else {
6505 // already have the lock
6506 assert(_collectorState == Resetting, "just checking");
6507 assert_lock_strong(bitMapLock());
6508 _markBitMap.clear_all();
6509 _collectorState = Idling;
6510 }
6511
6512 // Stop incremental mode after a cycle completes, so that any future cycles
6513 // are triggered by allocation.
6514 stop_icms();
6515
6516 NOT_PRODUCT(
6517 if (RotateCMSCollectionTypes) {
6518 _cmsGen->rotate_debug_collection_type();
6519 }
6520 )
6521
6522 register_gc_end();
6523 }
6524
6525 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
6526 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6527 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6528 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL, _gc_tracer_cm->gc_id());
6529 TraceCollectorStats tcs(counters());
6530
6531 switch (op) {
6532 case CMS_op_checkpointRootsInitial: {
6533 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6534 checkpointRootsInitial(true); // asynch
6535 if (PrintGC) {
6536 _cmsGen->printOccupancy("initial-mark");
6537 }
6538 break;
6539 }
6540 case CMS_op_checkpointRootsFinal: {
6541 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6542 checkpointRootsFinal(true, // asynch
6543 false, // !clear_all_soft_refs
6544 false); // !init_mark_was_synchronous
6545 if (PrintGC) {
6546 _cmsGen->printOccupancy("remark");
6547 }
6548 break;
6549 }
6550 default:
6551 fatal("No such CMS_op");
6552 }
6553 }
6554
6555 #ifndef PRODUCT
6556 size_t const CMSCollector::skip_header_HeapWords() {
6557 return FreeChunk::header_size();
6558 }
6559
6560 // Try and collect here conditions that should hold when
6561 // CMS thread is exiting. The idea is that the foreground GC
6562 // thread should not be blocked if it wants to terminate
6563 // the CMS thread and yet continue to run the VM for a while
6564 // after that.
6565 void CMSCollector::verify_ok_to_terminate() const {
6566 assert(Thread::current()->is_ConcurrentGC_thread(),
6567 "should be called by CMS thread");
6568 assert(!_foregroundGCShouldWait, "should be false");
6569 // We could check here that all the various low-level locks
6570 // are not held by the CMS thread, but that is overkill; see
6571 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6572 // is checked.
6573 }
6574 #endif
6575
6576 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6577 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6578 "missing Printezis mark?");
6579 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6580 size_t size = pointer_delta(nextOneAddr + 1, addr);
6581 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6582 "alignment problem");
6583 assert(size >= 3, "Necessary for Printezis marks to work");
6584 return size;
6585 }
6586
6587 // A variant of the above (block_size_using_printezis_bits()) except
6588 // that we return 0 if the P-bits are not yet set.
6589 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6590 if (_markBitMap.isMarked(addr + 1)) {
6591 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
6592 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6593 size_t size = pointer_delta(nextOneAddr + 1, addr);
6594 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6595 "alignment problem");
6596 assert(size >= 3, "Necessary for Printezis marks to work");
6597 return size;
6598 }
6599 return 0;
6600 }
6601
6602 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6603 size_t sz = 0;
6604 oop p = (oop)addr;
6605 if (p->klass_or_null() != NULL) {
6606 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6607 } else {
6608 sz = block_size_using_printezis_bits(addr);
6609 }
6610 assert(sz > 0, "size must be nonzero");
6611 HeapWord* next_block = addr + sz;
6612 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6613 CardTableModRefBS::card_size);
6614 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6615 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6616 "must be different cards");
6617 return next_card;
6618 }
6619
6620
6621 // CMS Bit Map Wrapper /////////////////////////////////////////
6622
6623 // Construct a CMS bit map infrastructure, but don't create the
6624 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6625 // further below.
6626 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6627 _bm(),
6628 _shifter(shifter),
6629 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6630 {
6631 _bmStartWord = 0;
6632 _bmWordSize = 0;
6633 }
6634
6635 bool CMSBitMap::allocate(MemRegion mr) {
6636 _bmStartWord = mr.start();
6637 _bmWordSize = mr.word_size();
6638 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6639 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6640 if (!brs.is_reserved()) {
6641 warning("CMS bit map allocation failure");
6642 return false;
6643 }
6644 // For now we'll just commit all of the bit map up front.
6645 // Later on we'll try to be more parsimonious with swap.
6646 if (!_virtual_space.initialize(brs, brs.size())) {
6647 warning("CMS bit map backing store failure");
6648 return false;
6649 }
6650 assert(_virtual_space.committed_size() == brs.size(),
6651 "didn't reserve backing store for all of CMS bit map?");
6652 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6653 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6654 _bmWordSize, "inconsistency in bit map sizing");
6655 _bm.set_size(_bmWordSize >> _shifter);
6656
6657 // bm.clear(); // can we rely on getting zero'd memory? verify below
6658 assert(isAllClear(),
6659 "Expected zero'd memory from ReservedSpace constructor");
6660 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6661 "consistency check");
6662 return true;
6663 }
6664
6665 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6666 HeapWord *next_addr, *end_addr, *last_addr;
6667 assert_locked();
6668 assert(covers(mr), "out-of-range error");
6669 // XXX assert that start and end are appropriately aligned
6670 for (next_addr = mr.start(), end_addr = mr.end();
6671 next_addr < end_addr; next_addr = last_addr) {
6672 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6673 last_addr = dirty_region.end();
6674 if (!dirty_region.is_empty()) {
6675 cl->do_MemRegion(dirty_region);
6676 } else {
6677 assert(last_addr == end_addr, "program logic");
6678 return;
6679 }
6680 }
6681 }
6682
6683 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
6684 _bm.print_on_error(st, prefix);
6685 }
6686
6687 #ifndef PRODUCT
6688 void CMSBitMap::assert_locked() const {
6689 CMSLockVerifier::assert_locked(lock());
6690 }
6691
6692 bool CMSBitMap::covers(MemRegion mr) const {
6693 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6694 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6695 "size inconsistency");
6696 return (mr.start() >= _bmStartWord) &&
6697 (mr.end() <= endWord());
6698 }
6699
6700 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6701 return (start >= _bmStartWord && (start + size) <= endWord());
6702 }
6703
6704 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6705 // verify that there are no 1 bits in the interval [left, right)
6706 FalseBitMapClosure falseBitMapClosure;
6707 iterate(&falseBitMapClosure, left, right);
6708 }
6709
6710 void CMSBitMap::region_invariant(MemRegion mr)
6711 {
6712 assert_locked();
6713 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6714 assert(!mr.is_empty(), "unexpected empty region");
6715 assert(covers(mr), "mr should be covered by bit map");
6716 // convert address range into offset range
6717 size_t start_ofs = heapWordToOffset(mr.start());
6718 // Make sure that end() is appropriately aligned
6719 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6720 (1 << (_shifter+LogHeapWordSize))),
6721 "Misaligned mr.end()");
6722 size_t end_ofs = heapWordToOffset(mr.end());
6723 assert(end_ofs > start_ofs, "Should mark at least one bit");
6724 }
6725
6726 #endif
6727
6728 bool CMSMarkStack::allocate(size_t size) {
6729 // allocate a stack of the requisite depth
6730 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6731 size * sizeof(oop)));
6732 if (!rs.is_reserved()) {
6733 warning("CMSMarkStack allocation failure");
6734 return false;
6735 }
6736 if (!_virtual_space.initialize(rs, rs.size())) {
6737 warning("CMSMarkStack backing store failure");
6738 return false;
6739 }
6740 assert(_virtual_space.committed_size() == rs.size(),
6741 "didn't reserve backing store for all of CMS stack?");
6742 _base = (oop*)(_virtual_space.low());
6743 _index = 0;
6744 _capacity = size;
6745 NOT_PRODUCT(_max_depth = 0);
6746 return true;
6747 }
6748
6749 // XXX FIX ME !!! In the MT case we come in here holding a
6750 // leaf lock. For printing we need to take a further lock
6751 // which has lower rank. We need to recalibrate the two
6752 // lock-ranks involved in order to be able to print the
6753 // messages below. (Or defer the printing to the caller.
6754 // For now we take the expedient path of just disabling the
6755 // messages for the problematic case.)
6756 void CMSMarkStack::expand() {
6757 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6758 if (_capacity == MarkStackSizeMax) {
6759 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6760 // We print a warning message only once per CMS cycle.
6761 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6762 }
6763 return;
6764 }
6765 // Double capacity if possible
6766 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6767 // Do not give up existing stack until we have managed to
6768 // get the double capacity that we desired.
6769 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6770 new_capacity * sizeof(oop)));
6771 if (rs.is_reserved()) {
6772 // Release the backing store associated with old stack
6773 _virtual_space.release();
6774 // Reinitialize virtual space for new stack
6775 if (!_virtual_space.initialize(rs, rs.size())) {
6776 fatal("Not enough swap for expanded marking stack");
6777 }
6778 _base = (oop*)(_virtual_space.low());
6779 _index = 0;
6780 _capacity = new_capacity;
6781 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6782 // Failed to double capacity, continue;
6783 // we print a detail message only once per CMS cycle.
6784 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6785 SIZE_FORMAT"K",
6786 _capacity / K, new_capacity / K);
6787 }
6788 }
6789
6790
6791 // Closures
6792 // XXX: there seems to be a lot of code duplication here;
6793 // should refactor and consolidate common code.
6794
6795 // This closure is used to mark refs into the CMS generation in
6796 // the CMS bit map. Called at the first checkpoint. This closure
6797 // assumes that we do not need to re-mark dirty cards; if the CMS
6798 // generation on which this is used is not an oldest
6799 // generation then this will lose younger_gen cards!
6800
6801 MarkRefsIntoClosure::MarkRefsIntoClosure(
6802 MemRegion span, CMSBitMap* bitMap):
6803 _span(span),
6804 _bitMap(bitMap)
6805 {
6806 assert(_ref_processor == NULL, "deliberately left NULL");
6807 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6808 }
6809
6810 void MarkRefsIntoClosure::do_oop(oop obj) {
6811 // if p points into _span, then mark corresponding bit in _markBitMap
6812 assert(obj->is_oop(), "expected an oop");
6813 HeapWord* addr = (HeapWord*)obj;
6814 if (_span.contains(addr)) {
6815 // this should be made more efficient
6816 _bitMap->mark(addr);
6817 }
6818 }
6819
6820 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6821 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6822
6823 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6824 MemRegion span, CMSBitMap* bitMap):
6825 _span(span),
6826 _bitMap(bitMap)
6827 {
6828 assert(_ref_processor == NULL, "deliberately left NULL");
6829 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6830 }
6831
6832 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6833 // if p points into _span, then mark corresponding bit in _markBitMap
6834 assert(obj->is_oop(), "expected an oop");
6835 HeapWord* addr = (HeapWord*)obj;
6836 if (_span.contains(addr)) {
6837 // this should be made more efficient
6838 _bitMap->par_mark(addr);
6839 }
6840 }
6841
6842 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6843 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6844
6845 // A variant of the above, used for CMS marking verification.
6846 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6847 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6848 _span(span),
6849 _verification_bm(verification_bm),
6850 _cms_bm(cms_bm)
6851 {
6852 assert(_ref_processor == NULL, "deliberately left NULL");
6853 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6854 }
6855
6856 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6857 // if p points into _span, then mark corresponding bit in _markBitMap
6858 assert(obj->is_oop(), "expected an oop");
6859 HeapWord* addr = (HeapWord*)obj;
6860 if (_span.contains(addr)) {
6861 _verification_bm->mark(addr);
6862 if (!_cms_bm->isMarked(addr)) {
6863 oop(addr)->print();
6864 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6865 fatal("... aborting");
6866 }
6867 }
6868 }
6869
6870 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6871 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6872
6873 //////////////////////////////////////////////////
6874 // MarkRefsIntoAndScanClosure
6875 //////////////////////////////////////////////////
6876
6877 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6878 ReferenceProcessor* rp,
6879 CMSBitMap* bit_map,
6880 CMSBitMap* mod_union_table,
6881 CMSMarkStack* mark_stack,
6882 CMSCollector* collector,
6883 bool should_yield,
6884 bool concurrent_precleaning):
6885 _collector(collector),
6886 _span(span),
6887 _bit_map(bit_map),
6888 _mark_stack(mark_stack),
6889 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6890 mark_stack, concurrent_precleaning),
6891 _yield(should_yield),
6892 _concurrent_precleaning(concurrent_precleaning),
6893 _freelistLock(NULL)
6894 {
6895 _ref_processor = rp;
6896 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6897 }
6898
6899 // This closure is used to mark refs into the CMS generation at the
6900 // second (final) checkpoint, and to scan and transitively follow
6901 // the unmarked oops. It is also used during the concurrent precleaning
6902 // phase while scanning objects on dirty cards in the CMS generation.
6903 // The marks are made in the marking bit map and the marking stack is
6904 // used for keeping the (newly) grey objects during the scan.
6905 // The parallel version (Par_...) appears further below.
6906 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6907 if (obj != NULL) {
6908 assert(obj->is_oop(), "expected an oop");
6909 HeapWord* addr = (HeapWord*)obj;
6910 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6911 assert(_collector->overflow_list_is_empty(),
6912 "overflow list should be empty");
6913 if (_span.contains(addr) &&
6914 !_bit_map->isMarked(addr)) {
6915 // mark bit map (object is now grey)
6916 _bit_map->mark(addr);
6917 // push on marking stack (stack should be empty), and drain the
6918 // stack by applying this closure to the oops in the oops popped
6919 // from the stack (i.e. blacken the grey objects)
6920 bool res = _mark_stack->push(obj);
6921 assert(res, "Should have space to push on empty stack");
6922 do {
6923 oop new_oop = _mark_stack->pop();
6924 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6925 assert(_bit_map->isMarked((HeapWord*)new_oop),
6926 "only grey objects on this stack");
6927 // iterate over the oops in this oop, marking and pushing
6928 // the ones in CMS heap (i.e. in _span).
6929 new_oop->oop_iterate(&_pushAndMarkClosure);
6930 // check if it's time to yield
6931 do_yield_check();
6932 } while (!_mark_stack->isEmpty() ||
6933 (!_concurrent_precleaning && take_from_overflow_list()));
6934 // if marking stack is empty, and we are not doing this
6935 // during precleaning, then check the overflow list
6936 }
6937 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6938 assert(_collector->overflow_list_is_empty(),
6939 "overflow list was drained above");
6940 // We could restore evacuated mark words, if any, used for
6941 // overflow list links here because the overflow list is
6942 // provably empty here. That would reduce the maximum
6943 // size requirements for preserved_{oop,mark}_stack.
6944 // But we'll just postpone it until we are all done
6945 // so we can just stream through.
6946 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6947 _collector->restore_preserved_marks_if_any();
6948 assert(_collector->no_preserved_marks(), "No preserved marks");
6949 }
6950 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6951 "All preserved marks should have been restored above");
6952 }
6953 }
6954
6955 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6956 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6957
6958 void MarkRefsIntoAndScanClosure::do_yield_work() {
6959 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6960 "CMS thread should hold CMS token");
6961 assert_lock_strong(_freelistLock);
6962 assert_lock_strong(_bit_map->lock());
6963 // relinquish the free_list_lock and bitMaplock()
6964 _bit_map->lock()->unlock();
6965 _freelistLock->unlock();
6966 ConcurrentMarkSweepThread::desynchronize(true);
6967 ConcurrentMarkSweepThread::acknowledge_yield_request();
6968 _collector->stopTimer();
6969 if (PrintCMSStatistics != 0) {
6970 _collector->incrementYields();
6971 }
6972 _collector->icms_wait();
6973
6974 // See the comment in coordinator_yield()
6975 for (unsigned i = 0;
6976 i < CMSYieldSleepCount &&
6977 ConcurrentMarkSweepThread::should_yield() &&
6978 !CMSCollector::foregroundGCIsActive();
6979 ++i) {
6980 os::sleep(Thread::current(), 1, false);
6981 ConcurrentMarkSweepThread::acknowledge_yield_request();
6982 }
6983
6984 ConcurrentMarkSweepThread::synchronize(true);
6985 _freelistLock->lock_without_safepoint_check();
6986 _bit_map->lock()->lock_without_safepoint_check();
6987 _collector->startTimer();
6988 }
6989
6990 ///////////////////////////////////////////////////////////
6991 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6992 // MarkRefsIntoAndScanClosure
6993 ///////////////////////////////////////////////////////////
6994 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6995 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6996 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6997 _span(span),
6998 _bit_map(bit_map),
6999 _work_queue(work_queue),
7000 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
7001 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
7002 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
7003 {
7004 _ref_processor = rp;
7005 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7006 }
7007
7008 // This closure is used to mark refs into the CMS generation at the
7009 // second (final) checkpoint, and to scan and transitively follow
7010 // the unmarked oops. The marks are made in the marking bit map and
7011 // the work_queue is used for keeping the (newly) grey objects during
7012 // the scan phase whence they are also available for stealing by parallel
7013 // threads. Since the marking bit map is shared, updates are
7014 // synchronized (via CAS).
7015 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
7016 if (obj != NULL) {
7017 // Ignore mark word because this could be an already marked oop
7018 // that may be chained at the end of the overflow list.
7019 assert(obj->is_oop(true), "expected an oop");
7020 HeapWord* addr = (HeapWord*)obj;
7021 if (_span.contains(addr) &&
7022 !_bit_map->isMarked(addr)) {
7023 // mark bit map (object will become grey):
7024 // It is possible for several threads to be
7025 // trying to "claim" this object concurrently;
7026 // the unique thread that succeeds in marking the
7027 // object first will do the subsequent push on
7028 // to the work queue (or overflow list).
7029 if (_bit_map->par_mark(addr)) {
7030 // push on work_queue (which may not be empty), and trim the
7031 // queue to an appropriate length by applying this closure to
7032 // the oops in the oops popped from the stack (i.e. blacken the
7033 // grey objects)
7034 bool res = _work_queue->push(obj);
7035 assert(res, "Low water mark should be less than capacity?");
7036 trim_queue(_low_water_mark);
7037 } // Else, another thread claimed the object
7038 }
7039 }
7040 }
7041
7042 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
7043 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
7044
7045 // This closure is used to rescan the marked objects on the dirty cards
7046 // in the mod union table and the card table proper.
7047 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
7048 oop p, MemRegion mr) {
7049
7050 size_t size = 0;
7051 HeapWord* addr = (HeapWord*)p;
7052 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7053 assert(_span.contains(addr), "we are scanning the CMS generation");
7054 // check if it's time to yield
7055 if (do_yield_check()) {
7056 // We yielded for some foreground stop-world work,
7057 // and we have been asked to abort this ongoing preclean cycle.
7058 return 0;
7059 }
7060 if (_bitMap->isMarked(addr)) {
7061 // it's marked; is it potentially uninitialized?
7062 if (p->klass_or_null() != NULL) {
7063 // an initialized object; ignore mark word in verification below
7064 // since we are running concurrent with mutators
7065 assert(p->is_oop(true), "should be an oop");
7066 if (p->is_objArray()) {
7067 // objArrays are precisely marked; restrict scanning
7068 // to dirty cards only.
7069 size = CompactibleFreeListSpace::adjustObjectSize(
7070 p->oop_iterate(_scanningClosure, mr));
7071 } else {
7072 // A non-array may have been imprecisely marked; we need
7073 // to scan object in its entirety.
7074 size = CompactibleFreeListSpace::adjustObjectSize(
7075 p->oop_iterate(_scanningClosure));
7076 }
7077 #ifdef ASSERT
7078 size_t direct_size =
7079 CompactibleFreeListSpace::adjustObjectSize(p->size());
7080 assert(size == direct_size, "Inconsistency in size");
7081 assert(size >= 3, "Necessary for Printezis marks to work");
7082 if (!_bitMap->isMarked(addr+1)) {
7083 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
7084 } else {
7085 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
7086 assert(_bitMap->isMarked(addr+size-1),
7087 "inconsistent Printezis mark");
7088 }
7089 #endif // ASSERT
7090 } else {
7091 // An uninitialized object.
7092 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
7093 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7094 size = pointer_delta(nextOneAddr + 1, addr);
7095 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7096 "alignment problem");
7097 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
7098 // will dirty the card when the klass pointer is installed in the
7099 // object (signaling the completion of initialization).
7100 }
7101 } else {
7102 // Either a not yet marked object or an uninitialized object
7103 if (p->klass_or_null() == NULL) {
7104 // An uninitialized object, skip to the next card, since
7105 // we may not be able to read its P-bits yet.
7106 assert(size == 0, "Initial value");
7107 } else {
7108 // An object not (yet) reached by marking: we merely need to
7109 // compute its size so as to go look at the next block.
7110 assert(p->is_oop(true), "should be an oop");
7111 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
7112 }
7113 }
7114 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7115 return size;
7116 }
7117
7118 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
7119 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7120 "CMS thread should hold CMS token");
7121 assert_lock_strong(_freelistLock);
7122 assert_lock_strong(_bitMap->lock());
7123 // relinquish the free_list_lock and bitMaplock()
7124 _bitMap->lock()->unlock();
7125 _freelistLock->unlock();
7126 ConcurrentMarkSweepThread::desynchronize(true);
7127 ConcurrentMarkSweepThread::acknowledge_yield_request();
7128 _collector->stopTimer();
7129 if (PrintCMSStatistics != 0) {
7130 _collector->incrementYields();
7131 }
7132 _collector->icms_wait();
7133
7134 // See the comment in coordinator_yield()
7135 for (unsigned i = 0; i < CMSYieldSleepCount &&
7136 ConcurrentMarkSweepThread::should_yield() &&
7137 !CMSCollector::foregroundGCIsActive(); ++i) {
7138 os::sleep(Thread::current(), 1, false);
7139 ConcurrentMarkSweepThread::acknowledge_yield_request();
7140 }
7141
7142 ConcurrentMarkSweepThread::synchronize(true);
7143 _freelistLock->lock_without_safepoint_check();
7144 _bitMap->lock()->lock_without_safepoint_check();
7145 _collector->startTimer();
7146 }
7147
7148
7149 //////////////////////////////////////////////////////////////////
7150 // SurvivorSpacePrecleanClosure
7151 //////////////////////////////////////////////////////////////////
7152 // This (single-threaded) closure is used to preclean the oops in
7153 // the survivor spaces.
7154 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
7155
7156 HeapWord* addr = (HeapWord*)p;
7157 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7158 assert(!_span.contains(addr), "we are scanning the survivor spaces");
7159 assert(p->klass_or_null() != NULL, "object should be initialized");
7160 // an initialized object; ignore mark word in verification below
7161 // since we are running concurrent with mutators
7162 assert(p->is_oop(true), "should be an oop");
7163 // Note that we do not yield while we iterate over
7164 // the interior oops of p, pushing the relevant ones
7165 // on our marking stack.
7166 size_t size = p->oop_iterate(_scanning_closure);
7167 do_yield_check();
7168 // Observe that below, we do not abandon the preclean
7169 // phase as soon as we should; rather we empty the
7170 // marking stack before returning. This is to satisfy
7171 // some existing assertions. In general, it may be a
7172 // good idea to abort immediately and complete the marking
7173 // from the grey objects at a later time.
7174 while (!_mark_stack->isEmpty()) {
7175 oop new_oop = _mark_stack->pop();
7176 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7177 assert(_bit_map->isMarked((HeapWord*)new_oop),
7178 "only grey objects on this stack");
7179 // iterate over the oops in this oop, marking and pushing
7180 // the ones in CMS heap (i.e. in _span).
7181 new_oop->oop_iterate(_scanning_closure);
7182 // check if it's time to yield
7183 do_yield_check();
7184 }
7185 unsigned int after_count =
7186 GenCollectedHeap::heap()->total_collections();
7187 bool abort = (_before_count != after_count) ||
7188 _collector->should_abort_preclean();
7189 return abort ? 0 : size;
7190 }
7191
7192 void SurvivorSpacePrecleanClosure::do_yield_work() {
7193 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7194 "CMS thread should hold CMS token");
7195 assert_lock_strong(_bit_map->lock());
7196 // Relinquish the bit map lock
7197 _bit_map->lock()->unlock();
7198 ConcurrentMarkSweepThread::desynchronize(true);
7199 ConcurrentMarkSweepThread::acknowledge_yield_request();
7200 _collector->stopTimer();
7201 if (PrintCMSStatistics != 0) {
7202 _collector->incrementYields();
7203 }
7204 _collector->icms_wait();
7205
7206 // See the comment in coordinator_yield()
7207 for (unsigned i = 0; i < CMSYieldSleepCount &&
7208 ConcurrentMarkSweepThread::should_yield() &&
7209 !CMSCollector::foregroundGCIsActive(); ++i) {
7210 os::sleep(Thread::current(), 1, false);
7211 ConcurrentMarkSweepThread::acknowledge_yield_request();
7212 }
7213
7214 ConcurrentMarkSweepThread::synchronize(true);
7215 _bit_map->lock()->lock_without_safepoint_check();
7216 _collector->startTimer();
7217 }
7218
7219 // This closure is used to rescan the marked objects on the dirty cards
7220 // in the mod union table and the card table proper. In the parallel
7221 // case, although the bitMap is shared, we do a single read so the
7222 // isMarked() query is "safe".
7223 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
7224 // Ignore mark word because we are running concurrent with mutators
7225 assert(p->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(p)));
7226 HeapWord* addr = (HeapWord*)p;
7227 assert(_span.contains(addr), "we are scanning the CMS generation");
7228 bool is_obj_array = false;
7229 #ifdef ASSERT
7230 if (!_parallel) {
7231 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7232 assert(_collector->overflow_list_is_empty(),
7233 "overflow list should be empty");
7234
7235 }
7236 #endif // ASSERT
7237 if (_bit_map->isMarked(addr)) {
7238 // Obj arrays are precisely marked, non-arrays are not;
7239 // so we scan objArrays precisely and non-arrays in their
7240 // entirety.
7241 if (p->is_objArray()) {
7242 is_obj_array = true;
7243 if (_parallel) {
7244 p->oop_iterate(_par_scan_closure, mr);
7245 } else {
7246 p->oop_iterate(_scan_closure, mr);
7247 }
7248 } else {
7249 if (_parallel) {
7250 p->oop_iterate(_par_scan_closure);
7251 } else {
7252 p->oop_iterate(_scan_closure);
7253 }
7254 }
7255 }
7256 #ifdef ASSERT
7257 if (!_parallel) {
7258 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7259 assert(_collector->overflow_list_is_empty(),
7260 "overflow list should be empty");
7261
7262 }
7263 #endif // ASSERT
7264 return is_obj_array;
7265 }
7266
7267 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7268 MemRegion span,
7269 CMSBitMap* bitMap, CMSMarkStack* markStack,
7270 bool should_yield, bool verifying):
7271 _collector(collector),
7272 _span(span),
7273 _bitMap(bitMap),
7274 _mut(&collector->_modUnionTable),
7275 _markStack(markStack),
7276 _yield(should_yield),
7277 _skipBits(0)
7278 {
7279 assert(_markStack->isEmpty(), "stack should be empty");
7280 _finger = _bitMap->startWord();
7281 _threshold = _finger;
7282 assert(_collector->_restart_addr == NULL, "Sanity check");
7283 assert(_span.contains(_finger), "Out of bounds _finger?");
7284 DEBUG_ONLY(_verifying = verifying;)
7285 }
7286
7287 void MarkFromRootsClosure::reset(HeapWord* addr) {
7288 assert(_markStack->isEmpty(), "would cause duplicates on stack");
7289 assert(_span.contains(addr), "Out of bounds _finger?");
7290 _finger = addr;
7291 _threshold = (HeapWord*)round_to(
7292 (intptr_t)_finger, CardTableModRefBS::card_size);
7293 }
7294
7295 // Should revisit to see if this should be restructured for
7296 // greater efficiency.
7297 bool MarkFromRootsClosure::do_bit(size_t offset) {
7298 if (_skipBits > 0) {
7299 _skipBits--;
7300 return true;
7301 }
7302 // convert offset into a HeapWord*
7303 HeapWord* addr = _bitMap->startWord() + offset;
7304 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7305 "address out of range");
7306 assert(_bitMap->isMarked(addr), "tautology");
7307 if (_bitMap->isMarked(addr+1)) {
7308 // this is an allocated but not yet initialized object
7309 assert(_skipBits == 0, "tautology");
7310 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
7311 oop p = oop(addr);
7312 if (p->klass_or_null() == NULL) {
7313 DEBUG_ONLY(if (!_verifying) {)
7314 // We re-dirty the cards on which this object lies and increase
7315 // the _threshold so that we'll come back to scan this object
7316 // during the preclean or remark phase. (CMSCleanOnEnter)
7317 if (CMSCleanOnEnter) {
7318 size_t sz = _collector->block_size_using_printezis_bits(addr);
7319 HeapWord* end_card_addr = (HeapWord*)round_to(
7320 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7321 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7322 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7323 // Bump _threshold to end_card_addr; note that
7324 // _threshold cannot possibly exceed end_card_addr, anyhow.
7325 // This prevents future clearing of the card as the scan proceeds
7326 // to the right.
7327 assert(_threshold <= end_card_addr,
7328 "Because we are just scanning into this object");
7329 if (_threshold < end_card_addr) {
7330 _threshold = end_card_addr;
7331 }
7332 if (p->klass_or_null() != NULL) {
7333 // Redirty the range of cards...
7334 _mut->mark_range(redirty_range);
7335 } // ...else the setting of klass will dirty the card anyway.
7336 }
7337 DEBUG_ONLY(})
7338 return true;
7339 }
7340 }
7341 scanOopsInOop(addr);
7342 return true;
7343 }
7344
7345 // We take a break if we've been at this for a while,
7346 // so as to avoid monopolizing the locks involved.
7347 void MarkFromRootsClosure::do_yield_work() {
7348 // First give up the locks, then yield, then re-lock
7349 // We should probably use a constructor/destructor idiom to
7350 // do this unlock/lock or modify the MutexUnlocker class to
7351 // serve our purpose. XXX
7352 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7353 "CMS thread should hold CMS token");
7354 assert_lock_strong(_bitMap->lock());
7355 _bitMap->lock()->unlock();
7356 ConcurrentMarkSweepThread::desynchronize(true);
7357 ConcurrentMarkSweepThread::acknowledge_yield_request();
7358 _collector->stopTimer();
7359 if (PrintCMSStatistics != 0) {
7360 _collector->incrementYields();
7361 }
7362 _collector->icms_wait();
7363
7364 // See the comment in coordinator_yield()
7365 for (unsigned i = 0; i < CMSYieldSleepCount &&
7366 ConcurrentMarkSweepThread::should_yield() &&
7367 !CMSCollector::foregroundGCIsActive(); ++i) {
7368 os::sleep(Thread::current(), 1, false);
7369 ConcurrentMarkSweepThread::acknowledge_yield_request();
7370 }
7371
7372 ConcurrentMarkSweepThread::synchronize(true);
7373 _bitMap->lock()->lock_without_safepoint_check();
7374 _collector->startTimer();
7375 }
7376
7377 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7378 assert(_bitMap->isMarked(ptr), "expected bit to be set");
7379 assert(_markStack->isEmpty(),
7380 "should drain stack to limit stack usage");
7381 // convert ptr to an oop preparatory to scanning
7382 oop obj = oop(ptr);
7383 // Ignore mark word in verification below, since we
7384 // may be running concurrent with mutators.
7385 assert(obj->is_oop(true), "should be an oop");
7386 assert(_finger <= ptr, "_finger runneth ahead");
7387 // advance the finger to right end of this object
7388 _finger = ptr + obj->size();
7389 assert(_finger > ptr, "we just incremented it above");
7390 // On large heaps, it may take us some time to get through
7391 // the marking phase (especially if running iCMS). During
7392 // this time it's possible that a lot of mutations have
7393 // accumulated in the card table and the mod union table --
7394 // these mutation records are redundant until we have
7395 // actually traced into the corresponding card.
7396 // Here, we check whether advancing the finger would make
7397 // us cross into a new card, and if so clear corresponding
7398 // cards in the MUT (preclean them in the card-table in the
7399 // future).
7400
7401 DEBUG_ONLY(if (!_verifying) {)
7402 // The clean-on-enter optimization is disabled by default,
7403 // until we fix 6178663.
7404 if (CMSCleanOnEnter && (_finger > _threshold)) {
7405 // [_threshold, _finger) represents the interval
7406 // of cards to be cleared in MUT (or precleaned in card table).
7407 // The set of cards to be cleared is all those that overlap
7408 // with the interval [_threshold, _finger); note that
7409 // _threshold is always kept card-aligned but _finger isn't
7410 // always card-aligned.
7411 HeapWord* old_threshold = _threshold;
7412 assert(old_threshold == (HeapWord*)round_to(
7413 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7414 "_threshold should always be card-aligned");
7415 _threshold = (HeapWord*)round_to(
7416 (intptr_t)_finger, CardTableModRefBS::card_size);
7417 MemRegion mr(old_threshold, _threshold);
7418 assert(!mr.is_empty(), "Control point invariant");
7419 assert(_span.contains(mr), "Should clear within span");
7420 _mut->clear_range(mr);
7421 }
7422 DEBUG_ONLY(})
7423 // Note: the finger doesn't advance while we drain
7424 // the stack below.
7425 PushOrMarkClosure pushOrMarkClosure(_collector,
7426 _span, _bitMap, _markStack,
7427 _finger, this);
7428 bool res = _markStack->push(obj);
7429 assert(res, "Empty non-zero size stack should have space for single push");
7430 while (!_markStack->isEmpty()) {
7431 oop new_oop = _markStack->pop();
7432 // Skip verifying header mark word below because we are
7433 // running concurrent with mutators.
7434 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7435 // now scan this oop's oops
7436 new_oop->oop_iterate(&pushOrMarkClosure);
7437 do_yield_check();
7438 }
7439 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7440 }
7441
7442 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7443 CMSCollector* collector, MemRegion span,
7444 CMSBitMap* bit_map,
7445 OopTaskQueue* work_queue,
7446 CMSMarkStack* overflow_stack,
7447 bool should_yield):
7448 _collector(collector),
7449 _whole_span(collector->_span),
7450 _span(span),
7451 _bit_map(bit_map),
7452 _mut(&collector->_modUnionTable),
7453 _work_queue(work_queue),
7454 _overflow_stack(overflow_stack),
7455 _yield(should_yield),
7456 _skip_bits(0),
7457 _task(task)
7458 {
7459 assert(_work_queue->size() == 0, "work_queue should be empty");
7460 _finger = span.start();
7461 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7462 assert(_span.contains(_finger), "Out of bounds _finger?");
7463 }
7464
7465 // Should revisit to see if this should be restructured for
7466 // greater efficiency.
7467 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7468 if (_skip_bits > 0) {
7469 _skip_bits--;
7470 return true;
7471 }
7472 // convert offset into a HeapWord*
7473 HeapWord* addr = _bit_map->startWord() + offset;
7474 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7475 "address out of range");
7476 assert(_bit_map->isMarked(addr), "tautology");
7477 if (_bit_map->isMarked(addr+1)) {
7478 // this is an allocated object that might not yet be initialized
7479 assert(_skip_bits == 0, "tautology");
7480 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7481 oop p = oop(addr);
7482 if (p->klass_or_null() == NULL) {
7483 // in the case of Clean-on-Enter optimization, redirty card
7484 // and avoid clearing card by increasing the threshold.
7485 return true;
7486 }
7487 }
7488 scan_oops_in_oop(addr);
7489 return true;
7490 }
7491
7492 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7493 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7494 // Should we assert that our work queue is empty or
7495 // below some drain limit?
7496 assert(_work_queue->size() == 0,
7497 "should drain stack to limit stack usage");
7498 // convert ptr to an oop preparatory to scanning
7499 oop obj = oop(ptr);
7500 // Ignore mark word in verification below, since we
7501 // may be running concurrent with mutators.
7502 assert(obj->is_oop(true), "should be an oop");
7503 assert(_finger <= ptr, "_finger runneth ahead");
7504 // advance the finger to right end of this object
7505 _finger = ptr + obj->size();
7506 assert(_finger > ptr, "we just incremented it above");
7507 // On large heaps, it may take us some time to get through
7508 // the marking phase (especially if running iCMS). During
7509 // this time it's possible that a lot of mutations have
7510 // accumulated in the card table and the mod union table --
7511 // these mutation records are redundant until we have
7512 // actually traced into the corresponding card.
7513 // Here, we check whether advancing the finger would make
7514 // us cross into a new card, and if so clear corresponding
7515 // cards in the MUT (preclean them in the card-table in the
7516 // future).
7517
7518 // The clean-on-enter optimization is disabled by default,
7519 // until we fix 6178663.
7520 if (CMSCleanOnEnter && (_finger > _threshold)) {
7521 // [_threshold, _finger) represents the interval
7522 // of cards to be cleared in MUT (or precleaned in card table).
7523 // The set of cards to be cleared is all those that overlap
7524 // with the interval [_threshold, _finger); note that
7525 // _threshold is always kept card-aligned but _finger isn't
7526 // always card-aligned.
7527 HeapWord* old_threshold = _threshold;
7528 assert(old_threshold == (HeapWord*)round_to(
7529 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7530 "_threshold should always be card-aligned");
7531 _threshold = (HeapWord*)round_to(
7532 (intptr_t)_finger, CardTableModRefBS::card_size);
7533 MemRegion mr(old_threshold, _threshold);
7534 assert(!mr.is_empty(), "Control point invariant");
7535 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7536 _mut->clear_range(mr);
7537 }
7538
7539 // Note: the local finger doesn't advance while we drain
7540 // the stack below, but the global finger sure can and will.
7541 HeapWord** gfa = _task->global_finger_addr();
7542 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7543 _span, _bit_map,
7544 _work_queue,
7545 _overflow_stack,
7546 _finger,
7547 gfa, this);
7548 bool res = _work_queue->push(obj); // overflow could occur here
7549 assert(res, "Will hold once we use workqueues");
7550 while (true) {
7551 oop new_oop;
7552 if (!_work_queue->pop_local(new_oop)) {
7553 // We emptied our work_queue; check if there's stuff that can
7554 // be gotten from the overflow stack.
7555 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7556 _overflow_stack, _work_queue)) {
7557 do_yield_check();
7558 continue;
7559 } else { // done
7560 break;
7561 }
7562 }
7563 // Skip verifying header mark word below because we are
7564 // running concurrent with mutators.
7565 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7566 // now scan this oop's oops
7567 new_oop->oop_iterate(&pushOrMarkClosure);
7568 do_yield_check();
7569 }
7570 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7571 }
7572
7573 // Yield in response to a request from VM Thread or
7574 // from mutators.
7575 void Par_MarkFromRootsClosure::do_yield_work() {
7576 assert(_task != NULL, "sanity");
7577 _task->yield();
7578 }
7579
7580 // A variant of the above used for verifying CMS marking work.
7581 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7582 MemRegion span,
7583 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7584 CMSMarkStack* mark_stack):
7585 _collector(collector),
7586 _span(span),
7587 _verification_bm(verification_bm),
7588 _cms_bm(cms_bm),
7589 _mark_stack(mark_stack),
7590 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7591 mark_stack)
7592 {
7593 assert(_mark_stack->isEmpty(), "stack should be empty");
7594 _finger = _verification_bm->startWord();
7595 assert(_collector->_restart_addr == NULL, "Sanity check");
7596 assert(_span.contains(_finger), "Out of bounds _finger?");
7597 }
7598
7599 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7600 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7601 assert(_span.contains(addr), "Out of bounds _finger?");
7602 _finger = addr;
7603 }
7604
7605 // Should revisit to see if this should be restructured for
7606 // greater efficiency.
7607 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7608 // convert offset into a HeapWord*
7609 HeapWord* addr = _verification_bm->startWord() + offset;
7610 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7611 "address out of range");
7612 assert(_verification_bm->isMarked(addr), "tautology");
7613 assert(_cms_bm->isMarked(addr), "tautology");
7614
7615 assert(_mark_stack->isEmpty(),
7616 "should drain stack to limit stack usage");
7617 // convert addr to an oop preparatory to scanning
7618 oop obj = oop(addr);
7619 assert(obj->is_oop(), "should be an oop");
7620 assert(_finger <= addr, "_finger runneth ahead");
7621 // advance the finger to right end of this object
7622 _finger = addr + obj->size();
7623 assert(_finger > addr, "we just incremented it above");
7624 // Note: the finger doesn't advance while we drain
7625 // the stack below.
7626 bool res = _mark_stack->push(obj);
7627 assert(res, "Empty non-zero size stack should have space for single push");
7628 while (!_mark_stack->isEmpty()) {
7629 oop new_oop = _mark_stack->pop();
7630 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7631 // now scan this oop's oops
7632 new_oop->oop_iterate(&_pam_verify_closure);
7633 }
7634 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7635 return true;
7636 }
7637
7638 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7639 CMSCollector* collector, MemRegion span,
7640 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7641 CMSMarkStack* mark_stack):
7642 MetadataAwareOopClosure(collector->ref_processor()),
7643 _collector(collector),
7644 _span(span),
7645 _verification_bm(verification_bm),
7646 _cms_bm(cms_bm),
7647 _mark_stack(mark_stack)
7648 { }
7649
7650 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7651 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7652
7653 // Upon stack overflow, we discard (part of) the stack,
7654 // remembering the least address amongst those discarded
7655 // in CMSCollector's _restart_address.
7656 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7657 // Remember the least grey address discarded
7658 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7659 _collector->lower_restart_addr(ra);
7660 _mark_stack->reset(); // discard stack contents
7661 _mark_stack->expand(); // expand the stack if possible
7662 }
7663
7664 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7665 assert(obj->is_oop_or_null(), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7666 HeapWord* addr = (HeapWord*)obj;
7667 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7668 // Oop lies in _span and isn't yet grey or black
7669 _verification_bm->mark(addr); // now grey
7670 if (!_cms_bm->isMarked(addr)) {
7671 oop(addr)->print();
7672 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7673 addr);
7674 fatal("... aborting");
7675 }
7676
7677 if (!_mark_stack->push(obj)) { // stack overflow
7678 if (PrintCMSStatistics != 0) {
7679 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7680 SIZE_FORMAT, _mark_stack->capacity());
7681 }
7682 assert(_mark_stack->isFull(), "Else push should have succeeded");
7683 handle_stack_overflow(addr);
7684 }
7685 // anything including and to the right of _finger
7686 // will be scanned as we iterate over the remainder of the
7687 // bit map
7688 }
7689 }
7690
7691 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7692 MemRegion span,
7693 CMSBitMap* bitMap, CMSMarkStack* markStack,
7694 HeapWord* finger, MarkFromRootsClosure* parent) :
7695 MetadataAwareOopClosure(collector->ref_processor()),
7696 _collector(collector),
7697 _span(span),
7698 _bitMap(bitMap),
7699 _markStack(markStack),
7700 _finger(finger),
7701 _parent(parent)
7702 { }
7703
7704 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7705 MemRegion span,
7706 CMSBitMap* bit_map,
7707 OopTaskQueue* work_queue,
7708 CMSMarkStack* overflow_stack,
7709 HeapWord* finger,
7710 HeapWord** global_finger_addr,
7711 Par_MarkFromRootsClosure* parent) :
7712 MetadataAwareOopClosure(collector->ref_processor()),
7713 _collector(collector),
7714 _whole_span(collector->_span),
7715 _span(span),
7716 _bit_map(bit_map),
7717 _work_queue(work_queue),
7718 _overflow_stack(overflow_stack),
7719 _finger(finger),
7720 _global_finger_addr(global_finger_addr),
7721 _parent(parent)
7722 { }
7723
7724 // Assumes thread-safe access by callers, who are
7725 // responsible for mutual exclusion.
7726 void CMSCollector::lower_restart_addr(HeapWord* low) {
7727 assert(_span.contains(low), "Out of bounds addr");
7728 if (_restart_addr == NULL) {
7729 _restart_addr = low;
7730 } else {
7731 _restart_addr = MIN2(_restart_addr, low);
7732 }
7733 }
7734
7735 // Upon stack overflow, we discard (part of) the stack,
7736 // remembering the least address amongst those discarded
7737 // in CMSCollector's _restart_address.
7738 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7739 // Remember the least grey address discarded
7740 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7741 _collector->lower_restart_addr(ra);
7742 _markStack->reset(); // discard stack contents
7743 _markStack->expand(); // expand the stack if possible
7744 }
7745
7746 // Upon stack overflow, we discard (part of) the stack,
7747 // remembering the least address amongst those discarded
7748 // in CMSCollector's _restart_address.
7749 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7750 // We need to do this under a mutex to prevent other
7751 // workers from interfering with the work done below.
7752 MutexLockerEx ml(_overflow_stack->par_lock(),
7753 Mutex::_no_safepoint_check_flag);
7754 // Remember the least grey address discarded
7755 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7756 _collector->lower_restart_addr(ra);
7757 _overflow_stack->reset(); // discard stack contents
7758 _overflow_stack->expand(); // expand the stack if possible
7759 }
7760
7761 void PushOrMarkClosure::do_oop(oop obj) {
7762 // Ignore mark word because we are running concurrent with mutators.
7763 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7764 HeapWord* addr = (HeapWord*)obj;
7765 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7766 // Oop lies in _span and isn't yet grey or black
7767 _bitMap->mark(addr); // now grey
7768 if (addr < _finger) {
7769 // the bit map iteration has already either passed, or
7770 // sampled, this bit in the bit map; we'll need to
7771 // use the marking stack to scan this oop's oops.
7772 bool simulate_overflow = false;
7773 NOT_PRODUCT(
7774 if (CMSMarkStackOverflowALot &&
7775 _collector->simulate_overflow()) {
7776 // simulate a stack overflow
7777 simulate_overflow = true;
7778 }
7779 )
7780 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7781 if (PrintCMSStatistics != 0) {
7782 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7783 SIZE_FORMAT, _markStack->capacity());
7784 }
7785 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7786 handle_stack_overflow(addr);
7787 }
7788 }
7789 // anything including and to the right of _finger
7790 // will be scanned as we iterate over the remainder of the
7791 // bit map
7792 do_yield_check();
7793 }
7794 }
7795
7796 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7797 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7798
7799 void Par_PushOrMarkClosure::do_oop(oop obj) {
7800 // Ignore mark word because we are running concurrent with mutators.
7801 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7802 HeapWord* addr = (HeapWord*)obj;
7803 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7804 // Oop lies in _span and isn't yet grey or black
7805 // We read the global_finger (volatile read) strictly after marking oop
7806 bool res = _bit_map->par_mark(addr); // now grey
7807 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7808 // Should we push this marked oop on our stack?
7809 // -- if someone else marked it, nothing to do
7810 // -- if target oop is above global finger nothing to do
7811 // -- if target oop is in chunk and above local finger
7812 // then nothing to do
7813 // -- else push on work queue
7814 if ( !res // someone else marked it, they will deal with it
7815 || (addr >= *gfa) // will be scanned in a later task
7816 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7817 return;
7818 }
7819 // the bit map iteration has already either passed, or
7820 // sampled, this bit in the bit map; we'll need to
7821 // use the marking stack to scan this oop's oops.
7822 bool simulate_overflow = false;
7823 NOT_PRODUCT(
7824 if (CMSMarkStackOverflowALot &&
7825 _collector->simulate_overflow()) {
7826 // simulate a stack overflow
7827 simulate_overflow = true;
7828 }
7829 )
7830 if (simulate_overflow ||
7831 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7832 // stack overflow
7833 if (PrintCMSStatistics != 0) {
7834 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7835 SIZE_FORMAT, _overflow_stack->capacity());
7836 }
7837 // We cannot assert that the overflow stack is full because
7838 // it may have been emptied since.
7839 assert(simulate_overflow ||
7840 _work_queue->size() == _work_queue->max_elems(),
7841 "Else push should have succeeded");
7842 handle_stack_overflow(addr);
7843 }
7844 do_yield_check();
7845 }
7846 }
7847
7848 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7849 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7850
7851 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7852 MemRegion span,
7853 ReferenceProcessor* rp,
7854 CMSBitMap* bit_map,
7855 CMSBitMap* mod_union_table,
7856 CMSMarkStack* mark_stack,
7857 bool concurrent_precleaning):
7858 MetadataAwareOopClosure(rp),
7859 _collector(collector),
7860 _span(span),
7861 _bit_map(bit_map),
7862 _mod_union_table(mod_union_table),
7863 _mark_stack(mark_stack),
7864 _concurrent_precleaning(concurrent_precleaning)
7865 {
7866 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7867 }
7868
7869 // Grey object rescan during pre-cleaning and second checkpoint phases --
7870 // the non-parallel version (the parallel version appears further below.)
7871 void PushAndMarkClosure::do_oop(oop obj) {
7872 // Ignore mark word verification. If during concurrent precleaning,
7873 // the object monitor may be locked. If during the checkpoint
7874 // phases, the object may already have been reached by a different
7875 // path and may be at the end of the global overflow list (so
7876 // the mark word may be NULL).
7877 assert(obj->is_oop_or_null(true /* ignore mark word */),
7878 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7879 HeapWord* addr = (HeapWord*)obj;
7880 // Check if oop points into the CMS generation
7881 // and is not marked
7882 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7883 // a white object ...
7884 _bit_map->mark(addr); // ... now grey
7885 // push on the marking stack (grey set)
7886 bool simulate_overflow = false;
7887 NOT_PRODUCT(
7888 if (CMSMarkStackOverflowALot &&
7889 _collector->simulate_overflow()) {
7890 // simulate a stack overflow
7891 simulate_overflow = true;
7892 }
7893 )
7894 if (simulate_overflow || !_mark_stack->push(obj)) {
7895 if (_concurrent_precleaning) {
7896 // During precleaning we can just dirty the appropriate card(s)
7897 // in the mod union table, thus ensuring that the object remains
7898 // in the grey set and continue. In the case of object arrays
7899 // we need to dirty all of the cards that the object spans,
7900 // since the rescan of object arrays will be limited to the
7901 // dirty cards.
7902 // Note that no one can be interfering with us in this action
7903 // of dirtying the mod union table, so no locking or atomics
7904 // are required.
7905 if (obj->is_objArray()) {
7906 size_t sz = obj->size();
7907 HeapWord* end_card_addr = (HeapWord*)round_to(
7908 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7909 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7910 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7911 _mod_union_table->mark_range(redirty_range);
7912 } else {
7913 _mod_union_table->mark(addr);
7914 }
7915 _collector->_ser_pmc_preclean_ovflw++;
7916 } else {
7917 // During the remark phase, we need to remember this oop
7918 // in the overflow list.
7919 _collector->push_on_overflow_list(obj);
7920 _collector->_ser_pmc_remark_ovflw++;
7921 }
7922 }
7923 }
7924 }
7925
7926 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7927 MemRegion span,
7928 ReferenceProcessor* rp,
7929 CMSBitMap* bit_map,
7930 OopTaskQueue* work_queue):
7931 MetadataAwareOopClosure(rp),
7932 _collector(collector),
7933 _span(span),
7934 _bit_map(bit_map),
7935 _work_queue(work_queue)
7936 {
7937 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7938 }
7939
7940 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7941 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7942
7943 // Grey object rescan during second checkpoint phase --
7944 // the parallel version.
7945 void Par_PushAndMarkClosure::do_oop(oop obj) {
7946 // In the assert below, we ignore the mark word because
7947 // this oop may point to an already visited object that is
7948 // on the overflow stack (in which case the mark word has
7949 // been hijacked for chaining into the overflow stack --
7950 // if this is the last object in the overflow stack then
7951 // its mark word will be NULL). Because this object may
7952 // have been subsequently popped off the global overflow
7953 // stack, and the mark word possibly restored to the prototypical
7954 // value, by the time we get to examined this failing assert in
7955 // the debugger, is_oop_or_null(false) may subsequently start
7956 // to hold.
7957 assert(obj->is_oop_or_null(true),
7958 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7959 HeapWord* addr = (HeapWord*)obj;
7960 // Check if oop points into the CMS generation
7961 // and is not marked
7962 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7963 // a white object ...
7964 // If we manage to "claim" the object, by being the
7965 // first thread to mark it, then we push it on our
7966 // marking stack
7967 if (_bit_map->par_mark(addr)) { // ... now grey
7968 // push on work queue (grey set)
7969 bool simulate_overflow = false;
7970 NOT_PRODUCT(
7971 if (CMSMarkStackOverflowALot &&
7972 _collector->par_simulate_overflow()) {
7973 // simulate a stack overflow
7974 simulate_overflow = true;
7975 }
7976 )
7977 if (simulate_overflow || !_work_queue->push(obj)) {
7978 _collector->par_push_on_overflow_list(obj);
7979 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7980 }
7981 } // Else, some other thread got there first
7982 }
7983 }
7984
7985 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7986 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7987
7988 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7989 Mutex* bml = _collector->bitMapLock();
7990 assert_lock_strong(bml);
7991 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7992 "CMS thread should hold CMS token");
7993
7994 bml->unlock();
7995 ConcurrentMarkSweepThread::desynchronize(true);
7996
7997 ConcurrentMarkSweepThread::acknowledge_yield_request();
7998
7999 _collector->stopTimer();
8000 if (PrintCMSStatistics != 0) {
8001 _collector->incrementYields();
8002 }
8003 _collector->icms_wait();
8004
8005 // See the comment in coordinator_yield()
8006 for (unsigned i = 0; i < CMSYieldSleepCount &&
8007 ConcurrentMarkSweepThread::should_yield() &&
8008 !CMSCollector::foregroundGCIsActive(); ++i) {
8009 os::sleep(Thread::current(), 1, false);
8010 ConcurrentMarkSweepThread::acknowledge_yield_request();
8011 }
8012
8013 ConcurrentMarkSweepThread::synchronize(true);
8014 bml->lock();
8015
8016 _collector->startTimer();
8017 }
8018
8019 bool CMSPrecleanRefsYieldClosure::should_return() {
8020 if (ConcurrentMarkSweepThread::should_yield()) {
8021 do_yield_work();
8022 }
8023 return _collector->foregroundGCIsActive();
8024 }
8025
8026 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
8027 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
8028 "mr should be aligned to start at a card boundary");
8029 // We'd like to assert:
8030 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
8031 // "mr should be a range of cards");
8032 // However, that would be too strong in one case -- the last
8033 // partition ends at _unallocated_block which, in general, can be
8034 // an arbitrary boundary, not necessarily card aligned.
8035 if (PrintCMSStatistics != 0) {
8036 _num_dirty_cards +=
8037 mr.word_size()/CardTableModRefBS::card_size_in_words;
8038 }
8039 _space->object_iterate_mem(mr, &_scan_cl);
8040 }
8041
8042 SweepClosure::SweepClosure(CMSCollector* collector,
8043 ConcurrentMarkSweepGeneration* g,
8044 CMSBitMap* bitMap, bool should_yield) :
8045 _collector(collector),
8046 _g(g),
8047 _sp(g->cmsSpace()),
8048 _limit(_sp->sweep_limit()),
8049 _freelistLock(_sp->freelistLock()),
8050 _bitMap(bitMap),
8051 _yield(should_yield),
8052 _inFreeRange(false), // No free range at beginning of sweep
8053 _freeRangeInFreeLists(false), // No free range at beginning of sweep
8054 _lastFreeRangeCoalesced(false),
8055 _freeFinger(g->used_region().start())
8056 {
8057 NOT_PRODUCT(
8058 _numObjectsFreed = 0;
8059 _numWordsFreed = 0;
8060 _numObjectsLive = 0;
8061 _numWordsLive = 0;
8062 _numObjectsAlreadyFree = 0;
8063 _numWordsAlreadyFree = 0;
8064 _last_fc = NULL;
8065
8066 _sp->initializeIndexedFreeListArrayReturnedBytes();
8067 _sp->dictionary()->initialize_dict_returned_bytes();
8068 )
8069 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8070 "sweep _limit out of bounds");
8071 if (CMSTraceSweeper) {
8072 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
8073 _limit);
8074 }
8075 }
8076
8077 void SweepClosure::print_on(outputStream* st) const {
8078 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
8079 _sp->bottom(), _sp->end());
8080 tty->print_cr("_limit = " PTR_FORMAT, _limit);
8081 tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
8082 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
8083 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
8084 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
8085 }
8086
8087 #ifndef PRODUCT
8088 // Assertion checking only: no useful work in product mode --
8089 // however, if any of the flags below become product flags,
8090 // you may need to review this code to see if it needs to be
8091 // enabled in product mode.
8092 SweepClosure::~SweepClosure() {
8093 assert_lock_strong(_freelistLock);
8094 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8095 "sweep _limit out of bounds");
8096 if (inFreeRange()) {
8097 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
8098 print();
8099 ShouldNotReachHere();
8100 }
8101 if (Verbose && PrintGC) {
8102 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
8103 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
8104 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
8105 SIZE_FORMAT" bytes "
8106 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
8107 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
8108 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
8109 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
8110 * sizeof(HeapWord);
8111 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
8112
8113 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
8114 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
8115 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
8116 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
8117 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
8118 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
8119 indexListReturnedBytes);
8120 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
8121 dict_returned_bytes);
8122 }
8123 }
8124 if (CMSTraceSweeper) {
8125 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
8126 _limit);
8127 }
8128 }
8129 #endif // PRODUCT
8130
8131 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
8132 bool freeRangeInFreeLists) {
8133 if (CMSTraceSweeper) {
8134 gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
8135 freeFinger, freeRangeInFreeLists);
8136 }
8137 assert(!inFreeRange(), "Trampling existing free range");
8138 set_inFreeRange(true);
8139 set_lastFreeRangeCoalesced(false);
8140
8141 set_freeFinger(freeFinger);
8142 set_freeRangeInFreeLists(freeRangeInFreeLists);
8143 if (CMSTestInFreeList) {
8144 if (freeRangeInFreeLists) {
8145 FreeChunk* fc = (FreeChunk*) freeFinger;
8146 assert(fc->is_free(), "A chunk on the free list should be free.");
8147 assert(fc->size() > 0, "Free range should have a size");
8148 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
8149 }
8150 }
8151 }
8152
8153 // Note that the sweeper runs concurrently with mutators. Thus,
8154 // it is possible for direct allocation in this generation to happen
8155 // in the middle of the sweep. Note that the sweeper also coalesces
8156 // contiguous free blocks. Thus, unless the sweeper and the allocator
8157 // synchronize appropriately freshly allocated blocks may get swept up.
8158 // This is accomplished by the sweeper locking the free lists while
8159 // it is sweeping. Thus blocks that are determined to be free are
8160 // indeed free. There is however one additional complication:
8161 // blocks that have been allocated since the final checkpoint and
8162 // mark, will not have been marked and so would be treated as
8163 // unreachable and swept up. To prevent this, the allocator marks
8164 // the bit map when allocating during the sweep phase. This leads,
8165 // however, to a further complication -- objects may have been allocated
8166 // but not yet initialized -- in the sense that the header isn't yet
8167 // installed. The sweeper can not then determine the size of the block
8168 // in order to skip over it. To deal with this case, we use a technique
8169 // (due to Printezis) to encode such uninitialized block sizes in the
8170 // bit map. Since the bit map uses a bit per every HeapWord, but the
8171 // CMS generation has a minimum object size of 3 HeapWords, it follows
8172 // that "normal marks" won't be adjacent in the bit map (there will
8173 // always be at least two 0 bits between successive 1 bits). We make use
8174 // of these "unused" bits to represent uninitialized blocks -- the bit
8175 // corresponding to the start of the uninitialized object and the next
8176 // bit are both set. Finally, a 1 bit marks the end of the object that
8177 // started with the two consecutive 1 bits to indicate its potentially
8178 // uninitialized state.
8179
8180 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
8181 FreeChunk* fc = (FreeChunk*)addr;
8182 size_t res;
8183
8184 // Check if we are done sweeping. Below we check "addr >= _limit" rather
8185 // than "addr == _limit" because although _limit was a block boundary when
8186 // we started the sweep, it may no longer be one because heap expansion
8187 // may have caused us to coalesce the block ending at the address _limit
8188 // with a newly expanded chunk (this happens when _limit was set to the
8189 // previous _end of the space), so we may have stepped past _limit:
8190 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
8191 if (addr >= _limit) { // we have swept up to or past the limit: finish up
8192 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8193 "sweep _limit out of bounds");
8194 assert(addr < _sp->end(), "addr out of bounds");
8195 // Flush any free range we might be holding as a single
8196 // coalesced chunk to the appropriate free list.
8197 if (inFreeRange()) {
8198 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
8199 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
8200 flush_cur_free_chunk(freeFinger(),
8201 pointer_delta(addr, freeFinger()));
8202 if (CMSTraceSweeper) {
8203 gclog_or_tty->print("Sweep: last chunk: ");
8204 gclog_or_tty->print("put_free_blk " PTR_FORMAT " ("SIZE_FORMAT") "
8205 "[coalesced:%d]\n",
8206 freeFinger(), pointer_delta(addr, freeFinger()),
8207 lastFreeRangeCoalesced() ? 1 : 0);
8208 }
8209 }
8210
8211 // help the iterator loop finish
8212 return pointer_delta(_sp->end(), addr);
8213 }
8214
8215 assert(addr < _limit, "sweep invariant");
8216 // check if we should yield
8217 do_yield_check(addr);
8218 if (fc->is_free()) {
8219 // Chunk that is already free
8220 res = fc->size();
8221 do_already_free_chunk(fc);
8222 debug_only(_sp->verifyFreeLists());
8223 // If we flush the chunk at hand in lookahead_and_flush()
8224 // and it's coalesced with a preceding chunk, then the
8225 // process of "mangling" the payload of the coalesced block
8226 // will cause erasure of the size information from the
8227 // (erstwhile) header of all the coalesced blocks but the
8228 // first, so the first disjunct in the assert will not hold
8229 // in that specific case (in which case the second disjunct
8230 // will hold).
8231 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
8232 "Otherwise the size info doesn't change at this step");
8233 NOT_PRODUCT(
8234 _numObjectsAlreadyFree++;
8235 _numWordsAlreadyFree += res;
8236 )
8237 NOT_PRODUCT(_last_fc = fc;)
8238 } else if (!_bitMap->isMarked(addr)) {
8239 // Chunk is fresh garbage
8240 res = do_garbage_chunk(fc);
8241 debug_only(_sp->verifyFreeLists());
8242 NOT_PRODUCT(
8243 _numObjectsFreed++;
8244 _numWordsFreed += res;
8245 )
8246 } else {
8247 // Chunk that is alive.
8248 res = do_live_chunk(fc);
8249 debug_only(_sp->verifyFreeLists());
8250 NOT_PRODUCT(
8251 _numObjectsLive++;
8252 _numWordsLive += res;
8253 )
8254 }
8255 return res;
8256 }
8257
8258 // For the smart allocation, record following
8259 // split deaths - a free chunk is removed from its free list because
8260 // it is being split into two or more chunks.
8261 // split birth - a free chunk is being added to its free list because
8262 // a larger free chunk has been split and resulted in this free chunk.
8263 // coal death - a free chunk is being removed from its free list because
8264 // it is being coalesced into a large free chunk.
8265 // coal birth - a free chunk is being added to its free list because
8266 // it was created when two or more free chunks where coalesced into
8267 // this free chunk.
8268 //
8269 // These statistics are used to determine the desired number of free
8270 // chunks of a given size. The desired number is chosen to be relative
8271 // to the end of a CMS sweep. The desired number at the end of a sweep
8272 // is the
8273 // count-at-end-of-previous-sweep (an amount that was enough)
8274 // - count-at-beginning-of-current-sweep (the excess)
8275 // + split-births (gains in this size during interval)
8276 // - split-deaths (demands on this size during interval)
8277 // where the interval is from the end of one sweep to the end of the
8278 // next.
8279 //
8280 // When sweeping the sweeper maintains an accumulated chunk which is
8281 // the chunk that is made up of chunks that have been coalesced. That
8282 // will be termed the left-hand chunk. A new chunk of garbage that
8283 // is being considered for coalescing will be referred to as the
8284 // right-hand chunk.
8285 //
8286 // When making a decision on whether to coalesce a right-hand chunk with
8287 // the current left-hand chunk, the current count vs. the desired count
8288 // of the left-hand chunk is considered. Also if the right-hand chunk
8289 // is near the large chunk at the end of the heap (see
8290 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8291 // left-hand chunk is coalesced.
8292 //
8293 // When making a decision about whether to split a chunk, the desired count
8294 // vs. the current count of the candidate to be split is also considered.
8295 // If the candidate is underpopulated (currently fewer chunks than desired)
8296 // a chunk of an overpopulated (currently more chunks than desired) size may
8297 // be chosen. The "hint" associated with a free list, if non-null, points
8298 // to a free list which may be overpopulated.
8299 //
8300
8301 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
8302 const size_t size = fc->size();
8303 // Chunks that cannot be coalesced are not in the
8304 // free lists.
8305 if (CMSTestInFreeList && !fc->cantCoalesce()) {
8306 assert(_sp->verify_chunk_in_free_list(fc),
8307 "free chunk should be in free lists");
8308 }
8309 // a chunk that is already free, should not have been
8310 // marked in the bit map
8311 HeapWord* const addr = (HeapWord*) fc;
8312 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8313 // Verify that the bit map has no bits marked between
8314 // addr and purported end of this block.
8315 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8316
8317 // Some chunks cannot be coalesced under any circumstances.
8318 // See the definition of cantCoalesce().
8319 if (!fc->cantCoalesce()) {
8320 // This chunk can potentially be coalesced.
8321 if (_sp->adaptive_freelists()) {
8322 // All the work is done in
8323 do_post_free_or_garbage_chunk(fc, size);
8324 } else { // Not adaptive free lists
8325 // this is a free chunk that can potentially be coalesced by the sweeper;
8326 if (!inFreeRange()) {
8327 // if the next chunk is a free block that can't be coalesced
8328 // it doesn't make sense to remove this chunk from the free lists
8329 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8330 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
8331 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
8332 nextChunk->is_free() && // ... which is free...
8333 nextChunk->cantCoalesce()) { // ... but can't be coalesced
8334 // nothing to do
8335 } else {
8336 // Potentially the start of a new free range:
8337 // Don't eagerly remove it from the free lists.
8338 // No need to remove it if it will just be put
8339 // back again. (Also from a pragmatic point of view
8340 // if it is a free block in a region that is beyond
8341 // any allocated blocks, an assertion will fail)
8342 // Remember the start of a free run.
8343 initialize_free_range(addr, true);
8344 // end - can coalesce with next chunk
8345 }
8346 } else {
8347 // the midst of a free range, we are coalescing
8348 print_free_block_coalesced(fc);
8349 if (CMSTraceSweeper) {
8350 gclog_or_tty->print(" -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", fc, size);
8351 }
8352 // remove it from the free lists
8353 _sp->removeFreeChunkFromFreeLists(fc);
8354 set_lastFreeRangeCoalesced(true);
8355 // If the chunk is being coalesced and the current free range is
8356 // in the free lists, remove the current free range so that it
8357 // will be returned to the free lists in its entirety - all
8358 // the coalesced pieces included.
8359 if (freeRangeInFreeLists()) {
8360 FreeChunk* ffc = (FreeChunk*) freeFinger();
8361 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8362 "Size of free range is inconsistent with chunk size.");
8363 if (CMSTestInFreeList) {
8364 assert(_sp->verify_chunk_in_free_list(ffc),
8365 "free range is not in free lists");
8366 }
8367 _sp->removeFreeChunkFromFreeLists(ffc);
8368 set_freeRangeInFreeLists(false);
8369 }
8370 }
8371 }
8372 // Note that if the chunk is not coalescable (the else arm
8373 // below), we unconditionally flush, without needing to do
8374 // a "lookahead," as we do below.
8375 if (inFreeRange()) lookahead_and_flush(fc, size);
8376 } else {
8377 // Code path common to both original and adaptive free lists.
8378
8379 // cant coalesce with previous block; this should be treated
8380 // as the end of a free run if any
8381 if (inFreeRange()) {
8382 // we kicked some butt; time to pick up the garbage
8383 assert(freeFinger() < addr, "freeFinger points too high");
8384 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8385 }
8386 // else, nothing to do, just continue
8387 }
8388 }
8389
8390 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
8391 // This is a chunk of garbage. It is not in any free list.
8392 // Add it to a free list or let it possibly be coalesced into
8393 // a larger chunk.
8394 HeapWord* const addr = (HeapWord*) fc;
8395 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8396
8397 if (_sp->adaptive_freelists()) {
8398 // Verify that the bit map has no bits marked between
8399 // addr and purported end of just dead object.
8400 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8401
8402 do_post_free_or_garbage_chunk(fc, size);
8403 } else {
8404 if (!inFreeRange()) {
8405 // start of a new free range
8406 assert(size > 0, "A free range should have a size");
8407 initialize_free_range(addr, false);
8408 } else {
8409 // this will be swept up when we hit the end of the
8410 // free range
8411 if (CMSTraceSweeper) {
8412 gclog_or_tty->print(" -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", fc, size);
8413 }
8414 // If the chunk is being coalesced and the current free range is
8415 // in the free lists, remove the current free range so that it
8416 // will be returned to the free lists in its entirety - all
8417 // the coalesced pieces included.
8418 if (freeRangeInFreeLists()) {
8419 FreeChunk* ffc = (FreeChunk*)freeFinger();
8420 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8421 "Size of free range is inconsistent with chunk size.");
8422 if (CMSTestInFreeList) {
8423 assert(_sp->verify_chunk_in_free_list(ffc),
8424 "free range is not in free lists");
8425 }
8426 _sp->removeFreeChunkFromFreeLists(ffc);
8427 set_freeRangeInFreeLists(false);
8428 }
8429 set_lastFreeRangeCoalesced(true);
8430 }
8431 // this will be swept up when we hit the end of the free range
8432
8433 // Verify that the bit map has no bits marked between
8434 // addr and purported end of just dead object.
8435 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8436 }
8437 assert(_limit >= addr + size,
8438 "A freshly garbage chunk can't possibly straddle over _limit");
8439 if (inFreeRange()) lookahead_and_flush(fc, size);
8440 return size;
8441 }
8442
8443 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
8444 HeapWord* addr = (HeapWord*) fc;
8445 // The sweeper has just found a live object. Return any accumulated
8446 // left hand chunk to the free lists.
8447 if (inFreeRange()) {
8448 assert(freeFinger() < addr, "freeFinger points too high");
8449 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8450 }
8451
8452 // This object is live: we'd normally expect this to be
8453 // an oop, and like to assert the following:
8454 // assert(oop(addr)->is_oop(), "live block should be an oop");
8455 // However, as we commented above, this may be an object whose
8456 // header hasn't yet been initialized.
8457 size_t size;
8458 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8459 if (_bitMap->isMarked(addr + 1)) {
8460 // Determine the size from the bit map, rather than trying to
8461 // compute it from the object header.
8462 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8463 size = pointer_delta(nextOneAddr + 1, addr);
8464 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8465 "alignment problem");
8466
8467 #ifdef ASSERT
8468 if (oop(addr)->klass_or_null() != NULL) {
8469 // Ignore mark word because we are running concurrent with mutators
8470 assert(oop(addr)->is_oop(true), "live block should be an oop");
8471 assert(size ==
8472 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8473 "P-mark and computed size do not agree");
8474 }
8475 #endif
8476
8477 } else {
8478 // This should be an initialized object that's alive.
8479 assert(oop(addr)->klass_or_null() != NULL,
8480 "Should be an initialized object");
8481 // Ignore mark word because we are running concurrent with mutators
8482 assert(oop(addr)->is_oop(true), "live block should be an oop");
8483 // Verify that the bit map has no bits marked between
8484 // addr and purported end of this block.
8485 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8486 assert(size >= 3, "Necessary for Printezis marks to work");
8487 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8488 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8489 }
8490 return size;
8491 }
8492
8493 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
8494 size_t chunkSize) {
8495 // do_post_free_or_garbage_chunk() should only be called in the case
8496 // of the adaptive free list allocator.
8497 const bool fcInFreeLists = fc->is_free();
8498 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8499 assert((HeapWord*)fc <= _limit, "sweep invariant");
8500 if (CMSTestInFreeList && fcInFreeLists) {
8501 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
8502 }
8503
8504 if (CMSTraceSweeper) {
8505 gclog_or_tty->print_cr(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", fc, chunkSize);
8506 }
8507
8508 HeapWord* const fc_addr = (HeapWord*) fc;
8509
8510 bool coalesce;
8511 const size_t left = pointer_delta(fc_addr, freeFinger());
8512 const size_t right = chunkSize;
8513 switch (FLSCoalescePolicy) {
8514 // numeric value forms a coalition aggressiveness metric
8515 case 0: { // never coalesce
8516 coalesce = false;
8517 break;
8518 }
8519 case 1: { // coalesce if left & right chunks on overpopulated lists
8520 coalesce = _sp->coalOverPopulated(left) &&
8521 _sp->coalOverPopulated(right);
8522 break;
8523 }
8524 case 2: { // coalesce if left chunk on overpopulated list (default)
8525 coalesce = _sp->coalOverPopulated(left);
8526 break;
8527 }
8528 case 3: { // coalesce if left OR right chunk on overpopulated list
8529 coalesce = _sp->coalOverPopulated(left) ||
8530 _sp->coalOverPopulated(right);
8531 break;
8532 }
8533 case 4: { // always coalesce
8534 coalesce = true;
8535 break;
8536 }
8537 default:
8538 ShouldNotReachHere();
8539 }
8540
8541 // Should the current free range be coalesced?
8542 // If the chunk is in a free range and either we decided to coalesce above
8543 // or the chunk is near the large block at the end of the heap
8544 // (isNearLargestChunk() returns true), then coalesce this chunk.
8545 const bool doCoalesce = inFreeRange()
8546 && (coalesce || _g->isNearLargestChunk(fc_addr));
8547 if (doCoalesce) {
8548 // Coalesce the current free range on the left with the new
8549 // chunk on the right. If either is on a free list,
8550 // it must be removed from the list and stashed in the closure.
8551 if (freeRangeInFreeLists()) {
8552 FreeChunk* const ffc = (FreeChunk*)freeFinger();
8553 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
8554 "Size of free range is inconsistent with chunk size.");
8555 if (CMSTestInFreeList) {
8556 assert(_sp->verify_chunk_in_free_list(ffc),
8557 "Chunk is not in free lists");
8558 }
8559 _sp->coalDeath(ffc->size());
8560 _sp->removeFreeChunkFromFreeLists(ffc);
8561 set_freeRangeInFreeLists(false);
8562 }
8563 if (fcInFreeLists) {
8564 _sp->coalDeath(chunkSize);
8565 assert(fc->size() == chunkSize,
8566 "The chunk has the wrong size or is not in the free lists");
8567 _sp->removeFreeChunkFromFreeLists(fc);
8568 }
8569 set_lastFreeRangeCoalesced(true);
8570 print_free_block_coalesced(fc);
8571 } else { // not in a free range and/or should not coalesce
8572 // Return the current free range and start a new one.
8573 if (inFreeRange()) {
8574 // In a free range but cannot coalesce with the right hand chunk.
8575 // Put the current free range into the free lists.
8576 flush_cur_free_chunk(freeFinger(),
8577 pointer_delta(fc_addr, freeFinger()));
8578 }
8579 // Set up for new free range. Pass along whether the right hand
8580 // chunk is in the free lists.
8581 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8582 }
8583 }
8584
8585 // Lookahead flush:
8586 // If we are tracking a free range, and this is the last chunk that
8587 // we'll look at because its end crosses past _limit, we'll preemptively
8588 // flush it along with any free range we may be holding on to. Note that
8589 // this can be the case only for an already free or freshly garbage
8590 // chunk. If this block is an object, it can never straddle
8591 // over _limit. The "straddling" occurs when _limit is set at
8592 // the previous end of the space when this cycle started, and
8593 // a subsequent heap expansion caused the previously co-terminal
8594 // free block to be coalesced with the newly expanded portion,
8595 // thus rendering _limit a non-block-boundary making it dangerous
8596 // for the sweeper to step over and examine.
8597 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
8598 assert(inFreeRange(), "Should only be called if currently in a free range.");
8599 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
8600 assert(_sp->used_region().contains(eob - 1),
8601 err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
8602 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
8603 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
8604 eob, eob-1, _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
8605 if (eob >= _limit) {
8606 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
8607 if (CMSTraceSweeper) {
8608 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
8609 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
8610 "[" PTR_FORMAT "," PTR_FORMAT ")",
8611 _limit, fc, eob, _sp->bottom(), _sp->end());
8612 }
8613 // Return the storage we are tracking back into the free lists.
8614 if (CMSTraceSweeper) {
8615 gclog_or_tty->print_cr("Flushing ... ");
8616 }
8617 assert(freeFinger() < eob, "Error");
8618 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8619 }
8620 }
8621
8622 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8623 assert(inFreeRange(), "Should only be called if currently in a free range.");
8624 assert(size > 0,
8625 "A zero sized chunk cannot be added to the free lists.");
8626 if (!freeRangeInFreeLists()) {
8627 if (CMSTestInFreeList) {
8628 FreeChunk* fc = (FreeChunk*) chunk;
8629 fc->set_size(size);
8630 assert(!_sp->verify_chunk_in_free_list(fc),
8631 "chunk should not be in free lists yet");
8632 }
8633 if (CMSTraceSweeper) {
8634 gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
8635 chunk, size);
8636 }
8637 // A new free range is going to be starting. The current
8638 // free range has not been added to the free lists yet or
8639 // was removed so add it back.
8640 // If the current free range was coalesced, then the death
8641 // of the free range was recorded. Record a birth now.
8642 if (lastFreeRangeCoalesced()) {
8643 _sp->coalBirth(size);
8644 }
8645 _sp->addChunkAndRepairOffsetTable(chunk, size,
8646 lastFreeRangeCoalesced());
8647 } else if (CMSTraceSweeper) {
8648 gclog_or_tty->print_cr("Already in free list: nothing to flush");
8649 }
8650 set_inFreeRange(false);
8651 set_freeRangeInFreeLists(false);
8652 }
8653
8654 // We take a break if we've been at this for a while,
8655 // so as to avoid monopolizing the locks involved.
8656 void SweepClosure::do_yield_work(HeapWord* addr) {
8657 // Return current free chunk being used for coalescing (if any)
8658 // to the appropriate freelist. After yielding, the next
8659 // free block encountered will start a coalescing range of
8660 // free blocks. If the next free block is adjacent to the
8661 // chunk just flushed, they will need to wait for the next
8662 // sweep to be coalesced.
8663 if (inFreeRange()) {
8664 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8665 }
8666
8667 // First give up the locks, then yield, then re-lock.
8668 // We should probably use a constructor/destructor idiom to
8669 // do this unlock/lock or modify the MutexUnlocker class to
8670 // serve our purpose. XXX
8671 assert_lock_strong(_bitMap->lock());
8672 assert_lock_strong(_freelistLock);
8673 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8674 "CMS thread should hold CMS token");
8675 _bitMap->lock()->unlock();
8676 _freelistLock->unlock();
8677 ConcurrentMarkSweepThread::desynchronize(true);
8678 ConcurrentMarkSweepThread::acknowledge_yield_request();
8679 _collector->stopTimer();
8680 if (PrintCMSStatistics != 0) {
8681 _collector->incrementYields();
8682 }
8683 _collector->icms_wait();
8684
8685 // See the comment in coordinator_yield()
8686 for (unsigned i = 0; i < CMSYieldSleepCount &&
8687 ConcurrentMarkSweepThread::should_yield() &&
8688 !CMSCollector::foregroundGCIsActive(); ++i) {
8689 os::sleep(Thread::current(), 1, false);
8690 ConcurrentMarkSweepThread::acknowledge_yield_request();
8691 }
8692
8693 ConcurrentMarkSweepThread::synchronize(true);
8694 _freelistLock->lock();
8695 _bitMap->lock()->lock_without_safepoint_check();
8696 _collector->startTimer();
8697 }
8698
8699 #ifndef PRODUCT
8700 // This is actually very useful in a product build if it can
8701 // be called from the debugger. Compile it into the product
8702 // as needed.
8703 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8704 return debug_cms_space->verify_chunk_in_free_list(fc);
8705 }
8706 #endif
8707
8708 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8709 if (CMSTraceSweeper) {
8710 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8711 fc, fc->size());
8712 }
8713 }
8714
8715 // CMSIsAliveClosure
8716 bool CMSIsAliveClosure::do_object_b(oop obj) {
8717 HeapWord* addr = (HeapWord*)obj;
8718 return addr != NULL &&
8719 (!_span.contains(addr) || _bit_map->isMarked(addr));
8720 }
8721
8722
8723 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8724 MemRegion span,
8725 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8726 bool cpc):
8727 _collector(collector),
8728 _span(span),
8729 _bit_map(bit_map),
8730 _mark_stack(mark_stack),
8731 _concurrent_precleaning(cpc) {
8732 assert(!_span.is_empty(), "Empty span could spell trouble");
8733 }
8734
8735
8736 // CMSKeepAliveClosure: the serial version
8737 void CMSKeepAliveClosure::do_oop(oop obj) {
8738 HeapWord* addr = (HeapWord*)obj;
8739 if (_span.contains(addr) &&
8740 !_bit_map->isMarked(addr)) {
8741 _bit_map->mark(addr);
8742 bool simulate_overflow = false;
8743 NOT_PRODUCT(
8744 if (CMSMarkStackOverflowALot &&
8745 _collector->simulate_overflow()) {
8746 // simulate a stack overflow
8747 simulate_overflow = true;
8748 }
8749 )
8750 if (simulate_overflow || !_mark_stack->push(obj)) {
8751 if (_concurrent_precleaning) {
8752 // We dirty the overflown object and let the remark
8753 // phase deal with it.
8754 assert(_collector->overflow_list_is_empty(), "Error");
8755 // In the case of object arrays, we need to dirty all of
8756 // the cards that the object spans. No locking or atomics
8757 // are needed since no one else can be mutating the mod union
8758 // table.
8759 if (obj->is_objArray()) {
8760 size_t sz = obj->size();
8761 HeapWord* end_card_addr =
8762 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8763 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8764 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8765 _collector->_modUnionTable.mark_range(redirty_range);
8766 } else {
8767 _collector->_modUnionTable.mark(addr);
8768 }
8769 _collector->_ser_kac_preclean_ovflw++;
8770 } else {
8771 _collector->push_on_overflow_list(obj);
8772 _collector->_ser_kac_ovflw++;
8773 }
8774 }
8775 }
8776 }
8777
8778 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8779 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8780
8781 // CMSParKeepAliveClosure: a parallel version of the above.
8782 // The work queues are private to each closure (thread),
8783 // but (may be) available for stealing by other threads.
8784 void CMSParKeepAliveClosure::do_oop(oop obj) {
8785 HeapWord* addr = (HeapWord*)obj;
8786 if (_span.contains(addr) &&
8787 !_bit_map->isMarked(addr)) {
8788 // In general, during recursive tracing, several threads
8789 // may be concurrently getting here; the first one to
8790 // "tag" it, claims it.
8791 if (_bit_map->par_mark(addr)) {
8792 bool res = _work_queue->push(obj);
8793 assert(res, "Low water mark should be much less than capacity");
8794 // Do a recursive trim in the hope that this will keep
8795 // stack usage lower, but leave some oops for potential stealers
8796 trim_queue(_low_water_mark);
8797 } // Else, another thread got there first
8798 }
8799 }
8800
8801 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8802 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8803
8804 void CMSParKeepAliveClosure::trim_queue(uint max) {
8805 while (_work_queue->size() > max) {
8806 oop new_oop;
8807 if (_work_queue->pop_local(new_oop)) {
8808 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8809 assert(_bit_map->isMarked((HeapWord*)new_oop),
8810 "no white objects on this stack!");
8811 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8812 // iterate over the oops in this oop, marking and pushing
8813 // the ones in CMS heap (i.e. in _span).
8814 new_oop->oop_iterate(&_mark_and_push);
8815 }
8816 }
8817 }
8818
8819 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8820 CMSCollector* collector,
8821 MemRegion span, CMSBitMap* bit_map,
8822 OopTaskQueue* work_queue):
8823 _collector(collector),
8824 _span(span),
8825 _bit_map(bit_map),
8826 _work_queue(work_queue) { }
8827
8828 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8829 HeapWord* addr = (HeapWord*)obj;
8830 if (_span.contains(addr) &&
8831 !_bit_map->isMarked(addr)) {
8832 if (_bit_map->par_mark(addr)) {
8833 bool simulate_overflow = false;
8834 NOT_PRODUCT(
8835 if (CMSMarkStackOverflowALot &&
8836 _collector->par_simulate_overflow()) {
8837 // simulate a stack overflow
8838 simulate_overflow = true;
8839 }
8840 )
8841 if (simulate_overflow || !_work_queue->push(obj)) {
8842 _collector->par_push_on_overflow_list(obj);
8843 _collector->_par_kac_ovflw++;
8844 }
8845 } // Else another thread got there already
8846 }
8847 }
8848
8849 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8850 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8851
8852 //////////////////////////////////////////////////////////////////
8853 // CMSExpansionCause /////////////////////////////
8854 //////////////////////////////////////////////////////////////////
8855 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8856 switch (cause) {
8857 case _no_expansion:
8858 return "No expansion";
8859 case _satisfy_free_ratio:
8860 return "Free ratio";
8861 case _satisfy_promotion:
8862 return "Satisfy promotion";
8863 case _satisfy_allocation:
8864 return "allocation";
8865 case _allocate_par_lab:
8866 return "Par LAB";
8867 case _allocate_par_spooling_space:
8868 return "Par Spooling Space";
8869 case _adaptive_size_policy:
8870 return "Ergonomics";
8871 default:
8872 return "unknown";
8873 }
8874 }
8875
8876 void CMSDrainMarkingStackClosure::do_void() {
8877 // the max number to take from overflow list at a time
8878 const size_t num = _mark_stack->capacity()/4;
8879 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8880 "Overflow list should be NULL during concurrent phases");
8881 while (!_mark_stack->isEmpty() ||
8882 // if stack is empty, check the overflow list
8883 _collector->take_from_overflow_list(num, _mark_stack)) {
8884 oop obj = _mark_stack->pop();
8885 HeapWord* addr = (HeapWord*)obj;
8886 assert(_span.contains(addr), "Should be within span");
8887 assert(_bit_map->isMarked(addr), "Should be marked");
8888 assert(obj->is_oop(), "Should be an oop");
8889 obj->oop_iterate(_keep_alive);
8890 }
8891 }
8892
8893 void CMSParDrainMarkingStackClosure::do_void() {
8894 // drain queue
8895 trim_queue(0);
8896 }
8897
8898 // Trim our work_queue so its length is below max at return
8899 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8900 while (_work_queue->size() > max) {
8901 oop new_oop;
8902 if (_work_queue->pop_local(new_oop)) {
8903 assert(new_oop->is_oop(), "Expected an oop");
8904 assert(_bit_map->isMarked((HeapWord*)new_oop),
8905 "no white objects on this stack!");
8906 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8907 // iterate over the oops in this oop, marking and pushing
8908 // the ones in CMS heap (i.e. in _span).
8909 new_oop->oop_iterate(&_mark_and_push);
8910 }
8911 }
8912 }
8913
8914 ////////////////////////////////////////////////////////////////////
8915 // Support for Marking Stack Overflow list handling and related code
8916 ////////////////////////////////////////////////////////////////////
8917 // Much of the following code is similar in shape and spirit to the
8918 // code used in ParNewGC. We should try and share that code
8919 // as much as possible in the future.
8920
8921 #ifndef PRODUCT
8922 // Debugging support for CMSStackOverflowALot
8923
8924 // It's OK to call this multi-threaded; the worst thing
8925 // that can happen is that we'll get a bunch of closely
8926 // spaced simulated overflows, but that's OK, in fact
8927 // probably good as it would exercise the overflow code
8928 // under contention.
8929 bool CMSCollector::simulate_overflow() {
8930 if (_overflow_counter-- <= 0) { // just being defensive
8931 _overflow_counter = CMSMarkStackOverflowInterval;
8932 return true;
8933 } else {
8934 return false;
8935 }
8936 }
8937
8938 bool CMSCollector::par_simulate_overflow() {
8939 return simulate_overflow();
8940 }
8941 #endif
8942
8943 // Single-threaded
8944 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8945 assert(stack->isEmpty(), "Expected precondition");
8946 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8947 size_t i = num;
8948 oop cur = _overflow_list;
8949 const markOop proto = markOopDesc::prototype();
8950 NOT_PRODUCT(ssize_t n = 0;)
8951 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8952 next = oop(cur->mark());
8953 cur->set_mark(proto); // until proven otherwise
8954 assert(cur->is_oop(), "Should be an oop");
8955 bool res = stack->push(cur);
8956 assert(res, "Bit off more than can chew?");
8957 NOT_PRODUCT(n++;)
8958 }
8959 _overflow_list = cur;
8960 #ifndef PRODUCT
8961 assert(_num_par_pushes >= n, "Too many pops?");
8962 _num_par_pushes -=n;
8963 #endif
8964 return !stack->isEmpty();
8965 }
8966
8967 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
8968 // (MT-safe) Get a prefix of at most "num" from the list.
8969 // The overflow list is chained through the mark word of
8970 // each object in the list. We fetch the entire list,
8971 // break off a prefix of the right size and return the
8972 // remainder. If other threads try to take objects from
8973 // the overflow list at that time, they will wait for
8974 // some time to see if data becomes available. If (and
8975 // only if) another thread places one or more object(s)
8976 // on the global list before we have returned the suffix
8977 // to the global list, we will walk down our local list
8978 // to find its end and append the global list to
8979 // our suffix before returning it. This suffix walk can
8980 // prove to be expensive (quadratic in the amount of traffic)
8981 // when there are many objects in the overflow list and
8982 // there is much producer-consumer contention on the list.
8983 // *NOTE*: The overflow list manipulation code here and
8984 // in ParNewGeneration:: are very similar in shape,
8985 // except that in the ParNew case we use the old (from/eden)
8986 // copy of the object to thread the list via its klass word.
8987 // Because of the common code, if you make any changes in
8988 // the code below, please check the ParNew version to see if
8989 // similar changes might be needed.
8990 // CR 6797058 has been filed to consolidate the common code.
8991 bool CMSCollector::par_take_from_overflow_list(size_t num,
8992 OopTaskQueue* work_q,
8993 int no_of_gc_threads) {
8994 assert(work_q->size() == 0, "First empty local work queue");
8995 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8996 if (_overflow_list == NULL) {
8997 return false;
8998 }
8999 // Grab the entire list; we'll put back a suffix
9000 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
9001 Thread* tid = Thread::current();
9002 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
9003 // set to ParallelGCThreads.
9004 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
9005 size_t sleep_time_millis = MAX2((size_t)1, num/100);
9006 // If the list is busy, we spin for a short while,
9007 // sleeping between attempts to get the list.
9008 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
9009 os::sleep(tid, sleep_time_millis, false);
9010 if (_overflow_list == NULL) {
9011 // Nothing left to take
9012 return false;
9013 } else if (_overflow_list != BUSY) {
9014 // Try and grab the prefix
9015 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
9016 }
9017 }
9018 // If the list was found to be empty, or we spun long
9019 // enough, we give up and return empty-handed. If we leave
9020 // the list in the BUSY state below, it must be the case that
9021 // some other thread holds the overflow list and will set it
9022 // to a non-BUSY state in the future.
9023 if (prefix == NULL || prefix == BUSY) {
9024 // Nothing to take or waited long enough
9025 if (prefix == NULL) {
9026 // Write back the NULL in case we overwrote it with BUSY above
9027 // and it is still the same value.
9028 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
9029 }
9030 return false;
9031 }
9032 assert(prefix != NULL && prefix != BUSY, "Error");
9033 size_t i = num;
9034 oop cur = prefix;
9035 // Walk down the first "num" objects, unless we reach the end.
9036 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
9037 if (cur->mark() == NULL) {
9038 // We have "num" or fewer elements in the list, so there
9039 // is nothing to return to the global list.
9040 // Write back the NULL in lieu of the BUSY we wrote
9041 // above, if it is still the same value.
9042 if (_overflow_list == BUSY) {
9043 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
9044 }
9045 } else {
9046 // Chop off the suffix and return it to the global list.
9047 assert(cur->mark() != BUSY, "Error");
9048 oop suffix_head = cur->mark(); // suffix will be put back on global list
9049 cur->set_mark(NULL); // break off suffix
9050 // It's possible that the list is still in the empty(busy) state
9051 // we left it in a short while ago; in that case we may be
9052 // able to place back the suffix without incurring the cost
9053 // of a walk down the list.
9054 oop observed_overflow_list = _overflow_list;
9055 oop cur_overflow_list = observed_overflow_list;
9056 bool attached = false;
9057 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
9058 observed_overflow_list =
9059 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9060 if (cur_overflow_list == observed_overflow_list) {
9061 attached = true;
9062 break;
9063 } else cur_overflow_list = observed_overflow_list;
9064 }
9065 if (!attached) {
9066 // Too bad, someone else sneaked in (at least) an element; we'll need
9067 // to do a splice. Find tail of suffix so we can prepend suffix to global
9068 // list.
9069 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
9070 oop suffix_tail = cur;
9071 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
9072 "Tautology");
9073 observed_overflow_list = _overflow_list;
9074 do {
9075 cur_overflow_list = observed_overflow_list;
9076 if (cur_overflow_list != BUSY) {
9077 // Do the splice ...
9078 suffix_tail->set_mark(markOop(cur_overflow_list));
9079 } else { // cur_overflow_list == BUSY
9080 suffix_tail->set_mark(NULL);
9081 }
9082 // ... and try to place spliced list back on overflow_list ...
9083 observed_overflow_list =
9084 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9085 } while (cur_overflow_list != observed_overflow_list);
9086 // ... until we have succeeded in doing so.
9087 }
9088 }
9089
9090 // Push the prefix elements on work_q
9091 assert(prefix != NULL, "control point invariant");
9092 const markOop proto = markOopDesc::prototype();
9093 oop next;
9094 NOT_PRODUCT(ssize_t n = 0;)
9095 for (cur = prefix; cur != NULL; cur = next) {
9096 next = oop(cur->mark());
9097 cur->set_mark(proto); // until proven otherwise
9098 assert(cur->is_oop(), "Should be an oop");
9099 bool res = work_q->push(cur);
9100 assert(res, "Bit off more than we can chew?");
9101 NOT_PRODUCT(n++;)
9102 }
9103 #ifndef PRODUCT
9104 assert(_num_par_pushes >= n, "Too many pops?");
9105 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
9106 #endif
9107 return true;
9108 }
9109
9110 // Single-threaded
9111 void CMSCollector::push_on_overflow_list(oop p) {
9112 NOT_PRODUCT(_num_par_pushes++;)
9113 assert(p->is_oop(), "Not an oop");
9114 preserve_mark_if_necessary(p);
9115 p->set_mark((markOop)_overflow_list);
9116 _overflow_list = p;
9117 }
9118
9119 // Multi-threaded; use CAS to prepend to overflow list
9120 void CMSCollector::par_push_on_overflow_list(oop p) {
9121 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
9122 assert(p->is_oop(), "Not an oop");
9123 par_preserve_mark_if_necessary(p);
9124 oop observed_overflow_list = _overflow_list;
9125 oop cur_overflow_list;
9126 do {
9127 cur_overflow_list = observed_overflow_list;
9128 if (cur_overflow_list != BUSY) {
9129 p->set_mark(markOop(cur_overflow_list));
9130 } else {
9131 p->set_mark(NULL);
9132 }
9133 observed_overflow_list =
9134 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
9135 } while (cur_overflow_list != observed_overflow_list);
9136 }
9137 #undef BUSY
9138
9139 // Single threaded
9140 // General Note on GrowableArray: pushes may silently fail
9141 // because we are (temporarily) out of C-heap for expanding
9142 // the stack. The problem is quite ubiquitous and affects
9143 // a lot of code in the JVM. The prudent thing for GrowableArray
9144 // to do (for now) is to exit with an error. However, that may
9145 // be too draconian in some cases because the caller may be
9146 // able to recover without much harm. For such cases, we
9147 // should probably introduce a "soft_push" method which returns
9148 // an indication of success or failure with the assumption that
9149 // the caller may be able to recover from a failure; code in
9150 // the VM can then be changed, incrementally, to deal with such
9151 // failures where possible, thus, incrementally hardening the VM
9152 // in such low resource situations.
9153 void CMSCollector::preserve_mark_work(oop p, markOop m) {
9154 _preserved_oop_stack.push(p);
9155 _preserved_mark_stack.push(m);
9156 assert(m == p->mark(), "Mark word changed");
9157 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9158 "bijection");
9159 }
9160
9161 // Single threaded
9162 void CMSCollector::preserve_mark_if_necessary(oop p) {
9163 markOop m = p->mark();
9164 if (m->must_be_preserved(p)) {
9165 preserve_mark_work(p, m);
9166 }
9167 }
9168
9169 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
9170 markOop m = p->mark();
9171 if (m->must_be_preserved(p)) {
9172 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
9173 // Even though we read the mark word without holding
9174 // the lock, we are assured that it will not change
9175 // because we "own" this oop, so no other thread can
9176 // be trying to push it on the overflow list; see
9177 // the assertion in preserve_mark_work() that checks
9178 // that m == p->mark().
9179 preserve_mark_work(p, m);
9180 }
9181 }
9182
9183 // We should be able to do this multi-threaded,
9184 // a chunk of stack being a task (this is
9185 // correct because each oop only ever appears
9186 // once in the overflow list. However, it's
9187 // not very easy to completely overlap this with
9188 // other operations, so will generally not be done
9189 // until all work's been completed. Because we
9190 // expect the preserved oop stack (set) to be small,
9191 // it's probably fine to do this single-threaded.
9192 // We can explore cleverer concurrent/overlapped/parallel
9193 // processing of preserved marks if we feel the
9194 // need for this in the future. Stack overflow should
9195 // be so rare in practice and, when it happens, its
9196 // effect on performance so great that this will
9197 // likely just be in the noise anyway.
9198 void CMSCollector::restore_preserved_marks_if_any() {
9199 assert(SafepointSynchronize::is_at_safepoint(),
9200 "world should be stopped");
9201 assert(Thread::current()->is_ConcurrentGC_thread() ||
9202 Thread::current()->is_VM_thread(),
9203 "should be single-threaded");
9204 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9205 "bijection");
9206
9207 while (!_preserved_oop_stack.is_empty()) {
9208 oop p = _preserved_oop_stack.pop();
9209 assert(p->is_oop(), "Should be an oop");
9210 assert(_span.contains(p), "oop should be in _span");
9211 assert(p->mark() == markOopDesc::prototype(),
9212 "Set when taken from overflow list");
9213 markOop m = _preserved_mark_stack.pop();
9214 p->set_mark(m);
9215 }
9216 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
9217 "stacks were cleared above");
9218 }
9219
9220 #ifndef PRODUCT
9221 bool CMSCollector::no_preserved_marks() const {
9222 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
9223 }
9224 #endif
9225
9226 // Transfer some number of overflown objects to usual marking
9227 // stack. Return true if some objects were transferred.
9228 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9229 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9230 (size_t)ParGCDesiredObjsFromOverflowList);
9231
9232 bool res = _collector->take_from_overflow_list(num, _mark_stack);
9233 assert(_collector->overflow_list_is_empty() || res,
9234 "If list is not empty, we should have taken something");
9235 assert(!res || !_mark_stack->isEmpty(),
9236 "If we took something, it should now be on our stack");
9237 return res;
9238 }
9239
9240 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9241 size_t res = _sp->block_size_no_stall(addr, _collector);
9242 if (_sp->block_is_obj(addr)) {
9243 if (_live_bit_map->isMarked(addr)) {
9244 // It can't have been dead in a previous cycle
9245 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9246 } else {
9247 _dead_bit_map->mark(addr); // mark the dead object
9248 }
9249 }
9250 // Could be 0, if the block size could not be computed without stalling.
9251 return res;
9252 }
9253
9254 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
9255
9256 switch (phase) {
9257 case CMSCollector::InitialMarking:
9258 initialize(true /* fullGC */ ,
9259 cause /* cause of the GC */,
9260 true /* recordGCBeginTime */,
9261 true /* recordPreGCUsage */,
9262 false /* recordPeakUsage */,
9263 false /* recordPostGCusage */,
9264 true /* recordAccumulatedGCTime */,
9265 false /* recordGCEndTime */,
9266 false /* countCollection */ );
9267 break;
9268
9269 case CMSCollector::FinalMarking:
9270 initialize(true /* fullGC */ ,
9271 cause /* cause of the GC */,
9272 false /* recordGCBeginTime */,
9273 false /* recordPreGCUsage */,
9274 false /* recordPeakUsage */,
9275 false /* recordPostGCusage */,
9276 true /* recordAccumulatedGCTime */,
9277 false /* recordGCEndTime */,
9278 false /* countCollection */ );
9279 break;
9280
9281 case CMSCollector::Sweeping:
9282 initialize(true /* fullGC */ ,
9283 cause /* cause of the GC */,
9284 false /* recordGCBeginTime */,
9285 false /* recordPreGCUsage */,
9286 true /* recordPeakUsage */,
9287 true /* recordPostGCusage */,
9288 false /* recordAccumulatedGCTime */,
9289 true /* recordGCEndTime */,
9290 true /* countCollection */ );
9291 break;
9292
9293 default:
9294 ShouldNotReachHere();
9295 }
9296 }