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
332 // Generation Counters - generation 1, 1 subspace
333 _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
334
335 _space_counters = new GSpaceCounters(gen_name, 0,
336 _virtual_space.reserved_size(),
337 this, _gen_counters);
338 }
339
340 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
341 _cms_gen(cms_gen)
342 {
343 assert(alpha <= 100, "bad value");
344 _saved_alpha = alpha;
345
346 // Initialize the alphas to the bootstrap value of 100.
347 _gc0_alpha = _cms_alpha = 100;
348
349 _cms_begin_time.update();
350 _cms_end_time.update();
351
352 _gc0_duration = 0.0;
353 _gc0_period = 0.0;
354 _gc0_promoted = 0;
355
356 _cms_duration = 0.0;
357 _cms_period = 0.0;
358 _cms_allocated = 0;
359
360 _cms_used_at_gc0_begin = 0;
361 _cms_used_at_gc0_end = 0;
362 _allow_duty_cycle_reduction = false;
363 _valid_bits = 0;
364 _icms_duty_cycle = CMSIncrementalDutyCycle;
365 }
366
367 double CMSStats::cms_free_adjustment_factor(size_t free) const {
368 // TBD: CR 6909490
369 return 1.0;
370 }
371
372 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
373 }
374
375 // If promotion failure handling is on use
376 // the padded average size of the promotion for each
377 // young generation collection.
378 double CMSStats::time_until_cms_gen_full() const {
379 size_t cms_free = _cms_gen->cmsSpace()->free();
380 GenCollectedHeap* gch = GenCollectedHeap::heap();
381 size_t expected_promotion = MIN2(gch->get_gen(0)->capacity(),
382 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
383 if (cms_free > expected_promotion) {
384 // Start a cms collection if there isn't enough space to promote
385 // for the next minor collection. Use the padded average as
386 // a safety factor.
387 cms_free -= expected_promotion;
388
389 // Adjust by the safety factor.
390 double cms_free_dbl = (double)cms_free;
391 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
392 // Apply a further correction factor which tries to adjust
393 // for recent occurance of concurrent mode failures.
394 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
395 cms_free_dbl = cms_free_dbl * cms_adjustment;
396
397 if (PrintGCDetails && Verbose) {
398 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
399 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
400 cms_free, expected_promotion);
401 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
402 cms_free_dbl, cms_consumption_rate() + 1.0);
403 }
404 // Add 1 in case the consumption rate goes to zero.
405 return cms_free_dbl / (cms_consumption_rate() + 1.0);
406 }
407 return 0.0;
408 }
409
410 // Compare the duration of the cms collection to the
411 // time remaining before the cms generation is empty.
412 // Note that the time from the start of the cms collection
413 // to the start of the cms sweep (less than the total
414 // duration of the cms collection) can be used. This
415 // has been tried and some applications experienced
416 // promotion failures early in execution. This was
417 // possibly because the averages were not accurate
418 // enough at the beginning.
419 double CMSStats::time_until_cms_start() const {
420 // We add "gc0_period" to the "work" calculation
421 // below because this query is done (mostly) at the
422 // end of a scavenge, so we need to conservatively
423 // account for that much possible delay
424 // in the query so as to avoid concurrent mode failures
425 // due to starting the collection just a wee bit too
426 // late.
427 double work = cms_duration() + gc0_period();
428 double deadline = time_until_cms_gen_full();
429 // If a concurrent mode failure occurred recently, we want to be
430 // more conservative and halve our expected time_until_cms_gen_full()
431 if (work > deadline) {
432 if (Verbose && PrintGCDetails) {
433 gclog_or_tty->print(
434 " CMSCollector: collect because of anticipated promotion "
435 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
436 gc0_period(), time_until_cms_gen_full());
437 }
438 return 0.0;
439 }
440 return work - deadline;
441 }
442
443 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
444 // amount of change to prevent wild oscillation.
445 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
446 unsigned int new_duty_cycle) {
447 assert(old_duty_cycle <= 100, "bad input value");
448 assert(new_duty_cycle <= 100, "bad input value");
449
450 // Note: use subtraction with caution since it may underflow (values are
451 // unsigned). Addition is safe since we're in the range 0-100.
452 unsigned int damped_duty_cycle = new_duty_cycle;
453 if (new_duty_cycle < old_duty_cycle) {
454 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
455 if (new_duty_cycle + largest_delta < old_duty_cycle) {
456 damped_duty_cycle = old_duty_cycle - largest_delta;
457 }
458 } else if (new_duty_cycle > old_duty_cycle) {
459 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
460 if (new_duty_cycle > old_duty_cycle + largest_delta) {
461 damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
462 }
463 }
464 assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
465
466 if (CMSTraceIncrementalPacing) {
467 gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
468 old_duty_cycle, new_duty_cycle, damped_duty_cycle);
469 }
470 return damped_duty_cycle;
471 }
472
473 unsigned int CMSStats::icms_update_duty_cycle_impl() {
474 assert(CMSIncrementalPacing && valid(),
475 "should be handled in icms_update_duty_cycle()");
476
477 double cms_time_so_far = cms_timer().seconds();
478 double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
479 double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
480
481 // Avoid division by 0.
482 double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
483 double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
484
485 unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
486 if (new_duty_cycle > _icms_duty_cycle) {
487 // Avoid very small duty cycles (1 or 2); 0 is allowed.
488 if (new_duty_cycle > 2) {
489 _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
490 new_duty_cycle);
491 }
492 } else if (_allow_duty_cycle_reduction) {
493 // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
494 new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
495 // Respect the minimum duty cycle.
496 unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
497 _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
498 }
499
500 if (PrintGCDetails || CMSTraceIncrementalPacing) {
501 gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
502 }
503
504 _allow_duty_cycle_reduction = false;
505 return _icms_duty_cycle;
506 }
507
508 #ifndef PRODUCT
509 void CMSStats::print_on(outputStream *st) const {
510 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
511 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
512 gc0_duration(), gc0_period(), gc0_promoted());
513 st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
514 cms_duration(), cms_duration_per_mb(),
515 cms_period(), cms_allocated());
516 st->print(",cms_since_beg=%g,cms_since_end=%g",
517 cms_time_since_begin(), cms_time_since_end());
518 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
519 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
520 if (CMSIncrementalMode) {
521 st->print(",dc=%d", icms_duty_cycle());
522 }
523
524 if (valid()) {
525 st->print(",promo_rate=%g,cms_alloc_rate=%g",
526 promotion_rate(), cms_allocation_rate());
527 st->print(",cms_consumption_rate=%g,time_until_full=%g",
528 cms_consumption_rate(), time_until_cms_gen_full());
529 }
530 st->print(" ");
531 }
532 #endif // #ifndef PRODUCT
533
534 CMSCollector::CollectorState CMSCollector::_collectorState =
535 CMSCollector::Idling;
536 bool CMSCollector::_foregroundGCIsActive = false;
537 bool CMSCollector::_foregroundGCShouldWait = false;
538
539 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
540 CardTableRS* ct,
541 ConcurrentMarkSweepPolicy* cp):
542 _cmsGen(cmsGen),
543 _ct(ct),
544 _ref_processor(NULL), // will be set later
545 _conc_workers(NULL), // may be set later
546 _abort_preclean(false),
547 _start_sampling(false),
548 _between_prologue_and_epilogue(false),
549 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
550 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
551 -1 /* lock-free */, "No_lock" /* dummy */),
552 _modUnionClosure(&_modUnionTable),
553 _modUnionClosurePar(&_modUnionTable),
554 // Adjust my span to cover old (cms) gen
555 _span(cmsGen->reserved()),
556 // Construct the is_alive_closure with _span & markBitMap
557 _is_alive_closure(_span, &_markBitMap),
558 _restart_addr(NULL),
559 _overflow_list(NULL),
560 _stats(cmsGen),
561 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true)),
562 _eden_chunk_array(NULL), // may be set in ctor body
563 _eden_chunk_capacity(0), // -- ditto --
564 _eden_chunk_index(0), // -- ditto --
565 _survivor_plab_array(NULL), // -- ditto --
566 _survivor_chunk_array(NULL), // -- ditto --
567 _survivor_chunk_capacity(0), // -- ditto --
568 _survivor_chunk_index(0), // -- ditto --
569 _ser_pmc_preclean_ovflw(0),
570 _ser_kac_preclean_ovflw(0),
571 _ser_pmc_remark_ovflw(0),
572 _par_pmc_remark_ovflw(0),
573 _ser_kac_ovflw(0),
574 _par_kac_ovflw(0),
575 #ifndef PRODUCT
576 _num_par_pushes(0),
577 #endif
578 _collection_count_start(0),
579 _verifying(false),
580 _icms_start_limit(NULL),
581 _icms_stop_limit(NULL),
582 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
583 _completed_initialization(false),
584 _collector_policy(cp),
585 _should_unload_classes(CMSClassUnloadingEnabled),
586 _concurrent_cycles_since_last_unload(0),
587 _roots_scanning_options(SharedHeap::SO_None),
588 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
589 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
590 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
591 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
592 _cms_start_registered(false)
593 {
594 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
595 ExplicitGCInvokesConcurrent = true;
596 }
597 // Now expand the span and allocate the collection support structures
598 // (MUT, marking bit map etc.) to cover both generations subject to
599 // collection.
600
601 // For use by dirty card to oop closures.
602 _cmsGen->cmsSpace()->set_collector(this);
603
604 // Allocate MUT and marking bit map
605 {
606 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
607 if (!_markBitMap.allocate(_span)) {
608 warning("Failed to allocate CMS Bit Map");
609 return;
610 }
611 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
612 }
613 {
614 _modUnionTable.allocate(_span);
615 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
616 }
617
618 if (!_markStack.allocate(MarkStackSize)) {
619 warning("Failed to allocate CMS Marking Stack");
620 return;
621 }
622
623 // Support for multi-threaded concurrent phases
624 if (CMSConcurrentMTEnabled) {
625 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
626 // just for now
627 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
628 }
629 if (ConcGCThreads > 1) {
630 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
631 ConcGCThreads, true);
632 if (_conc_workers == NULL) {
633 warning("GC/CMS: _conc_workers allocation failure: "
634 "forcing -CMSConcurrentMTEnabled");
635 CMSConcurrentMTEnabled = false;
636 } else {
637 _conc_workers->initialize_workers();
638 }
639 } else {
640 CMSConcurrentMTEnabled = false;
641 }
642 }
643 if (!CMSConcurrentMTEnabled) {
644 ConcGCThreads = 0;
645 } else {
646 // Turn off CMSCleanOnEnter optimization temporarily for
647 // the MT case where it's not fixed yet; see 6178663.
648 CMSCleanOnEnter = false;
649 }
650 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
651 "Inconsistency");
652
653 // Parallel task queues; these are shared for the
654 // concurrent and stop-world phases of CMS, but
655 // are not shared with parallel scavenge (ParNew).
656 {
657 uint i;
658 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
659
660 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
661 || ParallelRefProcEnabled)
662 && num_queues > 0) {
663 _task_queues = new OopTaskQueueSet(num_queues);
664 if (_task_queues == NULL) {
665 warning("task_queues allocation failure.");
666 return;
667 }
668 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
669 if (_hash_seed == NULL) {
670 warning("_hash_seed array allocation failure");
671 return;
672 }
673
674 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
675 for (i = 0; i < num_queues; i++) {
676 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
677 if (q == NULL) {
678 warning("work_queue allocation failure.");
679 return;
680 }
681 _task_queues->register_queue(i, q);
682 }
683 for (i = 0; i < num_queues; i++) {
684 _task_queues->queue(i)->initialize();
685 _hash_seed[i] = 17; // copied from ParNew
686 }
687 }
688 }
689
690 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
691
692 // Clip CMSBootstrapOccupancy between 0 and 100.
693 _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100;
694
695 _full_gcs_since_conc_gc = 0;
696
697 // Now tell CMS generations the identity of their collector
698 ConcurrentMarkSweepGeneration::set_collector(this);
699
700 // Create & start a CMS thread for this CMS collector
701 _cmsThread = ConcurrentMarkSweepThread::start(this);
702 assert(cmsThread() != NULL, "CMS Thread should have been created");
703 assert(cmsThread()->collector() == this,
704 "CMS Thread should refer to this gen");
705 assert(CGC_lock != NULL, "Where's the CGC_lock?");
706
707 // Support for parallelizing young gen rescan
708 GenCollectedHeap* gch = GenCollectedHeap::heap();
709 _young_gen = gch->prev_gen(_cmsGen);
710 if (gch->supports_inline_contig_alloc()) {
711 _top_addr = gch->top_addr();
712 _end_addr = gch->end_addr();
713 assert(_young_gen != NULL, "no _young_gen");
714 _eden_chunk_index = 0;
715 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
716 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
717 if (_eden_chunk_array == NULL) {
718 _eden_chunk_capacity = 0;
719 warning("GC/CMS: _eden_chunk_array allocation failure");
720 }
721 }
722 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
723
724 // Support for parallelizing survivor space rescan
725 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
726 const size_t max_plab_samples =
727 ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
728
729 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
730 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
731 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
732 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
733 || _cursor == NULL) {
734 warning("Failed to allocate survivor plab/chunk array");
735 if (_survivor_plab_array != NULL) {
736 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
737 _survivor_plab_array = NULL;
738 }
739 if (_survivor_chunk_array != NULL) {
740 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
741 _survivor_chunk_array = NULL;
742 }
743 if (_cursor != NULL) {
744 FREE_C_HEAP_ARRAY(size_t, _cursor, mtGC);
745 _cursor = NULL;
746 }
747 } else {
748 _survivor_chunk_capacity = 2*max_plab_samples;
749 for (uint i = 0; i < ParallelGCThreads; i++) {
750 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
751 if (vec == NULL) {
752 warning("Failed to allocate survivor plab array");
753 for (int j = i; j > 0; j--) {
754 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array(), mtGC);
755 }
756 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
757 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
758 _survivor_plab_array = NULL;
759 _survivor_chunk_array = NULL;
760 _survivor_chunk_capacity = 0;
761 break;
762 } else {
763 ChunkArray* cur =
764 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
765 max_plab_samples);
766 assert(cur->end() == 0, "Should be 0");
767 assert(cur->array() == vec, "Should be vec");
768 assert(cur->capacity() == max_plab_samples, "Error");
769 }
770 }
771 }
772 }
773 assert( ( _survivor_plab_array != NULL
774 && _survivor_chunk_array != NULL)
775 || ( _survivor_chunk_capacity == 0
776 && _survivor_chunk_index == 0),
777 "Error");
778
779 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
780 _gc_counters = new CollectorCounters("CMS", 1);
781 _completed_initialization = true;
782 _inter_sweep_timer.start(); // start of time
783 }
784
785 const char* ConcurrentMarkSweepGeneration::name() const {
786 return "concurrent mark-sweep generation";
787 }
788 void ConcurrentMarkSweepGeneration::update_counters() {
789 if (UsePerfData) {
790 _space_counters->update_all();
791 _gen_counters->update_all();
792 }
793 }
794
795 // this is an optimized version of update_counters(). it takes the
796 // used value as a parameter rather than computing it.
797 //
798 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
799 if (UsePerfData) {
800 _space_counters->update_used(used);
801 _space_counters->update_capacity();
802 _gen_counters->update_all();
803 }
804 }
805
806 void ConcurrentMarkSweepGeneration::print() const {
807 Generation::print();
808 cmsSpace()->print();
809 }
810
811 #ifndef PRODUCT
812 void ConcurrentMarkSweepGeneration::print_statistics() {
813 cmsSpace()->printFLCensus(0);
814 }
815 #endif
816
817 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
818 GenCollectedHeap* gch = GenCollectedHeap::heap();
819 if (PrintGCDetails) {
820 if (Verbose) {
821 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
822 level(), short_name(), s, used(), capacity());
823 } else {
824 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
825 level(), short_name(), s, used() / K, capacity() / K);
826 }
827 }
828 if (Verbose) {
829 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
830 gch->used(), gch->capacity());
831 } else {
832 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
833 gch->used() / K, gch->capacity() / K);
834 }
835 }
836
837 size_t
838 ConcurrentMarkSweepGeneration::contiguous_available() const {
839 // dld proposes an improvement in precision here. If the committed
840 // part of the space ends in a free block we should add that to
841 // uncommitted size in the calculation below. Will make this
842 // change later, staying with the approximation below for the
843 // time being. -- ysr.
844 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
845 }
846
847 size_t
848 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
849 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
850 }
851
852 size_t ConcurrentMarkSweepGeneration::max_available() const {
853 return free() + _virtual_space.uncommitted_size();
854 }
855
856 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
857 size_t available = max_available();
858 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
859 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
860 if (Verbose && PrintGCDetails) {
861 gclog_or_tty->print_cr(
862 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
863 "max_promo("SIZE_FORMAT")",
864 res? "":" not", available, res? ">=":"<",
865 av_promo, max_promotion_in_bytes);
866 }
867 return res;
868 }
869
870 // At a promotion failure dump information on block layout in heap
871 // (cms old generation).
872 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
873 if (CMSDumpAtPromotionFailure) {
874 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
875 }
876 }
877
878 CompactibleSpace*
879 ConcurrentMarkSweepGeneration::first_compaction_space() const {
880 return _cmsSpace;
881 }
882
883 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
884 // Clear the promotion information. These pointers can be adjusted
885 // along with all the other pointers into the heap but
886 // compaction is expected to be a rare event with
887 // a heap using cms so don't do it without seeing the need.
888 if (CollectedHeap::use_parallel_gc_threads()) {
889 for (uint i = 0; i < ParallelGCThreads; i++) {
890 _par_gc_thread_states[i]->promo.reset();
891 }
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->get_gen(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 if (CollectedHeap::use_parallel_gc_threads()) {
2806 for (uint i = 0; i < ParallelGCThreads; i++) {
2807 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2808 }
2809 }
2810 }
2811
2812 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2813 assert(!incremental_collection_failed(), "Should have been cleared");
2814 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2815 cmsSpace()->gc_epilogue();
2816 // Print stat counters
2817 NOT_PRODUCT(
2818 assert(_numObjectsAllocated == 0, "check");
2819 assert(_numWordsAllocated == 0, "check");
2820 if (Verbose && PrintGC) {
2821 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2822 SIZE_FORMAT" bytes",
2823 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2824 }
2825 _numObjectsPromoted = 0;
2826 _numWordsPromoted = 0;
2827 )
2828
2829 if (PrintGC && Verbose) {
2830 // Call down the chain in contiguous_available needs the freelistLock
2831 // so print this out before releasing the freeListLock.
2832 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2833 contiguous_available());
2834 }
2835 }
2836
2837 #ifndef PRODUCT
2838 bool CMSCollector::have_cms_token() {
2839 Thread* thr = Thread::current();
2840 if (thr->is_VM_thread()) {
2841 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2842 } else if (thr->is_ConcurrentGC_thread()) {
2843 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2844 } else if (thr->is_GC_task_thread()) {
2845 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2846 ParGCRareEvent_lock->owned_by_self();
2847 }
2848 return false;
2849 }
2850 #endif
2851
2852 // Check reachability of the given heap address in CMS generation,
2853 // treating all other generations as roots.
2854 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2855 // We could "guarantee" below, rather than assert, but I'll
2856 // leave these as "asserts" so that an adventurous debugger
2857 // could try this in the product build provided some subset of
2858 // the conditions were met, provided they were interested in the
2859 // results and knew that the computation below wouldn't interfere
2860 // with other concurrent computations mutating the structures
2861 // being read or written.
2862 assert(SafepointSynchronize::is_at_safepoint(),
2863 "Else mutations in object graph will make answer suspect");
2864 assert(have_cms_token(), "Should hold cms token");
2865 assert(haveFreelistLocks(), "must hold free list locks");
2866 assert_lock_strong(bitMapLock());
2867
2868 // Clear the marking bit map array before starting, but, just
2869 // for kicks, first report if the given address is already marked
2870 gclog_or_tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", addr,
2871 _markBitMap.isMarked(addr) ? "" : " not");
2872
2873 if (verify_after_remark()) {
2874 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2875 bool result = verification_mark_bm()->isMarked(addr);
2876 gclog_or_tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", addr,
2877 result ? "IS" : "is NOT");
2878 return result;
2879 } else {
2880 gclog_or_tty->print_cr("Could not compute result");
2881 return false;
2882 }
2883 }
2884
2885
2886 void
2887 CMSCollector::print_on_error(outputStream* st) {
2888 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2889 if (collector != NULL) {
2890 CMSBitMap* bitmap = &collector->_markBitMap;
2891 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, bitmap);
2892 bitmap->print_on_error(st, " Bits: ");
2893
2894 st->cr();
2895
2896 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2897 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, mut_bitmap);
2898 mut_bitmap->print_on_error(st, " Bits: ");
2899 }
2900 }
2901
2902 ////////////////////////////////////////////////////////
2903 // CMS Verification Support
2904 ////////////////////////////////////////////////////////
2905 // Following the remark phase, the following invariant
2906 // should hold -- each object in the CMS heap which is
2907 // marked in markBitMap() should be marked in the verification_mark_bm().
2908
2909 class VerifyMarkedClosure: public BitMapClosure {
2910 CMSBitMap* _marks;
2911 bool _failed;
2912
2913 public:
2914 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2915
2916 bool do_bit(size_t offset) {
2917 HeapWord* addr = _marks->offsetToHeapWord(offset);
2918 if (!_marks->isMarked(addr)) {
2919 oop(addr)->print_on(gclog_or_tty);
2920 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2921 _failed = true;
2922 }
2923 return true;
2924 }
2925
2926 bool failed() { return _failed; }
2927 };
2928
2929 bool CMSCollector::verify_after_remark(bool silent) {
2930 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2931 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2932 static bool init = false;
2933
2934 assert(SafepointSynchronize::is_at_safepoint(),
2935 "Else mutations in object graph will make answer suspect");
2936 assert(have_cms_token(),
2937 "Else there may be mutual interference in use of "
2938 " verification data structures");
2939 assert(_collectorState > Marking && _collectorState <= Sweeping,
2940 "Else marking info checked here may be obsolete");
2941 assert(haveFreelistLocks(), "must hold free list locks");
2942 assert_lock_strong(bitMapLock());
2943
2944
2945 // Allocate marking bit map if not already allocated
2946 if (!init) { // first time
2947 if (!verification_mark_bm()->allocate(_span)) {
2948 return false;
2949 }
2950 init = true;
2951 }
2952
2953 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2954
2955 // Turn off refs discovery -- so we will be tracing through refs.
2956 // This is as intended, because by this time
2957 // GC must already have cleared any refs that need to be cleared,
2958 // and traced those that need to be marked; moreover,
2959 // the marking done here is not going to interfere in any
2960 // way with the marking information used by GC.
2961 NoRefDiscovery no_discovery(ref_processor());
2962
2963 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2964
2965 // Clear any marks from a previous round
2966 verification_mark_bm()->clear_all();
2967 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2968 verify_work_stacks_empty();
2969
2970 GenCollectedHeap* gch = GenCollectedHeap::heap();
2971 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2972 // Update the saved marks which may affect the root scans.
2973 gch->save_marks();
2974
2975 if (CMSRemarkVerifyVariant == 1) {
2976 // In this first variant of verification, we complete
2977 // all marking, then check if the new marks-vector is
2978 // a subset of the CMS marks-vector.
2979 verify_after_remark_work_1();
2980 } else if (CMSRemarkVerifyVariant == 2) {
2981 // In this second variant of verification, we flag an error
2982 // (i.e. an object reachable in the new marks-vector not reachable
2983 // in the CMS marks-vector) immediately, also indicating the
2984 // identify of an object (A) that references the unmarked object (B) --
2985 // presumably, a mutation to A failed to be picked up by preclean/remark?
2986 verify_after_remark_work_2();
2987 } else {
2988 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2989 CMSRemarkVerifyVariant);
2990 }
2991 if (!silent) gclog_or_tty->print(" done] ");
2992 return true;
2993 }
2994
2995 void CMSCollector::verify_after_remark_work_1() {
2996 ResourceMark rm;
2997 HandleMark hm;
2998 GenCollectedHeap* gch = GenCollectedHeap::heap();
2999
3000 // Get a clear set of claim bits for the roots processing to work with.
3001 ClassLoaderDataGraph::clear_claimed_marks();
3002
3003 // Mark from roots one level into CMS
3004 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
3005 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3006
3007 gch->gen_process_roots(_cmsGen->level(),
3008 true, // younger gens are roots
3009 true, // activate StrongRootsScope
3010 SharedHeap::ScanningOption(roots_scanning_options()),
3011 should_unload_classes(),
3012 ¬Older,
3013 NULL,
3014 NULL); // SSS: Provide correct closure
3015
3016 // Now mark from the roots
3017 MarkFromRootsClosure markFromRootsClosure(this, _span,
3018 verification_mark_bm(), verification_mark_stack(),
3019 false /* don't yield */, true /* verifying */);
3020 assert(_restart_addr == NULL, "Expected pre-condition");
3021 verification_mark_bm()->iterate(&markFromRootsClosure);
3022 while (_restart_addr != NULL) {
3023 // Deal with stack overflow: by restarting at the indicated
3024 // address.
3025 HeapWord* ra = _restart_addr;
3026 markFromRootsClosure.reset(ra);
3027 _restart_addr = NULL;
3028 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3029 }
3030 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3031 verify_work_stacks_empty();
3032
3033 // Marking completed -- now verify that each bit marked in
3034 // verification_mark_bm() is also marked in markBitMap(); flag all
3035 // errors by printing corresponding objects.
3036 VerifyMarkedClosure vcl(markBitMap());
3037 verification_mark_bm()->iterate(&vcl);
3038 if (vcl.failed()) {
3039 gclog_or_tty->print("Verification failed");
3040 Universe::heap()->print_on(gclog_or_tty);
3041 fatal("CMS: failed marking verification after remark");
3042 }
3043 }
3044
3045 class VerifyKlassOopsKlassClosure : public KlassClosure {
3046 class VerifyKlassOopsClosure : public OopClosure {
3047 CMSBitMap* _bitmap;
3048 public:
3049 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
3050 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
3051 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
3052 } _oop_closure;
3053 public:
3054 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
3055 void do_klass(Klass* k) {
3056 k->oops_do(&_oop_closure);
3057 }
3058 };
3059
3060 void CMSCollector::verify_after_remark_work_2() {
3061 ResourceMark rm;
3062 HandleMark hm;
3063 GenCollectedHeap* gch = GenCollectedHeap::heap();
3064
3065 // Get a clear set of claim bits for the roots processing to work with.
3066 ClassLoaderDataGraph::clear_claimed_marks();
3067
3068 // Mark from roots one level into CMS
3069 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
3070 markBitMap());
3071 CLDToOopClosure cld_closure(¬Older, true);
3072
3073 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3074
3075 gch->gen_process_roots(_cmsGen->level(),
3076 true, // younger gens are roots
3077 true, // activate StrongRootsScope
3078 SharedHeap::ScanningOption(roots_scanning_options()),
3079 should_unload_classes(),
3080 ¬Older,
3081 NULL,
3082 &cld_closure);
3083
3084 // Now mark from the roots
3085 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
3086 verification_mark_bm(), markBitMap(), verification_mark_stack());
3087 assert(_restart_addr == NULL, "Expected pre-condition");
3088 verification_mark_bm()->iterate(&markFromRootsClosure);
3089 while (_restart_addr != NULL) {
3090 // Deal with stack overflow: by restarting at the indicated
3091 // address.
3092 HeapWord* ra = _restart_addr;
3093 markFromRootsClosure.reset(ra);
3094 _restart_addr = NULL;
3095 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3096 }
3097 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3098 verify_work_stacks_empty();
3099
3100 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
3101 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
3102
3103 // Marking completed -- now verify that each bit marked in
3104 // verification_mark_bm() is also marked in markBitMap(); flag all
3105 // errors by printing corresponding objects.
3106 VerifyMarkedClosure vcl(markBitMap());
3107 verification_mark_bm()->iterate(&vcl);
3108 assert(!vcl.failed(), "Else verification above should not have succeeded");
3109 }
3110
3111 void ConcurrentMarkSweepGeneration::save_marks() {
3112 // delegate to CMS space
3113 cmsSpace()->save_marks();
3114 for (uint i = 0; i < ParallelGCThreads; i++) {
3115 _par_gc_thread_states[i]->promo.startTrackingPromotions();
3116 }
3117 }
3118
3119 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
3120 return cmsSpace()->no_allocs_since_save_marks();
3121 }
3122
3123 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
3124 \
3125 void ConcurrentMarkSweepGeneration:: \
3126 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
3127 cl->set_generation(this); \
3128 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
3129 cl->reset_generation(); \
3130 save_marks(); \
3131 }
3132
3133 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
3134
3135 void
3136 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
3137 cl->set_generation(this);
3138 younger_refs_in_space_iterate(_cmsSpace, cl);
3139 cl->reset_generation();
3140 }
3141
3142 void
3143 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
3144 if (freelistLock()->owned_by_self()) {
3145 Generation::oop_iterate(cl);
3146 } else {
3147 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3148 Generation::oop_iterate(cl);
3149 }
3150 }
3151
3152 void
3153 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3154 if (freelistLock()->owned_by_self()) {
3155 Generation::object_iterate(cl);
3156 } else {
3157 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3158 Generation::object_iterate(cl);
3159 }
3160 }
3161
3162 void
3163 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3164 if (freelistLock()->owned_by_self()) {
3165 Generation::safe_object_iterate(cl);
3166 } else {
3167 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3168 Generation::safe_object_iterate(cl);
3169 }
3170 }
3171
3172 void
3173 ConcurrentMarkSweepGeneration::post_compact() {
3174 }
3175
3176 void
3177 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3178 // Fix the linear allocation blocks to look like free blocks.
3179
3180 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3181 // are not called when the heap is verified during universe initialization and
3182 // at vm shutdown.
3183 if (freelistLock()->owned_by_self()) {
3184 cmsSpace()->prepare_for_verify();
3185 } else {
3186 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3187 cmsSpace()->prepare_for_verify();
3188 }
3189 }
3190
3191 void
3192 ConcurrentMarkSweepGeneration::verify() {
3193 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3194 // are not called when the heap is verified during universe initialization and
3195 // at vm shutdown.
3196 if (freelistLock()->owned_by_self()) {
3197 cmsSpace()->verify();
3198 } else {
3199 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3200 cmsSpace()->verify();
3201 }
3202 }
3203
3204 void CMSCollector::verify() {
3205 _cmsGen->verify();
3206 }
3207
3208 #ifndef PRODUCT
3209 bool CMSCollector::overflow_list_is_empty() const {
3210 assert(_num_par_pushes >= 0, "Inconsistency");
3211 if (_overflow_list == NULL) {
3212 assert(_num_par_pushes == 0, "Inconsistency");
3213 }
3214 return _overflow_list == NULL;
3215 }
3216
3217 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3218 // merely consolidate assertion checks that appear to occur together frequently.
3219 void CMSCollector::verify_work_stacks_empty() const {
3220 assert(_markStack.isEmpty(), "Marking stack should be empty");
3221 assert(overflow_list_is_empty(), "Overflow list should be empty");
3222 }
3223
3224 void CMSCollector::verify_overflow_empty() const {
3225 assert(overflow_list_is_empty(), "Overflow list should be empty");
3226 assert(no_preserved_marks(), "No preserved marks");
3227 }
3228 #endif // PRODUCT
3229
3230 // Decide if we want to enable class unloading as part of the
3231 // ensuing concurrent GC cycle. We will collect and
3232 // unload classes if it's the case that:
3233 // (1) an explicit gc request has been made and the flag
3234 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3235 // (2) (a) class unloading is enabled at the command line, and
3236 // (b) old gen is getting really full
3237 // NOTE: Provided there is no change in the state of the heap between
3238 // calls to this method, it should have idempotent results. Moreover,
3239 // its results should be monotonically increasing (i.e. going from 0 to 1,
3240 // but not 1 to 0) between successive calls between which the heap was
3241 // not collected. For the implementation below, it must thus rely on
3242 // the property that concurrent_cycles_since_last_unload()
3243 // will not decrease unless a collection cycle happened and that
3244 // _cmsGen->is_too_full() are
3245 // themselves also monotonic in that sense. See check_monotonicity()
3246 // below.
3247 void CMSCollector::update_should_unload_classes() {
3248 _should_unload_classes = false;
3249 // Condition 1 above
3250 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3251 _should_unload_classes = true;
3252 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3253 // Disjuncts 2.b.(i,ii,iii) above
3254 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3255 CMSClassUnloadingMaxInterval)
3256 || _cmsGen->is_too_full();
3257 }
3258 }
3259
3260 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3261 bool res = should_concurrent_collect();
3262 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3263 return res;
3264 }
3265
3266 void CMSCollector::setup_cms_unloading_and_verification_state() {
3267 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3268 || VerifyBeforeExit;
3269 const int rso = SharedHeap::SO_AllCodeCache;
3270
3271 // We set the proper root for this CMS cycle here.
3272 if (should_unload_classes()) { // Should unload classes this cycle
3273 remove_root_scanning_option(rso); // Shrink the root set appropriately
3274 set_verifying(should_verify); // Set verification state for this cycle
3275 return; // Nothing else needs to be done at this time
3276 }
3277
3278 // Not unloading classes this cycle
3279 assert(!should_unload_classes(), "Inconsistency!");
3280
3281 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3282 // Include symbols, strings and code cache elements to prevent their resurrection.
3283 add_root_scanning_option(rso);
3284 set_verifying(true);
3285 } else if (verifying() && !should_verify) {
3286 // We were verifying, but some verification flags got disabled.
3287 set_verifying(false);
3288 // Exclude symbols, strings and code cache elements from root scanning to
3289 // reduce IM and RM pauses.
3290 remove_root_scanning_option(rso);
3291 }
3292 }
3293
3294
3295 #ifndef PRODUCT
3296 HeapWord* CMSCollector::block_start(const void* p) const {
3297 const HeapWord* addr = (HeapWord*)p;
3298 if (_span.contains(p)) {
3299 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3300 return _cmsGen->cmsSpace()->block_start(p);
3301 }
3302 }
3303 return NULL;
3304 }
3305 #endif
3306
3307 HeapWord*
3308 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3309 bool tlab,
3310 bool parallel) {
3311 CMSSynchronousYieldRequest yr;
3312 assert(!tlab, "Can't deal with TLAB allocation");
3313 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3314 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3315 CMSExpansionCause::_satisfy_allocation);
3316 if (GCExpandToAllocateDelayMillis > 0) {
3317 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3318 }
3319 return have_lock_and_allocate(word_size, tlab);
3320 }
3321
3322 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3323 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3324 // to CardGeneration and share it...
3325 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3326 return CardGeneration::expand(bytes, expand_bytes);
3327 }
3328
3329 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3330 CMSExpansionCause::Cause cause)
3331 {
3332
3333 bool success = expand(bytes, expand_bytes);
3334
3335 // remember why we expanded; this information is used
3336 // by shouldConcurrentCollect() when making decisions on whether to start
3337 // a new CMS cycle.
3338 if (success) {
3339 set_expansion_cause(cause);
3340 if (PrintGCDetails && Verbose) {
3341 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3342 CMSExpansionCause::to_string(cause));
3343 }
3344 }
3345 }
3346
3347 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3348 HeapWord* res = NULL;
3349 MutexLocker x(ParGCRareEvent_lock);
3350 while (true) {
3351 // Expansion by some other thread might make alloc OK now:
3352 res = ps->lab.alloc(word_sz);
3353 if (res != NULL) return res;
3354 // If there's not enough expansion space available, give up.
3355 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3356 return NULL;
3357 }
3358 // Otherwise, we try expansion.
3359 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3360 CMSExpansionCause::_allocate_par_lab);
3361 // Now go around the loop and try alloc again;
3362 // A competing par_promote might beat us to the expansion space,
3363 // so we may go around the loop again if promotion fails again.
3364 if (GCExpandToAllocateDelayMillis > 0) {
3365 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3366 }
3367 }
3368 }
3369
3370
3371 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3372 PromotionInfo* promo) {
3373 MutexLocker x(ParGCRareEvent_lock);
3374 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3375 while (true) {
3376 // Expansion by some other thread might make alloc OK now:
3377 if (promo->ensure_spooling_space()) {
3378 assert(promo->has_spooling_space(),
3379 "Post-condition of successful ensure_spooling_space()");
3380 return true;
3381 }
3382 // If there's not enough expansion space available, give up.
3383 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3384 return false;
3385 }
3386 // Otherwise, we try expansion.
3387 expand(refill_size_bytes, MinHeapDeltaBytes,
3388 CMSExpansionCause::_allocate_par_spooling_space);
3389 // Now go around the loop and try alloc again;
3390 // A competing allocation might beat us to the expansion space,
3391 // so we may go around the loop again if allocation fails again.
3392 if (GCExpandToAllocateDelayMillis > 0) {
3393 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3394 }
3395 }
3396 }
3397
3398
3399 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3400 assert_locked_or_safepoint(ExpandHeap_lock);
3401 // Shrink committed space
3402 _virtual_space.shrink_by(bytes);
3403 // Shrink space; this also shrinks the space's BOT
3404 _cmsSpace->set_end((HeapWord*) _virtual_space.high());
3405 size_t new_word_size = heap_word_size(_cmsSpace->capacity());
3406 // Shrink the shared block offset array
3407 _bts->resize(new_word_size);
3408 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3409 // Shrink the card table
3410 Universe::heap()->barrier_set()->resize_covered_region(mr);
3411
3412 if (Verbose && PrintGC) {
3413 size_t new_mem_size = _virtual_space.committed_size();
3414 size_t old_mem_size = new_mem_size + bytes;
3415 gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3416 name(), old_mem_size/K, new_mem_size/K);
3417 }
3418 }
3419
3420 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3421 assert_locked_or_safepoint(Heap_lock);
3422 size_t size = ReservedSpace::page_align_size_down(bytes);
3423 // Only shrink if a compaction was done so that all the free space
3424 // in the generation is in a contiguous block at the end.
3425 if (size > 0 && did_compact()) {
3426 shrink_by(size);
3427 }
3428 }
3429
3430 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3431 assert_locked_or_safepoint(Heap_lock);
3432 bool result = _virtual_space.expand_by(bytes);
3433 if (result) {
3434 size_t new_word_size =
3435 heap_word_size(_virtual_space.committed_size());
3436 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3437 _bts->resize(new_word_size); // resize the block offset shared array
3438 Universe::heap()->barrier_set()->resize_covered_region(mr);
3439 // Hmmmm... why doesn't CFLS::set_end verify locking?
3440 // This is quite ugly; FIX ME XXX
3441 _cmsSpace->assert_locked(freelistLock());
3442 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3443
3444 // update the space and generation capacity counters
3445 if (UsePerfData) {
3446 _space_counters->update_capacity();
3447 _gen_counters->update_all();
3448 }
3449
3450 if (Verbose && PrintGC) {
3451 size_t new_mem_size = _virtual_space.committed_size();
3452 size_t old_mem_size = new_mem_size - bytes;
3453 gclog_or_tty->print_cr("Expanding %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3454 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3455 }
3456 }
3457 return result;
3458 }
3459
3460 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3461 assert_locked_or_safepoint(Heap_lock);
3462 bool success = true;
3463 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3464 if (remaining_bytes > 0) {
3465 success = grow_by(remaining_bytes);
3466 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3467 }
3468 return success;
3469 }
3470
3471 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
3472 assert_locked_or_safepoint(Heap_lock);
3473 assert_lock_strong(freelistLock());
3474 if (PrintGCDetails && Verbose) {
3475 warning("Shrinking of CMS not yet implemented");
3476 }
3477 return;
3478 }
3479
3480
3481 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3482 // phases.
3483 class CMSPhaseAccounting: public StackObj {
3484 public:
3485 CMSPhaseAccounting(CMSCollector *collector,
3486 const char *phase,
3487 const GCId gc_id,
3488 bool print_cr = true);
3489 ~CMSPhaseAccounting();
3490
3491 private:
3492 CMSCollector *_collector;
3493 const char *_phase;
3494 elapsedTimer _wallclock;
3495 bool _print_cr;
3496 const GCId _gc_id;
3497
3498 public:
3499 // Not MT-safe; so do not pass around these StackObj's
3500 // where they may be accessed by other threads.
3501 jlong wallclock_millis() {
3502 assert(_wallclock.is_active(), "Wall clock should not stop");
3503 _wallclock.stop(); // to record time
3504 jlong ret = _wallclock.milliseconds();
3505 _wallclock.start(); // restart
3506 return ret;
3507 }
3508 };
3509
3510 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3511 const char *phase,
3512 const GCId gc_id,
3513 bool print_cr) :
3514 _collector(collector), _phase(phase), _print_cr(print_cr), _gc_id(gc_id) {
3515
3516 if (PrintCMSStatistics != 0) {
3517 _collector->resetYields();
3518 }
3519 if (PrintGCDetails) {
3520 gclog_or_tty->gclog_stamp(_gc_id);
3521 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
3522 _collector->cmsGen()->short_name(), _phase);
3523 }
3524 _collector->resetTimer();
3525 _wallclock.start();
3526 _collector->startTimer();
3527 }
3528
3529 CMSPhaseAccounting::~CMSPhaseAccounting() {
3530 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3531 _collector->stopTimer();
3532 _wallclock.stop();
3533 if (PrintGCDetails) {
3534 gclog_or_tty->gclog_stamp(_gc_id);
3535 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3536 _collector->cmsGen()->short_name(),
3537 _phase, _collector->timerValue(), _wallclock.seconds());
3538 if (_print_cr) {
3539 gclog_or_tty->cr();
3540 }
3541 if (PrintCMSStatistics != 0) {
3542 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3543 _collector->yields());
3544 }
3545 }
3546 }
3547
3548 // CMS work
3549
3550 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
3551 class CMSParMarkTask : public AbstractGangTask {
3552 protected:
3553 CMSCollector* _collector;
3554 int _n_workers;
3555 CMSParMarkTask(const char* name, CMSCollector* collector, int n_workers) :
3556 AbstractGangTask(name),
3557 _collector(collector),
3558 _n_workers(n_workers) {}
3559 // Work method in support of parallel rescan ... of young gen spaces
3560 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
3561 ContiguousSpace* space,
3562 HeapWord** chunk_array, size_t chunk_top);
3563 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
3564 };
3565
3566 // Parallel initial mark task
3567 class CMSParInitialMarkTask: public CMSParMarkTask {
3568 public:
3569 CMSParInitialMarkTask(CMSCollector* collector, int n_workers) :
3570 CMSParMarkTask("Scan roots and young gen for initial mark in parallel",
3571 collector, n_workers) {}
3572 void work(uint worker_id);
3573 };
3574
3575 // Checkpoint the roots into this generation from outside
3576 // this generation. [Note this initial checkpoint need only
3577 // be approximate -- we'll do a catch up phase subsequently.]
3578 void CMSCollector::checkpointRootsInitial(bool asynch) {
3579 assert(_collectorState == InitialMarking, "Wrong collector state");
3580 check_correct_thread_executing();
3581 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3582
3583 save_heap_summary();
3584 report_heap_summary(GCWhen::BeforeGC);
3585
3586 ReferenceProcessor* rp = ref_processor();
3587 SpecializationStats::clear();
3588 assert(_restart_addr == NULL, "Control point invariant");
3589 if (asynch) {
3590 // acquire locks for subsequent manipulations
3591 MutexLockerEx x(bitMapLock(),
3592 Mutex::_no_safepoint_check_flag);
3593 checkpointRootsInitialWork(asynch);
3594 // enable ("weak") refs discovery
3595 rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3596 _collectorState = Marking;
3597 } else {
3598 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3599 // which recognizes if we are a CMS generation, and doesn't try to turn on
3600 // discovery; verify that they aren't meddling.
3601 assert(!rp->discovery_is_atomic(),
3602 "incorrect setting of discovery predicate");
3603 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3604 "ref discovery for this generation kind");
3605 // already have locks
3606 checkpointRootsInitialWork(asynch);
3607 // now enable ("weak") refs discovery
3608 rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/);
3609 _collectorState = Marking;
3610 }
3611 SpecializationStats::print();
3612 }
3613
3614 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3615 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3616 assert(_collectorState == InitialMarking, "just checking");
3617
3618 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3619 // precede our marking with a collection of all
3620 // younger generations to keep floating garbage to a minimum.
3621 // XXX: we won't do this for now -- it's an optimization to be done later.
3622
3623 // already have locks
3624 assert_lock_strong(bitMapLock());
3625 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3626
3627 // Setup the verification and class unloading state for this
3628 // CMS collection cycle.
3629 setup_cms_unloading_and_verification_state();
3630
3631 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
3632 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
3633
3634 // Reset all the PLAB chunk arrays if necessary.
3635 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3636 reset_survivor_plab_arrays();
3637 }
3638
3639 ResourceMark rm;
3640 HandleMark hm;
3641
3642 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3643 GenCollectedHeap* gch = GenCollectedHeap::heap();
3644
3645 verify_work_stacks_empty();
3646 verify_overflow_empty();
3647
3648 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3649 // Update the saved marks which may affect the root scans.
3650 gch->save_marks();
3651
3652 // weak reference processing has not started yet.
3653 ref_processor()->set_enqueuing_is_done(false);
3654
3655 // Need to remember all newly created CLDs,
3656 // so that we can guarantee that the remark finds them.
3657 ClassLoaderDataGraph::remember_new_clds(true);
3658
3659 // Whenever a CLD is found, it will be claimed before proceeding to mark
3660 // the klasses. The claimed marks need to be cleared before marking starts.
3661 ClassLoaderDataGraph::clear_claimed_marks();
3662
3663 if (CMSPrintEdenSurvivorChunks) {
3664 print_eden_and_survivor_chunk_arrays();
3665 }
3666
3667 {
3668 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3669 if (CMSParallelInitialMarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
3670 // The parallel version.
3671 FlexibleWorkGang* workers = gch->workers();
3672 assert(workers != NULL, "Need parallel worker threads.");
3673 int n_workers = workers->active_workers();
3674 CMSParInitialMarkTask tsk(this, n_workers);
3675 gch->set_par_threads(n_workers);
3676 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3677 if (n_workers > 1) {
3678 GenCollectedHeap::StrongRootsScope srs(gch);
3679 workers->run_task(&tsk);
3680 } else {
3681 GenCollectedHeap::StrongRootsScope srs(gch);
3682 tsk.work(0);
3683 }
3684 gch->set_par_threads(0);
3685 } else {
3686 // The serial version.
3687 CLDToOopClosure cld_closure(¬Older, true);
3688 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3689 gch->gen_process_roots(_cmsGen->level(),
3690 true, // younger gens are roots
3691 true, // activate StrongRootsScope
3692 SharedHeap::ScanningOption(roots_scanning_options()),
3693 should_unload_classes(),
3694 ¬Older,
3695 NULL,
3696 &cld_closure);
3697 }
3698 }
3699
3700 // Clear mod-union table; it will be dirtied in the prologue of
3701 // CMS generation per each younger generation collection.
3702
3703 assert(_modUnionTable.isAllClear(),
3704 "Was cleared in most recent final checkpoint phase"
3705 " or no bits are set in the gc_prologue before the start of the next "
3706 "subsequent marking phase.");
3707
3708 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3709
3710 // Save the end of the used_region of the constituent generations
3711 // to be used to limit the extent of sweep in each generation.
3712 save_sweep_limits();
3713 verify_overflow_empty();
3714 }
3715
3716 bool CMSCollector::markFromRoots(bool asynch) {
3717 // we might be tempted to assert that:
3718 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3719 // "inconsistent argument?");
3720 // However that wouldn't be right, because it's possible that
3721 // a safepoint is indeed in progress as a younger generation
3722 // stop-the-world GC happens even as we mark in this generation.
3723 assert(_collectorState == Marking, "inconsistent state?");
3724 check_correct_thread_executing();
3725 verify_overflow_empty();
3726
3727 bool res;
3728 if (asynch) {
3729 // Weak ref discovery note: We may be discovering weak
3730 // refs in this generation concurrent (but interleaved) with
3731 // weak ref discovery by a younger generation collector.
3732
3733 CMSTokenSyncWithLocks ts(true, bitMapLock());
3734 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3735 CMSPhaseAccounting pa(this, "mark", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3736 res = markFromRootsWork(asynch);
3737 if (res) {
3738 _collectorState = Precleaning;
3739 } else { // We failed and a foreground collection wants to take over
3740 assert(_foregroundGCIsActive, "internal state inconsistency");
3741 assert(_restart_addr == NULL, "foreground will restart from scratch");
3742 if (PrintGCDetails) {
3743 gclog_or_tty->print_cr("bailing out to foreground collection");
3744 }
3745 }
3746 } else {
3747 assert(SafepointSynchronize::is_at_safepoint(),
3748 "inconsistent with asynch == false");
3749 // already have locks
3750 res = markFromRootsWork(asynch);
3751 _collectorState = FinalMarking;
3752 }
3753 verify_overflow_empty();
3754 return res;
3755 }
3756
3757 bool CMSCollector::markFromRootsWork(bool asynch) {
3758 // iterate over marked bits in bit map, doing a full scan and mark
3759 // from these roots using the following algorithm:
3760 // . if oop is to the right of the current scan pointer,
3761 // mark corresponding bit (we'll process it later)
3762 // . else (oop is to left of current scan pointer)
3763 // push oop on marking stack
3764 // . drain the marking stack
3765
3766 // Note that when we do a marking step we need to hold the
3767 // bit map lock -- recall that direct allocation (by mutators)
3768 // and promotion (by younger generation collectors) is also
3769 // marking the bit map. [the so-called allocate live policy.]
3770 // Because the implementation of bit map marking is not
3771 // robust wrt simultaneous marking of bits in the same word,
3772 // we need to make sure that there is no such interference
3773 // between concurrent such updates.
3774
3775 // already have locks
3776 assert_lock_strong(bitMapLock());
3777
3778 verify_work_stacks_empty();
3779 verify_overflow_empty();
3780 bool result = false;
3781 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3782 result = do_marking_mt(asynch);
3783 } else {
3784 result = do_marking_st(asynch);
3785 }
3786 return result;
3787 }
3788
3789 // Forward decl
3790 class CMSConcMarkingTask;
3791
3792 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3793 CMSCollector* _collector;
3794 CMSConcMarkingTask* _task;
3795 public:
3796 virtual void yield();
3797
3798 // "n_threads" is the number of threads to be terminated.
3799 // "queue_set" is a set of work queues of other threads.
3800 // "collector" is the CMS collector associated with this task terminator.
3801 // "yield" indicates whether we need the gang as a whole to yield.
3802 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3803 ParallelTaskTerminator(n_threads, queue_set),
3804 _collector(collector) { }
3805
3806 void set_task(CMSConcMarkingTask* task) {
3807 _task = task;
3808 }
3809 };
3810
3811 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3812 CMSConcMarkingTask* _task;
3813 public:
3814 bool should_exit_termination();
3815 void set_task(CMSConcMarkingTask* task) {
3816 _task = task;
3817 }
3818 };
3819
3820 // MT Concurrent Marking Task
3821 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3822 CMSCollector* _collector;
3823 int _n_workers; // requested/desired # workers
3824 bool _asynch;
3825 bool _result;
3826 CompactibleFreeListSpace* _cms_space;
3827 char _pad_front[64]; // padding to ...
3828 HeapWord* _global_finger; // ... avoid sharing cache line
3829 char _pad_back[64];
3830 HeapWord* _restart_addr;
3831
3832 // Exposed here for yielding support
3833 Mutex* const _bit_map_lock;
3834
3835 // The per thread work queues, available here for stealing
3836 OopTaskQueueSet* _task_queues;
3837
3838 // Termination (and yielding) support
3839 CMSConcMarkingTerminator _term;
3840 CMSConcMarkingTerminatorTerminator _term_term;
3841
3842 public:
3843 CMSConcMarkingTask(CMSCollector* collector,
3844 CompactibleFreeListSpace* cms_space,
3845 bool asynch,
3846 YieldingFlexibleWorkGang* workers,
3847 OopTaskQueueSet* task_queues):
3848 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3849 _collector(collector),
3850 _cms_space(cms_space),
3851 _asynch(asynch), _n_workers(0), _result(true),
3852 _task_queues(task_queues),
3853 _term(_n_workers, task_queues, _collector),
3854 _bit_map_lock(collector->bitMapLock())
3855 {
3856 _requested_size = _n_workers;
3857 _term.set_task(this);
3858 _term_term.set_task(this);
3859 _restart_addr = _global_finger = _cms_space->bottom();
3860 }
3861
3862
3863 OopTaskQueueSet* task_queues() { return _task_queues; }
3864
3865 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3866
3867 HeapWord** global_finger_addr() { return &_global_finger; }
3868
3869 CMSConcMarkingTerminator* terminator() { return &_term; }
3870
3871 virtual void set_for_termination(int active_workers) {
3872 terminator()->reset_for_reuse(active_workers);
3873 }
3874
3875 void work(uint worker_id);
3876 bool should_yield() {
3877 return ConcurrentMarkSweepThread::should_yield()
3878 && !_collector->foregroundGCIsActive()
3879 && _asynch;
3880 }
3881
3882 virtual void coordinator_yield(); // stuff done by coordinator
3883 bool result() { return _result; }
3884
3885 void reset(HeapWord* ra) {
3886 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3887 _restart_addr = _global_finger = ra;
3888 _term.reset_for_reuse();
3889 }
3890
3891 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3892 OopTaskQueue* work_q);
3893
3894 private:
3895 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3896 void do_work_steal(int i);
3897 void bump_global_finger(HeapWord* f);
3898 };
3899
3900 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3901 assert(_task != NULL, "Error");
3902 return _task->yielding();
3903 // Note that we do not need the disjunct || _task->should_yield() above
3904 // because we want terminating threads to yield only if the task
3905 // is already in the midst of yielding, which happens only after at least one
3906 // thread has yielded.
3907 }
3908
3909 void CMSConcMarkingTerminator::yield() {
3910 if (_task->should_yield()) {
3911 _task->yield();
3912 } else {
3913 ParallelTaskTerminator::yield();
3914 }
3915 }
3916
3917 ////////////////////////////////////////////////////////////////
3918 // Concurrent Marking Algorithm Sketch
3919 ////////////////////////////////////////////////////////////////
3920 // Until all tasks exhausted (both spaces):
3921 // -- claim next available chunk
3922 // -- bump global finger via CAS
3923 // -- find first object that starts in this chunk
3924 // and start scanning bitmap from that position
3925 // -- scan marked objects for oops
3926 // -- CAS-mark target, and if successful:
3927 // . if target oop is above global finger (volatile read)
3928 // nothing to do
3929 // . if target oop is in chunk and above local finger
3930 // then nothing to do
3931 // . else push on work-queue
3932 // -- Deal with possible overflow issues:
3933 // . local work-queue overflow causes stuff to be pushed on
3934 // global (common) overflow queue
3935 // . always first empty local work queue
3936 // . then get a batch of oops from global work queue if any
3937 // . then do work stealing
3938 // -- When all tasks claimed (both spaces)
3939 // and local work queue empty,
3940 // then in a loop do:
3941 // . check global overflow stack; steal a batch of oops and trace
3942 // . try to steal from other threads oif GOS is empty
3943 // . if neither is available, offer termination
3944 // -- Terminate and return result
3945 //
3946 void CMSConcMarkingTask::work(uint worker_id) {
3947 elapsedTimer _timer;
3948 ResourceMark rm;
3949 HandleMark hm;
3950
3951 DEBUG_ONLY(_collector->verify_overflow_empty();)
3952
3953 // Before we begin work, our work queue should be empty
3954 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3955 // Scan the bitmap covering _cms_space, tracing through grey objects.
3956 _timer.start();
3957 do_scan_and_mark(worker_id, _cms_space);
3958 _timer.stop();
3959 if (PrintCMSStatistics != 0) {
3960 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3961 worker_id, _timer.seconds());
3962 // XXX: need xxx/xxx type of notation, two timers
3963 }
3964
3965 // ... do work stealing
3966 _timer.reset();
3967 _timer.start();
3968 do_work_steal(worker_id);
3969 _timer.stop();
3970 if (PrintCMSStatistics != 0) {
3971 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3972 worker_id, _timer.seconds());
3973 // XXX: need xxx/xxx type of notation, two timers
3974 }
3975 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3976 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3977 // Note that under the current task protocol, the
3978 // following assertion is true even of the spaces
3979 // expanded since the completion of the concurrent
3980 // marking. XXX This will likely change under a strict
3981 // ABORT semantics.
3982 // After perm removal the comparison was changed to
3983 // greater than or equal to from strictly greater than.
3984 // Before perm removal the highest address sweep would
3985 // have been at the end of perm gen but now is at the
3986 // end of the tenured gen.
3987 assert(_global_finger >= _cms_space->end(),
3988 "All tasks have been completed");
3989 DEBUG_ONLY(_collector->verify_overflow_empty();)
3990 }
3991
3992 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3993 HeapWord* read = _global_finger;
3994 HeapWord* cur = read;
3995 while (f > read) {
3996 cur = read;
3997 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3998 if (cur == read) {
3999 // our cas succeeded
4000 assert(_global_finger >= f, "protocol consistency");
4001 break;
4002 }
4003 }
4004 }
4005
4006 // This is really inefficient, and should be redone by
4007 // using (not yet available) block-read and -write interfaces to the
4008 // stack and the work_queue. XXX FIX ME !!!
4009 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
4010 OopTaskQueue* work_q) {
4011 // Fast lock-free check
4012 if (ovflw_stk->length() == 0) {
4013 return false;
4014 }
4015 assert(work_q->size() == 0, "Shouldn't steal");
4016 MutexLockerEx ml(ovflw_stk->par_lock(),
4017 Mutex::_no_safepoint_check_flag);
4018 // Grab up to 1/4 the size of the work queue
4019 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4020 (size_t)ParGCDesiredObjsFromOverflowList);
4021 num = MIN2(num, ovflw_stk->length());
4022 for (int i = (int) num; i > 0; i--) {
4023 oop cur = ovflw_stk->pop();
4024 assert(cur != NULL, "Counted wrong?");
4025 work_q->push(cur);
4026 }
4027 return num > 0;
4028 }
4029
4030 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
4031 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4032 int n_tasks = pst->n_tasks();
4033 // We allow that there may be no tasks to do here because
4034 // we are restarting after a stack overflow.
4035 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
4036 uint nth_task = 0;
4037
4038 HeapWord* aligned_start = sp->bottom();
4039 if (sp->used_region().contains(_restart_addr)) {
4040 // Align down to a card boundary for the start of 0th task
4041 // for this space.
4042 aligned_start =
4043 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
4044 CardTableModRefBS::card_size);
4045 }
4046
4047 size_t chunk_size = sp->marking_task_size();
4048 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4049 // Having claimed the nth task in this space,
4050 // compute the chunk that it corresponds to:
4051 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
4052 aligned_start + (nth_task+1)*chunk_size);
4053 // Try and bump the global finger via a CAS;
4054 // note that we need to do the global finger bump
4055 // _before_ taking the intersection below, because
4056 // the task corresponding to that region will be
4057 // deemed done even if the used_region() expands
4058 // because of allocation -- as it almost certainly will
4059 // during start-up while the threads yield in the
4060 // closure below.
4061 HeapWord* finger = span.end();
4062 bump_global_finger(finger); // atomically
4063 // There are null tasks here corresponding to chunks
4064 // beyond the "top" address of the space.
4065 span = span.intersection(sp->used_region());
4066 if (!span.is_empty()) { // Non-null task
4067 HeapWord* prev_obj;
4068 assert(!span.contains(_restart_addr) || nth_task == 0,
4069 "Inconsistency");
4070 if (nth_task == 0) {
4071 // For the 0th task, we'll not need to compute a block_start.
4072 if (span.contains(_restart_addr)) {
4073 // In the case of a restart because of stack overflow,
4074 // we might additionally skip a chunk prefix.
4075 prev_obj = _restart_addr;
4076 } else {
4077 prev_obj = span.start();
4078 }
4079 } else {
4080 // We want to skip the first object because
4081 // the protocol is to scan any object in its entirety
4082 // that _starts_ in this span; a fortiori, any
4083 // object starting in an earlier span is scanned
4084 // as part of an earlier claimed task.
4085 // Below we use the "careful" version of block_start
4086 // so we do not try to navigate uninitialized objects.
4087 prev_obj = sp->block_start_careful(span.start());
4088 // Below we use a variant of block_size that uses the
4089 // Printezis bits to avoid waiting for allocated
4090 // objects to become initialized/parsable.
4091 while (prev_obj < span.start()) {
4092 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
4093 if (sz > 0) {
4094 prev_obj += sz;
4095 } else {
4096 // In this case we may end up doing a bit of redundant
4097 // scanning, but that appears unavoidable, short of
4098 // locking the free list locks; see bug 6324141.
4099 break;
4100 }
4101 }
4102 }
4103 if (prev_obj < span.end()) {
4104 MemRegion my_span = MemRegion(prev_obj, span.end());
4105 // Do the marking work within a non-empty span --
4106 // the last argument to the constructor indicates whether the
4107 // iteration should be incremental with periodic yields.
4108 Par_MarkFromRootsClosure cl(this, _collector, my_span,
4109 &_collector->_markBitMap,
4110 work_queue(i),
4111 &_collector->_markStack,
4112 _asynch);
4113 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
4114 } // else nothing to do for this task
4115 } // else nothing to do for this task
4116 }
4117 // We'd be tempted to assert here that since there are no
4118 // more tasks left to claim in this space, the global_finger
4119 // must exceed space->top() and a fortiori space->end(). However,
4120 // that would not quite be correct because the bumping of
4121 // global_finger occurs strictly after the claiming of a task,
4122 // so by the time we reach here the global finger may not yet
4123 // have been bumped up by the thread that claimed the last
4124 // task.
4125 pst->all_tasks_completed();
4126 }
4127
4128 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
4129 private:
4130 CMSCollector* _collector;
4131 CMSConcMarkingTask* _task;
4132 MemRegion _span;
4133 CMSBitMap* _bit_map;
4134 CMSMarkStack* _overflow_stack;
4135 OopTaskQueue* _work_queue;
4136 protected:
4137 DO_OOP_WORK_DEFN
4138 public:
4139 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
4140 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
4141 MetadataAwareOopClosure(collector->ref_processor()),
4142 _collector(collector),
4143 _task(task),
4144 _span(collector->_span),
4145 _work_queue(work_queue),
4146 _bit_map(bit_map),
4147 _overflow_stack(overflow_stack)
4148 { }
4149 virtual void do_oop(oop* p);
4150 virtual void do_oop(narrowOop* p);
4151
4152 void trim_queue(size_t max);
4153 void handle_stack_overflow(HeapWord* lost);
4154 void do_yield_check() {
4155 if (_task->should_yield()) {
4156 _task->yield();
4157 }
4158 }
4159 };
4160
4161 // Grey object scanning during work stealing phase --
4162 // the salient assumption here is that any references
4163 // that are in these stolen objects being scanned must
4164 // already have been initialized (else they would not have
4165 // been published), so we do not need to check for
4166 // uninitialized objects before pushing here.
4167 void Par_ConcMarkingClosure::do_oop(oop obj) {
4168 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
4169 HeapWord* addr = (HeapWord*)obj;
4170 // Check if oop points into the CMS generation
4171 // and is not marked
4172 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4173 // a white object ...
4174 // If we manage to "claim" the object, by being the
4175 // first thread to mark it, then we push it on our
4176 // marking stack
4177 if (_bit_map->par_mark(addr)) { // ... now grey
4178 // push on work queue (grey set)
4179 bool simulate_overflow = false;
4180 NOT_PRODUCT(
4181 if (CMSMarkStackOverflowALot &&
4182 _collector->simulate_overflow()) {
4183 // simulate a stack overflow
4184 simulate_overflow = true;
4185 }
4186 )
4187 if (simulate_overflow ||
4188 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4189 // stack overflow
4190 if (PrintCMSStatistics != 0) {
4191 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4192 SIZE_FORMAT, _overflow_stack->capacity());
4193 }
4194 // We cannot assert that the overflow stack is full because
4195 // it may have been emptied since.
4196 assert(simulate_overflow ||
4197 _work_queue->size() == _work_queue->max_elems(),
4198 "Else push should have succeeded");
4199 handle_stack_overflow(addr);
4200 }
4201 } // Else, some other thread got there first
4202 do_yield_check();
4203 }
4204 }
4205
4206 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4207 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4208
4209 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4210 while (_work_queue->size() > max) {
4211 oop new_oop;
4212 if (_work_queue->pop_local(new_oop)) {
4213 assert(new_oop->is_oop(), "Should be an oop");
4214 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4215 assert(_span.contains((HeapWord*)new_oop), "Not in span");
4216 new_oop->oop_iterate(this); // do_oop() above
4217 do_yield_check();
4218 }
4219 }
4220 }
4221
4222 // Upon stack overflow, we discard (part of) the stack,
4223 // remembering the least address amongst those discarded
4224 // in CMSCollector's _restart_address.
4225 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4226 // We need to do this under a mutex to prevent other
4227 // workers from interfering with the work done below.
4228 MutexLockerEx ml(_overflow_stack->par_lock(),
4229 Mutex::_no_safepoint_check_flag);
4230 // Remember the least grey address discarded
4231 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4232 _collector->lower_restart_addr(ra);
4233 _overflow_stack->reset(); // discard stack contents
4234 _overflow_stack->expand(); // expand the stack if possible
4235 }
4236
4237
4238 void CMSConcMarkingTask::do_work_steal(int i) {
4239 OopTaskQueue* work_q = work_queue(i);
4240 oop obj_to_scan;
4241 CMSBitMap* bm = &(_collector->_markBitMap);
4242 CMSMarkStack* ovflw = &(_collector->_markStack);
4243 int* seed = _collector->hash_seed(i);
4244 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
4245 while (true) {
4246 cl.trim_queue(0);
4247 assert(work_q->size() == 0, "Should have been emptied above");
4248 if (get_work_from_overflow_stack(ovflw, work_q)) {
4249 // Can't assert below because the work obtained from the
4250 // overflow stack may already have been stolen from us.
4251 // assert(work_q->size() > 0, "Work from overflow stack");
4252 continue;
4253 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4254 assert(obj_to_scan->is_oop(), "Should be an oop");
4255 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4256 obj_to_scan->oop_iterate(&cl);
4257 } else if (terminator()->offer_termination(&_term_term)) {
4258 assert(work_q->size() == 0, "Impossible!");
4259 break;
4260 } else if (yielding() || should_yield()) {
4261 yield();
4262 }
4263 }
4264 }
4265
4266 // This is run by the CMS (coordinator) thread.
4267 void CMSConcMarkingTask::coordinator_yield() {
4268 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4269 "CMS thread should hold CMS token");
4270 // First give up the locks, then yield, then re-lock
4271 // We should probably use a constructor/destructor idiom to
4272 // do this unlock/lock or modify the MutexUnlocker class to
4273 // serve our purpose. XXX
4274 assert_lock_strong(_bit_map_lock);
4275 _bit_map_lock->unlock();
4276 ConcurrentMarkSweepThread::desynchronize(true);
4277 ConcurrentMarkSweepThread::acknowledge_yield_request();
4278 _collector->stopTimer();
4279 if (PrintCMSStatistics != 0) {
4280 _collector->incrementYields();
4281 }
4282 _collector->icms_wait();
4283
4284 // It is possible for whichever thread initiated the yield request
4285 // not to get a chance to wake up and take the bitmap lock between
4286 // this thread releasing it and reacquiring it. So, while the
4287 // should_yield() flag is on, let's sleep for a bit to give the
4288 // other thread a chance to wake up. The limit imposed on the number
4289 // of iterations is defensive, to avoid any unforseen circumstances
4290 // putting us into an infinite loop. Since it's always been this
4291 // (coordinator_yield()) method that was observed to cause the
4292 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4293 // which is by default non-zero. For the other seven methods that
4294 // also perform the yield operation, as are using a different
4295 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4296 // can enable the sleeping for those methods too, if necessary.
4297 // See 6442774.
4298 //
4299 // We really need to reconsider the synchronization between the GC
4300 // thread and the yield-requesting threads in the future and we
4301 // should really use wait/notify, which is the recommended
4302 // way of doing this type of interaction. Additionally, we should
4303 // consolidate the eight methods that do the yield operation and they
4304 // are almost identical into one for better maintainability and
4305 // readability. See 6445193.
4306 //
4307 // Tony 2006.06.29
4308 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4309 ConcurrentMarkSweepThread::should_yield() &&
4310 !CMSCollector::foregroundGCIsActive(); ++i) {
4311 os::sleep(Thread::current(), 1, false);
4312 ConcurrentMarkSweepThread::acknowledge_yield_request();
4313 }
4314
4315 ConcurrentMarkSweepThread::synchronize(true);
4316 _bit_map_lock->lock_without_safepoint_check();
4317 _collector->startTimer();
4318 }
4319
4320 bool CMSCollector::do_marking_mt(bool asynch) {
4321 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4322 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
4323 conc_workers()->total_workers(),
4324 conc_workers()->active_workers(),
4325 Threads::number_of_non_daemon_threads());
4326 conc_workers()->set_active_workers(num_workers);
4327
4328 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4329
4330 CMSConcMarkingTask tsk(this,
4331 cms_space,
4332 asynch,
4333 conc_workers(),
4334 task_queues());
4335
4336 // Since the actual number of workers we get may be different
4337 // from the number we requested above, do we need to do anything different
4338 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4339 // class?? XXX
4340 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4341
4342 // Refs discovery is already non-atomic.
4343 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4344 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
4345 conc_workers()->start_task(&tsk);
4346 while (tsk.yielded()) {
4347 tsk.coordinator_yield();
4348 conc_workers()->continue_task(&tsk);
4349 }
4350 // If the task was aborted, _restart_addr will be non-NULL
4351 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4352 while (_restart_addr != NULL) {
4353 // XXX For now we do not make use of ABORTED state and have not
4354 // yet implemented the right abort semantics (even in the original
4355 // single-threaded CMS case). That needs some more investigation
4356 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4357 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4358 // If _restart_addr is non-NULL, a marking stack overflow
4359 // occurred; we need to do a fresh marking iteration from the
4360 // indicated restart address.
4361 if (_foregroundGCIsActive && asynch) {
4362 // We may be running into repeated stack overflows, having
4363 // reached the limit of the stack size, while making very
4364 // slow forward progress. It may be best to bail out and
4365 // let the foreground collector do its job.
4366 // Clear _restart_addr, so that foreground GC
4367 // works from scratch. This avoids the headache of
4368 // a "rescan" which would otherwise be needed because
4369 // of the dirty mod union table & card table.
4370 _restart_addr = NULL;
4371 return false;
4372 }
4373 // Adjust the task to restart from _restart_addr
4374 tsk.reset(_restart_addr);
4375 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4376 _restart_addr);
4377 _restart_addr = NULL;
4378 // Get the workers going again
4379 conc_workers()->start_task(&tsk);
4380 while (tsk.yielded()) {
4381 tsk.coordinator_yield();
4382 conc_workers()->continue_task(&tsk);
4383 }
4384 }
4385 assert(tsk.completed(), "Inconsistency");
4386 assert(tsk.result() == true, "Inconsistency");
4387 return true;
4388 }
4389
4390 bool CMSCollector::do_marking_st(bool asynch) {
4391 ResourceMark rm;
4392 HandleMark hm;
4393
4394 // Temporarily make refs discovery single threaded (non-MT)
4395 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
4396 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4397 &_markStack, CMSYield && asynch);
4398 // the last argument to iterate indicates whether the iteration
4399 // should be incremental with periodic yields.
4400 _markBitMap.iterate(&markFromRootsClosure);
4401 // If _restart_addr is non-NULL, a marking stack overflow
4402 // occurred; we need to do a fresh iteration from the
4403 // indicated restart address.
4404 while (_restart_addr != NULL) {
4405 if (_foregroundGCIsActive && asynch) {
4406 // We may be running into repeated stack overflows, having
4407 // reached the limit of the stack size, while making very
4408 // slow forward progress. It may be best to bail out and
4409 // let the foreground collector do its job.
4410 // Clear _restart_addr, so that foreground GC
4411 // works from scratch. This avoids the headache of
4412 // a "rescan" which would otherwise be needed because
4413 // of the dirty mod union table & card table.
4414 _restart_addr = NULL;
4415 return false; // indicating failure to complete marking
4416 }
4417 // Deal with stack overflow:
4418 // we restart marking from _restart_addr
4419 HeapWord* ra = _restart_addr;
4420 markFromRootsClosure.reset(ra);
4421 _restart_addr = NULL;
4422 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4423 }
4424 return true;
4425 }
4426
4427 void CMSCollector::preclean() {
4428 check_correct_thread_executing();
4429 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4430 verify_work_stacks_empty();
4431 verify_overflow_empty();
4432 _abort_preclean = false;
4433 if (CMSPrecleaningEnabled) {
4434 if (!CMSEdenChunksRecordAlways) {
4435 _eden_chunk_index = 0;
4436 }
4437 size_t used = get_eden_used();
4438 size_t capacity = get_eden_capacity();
4439 // Don't start sampling unless we will get sufficiently
4440 // many samples.
4441 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4442 * CMSScheduleRemarkEdenPenetration)) {
4443 _start_sampling = true;
4444 } else {
4445 _start_sampling = false;
4446 }
4447 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4448 CMSPhaseAccounting pa(this, "preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
4449 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4450 }
4451 CMSTokenSync x(true); // is cms thread
4452 if (CMSPrecleaningEnabled) {
4453 sample_eden();
4454 _collectorState = AbortablePreclean;
4455 } else {
4456 _collectorState = FinalMarking;
4457 }
4458 verify_work_stacks_empty();
4459 verify_overflow_empty();
4460 }
4461
4462 // Try and schedule the remark such that young gen
4463 // occupancy is CMSScheduleRemarkEdenPenetration %.
4464 void CMSCollector::abortable_preclean() {
4465 check_correct_thread_executing();
4466 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4467 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4468
4469 // If Eden's current occupancy is below this threshold,
4470 // immediately schedule the remark; else preclean
4471 // past the next scavenge in an effort to
4472 // schedule the pause as described above. By choosing
4473 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4474 // we will never do an actual abortable preclean cycle.
4475 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4476 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4477 CMSPhaseAccounting pa(this, "abortable-preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
4478 // We need more smarts in the abortable preclean
4479 // loop below to deal with cases where allocation
4480 // in young gen is very very slow, and our precleaning
4481 // is running a losing race against a horde of
4482 // mutators intent on flooding us with CMS updates
4483 // (dirty cards).
4484 // One, admittedly dumb, strategy is to give up
4485 // after a certain number of abortable precleaning loops
4486 // or after a certain maximum time. We want to make
4487 // this smarter in the next iteration.
4488 // XXX FIX ME!!! YSR
4489 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4490 while (!(should_abort_preclean() ||
4491 ConcurrentMarkSweepThread::should_terminate())) {
4492 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4493 cumworkdone += workdone;
4494 loops++;
4495 // Voluntarily terminate abortable preclean phase if we have
4496 // been at it for too long.
4497 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4498 loops >= CMSMaxAbortablePrecleanLoops) {
4499 if (PrintGCDetails) {
4500 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4501 }
4502 break;
4503 }
4504 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4505 if (PrintGCDetails) {
4506 gclog_or_tty->print(" CMS: abort preclean due to time ");
4507 }
4508 break;
4509 }
4510 // If we are doing little work each iteration, we should
4511 // take a short break.
4512 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4513 // Sleep for some time, waiting for work to accumulate
4514 stopTimer();
4515 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4516 startTimer();
4517 waited++;
4518 }
4519 }
4520 if (PrintCMSStatistics > 0) {
4521 gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
4522 loops, waited, cumworkdone);
4523 }
4524 }
4525 CMSTokenSync x(true); // is cms thread
4526 if (_collectorState != Idling) {
4527 assert(_collectorState == AbortablePreclean,
4528 "Spontaneous state transition?");
4529 _collectorState = FinalMarking;
4530 } // Else, a foreground collection completed this CMS cycle.
4531 return;
4532 }
4533
4534 // Respond to an Eden sampling opportunity
4535 void CMSCollector::sample_eden() {
4536 // Make sure a young gc cannot sneak in between our
4537 // reading and recording of a sample.
4538 assert(Thread::current()->is_ConcurrentGC_thread(),
4539 "Only the cms thread may collect Eden samples");
4540 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4541 "Should collect samples while holding CMS token");
4542 if (!_start_sampling) {
4543 return;
4544 }
4545 // When CMSEdenChunksRecordAlways is true, the eden chunk array
4546 // is populated by the young generation.
4547 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
4548 if (_eden_chunk_index < _eden_chunk_capacity) {
4549 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4550 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4551 "Unexpected state of Eden");
4552 // We'd like to check that what we just sampled is an oop-start address;
4553 // however, we cannot do that here since the object may not yet have been
4554 // initialized. So we'll instead do the check when we _use_ this sample
4555 // later.
4556 if (_eden_chunk_index == 0 ||
4557 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4558 _eden_chunk_array[_eden_chunk_index-1])
4559 >= CMSSamplingGrain)) {
4560 _eden_chunk_index++; // commit sample
4561 }
4562 }
4563 }
4564 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4565 size_t used = get_eden_used();
4566 size_t capacity = get_eden_capacity();
4567 assert(used <= capacity, "Unexpected state of Eden");
4568 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4569 _abort_preclean = true;
4570 }
4571 }
4572 }
4573
4574
4575 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4576 assert(_collectorState == Precleaning ||
4577 _collectorState == AbortablePreclean, "incorrect state");
4578 ResourceMark rm;
4579 HandleMark hm;
4580
4581 // Precleaning is currently not MT but the reference processor
4582 // may be set for MT. Disable it temporarily here.
4583 ReferenceProcessor* rp = ref_processor();
4584 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4585
4586 // Do one pass of scrubbing the discovered reference lists
4587 // to remove any reference objects with strongly-reachable
4588 // referents.
4589 if (clean_refs) {
4590 CMSPrecleanRefsYieldClosure yield_cl(this);
4591 assert(rp->span().equals(_span), "Spans should be equal");
4592 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4593 &_markStack, true /* preclean */);
4594 CMSDrainMarkingStackClosure complete_trace(this,
4595 _span, &_markBitMap, &_markStack,
4596 &keep_alive, true /* preclean */);
4597
4598 // We don't want this step to interfere with a young
4599 // collection because we don't want to take CPU
4600 // or memory bandwidth away from the young GC threads
4601 // (which may be as many as there are CPUs).
4602 // Note that we don't need to protect ourselves from
4603 // interference with mutators because they can't
4604 // manipulate the discovered reference lists nor affect
4605 // the computed reachability of the referents, the
4606 // only properties manipulated by the precleaning
4607 // of these reference lists.
4608 stopTimer();
4609 CMSTokenSyncWithLocks x(true /* is cms thread */,
4610 bitMapLock());
4611 startTimer();
4612 sample_eden();
4613
4614 // The following will yield to allow foreground
4615 // collection to proceed promptly. XXX YSR:
4616 // The code in this method may need further
4617 // tweaking for better performance and some restructuring
4618 // for cleaner interfaces.
4619 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
4620 rp->preclean_discovered_references(
4621 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
4622 gc_timer, _gc_tracer_cm->gc_id());
4623 }
4624
4625 if (clean_survivor) { // preclean the active survivor space(s)
4626 assert(_young_gen->kind() == Generation::DefNew ||
4627 _young_gen->kind() == Generation::ParNew,
4628 "incorrect type for cast");
4629 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4630 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4631 &_markBitMap, &_modUnionTable,
4632 &_markStack, true /* precleaning phase */);
4633 stopTimer();
4634 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4635 bitMapLock());
4636 startTimer();
4637 unsigned int before_count =
4638 GenCollectedHeap::heap()->total_collections();
4639 SurvivorSpacePrecleanClosure
4640 sss_cl(this, _span, &_markBitMap, &_markStack,
4641 &pam_cl, before_count, CMSYield);
4642 dng->from()->object_iterate_careful(&sss_cl);
4643 dng->to()->object_iterate_careful(&sss_cl);
4644 }
4645 MarkRefsIntoAndScanClosure
4646 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4647 &_markStack, this, CMSYield,
4648 true /* precleaning phase */);
4649 // CAUTION: The following closure has persistent state that may need to
4650 // be reset upon a decrease in the sequence of addresses it
4651 // processes.
4652 ScanMarkedObjectsAgainCarefullyClosure
4653 smoac_cl(this, _span,
4654 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
4655
4656 // Preclean dirty cards in ModUnionTable and CardTable using
4657 // appropriate convergence criterion;
4658 // repeat CMSPrecleanIter times unless we find that
4659 // we are losing.
4660 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4661 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4662 "Bad convergence multiplier");
4663 assert(CMSPrecleanThreshold >= 100,
4664 "Unreasonably low CMSPrecleanThreshold");
4665
4666 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4667 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4668 numIter < CMSPrecleanIter;
4669 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4670 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4671 if (Verbose && PrintGCDetails) {
4672 gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
4673 }
4674 // Either there are very few dirty cards, so re-mark
4675 // pause will be small anyway, or our pre-cleaning isn't
4676 // that much faster than the rate at which cards are being
4677 // dirtied, so we might as well stop and re-mark since
4678 // precleaning won't improve our re-mark time by much.
4679 if (curNumCards <= CMSPrecleanThreshold ||
4680 (numIter > 0 &&
4681 (curNumCards * CMSPrecleanDenominator >
4682 lastNumCards * CMSPrecleanNumerator))) {
4683 numIter++;
4684 cumNumCards += curNumCards;
4685 break;
4686 }
4687 }
4688
4689 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4690
4691 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4692 cumNumCards += curNumCards;
4693 if (PrintGCDetails && PrintCMSStatistics != 0) {
4694 gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
4695 curNumCards, cumNumCards, numIter);
4696 }
4697 return cumNumCards; // as a measure of useful work done
4698 }
4699
4700 // PRECLEANING NOTES:
4701 // Precleaning involves:
4702 // . reading the bits of the modUnionTable and clearing the set bits.
4703 // . For the cards corresponding to the set bits, we scan the
4704 // objects on those cards. This means we need the free_list_lock
4705 // so that we can safely iterate over the CMS space when scanning
4706 // for oops.
4707 // . When we scan the objects, we'll be both reading and setting
4708 // marks in the marking bit map, so we'll need the marking bit map.
4709 // . For protecting _collector_state transitions, we take the CGC_lock.
4710 // Note that any races in the reading of of card table entries by the
4711 // CMS thread on the one hand and the clearing of those entries by the
4712 // VM thread or the setting of those entries by the mutator threads on the
4713 // other are quite benign. However, for efficiency it makes sense to keep
4714 // the VM thread from racing with the CMS thread while the latter is
4715 // dirty card info to the modUnionTable. We therefore also use the
4716 // CGC_lock to protect the reading of the card table and the mod union
4717 // table by the CM thread.
4718 // . We run concurrently with mutator updates, so scanning
4719 // needs to be done carefully -- we should not try to scan
4720 // potentially uninitialized objects.
4721 //
4722 // Locking strategy: While holding the CGC_lock, we scan over and
4723 // reset a maximal dirty range of the mod union / card tables, then lock
4724 // the free_list_lock and bitmap lock to do a full marking, then
4725 // release these locks; and repeat the cycle. This allows for a
4726 // certain amount of fairness in the sharing of these locks between
4727 // the CMS collector on the one hand, and the VM thread and the
4728 // mutators on the other.
4729
4730 // NOTE: preclean_mod_union_table() and preclean_card_table()
4731 // further below are largely identical; if you need to modify
4732 // one of these methods, please check the other method too.
4733
4734 size_t CMSCollector::preclean_mod_union_table(
4735 ConcurrentMarkSweepGeneration* gen,
4736 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4737 verify_work_stacks_empty();
4738 verify_overflow_empty();
4739
4740 // strategy: starting with the first card, accumulate contiguous
4741 // ranges of dirty cards; clear these cards, then scan the region
4742 // covered by these cards.
4743
4744 // Since all of the MUT is committed ahead, we can just use
4745 // that, in case the generations expand while we are precleaning.
4746 // It might also be fine to just use the committed part of the
4747 // generation, but we might potentially miss cards when the
4748 // generation is rapidly expanding while we are in the midst
4749 // of precleaning.
4750 HeapWord* startAddr = gen->reserved().start();
4751 HeapWord* endAddr = gen->reserved().end();
4752
4753 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4754
4755 size_t numDirtyCards, cumNumDirtyCards;
4756 HeapWord *nextAddr, *lastAddr;
4757 for (cumNumDirtyCards = numDirtyCards = 0,
4758 nextAddr = lastAddr = startAddr;
4759 nextAddr < endAddr;
4760 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4761
4762 ResourceMark rm;
4763 HandleMark hm;
4764
4765 MemRegion dirtyRegion;
4766 {
4767 stopTimer();
4768 // Potential yield point
4769 CMSTokenSync ts(true);
4770 startTimer();
4771 sample_eden();
4772 // Get dirty region starting at nextOffset (inclusive),
4773 // simultaneously clearing it.
4774 dirtyRegion =
4775 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4776 assert(dirtyRegion.start() >= nextAddr,
4777 "returned region inconsistent?");
4778 }
4779 // Remember where the next search should begin.
4780 // The returned region (if non-empty) is a right open interval,
4781 // so lastOffset is obtained from the right end of that
4782 // interval.
4783 lastAddr = dirtyRegion.end();
4784 // Should do something more transparent and less hacky XXX
4785 numDirtyCards =
4786 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4787
4788 // We'll scan the cards in the dirty region (with periodic
4789 // yields for foreground GC as needed).
4790 if (!dirtyRegion.is_empty()) {
4791 assert(numDirtyCards > 0, "consistency check");
4792 HeapWord* stop_point = NULL;
4793 stopTimer();
4794 // Potential yield point
4795 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4796 bitMapLock());
4797 startTimer();
4798 {
4799 verify_work_stacks_empty();
4800 verify_overflow_empty();
4801 sample_eden();
4802 stop_point =
4803 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4804 }
4805 if (stop_point != NULL) {
4806 // The careful iteration stopped early either because it found an
4807 // uninitialized object, or because we were in the midst of an
4808 // "abortable preclean", which should now be aborted. Redirty
4809 // the bits corresponding to the partially-scanned or unscanned
4810 // cards. We'll either restart at the next block boundary or
4811 // abort the preclean.
4812 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4813 "Should only be AbortablePreclean.");
4814 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4815 if (should_abort_preclean()) {
4816 break; // out of preclean loop
4817 } else {
4818 // Compute the next address at which preclean should pick up;
4819 // might need bitMapLock in order to read P-bits.
4820 lastAddr = next_card_start_after_block(stop_point);
4821 }
4822 }
4823 } else {
4824 assert(lastAddr == endAddr, "consistency check");
4825 assert(numDirtyCards == 0, "consistency check");
4826 break;
4827 }
4828 }
4829 verify_work_stacks_empty();
4830 verify_overflow_empty();
4831 return cumNumDirtyCards;
4832 }
4833
4834 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4835 // below are largely identical; if you need to modify
4836 // one of these methods, please check the other method too.
4837
4838 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4839 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4840 // strategy: it's similar to precleamModUnionTable above, in that
4841 // we accumulate contiguous ranges of dirty cards, mark these cards
4842 // precleaned, then scan the region covered by these cards.
4843 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4844 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4845
4846 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4847
4848 size_t numDirtyCards, cumNumDirtyCards;
4849 HeapWord *lastAddr, *nextAddr;
4850
4851 for (cumNumDirtyCards = numDirtyCards = 0,
4852 nextAddr = lastAddr = startAddr;
4853 nextAddr < endAddr;
4854 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4855
4856 ResourceMark rm;
4857 HandleMark hm;
4858
4859 MemRegion dirtyRegion;
4860 {
4861 // See comments in "Precleaning notes" above on why we
4862 // do this locking. XXX Could the locking overheads be
4863 // too high when dirty cards are sparse? [I don't think so.]
4864 stopTimer();
4865 CMSTokenSync x(true); // is cms thread
4866 startTimer();
4867 sample_eden();
4868 // Get and clear dirty region from card table
4869 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4870 MemRegion(nextAddr, endAddr),
4871 true,
4872 CardTableModRefBS::precleaned_card_val());
4873
4874 assert(dirtyRegion.start() >= nextAddr,
4875 "returned region inconsistent?");
4876 }
4877 lastAddr = dirtyRegion.end();
4878 numDirtyCards =
4879 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4880
4881 if (!dirtyRegion.is_empty()) {
4882 stopTimer();
4883 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4884 startTimer();
4885 sample_eden();
4886 verify_work_stacks_empty();
4887 verify_overflow_empty();
4888 HeapWord* stop_point =
4889 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4890 if (stop_point != NULL) {
4891 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4892 "Should only be AbortablePreclean.");
4893 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4894 if (should_abort_preclean()) {
4895 break; // out of preclean loop
4896 } else {
4897 // Compute the next address at which preclean should pick up.
4898 lastAddr = next_card_start_after_block(stop_point);
4899 }
4900 }
4901 } else {
4902 break;
4903 }
4904 }
4905 verify_work_stacks_empty();
4906 verify_overflow_empty();
4907 return cumNumDirtyCards;
4908 }
4909
4910 class PrecleanKlassClosure : public KlassClosure {
4911 KlassToOopClosure _cm_klass_closure;
4912 public:
4913 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4914 void do_klass(Klass* k) {
4915 if (k->has_accumulated_modified_oops()) {
4916 k->clear_accumulated_modified_oops();
4917
4918 _cm_klass_closure.do_klass(k);
4919 }
4920 }
4921 };
4922
4923 // The freelist lock is needed to prevent asserts, is it really needed?
4924 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4925
4926 cl->set_freelistLock(freelistLock);
4927
4928 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4929
4930 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4931 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4932 PrecleanKlassClosure preclean_klass_closure(cl);
4933 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4934
4935 verify_work_stacks_empty();
4936 verify_overflow_empty();
4937 }
4938
4939 void CMSCollector::checkpointRootsFinal(bool asynch,
4940 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4941 assert(_collectorState == FinalMarking, "incorrect state transition?");
4942 check_correct_thread_executing();
4943 // world is stopped at this checkpoint
4944 assert(SafepointSynchronize::is_at_safepoint(),
4945 "world should be stopped");
4946 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4947
4948 verify_work_stacks_empty();
4949 verify_overflow_empty();
4950
4951 SpecializationStats::clear();
4952 if (PrintGCDetails) {
4953 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4954 _young_gen->used() / K,
4955 _young_gen->capacity() / K);
4956 }
4957 if (asynch) {
4958 if (CMSScavengeBeforeRemark) {
4959 GenCollectedHeap* gch = GenCollectedHeap::heap();
4960 // Temporarily set flag to false, GCH->do_collection will
4961 // expect it to be false and set to true
4962 FlagSetting fl(gch->_is_gc_active, false);
4963 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4964 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4965 int level = _cmsGen->level() - 1;
4966 if (level >= 0) {
4967 gch->do_collection(true, // full (i.e. force, see below)
4968 false, // !clear_all_soft_refs
4969 0, // size
4970 false, // is_tlab
4971 level // max_level
4972 );
4973 }
4974 }
4975 FreelistLocker x(this);
4976 MutexLockerEx y(bitMapLock(),
4977 Mutex::_no_safepoint_check_flag);
4978 assert(!init_mark_was_synchronous, "but that's impossible!");
4979 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4980 } else {
4981 // already have all the locks
4982 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4983 init_mark_was_synchronous);
4984 }
4985 verify_work_stacks_empty();
4986 verify_overflow_empty();
4987 SpecializationStats::print();
4988 }
4989
4990 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4991 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4992
4993 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4994
4995 assert(haveFreelistLocks(), "must have free list locks");
4996 assert_lock_strong(bitMapLock());
4997
4998 ResourceMark rm;
4999 HandleMark hm;
5000
5001 GenCollectedHeap* gch = GenCollectedHeap::heap();
5002
5003 if (should_unload_classes()) {
5004 CodeCache::gc_prologue();
5005 }
5006 assert(haveFreelistLocks(), "must have free list locks");
5007 assert_lock_strong(bitMapLock());
5008
5009 if (!init_mark_was_synchronous) {
5010 // We might assume that we need not fill TLAB's when
5011 // CMSScavengeBeforeRemark is set, because we may have just done
5012 // a scavenge which would have filled all TLAB's -- and besides
5013 // Eden would be empty. This however may not always be the case --
5014 // for instance although we asked for a scavenge, it may not have
5015 // happened because of a JNI critical section. We probably need
5016 // a policy for deciding whether we can in that case wait until
5017 // the critical section releases and then do the remark following
5018 // the scavenge, and skip it here. In the absence of that policy,
5019 // or of an indication of whether the scavenge did indeed occur,
5020 // we cannot rely on TLAB's having been filled and must do
5021 // so here just in case a scavenge did not happen.
5022 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
5023 // Update the saved marks which may affect the root scans.
5024 gch->save_marks();
5025
5026 if (CMSPrintEdenSurvivorChunks) {
5027 print_eden_and_survivor_chunk_arrays();
5028 }
5029
5030 {
5031 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
5032
5033 // Note on the role of the mod union table:
5034 // Since the marker in "markFromRoots" marks concurrently with
5035 // mutators, it is possible for some reachable objects not to have been
5036 // scanned. For instance, an only reference to an object A was
5037 // placed in object B after the marker scanned B. Unless B is rescanned,
5038 // A would be collected. Such updates to references in marked objects
5039 // are detected via the mod union table which is the set of all cards
5040 // dirtied since the first checkpoint in this GC cycle and prior to
5041 // the most recent young generation GC, minus those cleaned up by the
5042 // concurrent precleaning.
5043 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
5044 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5045 do_remark_parallel();
5046 } else {
5047 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
5048 _gc_timer_cm, _gc_tracer_cm->gc_id());
5049 do_remark_non_parallel();
5050 }
5051 }
5052 } else {
5053 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
5054 // The initial mark was stop-world, so there's no rescanning to
5055 // do; go straight on to the next step below.
5056 }
5057 verify_work_stacks_empty();
5058 verify_overflow_empty();
5059
5060 {
5061 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
5062 refProcessingWork(asynch, clear_all_soft_refs);
5063 }
5064 verify_work_stacks_empty();
5065 verify_overflow_empty();
5066
5067 if (should_unload_classes()) {
5068 CodeCache::gc_epilogue();
5069 }
5070 JvmtiExport::gc_epilogue();
5071
5072 // If we encountered any (marking stack / work queue) overflow
5073 // events during the current CMS cycle, take appropriate
5074 // remedial measures, where possible, so as to try and avoid
5075 // recurrence of that condition.
5076 assert(_markStack.isEmpty(), "No grey objects");
5077 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
5078 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
5079 if (ser_ovflw > 0) {
5080 if (PrintCMSStatistics != 0) {
5081 gclog_or_tty->print_cr("Marking stack overflow (benign) "
5082 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
5083 ", kac_preclean="SIZE_FORMAT")",
5084 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
5085 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
5086 }
5087 _markStack.expand();
5088 _ser_pmc_remark_ovflw = 0;
5089 _ser_pmc_preclean_ovflw = 0;
5090 _ser_kac_preclean_ovflw = 0;
5091 _ser_kac_ovflw = 0;
5092 }
5093 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
5094 if (PrintCMSStatistics != 0) {
5095 gclog_or_tty->print_cr("Work queue overflow (benign) "
5096 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
5097 _par_pmc_remark_ovflw, _par_kac_ovflw);
5098 }
5099 _par_pmc_remark_ovflw = 0;
5100 _par_kac_ovflw = 0;
5101 }
5102 if (PrintCMSStatistics != 0) {
5103 if (_markStack._hit_limit > 0) {
5104 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
5105 _markStack._hit_limit);
5106 }
5107 if (_markStack._failed_double > 0) {
5108 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
5109 " current capacity "SIZE_FORMAT,
5110 _markStack._failed_double,
5111 _markStack.capacity());
5112 }
5113 }
5114 _markStack._hit_limit = 0;
5115 _markStack._failed_double = 0;
5116
5117 if ((VerifyAfterGC || VerifyDuringGC) &&
5118 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5119 verify_after_remark();
5120 }
5121
5122 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
5123
5124 // Change under the freelistLocks.
5125 _collectorState = Sweeping;
5126 // Call isAllClear() under bitMapLock
5127 assert(_modUnionTable.isAllClear(),
5128 "Should be clear by end of the final marking");
5129 assert(_ct->klass_rem_set()->mod_union_is_clear(),
5130 "Should be clear by end of the final marking");
5131 }
5132
5133 void CMSParInitialMarkTask::work(uint worker_id) {
5134 elapsedTimer _timer;
5135 ResourceMark rm;
5136 HandleMark hm;
5137
5138 // ---------- scan from roots --------------
5139 _timer.start();
5140 GenCollectedHeap* gch = GenCollectedHeap::heap();
5141 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
5142
5143 // ---------- young gen roots --------------
5144 {
5145 work_on_young_gen_roots(worker_id, &par_mri_cl);
5146 _timer.stop();
5147 if (PrintCMSStatistics != 0) {
5148 gclog_or_tty->print_cr(
5149 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
5150 worker_id, _timer.seconds());
5151 }
5152 }
5153
5154 // ---------- remaining roots --------------
5155 _timer.reset();
5156 _timer.start();
5157
5158 CLDToOopClosure cld_closure(&par_mri_cl, true);
5159
5160 gch->gen_process_roots(_collector->_cmsGen->level(),
5161 false, // yg was scanned above
5162 false, // this is parallel code
5163 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5164 _collector->should_unload_classes(),
5165 &par_mri_cl,
5166 NULL,
5167 &cld_closure);
5168 assert(_collector->should_unload_classes()
5169 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5170 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5171 _timer.stop();
5172 if (PrintCMSStatistics != 0) {
5173 gclog_or_tty->print_cr(
5174 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
5175 worker_id, _timer.seconds());
5176 }
5177 }
5178
5179 // Parallel remark task
5180 class CMSParRemarkTask: public CMSParMarkTask {
5181 CompactibleFreeListSpace* _cms_space;
5182
5183 // The per-thread work queues, available here for stealing.
5184 OopTaskQueueSet* _task_queues;
5185 ParallelTaskTerminator _term;
5186
5187 public:
5188 // A value of 0 passed to n_workers will cause the number of
5189 // workers to be taken from the active workers in the work gang.
5190 CMSParRemarkTask(CMSCollector* collector,
5191 CompactibleFreeListSpace* cms_space,
5192 int n_workers, FlexibleWorkGang* workers,
5193 OopTaskQueueSet* task_queues):
5194 CMSParMarkTask("Rescan roots and grey objects in parallel",
5195 collector, n_workers),
5196 _cms_space(cms_space),
5197 _task_queues(task_queues),
5198 _term(n_workers, task_queues) { }
5199
5200 OopTaskQueueSet* task_queues() { return _task_queues; }
5201
5202 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5203
5204 ParallelTaskTerminator* terminator() { return &_term; }
5205 int n_workers() { return _n_workers; }
5206
5207 void work(uint worker_id);
5208
5209 private:
5210 // ... of dirty cards in old space
5211 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
5212 Par_MarkRefsIntoAndScanClosure* cl);
5213
5214 // ... work stealing for the above
5215 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
5216 };
5217
5218 class RemarkKlassClosure : public KlassClosure {
5219 KlassToOopClosure _cm_klass_closure;
5220 public:
5221 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
5222 void do_klass(Klass* k) {
5223 // Check if we have modified any oops in the Klass during the concurrent marking.
5224 if (k->has_accumulated_modified_oops()) {
5225 k->clear_accumulated_modified_oops();
5226
5227 // We could have transfered the current modified marks to the accumulated marks,
5228 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
5229 } else if (k->has_modified_oops()) {
5230 // Don't clear anything, this info is needed by the next young collection.
5231 } else {
5232 // No modified oops in the Klass.
5233 return;
5234 }
5235
5236 // The klass has modified fields, need to scan the klass.
5237 _cm_klass_closure.do_klass(k);
5238 }
5239 };
5240
5241 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
5242 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5243 EdenSpace* eden_space = dng->eden();
5244 ContiguousSpace* from_space = dng->from();
5245 ContiguousSpace* to_space = dng->to();
5246
5247 HeapWord** eca = _collector->_eden_chunk_array;
5248 size_t ect = _collector->_eden_chunk_index;
5249 HeapWord** sca = _collector->_survivor_chunk_array;
5250 size_t sct = _collector->_survivor_chunk_index;
5251
5252 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5253 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5254
5255 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
5256 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
5257 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
5258 }
5259
5260 // work_queue(i) is passed to the closure
5261 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
5262 // also is passed to do_dirty_card_rescan_tasks() and to
5263 // do_work_steal() to select the i-th task_queue.
5264
5265 void CMSParRemarkTask::work(uint worker_id) {
5266 elapsedTimer _timer;
5267 ResourceMark rm;
5268 HandleMark hm;
5269
5270 // ---------- rescan from roots --------------
5271 _timer.start();
5272 GenCollectedHeap* gch = GenCollectedHeap::heap();
5273 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5274 _collector->_span, _collector->ref_processor(),
5275 &(_collector->_markBitMap),
5276 work_queue(worker_id));
5277
5278 // Rescan young gen roots first since these are likely
5279 // coarsely partitioned and may, on that account, constitute
5280 // the critical path; thus, it's best to start off that
5281 // work first.
5282 // ---------- young gen roots --------------
5283 {
5284 work_on_young_gen_roots(worker_id, &par_mrias_cl);
5285 _timer.stop();
5286 if (PrintCMSStatistics != 0) {
5287 gclog_or_tty->print_cr(
5288 "Finished young gen rescan work in %dth thread: %3.3f sec",
5289 worker_id, _timer.seconds());
5290 }
5291 }
5292
5293 // ---------- remaining roots --------------
5294 _timer.reset();
5295 _timer.start();
5296 gch->gen_process_roots(_collector->_cmsGen->level(),
5297 false, // yg was scanned above
5298 false, // this is parallel code
5299 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5300 _collector->should_unload_classes(),
5301 &par_mrias_cl,
5302 NULL,
5303 NULL); // The dirty klasses will be handled below
5304
5305 assert(_collector->should_unload_classes()
5306 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5307 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5308 _timer.stop();
5309 if (PrintCMSStatistics != 0) {
5310 gclog_or_tty->print_cr(
5311 "Finished remaining root rescan work in %dth thread: %3.3f sec",
5312 worker_id, _timer.seconds());
5313 }
5314
5315 // ---------- unhandled CLD scanning ----------
5316 if (worker_id == 0) { // Single threaded at the moment.
5317 _timer.reset();
5318 _timer.start();
5319
5320 // Scan all new class loader data objects and new dependencies that were
5321 // introduced during concurrent marking.
5322 ResourceMark rm;
5323 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5324 for (int i = 0; i < array->length(); i++) {
5325 par_mrias_cl.do_class_loader_data(array->at(i));
5326 }
5327
5328 // We don't need to keep track of new CLDs anymore.
5329 ClassLoaderDataGraph::remember_new_clds(false);
5330
5331 _timer.stop();
5332 if (PrintCMSStatistics != 0) {
5333 gclog_or_tty->print_cr(
5334 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
5335 worker_id, _timer.seconds());
5336 }
5337 }
5338
5339 // ---------- dirty klass scanning ----------
5340 if (worker_id == 0) { // Single threaded at the moment.
5341 _timer.reset();
5342 _timer.start();
5343
5344 // Scan all classes that was dirtied during the concurrent marking phase.
5345 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
5346 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5347
5348 _timer.stop();
5349 if (PrintCMSStatistics != 0) {
5350 gclog_or_tty->print_cr(
5351 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
5352 worker_id, _timer.seconds());
5353 }
5354 }
5355
5356 // We might have added oops to ClassLoaderData::_handles during the
5357 // concurrent marking phase. These oops point to newly allocated objects
5358 // that are guaranteed to be kept alive. Either by the direct allocation
5359 // code, or when the young collector processes the roots. Hence,
5360 // we don't have to revisit the _handles block during the remark phase.
5361
5362 // ---------- rescan dirty cards ------------
5363 _timer.reset();
5364 _timer.start();
5365
5366 // Do the rescan tasks for each of the two spaces
5367 // (cms_space) in turn.
5368 // "worker_id" is passed to select the task_queue for "worker_id"
5369 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
5370 _timer.stop();
5371 if (PrintCMSStatistics != 0) {
5372 gclog_or_tty->print_cr(
5373 "Finished dirty card rescan work in %dth thread: %3.3f sec",
5374 worker_id, _timer.seconds());
5375 }
5376
5377 // ---------- steal work from other threads ...
5378 // ---------- ... and drain overflow list.
5379 _timer.reset();
5380 _timer.start();
5381 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
5382 _timer.stop();
5383 if (PrintCMSStatistics != 0) {
5384 gclog_or_tty->print_cr(
5385 "Finished work stealing in %dth thread: %3.3f sec",
5386 worker_id, _timer.seconds());
5387 }
5388 }
5389
5390 // Note that parameter "i" is not used.
5391 void
5392 CMSParMarkTask::do_young_space_rescan(uint worker_id,
5393 OopsInGenClosure* cl, ContiguousSpace* space,
5394 HeapWord** chunk_array, size_t chunk_top) {
5395 // Until all tasks completed:
5396 // . claim an unclaimed task
5397 // . compute region boundaries corresponding to task claimed
5398 // using chunk_array
5399 // . par_oop_iterate(cl) over that region
5400
5401 ResourceMark rm;
5402 HandleMark hm;
5403
5404 SequentialSubTasksDone* pst = space->par_seq_tasks();
5405
5406 uint nth_task = 0;
5407 uint n_tasks = pst->n_tasks();
5408
5409 if (n_tasks > 0) {
5410 assert(pst->valid(), "Uninitialized use?");
5411 HeapWord *start, *end;
5412 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5413 // We claimed task # nth_task; compute its boundaries.
5414 if (chunk_top == 0) { // no samples were taken
5415 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5416 start = space->bottom();
5417 end = space->top();
5418 } else if (nth_task == 0) {
5419 start = space->bottom();
5420 end = chunk_array[nth_task];
5421 } else if (nth_task < (uint)chunk_top) {
5422 assert(nth_task >= 1, "Control point invariant");
5423 start = chunk_array[nth_task - 1];
5424 end = chunk_array[nth_task];
5425 } else {
5426 assert(nth_task == (uint)chunk_top, "Control point invariant");
5427 start = chunk_array[chunk_top - 1];
5428 end = space->top();
5429 }
5430 MemRegion mr(start, end);
5431 // Verify that mr is in space
5432 assert(mr.is_empty() || space->used_region().contains(mr),
5433 "Should be in space");
5434 // Verify that "start" is an object boundary
5435 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5436 "Should be an oop");
5437 space->par_oop_iterate(mr, cl);
5438 }
5439 pst->all_tasks_completed();
5440 }
5441 }
5442
5443 void
5444 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5445 CompactibleFreeListSpace* sp, int i,
5446 Par_MarkRefsIntoAndScanClosure* cl) {
5447 // Until all tasks completed:
5448 // . claim an unclaimed task
5449 // . compute region boundaries corresponding to task claimed
5450 // . transfer dirty bits ct->mut for that region
5451 // . apply rescanclosure to dirty mut bits for that region
5452
5453 ResourceMark rm;
5454 HandleMark hm;
5455
5456 OopTaskQueue* work_q = work_queue(i);
5457 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5458 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5459 // CAUTION: This closure has state that persists across calls to
5460 // the work method dirty_range_iterate_clear() in that it has
5461 // embedded in it a (subtype of) UpwardsObjectClosure. The
5462 // use of that state in the embedded UpwardsObjectClosure instance
5463 // assumes that the cards are always iterated (even if in parallel
5464 // by several threads) in monotonically increasing order per each
5465 // thread. This is true of the implementation below which picks
5466 // card ranges (chunks) in monotonically increasing order globally
5467 // and, a-fortiori, in monotonically increasing order per thread
5468 // (the latter order being a subsequence of the former).
5469 // If the work code below is ever reorganized into a more chaotic
5470 // work-partitioning form than the current "sequential tasks"
5471 // paradigm, the use of that persistent state will have to be
5472 // revisited and modified appropriately. See also related
5473 // bug 4756801 work on which should examine this code to make
5474 // sure that the changes there do not run counter to the
5475 // assumptions made here and necessary for correctness and
5476 // efficiency. Note also that this code might yield inefficient
5477 // behavior in the case of very large objects that span one or
5478 // more work chunks. Such objects would potentially be scanned
5479 // several times redundantly. Work on 4756801 should try and
5480 // address that performance anomaly if at all possible. XXX
5481 MemRegion full_span = _collector->_span;
5482 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5483 MarkFromDirtyCardsClosure
5484 greyRescanClosure(_collector, full_span, // entire span of interest
5485 sp, bm, work_q, cl);
5486
5487 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5488 assert(pst->valid(), "Uninitialized use?");
5489 uint nth_task = 0;
5490 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5491 MemRegion span = sp->used_region();
5492 HeapWord* start_addr = span.start();
5493 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5494 alignment);
5495 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5496 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5497 start_addr, "Check alignment");
5498 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5499 chunk_size, "Check alignment");
5500
5501 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5502 // Having claimed the nth_task, compute corresponding mem-region,
5503 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
5504 // The alignment restriction ensures that we do not need any
5505 // synchronization with other gang-workers while setting or
5506 // clearing bits in thus chunk of the MUT.
5507 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5508 start_addr + (nth_task+1)*chunk_size);
5509 // The last chunk's end might be way beyond end of the
5510 // used region. In that case pull back appropriately.
5511 if (this_span.end() > end_addr) {
5512 this_span.set_end(end_addr);
5513 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5514 }
5515 // Iterate over the dirty cards covering this chunk, marking them
5516 // precleaned, and setting the corresponding bits in the mod union
5517 // table. Since we have been careful to partition at Card and MUT-word
5518 // boundaries no synchronization is needed between parallel threads.
5519 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5520 &modUnionClosure);
5521
5522 // Having transferred these marks into the modUnionTable,
5523 // rescan the marked objects on the dirty cards in the modUnionTable.
5524 // Even if this is at a synchronous collection, the initial marking
5525 // may have been done during an asynchronous collection so there
5526 // may be dirty bits in the mod-union table.
5527 _collector->_modUnionTable.dirty_range_iterate_clear(
5528 this_span, &greyRescanClosure);
5529 _collector->_modUnionTable.verifyNoOneBitsInRange(
5530 this_span.start(),
5531 this_span.end());
5532 }
5533 pst->all_tasks_completed(); // declare that i am done
5534 }
5535
5536 // . see if we can share work_queues with ParNew? XXX
5537 void
5538 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5539 int* seed) {
5540 OopTaskQueue* work_q = work_queue(i);
5541 NOT_PRODUCT(int num_steals = 0;)
5542 oop obj_to_scan;
5543 CMSBitMap* bm = &(_collector->_markBitMap);
5544
5545 while (true) {
5546 // Completely finish any left over work from (an) earlier round(s)
5547 cl->trim_queue(0);
5548 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5549 (size_t)ParGCDesiredObjsFromOverflowList);
5550 // Now check if there's any work in the overflow list
5551 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5552 // only affects the number of attempts made to get work from the
5553 // overflow list and does not affect the number of workers. Just
5554 // pass ParallelGCThreads so this behavior is unchanged.
5555 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5556 work_q,
5557 ParallelGCThreads)) {
5558 // found something in global overflow list;
5559 // not yet ready to go stealing work from others.
5560 // We'd like to assert(work_q->size() != 0, ...)
5561 // because we just took work from the overflow list,
5562 // but of course we can't since all of that could have
5563 // been already stolen from us.
5564 // "He giveth and He taketh away."
5565 continue;
5566 }
5567 // Verify that we have no work before we resort to stealing
5568 assert(work_q->size() == 0, "Have work, shouldn't steal");
5569 // Try to steal from other queues that have work
5570 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5571 NOT_PRODUCT(num_steals++;)
5572 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5573 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5574 // Do scanning work
5575 obj_to_scan->oop_iterate(cl);
5576 // Loop around, finish this work, and try to steal some more
5577 } else if (terminator()->offer_termination()) {
5578 break; // nirvana from the infinite cycle
5579 }
5580 }
5581 NOT_PRODUCT(
5582 if (PrintCMSStatistics != 0) {
5583 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5584 }
5585 )
5586 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5587 "Else our work is not yet done");
5588 }
5589
5590 // Record object boundaries in _eden_chunk_array by sampling the eden
5591 // top in the slow-path eden object allocation code path and record
5592 // the boundaries, if CMSEdenChunksRecordAlways is true. If
5593 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
5594 // sampling in sample_eden() that activates during the part of the
5595 // preclean phase.
5596 void CMSCollector::sample_eden_chunk() {
5597 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
5598 if (_eden_chunk_lock->try_lock()) {
5599 // Record a sample. This is the critical section. The contents
5600 // of the _eden_chunk_array have to be non-decreasing in the
5601 // address order.
5602 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
5603 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
5604 "Unexpected state of Eden");
5605 if (_eden_chunk_index == 0 ||
5606 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
5607 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
5608 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
5609 _eden_chunk_index++; // commit sample
5610 }
5611 _eden_chunk_lock->unlock();
5612 }
5613 }
5614 }
5615
5616 // Return a thread-local PLAB recording array, as appropriate.
5617 void* CMSCollector::get_data_recorder(int thr_num) {
5618 if (_survivor_plab_array != NULL &&
5619 (CMSPLABRecordAlways ||
5620 (_collectorState > Marking && _collectorState < FinalMarking))) {
5621 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5622 ChunkArray* ca = &_survivor_plab_array[thr_num];
5623 ca->reset(); // clear it so that fresh data is recorded
5624 return (void*) ca;
5625 } else {
5626 return NULL;
5627 }
5628 }
5629
5630 // Reset all the thread-local PLAB recording arrays
5631 void CMSCollector::reset_survivor_plab_arrays() {
5632 for (uint i = 0; i < ParallelGCThreads; i++) {
5633 _survivor_plab_array[i].reset();
5634 }
5635 }
5636
5637 // Merge the per-thread plab arrays into the global survivor chunk
5638 // array which will provide the partitioning of the survivor space
5639 // for CMS initial scan and rescan.
5640 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5641 int no_of_gc_threads) {
5642 assert(_survivor_plab_array != NULL, "Error");
5643 assert(_survivor_chunk_array != NULL, "Error");
5644 assert(_collectorState == FinalMarking ||
5645 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
5646 for (int j = 0; j < no_of_gc_threads; j++) {
5647 _cursor[j] = 0;
5648 }
5649 HeapWord* top = surv->top();
5650 size_t i;
5651 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5652 HeapWord* min_val = top; // Higher than any PLAB address
5653 uint min_tid = 0; // position of min_val this round
5654 for (int j = 0; j < no_of_gc_threads; j++) {
5655 ChunkArray* cur_sca = &_survivor_plab_array[j];
5656 if (_cursor[j] == cur_sca->end()) {
5657 continue;
5658 }
5659 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5660 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5661 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5662 if (cur_val < min_val) {
5663 min_tid = j;
5664 min_val = cur_val;
5665 } else {
5666 assert(cur_val < top, "All recorded addresses should be less");
5667 }
5668 }
5669 // At this point min_val and min_tid are respectively
5670 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5671 // and the thread (j) that witnesses that address.
5672 // We record this address in the _survivor_chunk_array[i]
5673 // and increment _cursor[min_tid] prior to the next round i.
5674 if (min_val == top) {
5675 break;
5676 }
5677 _survivor_chunk_array[i] = min_val;
5678 _cursor[min_tid]++;
5679 }
5680 // We are all done; record the size of the _survivor_chunk_array
5681 _survivor_chunk_index = i; // exclusive: [0, i)
5682 if (PrintCMSStatistics > 0) {
5683 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5684 }
5685 // Verify that we used up all the recorded entries
5686 #ifdef ASSERT
5687 size_t total = 0;
5688 for (int j = 0; j < no_of_gc_threads; j++) {
5689 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5690 total += _cursor[j];
5691 }
5692 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5693 // Check that the merged array is in sorted order
5694 if (total > 0) {
5695 for (size_t i = 0; i < total - 1; i++) {
5696 if (PrintCMSStatistics > 0) {
5697 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5698 i, _survivor_chunk_array[i]);
5699 }
5700 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5701 "Not sorted");
5702 }
5703 }
5704 #endif // ASSERT
5705 }
5706
5707 // Set up the space's par_seq_tasks structure for work claiming
5708 // for parallel initial scan and rescan of young gen.
5709 // See ParRescanTask where this is currently used.
5710 void
5711 CMSCollector::
5712 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5713 assert(n_threads > 0, "Unexpected n_threads argument");
5714 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5715
5716 // Eden space
5717 if (!dng->eden()->is_empty()) {
5718 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5719 assert(!pst->valid(), "Clobbering existing data?");
5720 // Each valid entry in [0, _eden_chunk_index) represents a task.
5721 size_t n_tasks = _eden_chunk_index + 1;
5722 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5723 // Sets the condition for completion of the subtask (how many threads
5724 // need to finish in order to be done).
5725 pst->set_n_threads(n_threads);
5726 pst->set_n_tasks((int)n_tasks);
5727 }
5728
5729 // Merge the survivor plab arrays into _survivor_chunk_array
5730 if (_survivor_plab_array != NULL) {
5731 merge_survivor_plab_arrays(dng->from(), n_threads);
5732 } else {
5733 assert(_survivor_chunk_index == 0, "Error");
5734 }
5735
5736 // To space
5737 {
5738 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5739 assert(!pst->valid(), "Clobbering existing data?");
5740 // Sets the condition for completion of the subtask (how many threads
5741 // need to finish in order to be done).
5742 pst->set_n_threads(n_threads);
5743 pst->set_n_tasks(1);
5744 assert(pst->valid(), "Error");
5745 }
5746
5747 // From space
5748 {
5749 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5750 assert(!pst->valid(), "Clobbering existing data?");
5751 size_t n_tasks = _survivor_chunk_index + 1;
5752 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5753 // Sets the condition for completion of the subtask (how many threads
5754 // need to finish in order to be done).
5755 pst->set_n_threads(n_threads);
5756 pst->set_n_tasks((int)n_tasks);
5757 assert(pst->valid(), "Error");
5758 }
5759 }
5760
5761 // Parallel version of remark
5762 void CMSCollector::do_remark_parallel() {
5763 GenCollectedHeap* gch = GenCollectedHeap::heap();
5764 FlexibleWorkGang* workers = gch->workers();
5765 assert(workers != NULL, "Need parallel worker threads.");
5766 // Choose to use the number of GC workers most recently set
5767 // into "active_workers". If active_workers is not set, set it
5768 // to ParallelGCThreads.
5769 int n_workers = workers->active_workers();
5770 if (n_workers == 0) {
5771 assert(n_workers > 0, "Should have been set during scavenge");
5772 n_workers = ParallelGCThreads;
5773 workers->set_active_workers(n_workers);
5774 }
5775 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5776
5777 CMSParRemarkTask tsk(this,
5778 cms_space,
5779 n_workers, workers, task_queues());
5780
5781 // Set up for parallel process_roots work.
5782 gch->set_par_threads(n_workers);
5783 // We won't be iterating over the cards in the card table updating
5784 // the younger_gen cards, so we shouldn't call the following else
5785 // the verification code as well as subsequent younger_refs_iterate
5786 // code would get confused. XXX
5787 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5788
5789 // The young gen rescan work will not be done as part of
5790 // process_roots (which currently doesn't know how to
5791 // parallelize such a scan), but rather will be broken up into
5792 // a set of parallel tasks (via the sampling that the [abortable]
5793 // preclean phase did of EdenSpace, plus the [two] tasks of
5794 // scanning the [two] survivor spaces. Further fine-grain
5795 // parallelization of the scanning of the survivor spaces
5796 // themselves, and of precleaning of the younger gen itself
5797 // is deferred to the future.
5798 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5799
5800 // The dirty card rescan work is broken up into a "sequence"
5801 // of parallel tasks (per constituent space) that are dynamically
5802 // claimed by the parallel threads.
5803 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5804
5805 // It turns out that even when we're using 1 thread, doing the work in a
5806 // separate thread causes wide variance in run times. We can't help this
5807 // in the multi-threaded case, but we special-case n=1 here to get
5808 // repeatable measurements of the 1-thread overhead of the parallel code.
5809 if (n_workers > 1) {
5810 // Make refs discovery MT-safe, if it isn't already: it may not
5811 // necessarily be so, since it's possible that we are doing
5812 // ST marking.
5813 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5814 GenCollectedHeap::StrongRootsScope srs(gch);
5815 workers->run_task(&tsk);
5816 } else {
5817 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5818 GenCollectedHeap::StrongRootsScope srs(gch);
5819 tsk.work(0);
5820 }
5821
5822 gch->set_par_threads(0); // 0 ==> non-parallel.
5823 // restore, single-threaded for now, any preserved marks
5824 // as a result of work_q overflow
5825 restore_preserved_marks_if_any();
5826 }
5827
5828 // Non-parallel version of remark
5829 void CMSCollector::do_remark_non_parallel() {
5830 ResourceMark rm;
5831 HandleMark hm;
5832 GenCollectedHeap* gch = GenCollectedHeap::heap();
5833 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5834
5835 MarkRefsIntoAndScanClosure
5836 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5837 &_markStack, this,
5838 false /* should_yield */, false /* not precleaning */);
5839 MarkFromDirtyCardsClosure
5840 markFromDirtyCardsClosure(this, _span,
5841 NULL, // space is set further below
5842 &_markBitMap, &_markStack, &mrias_cl);
5843 {
5844 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5845 // Iterate over the dirty cards, setting the corresponding bits in the
5846 // mod union table.
5847 {
5848 ModUnionClosure modUnionClosure(&_modUnionTable);
5849 _ct->ct_bs()->dirty_card_iterate(
5850 _cmsGen->used_region(),
5851 &modUnionClosure);
5852 }
5853 // Having transferred these marks into the modUnionTable, we just need
5854 // to rescan the marked objects on the dirty cards in the modUnionTable.
5855 // The initial marking may have been done during an asynchronous
5856 // collection so there may be dirty bits in the mod-union table.
5857 const int alignment =
5858 CardTableModRefBS::card_size * BitsPerWord;
5859 {
5860 // ... First handle dirty cards in CMS gen
5861 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5862 MemRegion ur = _cmsGen->used_region();
5863 HeapWord* lb = ur.start();
5864 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5865 MemRegion cms_span(lb, ub);
5866 _modUnionTable.dirty_range_iterate_clear(cms_span,
5867 &markFromDirtyCardsClosure);
5868 verify_work_stacks_empty();
5869 if (PrintCMSStatistics != 0) {
5870 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5871 markFromDirtyCardsClosure.num_dirty_cards());
5872 }
5873 }
5874 }
5875 if (VerifyDuringGC &&
5876 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5877 HandleMark hm; // Discard invalid handles created during verification
5878 Universe::verify();
5879 }
5880 {
5881 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5882
5883 verify_work_stacks_empty();
5884
5885 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5886 GenCollectedHeap::StrongRootsScope srs(gch);
5887
5888 gch->gen_process_roots(_cmsGen->level(),
5889 true, // younger gens as roots
5890 false, // use the local StrongRootsScope
5891 SharedHeap::ScanningOption(roots_scanning_options()),
5892 should_unload_classes(),
5893 &mrias_cl,
5894 NULL,
5895 NULL); // The dirty klasses will be handled below
5896
5897 assert(should_unload_classes()
5898 || (roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5899 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5900 }
5901
5902 {
5903 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5904
5905 verify_work_stacks_empty();
5906
5907 // Scan all class loader data objects that might have been introduced
5908 // during concurrent marking.
5909 ResourceMark rm;
5910 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5911 for (int i = 0; i < array->length(); i++) {
5912 mrias_cl.do_class_loader_data(array->at(i));
5913 }
5914
5915 // We don't need to keep track of new CLDs anymore.
5916 ClassLoaderDataGraph::remember_new_clds(false);
5917
5918 verify_work_stacks_empty();
5919 }
5920
5921 {
5922 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5923
5924 verify_work_stacks_empty();
5925
5926 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5927 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5928
5929 verify_work_stacks_empty();
5930 }
5931
5932 // We might have added oops to ClassLoaderData::_handles during the
5933 // concurrent marking phase. These oops point to newly allocated objects
5934 // that are guaranteed to be kept alive. Either by the direct allocation
5935 // code, or when the young collector processes the roots. Hence,
5936 // we don't have to revisit the _handles block during the remark phase.
5937
5938 verify_work_stacks_empty();
5939 // Restore evacuated mark words, if any, used for overflow list links
5940 if (!CMSOverflowEarlyRestoration) {
5941 restore_preserved_marks_if_any();
5942 }
5943 verify_overflow_empty();
5944 }
5945
5946 ////////////////////////////////////////////////////////
5947 // Parallel Reference Processing Task Proxy Class
5948 ////////////////////////////////////////////////////////
5949 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5950 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5951 CMSCollector* _collector;
5952 CMSBitMap* _mark_bit_map;
5953 const MemRegion _span;
5954 ProcessTask& _task;
5955
5956 public:
5957 CMSRefProcTaskProxy(ProcessTask& task,
5958 CMSCollector* collector,
5959 const MemRegion& span,
5960 CMSBitMap* mark_bit_map,
5961 AbstractWorkGang* workers,
5962 OopTaskQueueSet* task_queues):
5963 // XXX Should superclass AGTWOQ also know about AWG since it knows
5964 // about the task_queues used by the AWG? Then it could initialize
5965 // the terminator() object. See 6984287. The set_for_termination()
5966 // below is a temporary band-aid for the regression in 6984287.
5967 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5968 task_queues),
5969 _task(task),
5970 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5971 {
5972 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5973 "Inconsistency in _span");
5974 set_for_termination(workers->active_workers());
5975 }
5976
5977 OopTaskQueueSet* task_queues() { return queues(); }
5978
5979 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5980
5981 void do_work_steal(int i,
5982 CMSParDrainMarkingStackClosure* drain,
5983 CMSParKeepAliveClosure* keep_alive,
5984 int* seed);
5985
5986 virtual void work(uint worker_id);
5987 };
5988
5989 void CMSRefProcTaskProxy::work(uint worker_id) {
5990 ResourceMark rm;
5991 HandleMark hm;
5992 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5993 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5994 _mark_bit_map,
5995 work_queue(worker_id));
5996 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5997 _mark_bit_map,
5998 work_queue(worker_id));
5999 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
6000 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
6001 if (_task.marks_oops_alive()) {
6002 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
6003 _collector->hash_seed(worker_id));
6004 }
6005 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
6006 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
6007 }
6008
6009 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
6010 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
6011 EnqueueTask& _task;
6012
6013 public:
6014 CMSRefEnqueueTaskProxy(EnqueueTask& task)
6015 : AbstractGangTask("Enqueue reference objects in parallel"),
6016 _task(task)
6017 { }
6018
6019 virtual void work(uint worker_id)
6020 {
6021 _task.work(worker_id);
6022 }
6023 };
6024
6025 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
6026 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
6027 _span(span),
6028 _bit_map(bit_map),
6029 _work_queue(work_queue),
6030 _mark_and_push(collector, span, bit_map, work_queue),
6031 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6032 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
6033 { }
6034
6035 // . see if we can share work_queues with ParNew? XXX
6036 void CMSRefProcTaskProxy::do_work_steal(int i,
6037 CMSParDrainMarkingStackClosure* drain,
6038 CMSParKeepAliveClosure* keep_alive,
6039 int* seed) {
6040 OopTaskQueue* work_q = work_queue(i);
6041 NOT_PRODUCT(int num_steals = 0;)
6042 oop obj_to_scan;
6043
6044 while (true) {
6045 // Completely finish any left over work from (an) earlier round(s)
6046 drain->trim_queue(0);
6047 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
6048 (size_t)ParGCDesiredObjsFromOverflowList);
6049 // Now check if there's any work in the overflow list
6050 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
6051 // only affects the number of attempts made to get work from the
6052 // overflow list and does not affect the number of workers. Just
6053 // pass ParallelGCThreads so this behavior is unchanged.
6054 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
6055 work_q,
6056 ParallelGCThreads)) {
6057 // Found something in global overflow list;
6058 // not yet ready to go stealing work from others.
6059 // We'd like to assert(work_q->size() != 0, ...)
6060 // because we just took work from the overflow list,
6061 // but of course we can't, since all of that might have
6062 // been already stolen from us.
6063 continue;
6064 }
6065 // Verify that we have no work before we resort to stealing
6066 assert(work_q->size() == 0, "Have work, shouldn't steal");
6067 // Try to steal from other queues that have work
6068 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
6069 NOT_PRODUCT(num_steals++;)
6070 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
6071 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
6072 // Do scanning work
6073 obj_to_scan->oop_iterate(keep_alive);
6074 // Loop around, finish this work, and try to steal some more
6075 } else if (terminator()->offer_termination()) {
6076 break; // nirvana from the infinite cycle
6077 }
6078 }
6079 NOT_PRODUCT(
6080 if (PrintCMSStatistics != 0) {
6081 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
6082 }
6083 )
6084 }
6085
6086 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
6087 {
6088 GenCollectedHeap* gch = GenCollectedHeap::heap();
6089 FlexibleWorkGang* workers = gch->workers();
6090 assert(workers != NULL, "Need parallel worker threads.");
6091 CMSRefProcTaskProxy rp_task(task, &_collector,
6092 _collector.ref_processor()->span(),
6093 _collector.markBitMap(),
6094 workers, _collector.task_queues());
6095 workers->run_task(&rp_task);
6096 }
6097
6098 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
6099 {
6100
6101 GenCollectedHeap* gch = GenCollectedHeap::heap();
6102 FlexibleWorkGang* workers = gch->workers();
6103 assert(workers != NULL, "Need parallel worker threads.");
6104 CMSRefEnqueueTaskProxy enq_task(task);
6105 workers->run_task(&enq_task);
6106 }
6107
6108 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
6109
6110 ResourceMark rm;
6111 HandleMark hm;
6112
6113 ReferenceProcessor* rp = ref_processor();
6114 assert(rp->span().equals(_span), "Spans should be equal");
6115 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
6116 // Process weak references.
6117 rp->setup_policy(clear_all_soft_refs);
6118 verify_work_stacks_empty();
6119
6120 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
6121 &_markStack, false /* !preclean */);
6122 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
6123 _span, &_markBitMap, &_markStack,
6124 &cmsKeepAliveClosure, false /* !preclean */);
6125 {
6126 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6127
6128 ReferenceProcessorStats stats;
6129 if (rp->processing_is_mt()) {
6130 // Set the degree of MT here. If the discovery is done MT, there
6131 // may have been a different number of threads doing the discovery
6132 // and a different number of discovered lists may have Ref objects.
6133 // That is OK as long as the Reference lists are balanced (see
6134 // balance_all_queues() and balance_queues()).
6135 GenCollectedHeap* gch = GenCollectedHeap::heap();
6136 int active_workers = ParallelGCThreads;
6137 FlexibleWorkGang* workers = gch->workers();
6138 if (workers != NULL) {
6139 active_workers = workers->active_workers();
6140 // The expectation is that active_workers will have already
6141 // been set to a reasonable value. If it has not been set,
6142 // investigate.
6143 assert(active_workers > 0, "Should have been set during scavenge");
6144 }
6145 rp->set_active_mt_degree(active_workers);
6146 CMSRefProcTaskExecutor task_executor(*this);
6147 stats = rp->process_discovered_references(&_is_alive_closure,
6148 &cmsKeepAliveClosure,
6149 &cmsDrainMarkingStackClosure,
6150 &task_executor,
6151 _gc_timer_cm,
6152 _gc_tracer_cm->gc_id());
6153 } else {
6154 stats = rp->process_discovered_references(&_is_alive_closure,
6155 &cmsKeepAliveClosure,
6156 &cmsDrainMarkingStackClosure,
6157 NULL,
6158 _gc_timer_cm,
6159 _gc_tracer_cm->gc_id());
6160 }
6161 _gc_tracer_cm->report_gc_reference_stats(stats);
6162
6163 }
6164
6165 // This is the point where the entire marking should have completed.
6166 verify_work_stacks_empty();
6167
6168 if (should_unload_classes()) {
6169 {
6170 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6171
6172 // Unload classes and purge the SystemDictionary.
6173 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
6174
6175 // Unload nmethods.
6176 CodeCache::do_unloading(&_is_alive_closure, purged_class);
6177
6178 // Prune dead klasses from subklass/sibling/implementor lists.
6179 Klass::clean_weak_klass_links(&_is_alive_closure);
6180 }
6181
6182 {
6183 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6184 // Clean up unreferenced symbols in symbol table.
6185 SymbolTable::unlink();
6186 }
6187
6188 {
6189 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6190 // Delete entries for dead interned strings.
6191 StringTable::unlink(&_is_alive_closure);
6192 }
6193 }
6194
6195
6196 // Restore any preserved marks as a result of mark stack or
6197 // work queue overflow
6198 restore_preserved_marks_if_any(); // done single-threaded for now
6199
6200 rp->set_enqueuing_is_done(true);
6201 if (rp->processing_is_mt()) {
6202 rp->balance_all_queues();
6203 CMSRefProcTaskExecutor task_executor(*this);
6204 rp->enqueue_discovered_references(&task_executor);
6205 } else {
6206 rp->enqueue_discovered_references(NULL);
6207 }
6208 rp->verify_no_references_recorded();
6209 assert(!rp->discovery_enabled(), "should have been disabled");
6210 }
6211
6212 #ifndef PRODUCT
6213 void CMSCollector::check_correct_thread_executing() {
6214 Thread* t = Thread::current();
6215 // Only the VM thread or the CMS thread should be here.
6216 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
6217 "Unexpected thread type");
6218 // If this is the vm thread, the foreground process
6219 // should not be waiting. Note that _foregroundGCIsActive is
6220 // true while the foreground collector is waiting.
6221 if (_foregroundGCShouldWait) {
6222 // We cannot be the VM thread
6223 assert(t->is_ConcurrentGC_thread(),
6224 "Should be CMS thread");
6225 } else {
6226 // We can be the CMS thread only if we are in a stop-world
6227 // phase of CMS collection.
6228 if (t->is_ConcurrentGC_thread()) {
6229 assert(_collectorState == InitialMarking ||
6230 _collectorState == FinalMarking,
6231 "Should be a stop-world phase");
6232 // The CMS thread should be holding the CMS_token.
6233 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6234 "Potential interference with concurrently "
6235 "executing VM thread");
6236 }
6237 }
6238 }
6239 #endif
6240
6241 void CMSCollector::sweep(bool asynch) {
6242 assert(_collectorState == Sweeping, "just checking");
6243 check_correct_thread_executing();
6244 verify_work_stacks_empty();
6245 verify_overflow_empty();
6246 increment_sweep_count();
6247 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
6248
6249 _inter_sweep_timer.stop();
6250 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6251
6252 assert(!_intra_sweep_timer.is_active(), "Should not be active");
6253 _intra_sweep_timer.reset();
6254 _intra_sweep_timer.start();
6255 if (asynch) {
6256 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6257 CMSPhaseAccounting pa(this, "sweep", _gc_tracer_cm->gc_id(), !PrintGCDetails);
6258 // First sweep the old gen
6259 {
6260 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6261 bitMapLock());
6262 sweepWork(_cmsGen, asynch);
6263 }
6264
6265 // Update Universe::_heap_*_at_gc figures.
6266 // We need all the free list locks to make the abstract state
6267 // transition from Sweeping to Resetting. See detailed note
6268 // further below.
6269 {
6270 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
6271 // Update heap occupancy information which is used as
6272 // input to soft ref clearing policy at the next gc.
6273 Universe::update_heap_info_at_gc();
6274 _collectorState = Resizing;
6275 }
6276 } else {
6277 // already have needed locks
6278 sweepWork(_cmsGen, asynch);
6279 // Update heap occupancy information which is used as
6280 // input to soft ref clearing policy at the next gc.
6281 Universe::update_heap_info_at_gc();
6282 _collectorState = Resizing;
6283 }
6284 verify_work_stacks_empty();
6285 verify_overflow_empty();
6286
6287 if (should_unload_classes()) {
6288 // Delay purge to the beginning of the next safepoint. Metaspace::contains
6289 // requires that the virtual spaces are stable and not deleted.
6290 ClassLoaderDataGraph::set_should_purge(true);
6291 }
6292
6293 _intra_sweep_timer.stop();
6294 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6295
6296 _inter_sweep_timer.reset();
6297 _inter_sweep_timer.start();
6298
6299 // We need to use a monotonically non-decreasing time in ms
6300 // or we will see time-warp warnings and os::javaTimeMillis()
6301 // does not guarantee monotonicity.
6302 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
6303 update_time_of_last_gc(now);
6304
6305 // NOTE on abstract state transitions:
6306 // Mutators allocate-live and/or mark the mod-union table dirty
6307 // based on the state of the collection. The former is done in
6308 // the interval [Marking, Sweeping] and the latter in the interval
6309 // [Marking, Sweeping). Thus the transitions into the Marking state
6310 // and out of the Sweeping state must be synchronously visible
6311 // globally to the mutators.
6312 // The transition into the Marking state happens with the world
6313 // stopped so the mutators will globally see it. Sweeping is
6314 // done asynchronously by the background collector so the transition
6315 // from the Sweeping state to the Resizing state must be done
6316 // under the freelistLock (as is the check for whether to
6317 // allocate-live and whether to dirty the mod-union table).
6318 assert(_collectorState == Resizing, "Change of collector state to"
6319 " Resizing must be done under the freelistLocks (plural)");
6320
6321 // Now that sweeping has been completed, we clear
6322 // the incremental_collection_failed flag,
6323 // thus inviting a younger gen collection to promote into
6324 // this generation. If such a promotion may still fail,
6325 // the flag will be set again when a young collection is
6326 // attempted.
6327 GenCollectedHeap* gch = GenCollectedHeap::heap();
6328 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
6329 gch->update_full_collections_completed(_collection_count_start);
6330 }
6331
6332 // FIX ME!!! Looks like this belongs in CFLSpace, with
6333 // CMSGen merely delegating to it.
6334 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6335 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6336 HeapWord* minAddr = _cmsSpace->bottom();
6337 HeapWord* largestAddr =
6338 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
6339 if (largestAddr == NULL) {
6340 // The dictionary appears to be empty. In this case
6341 // try to coalesce at the end of the heap.
6342 largestAddr = _cmsSpace->end();
6343 }
6344 size_t largestOffset = pointer_delta(largestAddr, minAddr);
6345 size_t nearLargestOffset =
6346 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6347 if (PrintFLSStatistics != 0) {
6348 gclog_or_tty->print_cr(
6349 "CMS: Large Block: " PTR_FORMAT ";"
6350 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6351 largestAddr,
6352 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6353 }
6354 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6355 }
6356
6357 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6358 return addr >= _cmsSpace->nearLargestChunk();
6359 }
6360
6361 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6362 return _cmsSpace->find_chunk_at_end();
6363 }
6364
6365 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6366 bool full) {
6367 // The next lower level has been collected. Gather any statistics
6368 // that are of interest at this point.
6369 if (!full && (current_level + 1) == level()) {
6370 // Gather statistics on the young generation collection.
6371 collector()->stats().record_gc0_end(used());
6372 }
6373 }
6374
6375 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6376 if (PrintGCDetails && Verbose) {
6377 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6378 }
6379 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6380 _debug_collection_type =
6381 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6382 if (PrintGCDetails && Verbose) {
6383 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6384 }
6385 }
6386
6387 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6388 bool asynch) {
6389 // We iterate over the space(s) underlying this generation,
6390 // checking the mark bit map to see if the bits corresponding
6391 // to specific blocks are marked or not. Blocks that are
6392 // marked are live and are not swept up. All remaining blocks
6393 // are swept up, with coalescing on-the-fly as we sweep up
6394 // contiguous free and/or garbage blocks:
6395 // We need to ensure that the sweeper synchronizes with allocators
6396 // and stop-the-world collectors. In particular, the following
6397 // locks are used:
6398 // . CMS token: if this is held, a stop the world collection cannot occur
6399 // . freelistLock: if this is held no allocation can occur from this
6400 // generation by another thread
6401 // . bitMapLock: if this is held, no other thread can access or update
6402 //
6403
6404 // Note that we need to hold the freelistLock if we use
6405 // block iterate below; else the iterator might go awry if
6406 // a mutator (or promotion) causes block contents to change
6407 // (for instance if the allocator divvies up a block).
6408 // If we hold the free list lock, for all practical purposes
6409 // young generation GC's can't occur (they'll usually need to
6410 // promote), so we might as well prevent all young generation
6411 // GC's while we do a sweeping step. For the same reason, we might
6412 // as well take the bit map lock for the entire duration
6413
6414 // check that we hold the requisite locks
6415 assert(have_cms_token(), "Should hold cms token");
6416 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6417 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6418 "Should possess CMS token to sweep");
6419 assert_lock_strong(gen->freelistLock());
6420 assert_lock_strong(bitMapLock());
6421
6422 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6423 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
6424 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6425 _inter_sweep_estimate.padded_average(),
6426 _intra_sweep_estimate.padded_average());
6427 gen->setNearLargestChunk();
6428
6429 {
6430 SweepClosure sweepClosure(this, gen, &_markBitMap,
6431 CMSYield && asynch);
6432 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6433 // We need to free-up/coalesce garbage/blocks from a
6434 // co-terminal free run. This is done in the SweepClosure
6435 // destructor; so, do not remove this scope, else the
6436 // end-of-sweep-census below will be off by a little bit.
6437 }
6438 gen->cmsSpace()->sweep_completed();
6439 gen->cmsSpace()->endSweepFLCensus(sweep_count());
6440 if (should_unload_classes()) { // unloaded classes this cycle,
6441 _concurrent_cycles_since_last_unload = 0; // ... reset count
6442 } else { // did not unload classes,
6443 _concurrent_cycles_since_last_unload++; // ... increment count
6444 }
6445 }
6446
6447 // Reset CMS data structures (for now just the marking bit map)
6448 // preparatory for the next cycle.
6449 void CMSCollector::reset(bool asynch) {
6450 if (asynch) {
6451 CMSTokenSyncWithLocks ts(true, bitMapLock());
6452
6453 // If the state is not "Resetting", the foreground thread
6454 // has done a collection and the resetting.
6455 if (_collectorState != Resetting) {
6456 assert(_collectorState == Idling, "The state should only change"
6457 " because the foreground collector has finished the collection");
6458 return;
6459 }
6460
6461 // Clear the mark bitmap (no grey objects to start with)
6462 // for the next cycle.
6463 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6464 CMSPhaseAccounting cmspa(this, "reset", _gc_tracer_cm->gc_id(), !PrintGCDetails);
6465
6466 HeapWord* curAddr = _markBitMap.startWord();
6467 while (curAddr < _markBitMap.endWord()) {
6468 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6469 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6470 _markBitMap.clear_large_range(chunk);
6471 if (ConcurrentMarkSweepThread::should_yield() &&
6472 !foregroundGCIsActive() &&
6473 CMSYield) {
6474 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6475 "CMS thread should hold CMS token");
6476 assert_lock_strong(bitMapLock());
6477 bitMapLock()->unlock();
6478 ConcurrentMarkSweepThread::desynchronize(true);
6479 ConcurrentMarkSweepThread::acknowledge_yield_request();
6480 stopTimer();
6481 if (PrintCMSStatistics != 0) {
6482 incrementYields();
6483 }
6484 icms_wait();
6485
6486 // See the comment in coordinator_yield()
6487 for (unsigned i = 0; i < CMSYieldSleepCount &&
6488 ConcurrentMarkSweepThread::should_yield() &&
6489 !CMSCollector::foregroundGCIsActive(); ++i) {
6490 os::sleep(Thread::current(), 1, false);
6491 ConcurrentMarkSweepThread::acknowledge_yield_request();
6492 }
6493
6494 ConcurrentMarkSweepThread::synchronize(true);
6495 bitMapLock()->lock_without_safepoint_check();
6496 startTimer();
6497 }
6498 curAddr = chunk.end();
6499 }
6500 // A successful mostly concurrent collection has been done.
6501 // Because only the full (i.e., concurrent mode failure) collections
6502 // are being measured for gc overhead limits, clean the "near" flag
6503 // and count.
6504 size_policy()->reset_gc_overhead_limit_count();
6505 _collectorState = Idling;
6506 } else {
6507 // already have the lock
6508 assert(_collectorState == Resetting, "just checking");
6509 assert_lock_strong(bitMapLock());
6510 _markBitMap.clear_all();
6511 _collectorState = Idling;
6512 }
6513
6514 // Stop incremental mode after a cycle completes, so that any future cycles
6515 // are triggered by allocation.
6516 stop_icms();
6517
6518 NOT_PRODUCT(
6519 if (RotateCMSCollectionTypes) {
6520 _cmsGen->rotate_debug_collection_type();
6521 }
6522 )
6523
6524 register_gc_end();
6525 }
6526
6527 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
6528 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6529 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6530 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL, _gc_tracer_cm->gc_id());
6531 TraceCollectorStats tcs(counters());
6532
6533 switch (op) {
6534 case CMS_op_checkpointRootsInitial: {
6535 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6536 checkpointRootsInitial(true); // asynch
6537 if (PrintGC) {
6538 _cmsGen->printOccupancy("initial-mark");
6539 }
6540 break;
6541 }
6542 case CMS_op_checkpointRootsFinal: {
6543 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6544 checkpointRootsFinal(true, // asynch
6545 false, // !clear_all_soft_refs
6546 false); // !init_mark_was_synchronous
6547 if (PrintGC) {
6548 _cmsGen->printOccupancy("remark");
6549 }
6550 break;
6551 }
6552 default:
6553 fatal("No such CMS_op");
6554 }
6555 }
6556
6557 #ifndef PRODUCT
6558 size_t const CMSCollector::skip_header_HeapWords() {
6559 return FreeChunk::header_size();
6560 }
6561
6562 // Try and collect here conditions that should hold when
6563 // CMS thread is exiting. The idea is that the foreground GC
6564 // thread should not be blocked if it wants to terminate
6565 // the CMS thread and yet continue to run the VM for a while
6566 // after that.
6567 void CMSCollector::verify_ok_to_terminate() const {
6568 assert(Thread::current()->is_ConcurrentGC_thread(),
6569 "should be called by CMS thread");
6570 assert(!_foregroundGCShouldWait, "should be false");
6571 // We could check here that all the various low-level locks
6572 // are not held by the CMS thread, but that is overkill; see
6573 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6574 // is checked.
6575 }
6576 #endif
6577
6578 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6579 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6580 "missing Printezis mark?");
6581 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6582 size_t size = pointer_delta(nextOneAddr + 1, addr);
6583 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6584 "alignment problem");
6585 assert(size >= 3, "Necessary for Printezis marks to work");
6586 return size;
6587 }
6588
6589 // A variant of the above (block_size_using_printezis_bits()) except
6590 // that we return 0 if the P-bits are not yet set.
6591 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6592 if (_markBitMap.isMarked(addr + 1)) {
6593 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
6594 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6595 size_t size = pointer_delta(nextOneAddr + 1, addr);
6596 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6597 "alignment problem");
6598 assert(size >= 3, "Necessary for Printezis marks to work");
6599 return size;
6600 }
6601 return 0;
6602 }
6603
6604 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6605 size_t sz = 0;
6606 oop p = (oop)addr;
6607 if (p->klass_or_null() != NULL) {
6608 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6609 } else {
6610 sz = block_size_using_printezis_bits(addr);
6611 }
6612 assert(sz > 0, "size must be nonzero");
6613 HeapWord* next_block = addr + sz;
6614 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6615 CardTableModRefBS::card_size);
6616 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6617 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6618 "must be different cards");
6619 return next_card;
6620 }
6621
6622
6623 // CMS Bit Map Wrapper /////////////////////////////////////////
6624
6625 // Construct a CMS bit map infrastructure, but don't create the
6626 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6627 // further below.
6628 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6629 _bm(),
6630 _shifter(shifter),
6631 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6632 {
6633 _bmStartWord = 0;
6634 _bmWordSize = 0;
6635 }
6636
6637 bool CMSBitMap::allocate(MemRegion mr) {
6638 _bmStartWord = mr.start();
6639 _bmWordSize = mr.word_size();
6640 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6641 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6642 if (!brs.is_reserved()) {
6643 warning("CMS bit map allocation failure");
6644 return false;
6645 }
6646 // For now we'll just commit all of the bit map up front.
6647 // Later on we'll try to be more parsimonious with swap.
6648 if (!_virtual_space.initialize(brs, brs.size())) {
6649 warning("CMS bit map backing store failure");
6650 return false;
6651 }
6652 assert(_virtual_space.committed_size() == brs.size(),
6653 "didn't reserve backing store for all of CMS bit map?");
6654 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6655 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6656 _bmWordSize, "inconsistency in bit map sizing");
6657 _bm.set_size(_bmWordSize >> _shifter);
6658
6659 // bm.clear(); // can we rely on getting zero'd memory? verify below
6660 assert(isAllClear(),
6661 "Expected zero'd memory from ReservedSpace constructor");
6662 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6663 "consistency check");
6664 return true;
6665 }
6666
6667 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6668 HeapWord *next_addr, *end_addr, *last_addr;
6669 assert_locked();
6670 assert(covers(mr), "out-of-range error");
6671 // XXX assert that start and end are appropriately aligned
6672 for (next_addr = mr.start(), end_addr = mr.end();
6673 next_addr < end_addr; next_addr = last_addr) {
6674 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6675 last_addr = dirty_region.end();
6676 if (!dirty_region.is_empty()) {
6677 cl->do_MemRegion(dirty_region);
6678 } else {
6679 assert(last_addr == end_addr, "program logic");
6680 return;
6681 }
6682 }
6683 }
6684
6685 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
6686 _bm.print_on_error(st, prefix);
6687 }
6688
6689 #ifndef PRODUCT
6690 void CMSBitMap::assert_locked() const {
6691 CMSLockVerifier::assert_locked(lock());
6692 }
6693
6694 bool CMSBitMap::covers(MemRegion mr) const {
6695 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6696 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6697 "size inconsistency");
6698 return (mr.start() >= _bmStartWord) &&
6699 (mr.end() <= endWord());
6700 }
6701
6702 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6703 return (start >= _bmStartWord && (start + size) <= endWord());
6704 }
6705
6706 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6707 // verify that there are no 1 bits in the interval [left, right)
6708 FalseBitMapClosure falseBitMapClosure;
6709 iterate(&falseBitMapClosure, left, right);
6710 }
6711
6712 void CMSBitMap::region_invariant(MemRegion mr)
6713 {
6714 assert_locked();
6715 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6716 assert(!mr.is_empty(), "unexpected empty region");
6717 assert(covers(mr), "mr should be covered by bit map");
6718 // convert address range into offset range
6719 size_t start_ofs = heapWordToOffset(mr.start());
6720 // Make sure that end() is appropriately aligned
6721 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6722 (1 << (_shifter+LogHeapWordSize))),
6723 "Misaligned mr.end()");
6724 size_t end_ofs = heapWordToOffset(mr.end());
6725 assert(end_ofs > start_ofs, "Should mark at least one bit");
6726 }
6727
6728 #endif
6729
6730 bool CMSMarkStack::allocate(size_t size) {
6731 // allocate a stack of the requisite depth
6732 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6733 size * sizeof(oop)));
6734 if (!rs.is_reserved()) {
6735 warning("CMSMarkStack allocation failure");
6736 return false;
6737 }
6738 if (!_virtual_space.initialize(rs, rs.size())) {
6739 warning("CMSMarkStack backing store failure");
6740 return false;
6741 }
6742 assert(_virtual_space.committed_size() == rs.size(),
6743 "didn't reserve backing store for all of CMS stack?");
6744 _base = (oop*)(_virtual_space.low());
6745 _index = 0;
6746 _capacity = size;
6747 NOT_PRODUCT(_max_depth = 0);
6748 return true;
6749 }
6750
6751 // XXX FIX ME !!! In the MT case we come in here holding a
6752 // leaf lock. For printing we need to take a further lock
6753 // which has lower rank. We need to recalibrate the two
6754 // lock-ranks involved in order to be able to print the
6755 // messages below. (Or defer the printing to the caller.
6756 // For now we take the expedient path of just disabling the
6757 // messages for the problematic case.)
6758 void CMSMarkStack::expand() {
6759 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6760 if (_capacity == MarkStackSizeMax) {
6761 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6762 // We print a warning message only once per CMS cycle.
6763 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6764 }
6765 return;
6766 }
6767 // Double capacity if possible
6768 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6769 // Do not give up existing stack until we have managed to
6770 // get the double capacity that we desired.
6771 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6772 new_capacity * sizeof(oop)));
6773 if (rs.is_reserved()) {
6774 // Release the backing store associated with old stack
6775 _virtual_space.release();
6776 // Reinitialize virtual space for new stack
6777 if (!_virtual_space.initialize(rs, rs.size())) {
6778 fatal("Not enough swap for expanded marking stack");
6779 }
6780 _base = (oop*)(_virtual_space.low());
6781 _index = 0;
6782 _capacity = new_capacity;
6783 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6784 // Failed to double capacity, continue;
6785 // we print a detail message only once per CMS cycle.
6786 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6787 SIZE_FORMAT"K",
6788 _capacity / K, new_capacity / K);
6789 }
6790 }
6791
6792
6793 // Closures
6794 // XXX: there seems to be a lot of code duplication here;
6795 // should refactor and consolidate common code.
6796
6797 // This closure is used to mark refs into the CMS generation in
6798 // the CMS bit map. Called at the first checkpoint. This closure
6799 // assumes that we do not need to re-mark dirty cards; if the CMS
6800 // generation on which this is used is not an oldest
6801 // generation then this will lose younger_gen cards!
6802
6803 MarkRefsIntoClosure::MarkRefsIntoClosure(
6804 MemRegion span, CMSBitMap* bitMap):
6805 _span(span),
6806 _bitMap(bitMap)
6807 {
6808 assert(_ref_processor == NULL, "deliberately left NULL");
6809 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6810 }
6811
6812 void MarkRefsIntoClosure::do_oop(oop obj) {
6813 // if p points into _span, then mark corresponding bit in _markBitMap
6814 assert(obj->is_oop(), "expected an oop");
6815 HeapWord* addr = (HeapWord*)obj;
6816 if (_span.contains(addr)) {
6817 // this should be made more efficient
6818 _bitMap->mark(addr);
6819 }
6820 }
6821
6822 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6823 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6824
6825 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6826 MemRegion span, CMSBitMap* bitMap):
6827 _span(span),
6828 _bitMap(bitMap)
6829 {
6830 assert(_ref_processor == NULL, "deliberately left NULL");
6831 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6832 }
6833
6834 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6835 // if p points into _span, then mark corresponding bit in _markBitMap
6836 assert(obj->is_oop(), "expected an oop");
6837 HeapWord* addr = (HeapWord*)obj;
6838 if (_span.contains(addr)) {
6839 // this should be made more efficient
6840 _bitMap->par_mark(addr);
6841 }
6842 }
6843
6844 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6845 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6846
6847 // A variant of the above, used for CMS marking verification.
6848 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6849 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6850 _span(span),
6851 _verification_bm(verification_bm),
6852 _cms_bm(cms_bm)
6853 {
6854 assert(_ref_processor == NULL, "deliberately left NULL");
6855 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6856 }
6857
6858 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6859 // if p points into _span, then mark corresponding bit in _markBitMap
6860 assert(obj->is_oop(), "expected an oop");
6861 HeapWord* addr = (HeapWord*)obj;
6862 if (_span.contains(addr)) {
6863 _verification_bm->mark(addr);
6864 if (!_cms_bm->isMarked(addr)) {
6865 oop(addr)->print();
6866 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6867 fatal("... aborting");
6868 }
6869 }
6870 }
6871
6872 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6873 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6874
6875 //////////////////////////////////////////////////
6876 // MarkRefsIntoAndScanClosure
6877 //////////////////////////////////////////////////
6878
6879 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6880 ReferenceProcessor* rp,
6881 CMSBitMap* bit_map,
6882 CMSBitMap* mod_union_table,
6883 CMSMarkStack* mark_stack,
6884 CMSCollector* collector,
6885 bool should_yield,
6886 bool concurrent_precleaning):
6887 _collector(collector),
6888 _span(span),
6889 _bit_map(bit_map),
6890 _mark_stack(mark_stack),
6891 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6892 mark_stack, concurrent_precleaning),
6893 _yield(should_yield),
6894 _concurrent_precleaning(concurrent_precleaning),
6895 _freelistLock(NULL)
6896 {
6897 _ref_processor = rp;
6898 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6899 }
6900
6901 // This closure is used to mark refs into the CMS generation at the
6902 // second (final) checkpoint, and to scan and transitively follow
6903 // the unmarked oops. It is also used during the concurrent precleaning
6904 // phase while scanning objects on dirty cards in the CMS generation.
6905 // The marks are made in the marking bit map and the marking stack is
6906 // used for keeping the (newly) grey objects during the scan.
6907 // The parallel version (Par_...) appears further below.
6908 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6909 if (obj != NULL) {
6910 assert(obj->is_oop(), "expected an oop");
6911 HeapWord* addr = (HeapWord*)obj;
6912 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6913 assert(_collector->overflow_list_is_empty(),
6914 "overflow list should be empty");
6915 if (_span.contains(addr) &&
6916 !_bit_map->isMarked(addr)) {
6917 // mark bit map (object is now grey)
6918 _bit_map->mark(addr);
6919 // push on marking stack (stack should be empty), and drain the
6920 // stack by applying this closure to the oops in the oops popped
6921 // from the stack (i.e. blacken the grey objects)
6922 bool res = _mark_stack->push(obj);
6923 assert(res, "Should have space to push on empty stack");
6924 do {
6925 oop new_oop = _mark_stack->pop();
6926 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6927 assert(_bit_map->isMarked((HeapWord*)new_oop),
6928 "only grey objects on this stack");
6929 // iterate over the oops in this oop, marking and pushing
6930 // the ones in CMS heap (i.e. in _span).
6931 new_oop->oop_iterate(&_pushAndMarkClosure);
6932 // check if it's time to yield
6933 do_yield_check();
6934 } while (!_mark_stack->isEmpty() ||
6935 (!_concurrent_precleaning && take_from_overflow_list()));
6936 // if marking stack is empty, and we are not doing this
6937 // during precleaning, then check the overflow list
6938 }
6939 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6940 assert(_collector->overflow_list_is_empty(),
6941 "overflow list was drained above");
6942 // We could restore evacuated mark words, if any, used for
6943 // overflow list links here because the overflow list is
6944 // provably empty here. That would reduce the maximum
6945 // size requirements for preserved_{oop,mark}_stack.
6946 // But we'll just postpone it until we are all done
6947 // so we can just stream through.
6948 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6949 _collector->restore_preserved_marks_if_any();
6950 assert(_collector->no_preserved_marks(), "No preserved marks");
6951 }
6952 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6953 "All preserved marks should have been restored above");
6954 }
6955 }
6956
6957 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6958 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6959
6960 void MarkRefsIntoAndScanClosure::do_yield_work() {
6961 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6962 "CMS thread should hold CMS token");
6963 assert_lock_strong(_freelistLock);
6964 assert_lock_strong(_bit_map->lock());
6965 // relinquish the free_list_lock and bitMaplock()
6966 _bit_map->lock()->unlock();
6967 _freelistLock->unlock();
6968 ConcurrentMarkSweepThread::desynchronize(true);
6969 ConcurrentMarkSweepThread::acknowledge_yield_request();
6970 _collector->stopTimer();
6971 if (PrintCMSStatistics != 0) {
6972 _collector->incrementYields();
6973 }
6974 _collector->icms_wait();
6975
6976 // See the comment in coordinator_yield()
6977 for (unsigned i = 0;
6978 i < CMSYieldSleepCount &&
6979 ConcurrentMarkSweepThread::should_yield() &&
6980 !CMSCollector::foregroundGCIsActive();
6981 ++i) {
6982 os::sleep(Thread::current(), 1, false);
6983 ConcurrentMarkSweepThread::acknowledge_yield_request();
6984 }
6985
6986 ConcurrentMarkSweepThread::synchronize(true);
6987 _freelistLock->lock_without_safepoint_check();
6988 _bit_map->lock()->lock_without_safepoint_check();
6989 _collector->startTimer();
6990 }
6991
6992 ///////////////////////////////////////////////////////////
6993 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6994 // MarkRefsIntoAndScanClosure
6995 ///////////////////////////////////////////////////////////
6996 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6997 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6998 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6999 _span(span),
7000 _bit_map(bit_map),
7001 _work_queue(work_queue),
7002 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
7003 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
7004 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
7005 {
7006 _ref_processor = rp;
7007 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7008 }
7009
7010 // This closure is used to mark refs into the CMS generation at the
7011 // second (final) checkpoint, and to scan and transitively follow
7012 // the unmarked oops. The marks are made in the marking bit map and
7013 // the work_queue is used for keeping the (newly) grey objects during
7014 // the scan phase whence they are also available for stealing by parallel
7015 // threads. Since the marking bit map is shared, updates are
7016 // synchronized (via CAS).
7017 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
7018 if (obj != NULL) {
7019 // Ignore mark word because this could be an already marked oop
7020 // that may be chained at the end of the overflow list.
7021 assert(obj->is_oop(true), "expected an oop");
7022 HeapWord* addr = (HeapWord*)obj;
7023 if (_span.contains(addr) &&
7024 !_bit_map->isMarked(addr)) {
7025 // mark bit map (object will become grey):
7026 // It is possible for several threads to be
7027 // trying to "claim" this object concurrently;
7028 // the unique thread that succeeds in marking the
7029 // object first will do the subsequent push on
7030 // to the work queue (or overflow list).
7031 if (_bit_map->par_mark(addr)) {
7032 // push on work_queue (which may not be empty), and trim the
7033 // queue to an appropriate length by applying this closure to
7034 // the oops in the oops popped from the stack (i.e. blacken the
7035 // grey objects)
7036 bool res = _work_queue->push(obj);
7037 assert(res, "Low water mark should be less than capacity?");
7038 trim_queue(_low_water_mark);
7039 } // Else, another thread claimed the object
7040 }
7041 }
7042 }
7043
7044 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
7045 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
7046
7047 // This closure is used to rescan the marked objects on the dirty cards
7048 // in the mod union table and the card table proper.
7049 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
7050 oop p, MemRegion mr) {
7051
7052 size_t size = 0;
7053 HeapWord* addr = (HeapWord*)p;
7054 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7055 assert(_span.contains(addr), "we are scanning the CMS generation");
7056 // check if it's time to yield
7057 if (do_yield_check()) {
7058 // We yielded for some foreground stop-world work,
7059 // and we have been asked to abort this ongoing preclean cycle.
7060 return 0;
7061 }
7062 if (_bitMap->isMarked(addr)) {
7063 // it's marked; is it potentially uninitialized?
7064 if (p->klass_or_null() != NULL) {
7065 // an initialized object; ignore mark word in verification below
7066 // since we are running concurrent with mutators
7067 assert(p->is_oop(true), "should be an oop");
7068 if (p->is_objArray()) {
7069 // objArrays are precisely marked; restrict scanning
7070 // to dirty cards only.
7071 size = CompactibleFreeListSpace::adjustObjectSize(
7072 p->oop_iterate(_scanningClosure, mr));
7073 } else {
7074 // A non-array may have been imprecisely marked; we need
7075 // to scan object in its entirety.
7076 size = CompactibleFreeListSpace::adjustObjectSize(
7077 p->oop_iterate(_scanningClosure));
7078 }
7079 #ifdef ASSERT
7080 size_t direct_size =
7081 CompactibleFreeListSpace::adjustObjectSize(p->size());
7082 assert(size == direct_size, "Inconsistency in size");
7083 assert(size >= 3, "Necessary for Printezis marks to work");
7084 if (!_bitMap->isMarked(addr+1)) {
7085 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
7086 } else {
7087 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
7088 assert(_bitMap->isMarked(addr+size-1),
7089 "inconsistent Printezis mark");
7090 }
7091 #endif // ASSERT
7092 } else {
7093 // An uninitialized object.
7094 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
7095 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7096 size = pointer_delta(nextOneAddr + 1, addr);
7097 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7098 "alignment problem");
7099 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
7100 // will dirty the card when the klass pointer is installed in the
7101 // object (signaling the completion of initialization).
7102 }
7103 } else {
7104 // Either a not yet marked object or an uninitialized object
7105 if (p->klass_or_null() == NULL) {
7106 // An uninitialized object, skip to the next card, since
7107 // we may not be able to read its P-bits yet.
7108 assert(size == 0, "Initial value");
7109 } else {
7110 // An object not (yet) reached by marking: we merely need to
7111 // compute its size so as to go look at the next block.
7112 assert(p->is_oop(true), "should be an oop");
7113 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
7114 }
7115 }
7116 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7117 return size;
7118 }
7119
7120 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
7121 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7122 "CMS thread should hold CMS token");
7123 assert_lock_strong(_freelistLock);
7124 assert_lock_strong(_bitMap->lock());
7125 // relinquish the free_list_lock and bitMaplock()
7126 _bitMap->lock()->unlock();
7127 _freelistLock->unlock();
7128 ConcurrentMarkSweepThread::desynchronize(true);
7129 ConcurrentMarkSweepThread::acknowledge_yield_request();
7130 _collector->stopTimer();
7131 if (PrintCMSStatistics != 0) {
7132 _collector->incrementYields();
7133 }
7134 _collector->icms_wait();
7135
7136 // See the comment in coordinator_yield()
7137 for (unsigned i = 0; i < CMSYieldSleepCount &&
7138 ConcurrentMarkSweepThread::should_yield() &&
7139 !CMSCollector::foregroundGCIsActive(); ++i) {
7140 os::sleep(Thread::current(), 1, false);
7141 ConcurrentMarkSweepThread::acknowledge_yield_request();
7142 }
7143
7144 ConcurrentMarkSweepThread::synchronize(true);
7145 _freelistLock->lock_without_safepoint_check();
7146 _bitMap->lock()->lock_without_safepoint_check();
7147 _collector->startTimer();
7148 }
7149
7150
7151 //////////////////////////////////////////////////////////////////
7152 // SurvivorSpacePrecleanClosure
7153 //////////////////////////////////////////////////////////////////
7154 // This (single-threaded) closure is used to preclean the oops in
7155 // the survivor spaces.
7156 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
7157
7158 HeapWord* addr = (HeapWord*)p;
7159 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7160 assert(!_span.contains(addr), "we are scanning the survivor spaces");
7161 assert(p->klass_or_null() != NULL, "object should be initialized");
7162 // an initialized object; ignore mark word in verification below
7163 // since we are running concurrent with mutators
7164 assert(p->is_oop(true), "should be an oop");
7165 // Note that we do not yield while we iterate over
7166 // the interior oops of p, pushing the relevant ones
7167 // on our marking stack.
7168 size_t size = p->oop_iterate(_scanning_closure);
7169 do_yield_check();
7170 // Observe that below, we do not abandon the preclean
7171 // phase as soon as we should; rather we empty the
7172 // marking stack before returning. This is to satisfy
7173 // some existing assertions. In general, it may be a
7174 // good idea to abort immediately and complete the marking
7175 // from the grey objects at a later time.
7176 while (!_mark_stack->isEmpty()) {
7177 oop new_oop = _mark_stack->pop();
7178 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7179 assert(_bit_map->isMarked((HeapWord*)new_oop),
7180 "only grey objects on this stack");
7181 // iterate over the oops in this oop, marking and pushing
7182 // the ones in CMS heap (i.e. in _span).
7183 new_oop->oop_iterate(_scanning_closure);
7184 // check if it's time to yield
7185 do_yield_check();
7186 }
7187 unsigned int after_count =
7188 GenCollectedHeap::heap()->total_collections();
7189 bool abort = (_before_count != after_count) ||
7190 _collector->should_abort_preclean();
7191 return abort ? 0 : size;
7192 }
7193
7194 void SurvivorSpacePrecleanClosure::do_yield_work() {
7195 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7196 "CMS thread should hold CMS token");
7197 assert_lock_strong(_bit_map->lock());
7198 // Relinquish the bit map lock
7199 _bit_map->lock()->unlock();
7200 ConcurrentMarkSweepThread::desynchronize(true);
7201 ConcurrentMarkSweepThread::acknowledge_yield_request();
7202 _collector->stopTimer();
7203 if (PrintCMSStatistics != 0) {
7204 _collector->incrementYields();
7205 }
7206 _collector->icms_wait();
7207
7208 // See the comment in coordinator_yield()
7209 for (unsigned i = 0; i < CMSYieldSleepCount &&
7210 ConcurrentMarkSweepThread::should_yield() &&
7211 !CMSCollector::foregroundGCIsActive(); ++i) {
7212 os::sleep(Thread::current(), 1, false);
7213 ConcurrentMarkSweepThread::acknowledge_yield_request();
7214 }
7215
7216 ConcurrentMarkSweepThread::synchronize(true);
7217 _bit_map->lock()->lock_without_safepoint_check();
7218 _collector->startTimer();
7219 }
7220
7221 // This closure is used to rescan the marked objects on the dirty cards
7222 // in the mod union table and the card table proper. In the parallel
7223 // case, although the bitMap is shared, we do a single read so the
7224 // isMarked() query is "safe".
7225 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
7226 // Ignore mark word because we are running concurrent with mutators
7227 assert(p->is_oop_or_null(true), "expected an oop or null");
7228 HeapWord* addr = (HeapWord*)p;
7229 assert(_span.contains(addr), "we are scanning the CMS generation");
7230 bool is_obj_array = false;
7231 #ifdef ASSERT
7232 if (!_parallel) {
7233 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7234 assert(_collector->overflow_list_is_empty(),
7235 "overflow list should be empty");
7236
7237 }
7238 #endif // ASSERT
7239 if (_bit_map->isMarked(addr)) {
7240 // Obj arrays are precisely marked, non-arrays are not;
7241 // so we scan objArrays precisely and non-arrays in their
7242 // entirety.
7243 if (p->is_objArray()) {
7244 is_obj_array = true;
7245 if (_parallel) {
7246 p->oop_iterate(_par_scan_closure, mr);
7247 } else {
7248 p->oop_iterate(_scan_closure, mr);
7249 }
7250 } else {
7251 if (_parallel) {
7252 p->oop_iterate(_par_scan_closure);
7253 } else {
7254 p->oop_iterate(_scan_closure);
7255 }
7256 }
7257 }
7258 #ifdef ASSERT
7259 if (!_parallel) {
7260 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7261 assert(_collector->overflow_list_is_empty(),
7262 "overflow list should be empty");
7263
7264 }
7265 #endif // ASSERT
7266 return is_obj_array;
7267 }
7268
7269 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7270 MemRegion span,
7271 CMSBitMap* bitMap, CMSMarkStack* markStack,
7272 bool should_yield, bool verifying):
7273 _collector(collector),
7274 _span(span),
7275 _bitMap(bitMap),
7276 _mut(&collector->_modUnionTable),
7277 _markStack(markStack),
7278 _yield(should_yield),
7279 _skipBits(0)
7280 {
7281 assert(_markStack->isEmpty(), "stack should be empty");
7282 _finger = _bitMap->startWord();
7283 _threshold = _finger;
7284 assert(_collector->_restart_addr == NULL, "Sanity check");
7285 assert(_span.contains(_finger), "Out of bounds _finger?");
7286 DEBUG_ONLY(_verifying = verifying;)
7287 }
7288
7289 void MarkFromRootsClosure::reset(HeapWord* addr) {
7290 assert(_markStack->isEmpty(), "would cause duplicates on stack");
7291 assert(_span.contains(addr), "Out of bounds _finger?");
7292 _finger = addr;
7293 _threshold = (HeapWord*)round_to(
7294 (intptr_t)_finger, CardTableModRefBS::card_size);
7295 }
7296
7297 // Should revisit to see if this should be restructured for
7298 // greater efficiency.
7299 bool MarkFromRootsClosure::do_bit(size_t offset) {
7300 if (_skipBits > 0) {
7301 _skipBits--;
7302 return true;
7303 }
7304 // convert offset into a HeapWord*
7305 HeapWord* addr = _bitMap->startWord() + offset;
7306 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7307 "address out of range");
7308 assert(_bitMap->isMarked(addr), "tautology");
7309 if (_bitMap->isMarked(addr+1)) {
7310 // this is an allocated but not yet initialized object
7311 assert(_skipBits == 0, "tautology");
7312 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
7313 oop p = oop(addr);
7314 if (p->klass_or_null() == NULL) {
7315 DEBUG_ONLY(if (!_verifying) {)
7316 // We re-dirty the cards on which this object lies and increase
7317 // the _threshold so that we'll come back to scan this object
7318 // during the preclean or remark phase. (CMSCleanOnEnter)
7319 if (CMSCleanOnEnter) {
7320 size_t sz = _collector->block_size_using_printezis_bits(addr);
7321 HeapWord* end_card_addr = (HeapWord*)round_to(
7322 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7323 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7324 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7325 // Bump _threshold to end_card_addr; note that
7326 // _threshold cannot possibly exceed end_card_addr, anyhow.
7327 // This prevents future clearing of the card as the scan proceeds
7328 // to the right.
7329 assert(_threshold <= end_card_addr,
7330 "Because we are just scanning into this object");
7331 if (_threshold < end_card_addr) {
7332 _threshold = end_card_addr;
7333 }
7334 if (p->klass_or_null() != NULL) {
7335 // Redirty the range of cards...
7336 _mut->mark_range(redirty_range);
7337 } // ...else the setting of klass will dirty the card anyway.
7338 }
7339 DEBUG_ONLY(})
7340 return true;
7341 }
7342 }
7343 scanOopsInOop(addr);
7344 return true;
7345 }
7346
7347 // We take a break if we've been at this for a while,
7348 // so as to avoid monopolizing the locks involved.
7349 void MarkFromRootsClosure::do_yield_work() {
7350 // First give up the locks, then yield, then re-lock
7351 // We should probably use a constructor/destructor idiom to
7352 // do this unlock/lock or modify the MutexUnlocker class to
7353 // serve our purpose. XXX
7354 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7355 "CMS thread should hold CMS token");
7356 assert_lock_strong(_bitMap->lock());
7357 _bitMap->lock()->unlock();
7358 ConcurrentMarkSweepThread::desynchronize(true);
7359 ConcurrentMarkSweepThread::acknowledge_yield_request();
7360 _collector->stopTimer();
7361 if (PrintCMSStatistics != 0) {
7362 _collector->incrementYields();
7363 }
7364 _collector->icms_wait();
7365
7366 // See the comment in coordinator_yield()
7367 for (unsigned i = 0; i < CMSYieldSleepCount &&
7368 ConcurrentMarkSweepThread::should_yield() &&
7369 !CMSCollector::foregroundGCIsActive(); ++i) {
7370 os::sleep(Thread::current(), 1, false);
7371 ConcurrentMarkSweepThread::acknowledge_yield_request();
7372 }
7373
7374 ConcurrentMarkSweepThread::synchronize(true);
7375 _bitMap->lock()->lock_without_safepoint_check();
7376 _collector->startTimer();
7377 }
7378
7379 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7380 assert(_bitMap->isMarked(ptr), "expected bit to be set");
7381 assert(_markStack->isEmpty(),
7382 "should drain stack to limit stack usage");
7383 // convert ptr to an oop preparatory to scanning
7384 oop obj = oop(ptr);
7385 // Ignore mark word in verification below, since we
7386 // may be running concurrent with mutators.
7387 assert(obj->is_oop(true), "should be an oop");
7388 assert(_finger <= ptr, "_finger runneth ahead");
7389 // advance the finger to right end of this object
7390 _finger = ptr + obj->size();
7391 assert(_finger > ptr, "we just incremented it above");
7392 // On large heaps, it may take us some time to get through
7393 // the marking phase (especially if running iCMS). During
7394 // this time it's possible that a lot of mutations have
7395 // accumulated in the card table and the mod union table --
7396 // these mutation records are redundant until we have
7397 // actually traced into the corresponding card.
7398 // Here, we check whether advancing the finger would make
7399 // us cross into a new card, and if so clear corresponding
7400 // cards in the MUT (preclean them in the card-table in the
7401 // future).
7402
7403 DEBUG_ONLY(if (!_verifying) {)
7404 // The clean-on-enter optimization is disabled by default,
7405 // until we fix 6178663.
7406 if (CMSCleanOnEnter && (_finger > _threshold)) {
7407 // [_threshold, _finger) represents the interval
7408 // of cards to be cleared in MUT (or precleaned in card table).
7409 // The set of cards to be cleared is all those that overlap
7410 // with the interval [_threshold, _finger); note that
7411 // _threshold is always kept card-aligned but _finger isn't
7412 // always card-aligned.
7413 HeapWord* old_threshold = _threshold;
7414 assert(old_threshold == (HeapWord*)round_to(
7415 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7416 "_threshold should always be card-aligned");
7417 _threshold = (HeapWord*)round_to(
7418 (intptr_t)_finger, CardTableModRefBS::card_size);
7419 MemRegion mr(old_threshold, _threshold);
7420 assert(!mr.is_empty(), "Control point invariant");
7421 assert(_span.contains(mr), "Should clear within span");
7422 _mut->clear_range(mr);
7423 }
7424 DEBUG_ONLY(})
7425 // Note: the finger doesn't advance while we drain
7426 // the stack below.
7427 PushOrMarkClosure pushOrMarkClosure(_collector,
7428 _span, _bitMap, _markStack,
7429 _finger, this);
7430 bool res = _markStack->push(obj);
7431 assert(res, "Empty non-zero size stack should have space for single push");
7432 while (!_markStack->isEmpty()) {
7433 oop new_oop = _markStack->pop();
7434 // Skip verifying header mark word below because we are
7435 // running concurrent with mutators.
7436 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7437 // now scan this oop's oops
7438 new_oop->oop_iterate(&pushOrMarkClosure);
7439 do_yield_check();
7440 }
7441 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7442 }
7443
7444 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7445 CMSCollector* collector, MemRegion span,
7446 CMSBitMap* bit_map,
7447 OopTaskQueue* work_queue,
7448 CMSMarkStack* overflow_stack,
7449 bool should_yield):
7450 _collector(collector),
7451 _whole_span(collector->_span),
7452 _span(span),
7453 _bit_map(bit_map),
7454 _mut(&collector->_modUnionTable),
7455 _work_queue(work_queue),
7456 _overflow_stack(overflow_stack),
7457 _yield(should_yield),
7458 _skip_bits(0),
7459 _task(task)
7460 {
7461 assert(_work_queue->size() == 0, "work_queue should be empty");
7462 _finger = span.start();
7463 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7464 assert(_span.contains(_finger), "Out of bounds _finger?");
7465 }
7466
7467 // Should revisit to see if this should be restructured for
7468 // greater efficiency.
7469 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7470 if (_skip_bits > 0) {
7471 _skip_bits--;
7472 return true;
7473 }
7474 // convert offset into a HeapWord*
7475 HeapWord* addr = _bit_map->startWord() + offset;
7476 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7477 "address out of range");
7478 assert(_bit_map->isMarked(addr), "tautology");
7479 if (_bit_map->isMarked(addr+1)) {
7480 // this is an allocated object that might not yet be initialized
7481 assert(_skip_bits == 0, "tautology");
7482 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7483 oop p = oop(addr);
7484 if (p->klass_or_null() == NULL) {
7485 // in the case of Clean-on-Enter optimization, redirty card
7486 // and avoid clearing card by increasing the threshold.
7487 return true;
7488 }
7489 }
7490 scan_oops_in_oop(addr);
7491 return true;
7492 }
7493
7494 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7495 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7496 // Should we assert that our work queue is empty or
7497 // below some drain limit?
7498 assert(_work_queue->size() == 0,
7499 "should drain stack to limit stack usage");
7500 // convert ptr to an oop preparatory to scanning
7501 oop obj = oop(ptr);
7502 // Ignore mark word in verification below, since we
7503 // may be running concurrent with mutators.
7504 assert(obj->is_oop(true), "should be an oop");
7505 assert(_finger <= ptr, "_finger runneth ahead");
7506 // advance the finger to right end of this object
7507 _finger = ptr + obj->size();
7508 assert(_finger > ptr, "we just incremented it above");
7509 // On large heaps, it may take us some time to get through
7510 // the marking phase (especially if running iCMS). During
7511 // this time it's possible that a lot of mutations have
7512 // accumulated in the card table and the mod union table --
7513 // these mutation records are redundant until we have
7514 // actually traced into the corresponding card.
7515 // Here, we check whether advancing the finger would make
7516 // us cross into a new card, and if so clear corresponding
7517 // cards in the MUT (preclean them in the card-table in the
7518 // future).
7519
7520 // The clean-on-enter optimization is disabled by default,
7521 // until we fix 6178663.
7522 if (CMSCleanOnEnter && (_finger > _threshold)) {
7523 // [_threshold, _finger) represents the interval
7524 // of cards to be cleared in MUT (or precleaned in card table).
7525 // The set of cards to be cleared is all those that overlap
7526 // with the interval [_threshold, _finger); note that
7527 // _threshold is always kept card-aligned but _finger isn't
7528 // always card-aligned.
7529 HeapWord* old_threshold = _threshold;
7530 assert(old_threshold == (HeapWord*)round_to(
7531 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7532 "_threshold should always be card-aligned");
7533 _threshold = (HeapWord*)round_to(
7534 (intptr_t)_finger, CardTableModRefBS::card_size);
7535 MemRegion mr(old_threshold, _threshold);
7536 assert(!mr.is_empty(), "Control point invariant");
7537 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7538 _mut->clear_range(mr);
7539 }
7540
7541 // Note: the local finger doesn't advance while we drain
7542 // the stack below, but the global finger sure can and will.
7543 HeapWord** gfa = _task->global_finger_addr();
7544 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7545 _span, _bit_map,
7546 _work_queue,
7547 _overflow_stack,
7548 _finger,
7549 gfa, this);
7550 bool res = _work_queue->push(obj); // overflow could occur here
7551 assert(res, "Will hold once we use workqueues");
7552 while (true) {
7553 oop new_oop;
7554 if (!_work_queue->pop_local(new_oop)) {
7555 // We emptied our work_queue; check if there's stuff that can
7556 // be gotten from the overflow stack.
7557 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7558 _overflow_stack, _work_queue)) {
7559 do_yield_check();
7560 continue;
7561 } else { // done
7562 break;
7563 }
7564 }
7565 // Skip verifying header mark word below because we are
7566 // running concurrent with mutators.
7567 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7568 // now scan this oop's oops
7569 new_oop->oop_iterate(&pushOrMarkClosure);
7570 do_yield_check();
7571 }
7572 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7573 }
7574
7575 // Yield in response to a request from VM Thread or
7576 // from mutators.
7577 void Par_MarkFromRootsClosure::do_yield_work() {
7578 assert(_task != NULL, "sanity");
7579 _task->yield();
7580 }
7581
7582 // A variant of the above used for verifying CMS marking work.
7583 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7584 MemRegion span,
7585 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7586 CMSMarkStack* mark_stack):
7587 _collector(collector),
7588 _span(span),
7589 _verification_bm(verification_bm),
7590 _cms_bm(cms_bm),
7591 _mark_stack(mark_stack),
7592 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7593 mark_stack)
7594 {
7595 assert(_mark_stack->isEmpty(), "stack should be empty");
7596 _finger = _verification_bm->startWord();
7597 assert(_collector->_restart_addr == NULL, "Sanity check");
7598 assert(_span.contains(_finger), "Out of bounds _finger?");
7599 }
7600
7601 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7602 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7603 assert(_span.contains(addr), "Out of bounds _finger?");
7604 _finger = addr;
7605 }
7606
7607 // Should revisit to see if this should be restructured for
7608 // greater efficiency.
7609 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7610 // convert offset into a HeapWord*
7611 HeapWord* addr = _verification_bm->startWord() + offset;
7612 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7613 "address out of range");
7614 assert(_verification_bm->isMarked(addr), "tautology");
7615 assert(_cms_bm->isMarked(addr), "tautology");
7616
7617 assert(_mark_stack->isEmpty(),
7618 "should drain stack to limit stack usage");
7619 // convert addr to an oop preparatory to scanning
7620 oop obj = oop(addr);
7621 assert(obj->is_oop(), "should be an oop");
7622 assert(_finger <= addr, "_finger runneth ahead");
7623 // advance the finger to right end of this object
7624 _finger = addr + obj->size();
7625 assert(_finger > addr, "we just incremented it above");
7626 // Note: the finger doesn't advance while we drain
7627 // the stack below.
7628 bool res = _mark_stack->push(obj);
7629 assert(res, "Empty non-zero size stack should have space for single push");
7630 while (!_mark_stack->isEmpty()) {
7631 oop new_oop = _mark_stack->pop();
7632 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7633 // now scan this oop's oops
7634 new_oop->oop_iterate(&_pam_verify_closure);
7635 }
7636 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7637 return true;
7638 }
7639
7640 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7641 CMSCollector* collector, MemRegion span,
7642 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7643 CMSMarkStack* mark_stack):
7644 MetadataAwareOopClosure(collector->ref_processor()),
7645 _collector(collector),
7646 _span(span),
7647 _verification_bm(verification_bm),
7648 _cms_bm(cms_bm),
7649 _mark_stack(mark_stack)
7650 { }
7651
7652 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7653 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7654
7655 // Upon stack overflow, we discard (part of) the stack,
7656 // remembering the least address amongst those discarded
7657 // in CMSCollector's _restart_address.
7658 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7659 // Remember the least grey address discarded
7660 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7661 _collector->lower_restart_addr(ra);
7662 _mark_stack->reset(); // discard stack contents
7663 _mark_stack->expand(); // expand the stack if possible
7664 }
7665
7666 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7667 assert(obj->is_oop_or_null(), "expected an oop or NULL");
7668 HeapWord* addr = (HeapWord*)obj;
7669 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7670 // Oop lies in _span and isn't yet grey or black
7671 _verification_bm->mark(addr); // now grey
7672 if (!_cms_bm->isMarked(addr)) {
7673 oop(addr)->print();
7674 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7675 addr);
7676 fatal("... aborting");
7677 }
7678
7679 if (!_mark_stack->push(obj)) { // stack overflow
7680 if (PrintCMSStatistics != 0) {
7681 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7682 SIZE_FORMAT, _mark_stack->capacity());
7683 }
7684 assert(_mark_stack->isFull(), "Else push should have succeeded");
7685 handle_stack_overflow(addr);
7686 }
7687 // anything including and to the right of _finger
7688 // will be scanned as we iterate over the remainder of the
7689 // bit map
7690 }
7691 }
7692
7693 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7694 MemRegion span,
7695 CMSBitMap* bitMap, CMSMarkStack* markStack,
7696 HeapWord* finger, MarkFromRootsClosure* parent) :
7697 MetadataAwareOopClosure(collector->ref_processor()),
7698 _collector(collector),
7699 _span(span),
7700 _bitMap(bitMap),
7701 _markStack(markStack),
7702 _finger(finger),
7703 _parent(parent)
7704 { }
7705
7706 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7707 MemRegion span,
7708 CMSBitMap* bit_map,
7709 OopTaskQueue* work_queue,
7710 CMSMarkStack* overflow_stack,
7711 HeapWord* finger,
7712 HeapWord** global_finger_addr,
7713 Par_MarkFromRootsClosure* parent) :
7714 MetadataAwareOopClosure(collector->ref_processor()),
7715 _collector(collector),
7716 _whole_span(collector->_span),
7717 _span(span),
7718 _bit_map(bit_map),
7719 _work_queue(work_queue),
7720 _overflow_stack(overflow_stack),
7721 _finger(finger),
7722 _global_finger_addr(global_finger_addr),
7723 _parent(parent)
7724 { }
7725
7726 // Assumes thread-safe access by callers, who are
7727 // responsible for mutual exclusion.
7728 void CMSCollector::lower_restart_addr(HeapWord* low) {
7729 assert(_span.contains(low), "Out of bounds addr");
7730 if (_restart_addr == NULL) {
7731 _restart_addr = low;
7732 } else {
7733 _restart_addr = MIN2(_restart_addr, low);
7734 }
7735 }
7736
7737 // Upon stack overflow, we discard (part of) the stack,
7738 // remembering the least address amongst those discarded
7739 // in CMSCollector's _restart_address.
7740 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7741 // Remember the least grey address discarded
7742 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7743 _collector->lower_restart_addr(ra);
7744 _markStack->reset(); // discard stack contents
7745 _markStack->expand(); // expand the stack if possible
7746 }
7747
7748 // Upon stack overflow, we discard (part of) the stack,
7749 // remembering the least address amongst those discarded
7750 // in CMSCollector's _restart_address.
7751 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7752 // We need to do this under a mutex to prevent other
7753 // workers from interfering with the work done below.
7754 MutexLockerEx ml(_overflow_stack->par_lock(),
7755 Mutex::_no_safepoint_check_flag);
7756 // Remember the least grey address discarded
7757 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7758 _collector->lower_restart_addr(ra);
7759 _overflow_stack->reset(); // discard stack contents
7760 _overflow_stack->expand(); // expand the stack if possible
7761 }
7762
7763 void PushOrMarkClosure::do_oop(oop obj) {
7764 // Ignore mark word because we are running concurrent with mutators.
7765 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7766 HeapWord* addr = (HeapWord*)obj;
7767 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7768 // Oop lies in _span and isn't yet grey or black
7769 _bitMap->mark(addr); // now grey
7770 if (addr < _finger) {
7771 // the bit map iteration has already either passed, or
7772 // sampled, this bit in the bit map; we'll need to
7773 // use the marking stack to scan this oop's oops.
7774 bool simulate_overflow = false;
7775 NOT_PRODUCT(
7776 if (CMSMarkStackOverflowALot &&
7777 _collector->simulate_overflow()) {
7778 // simulate a stack overflow
7779 simulate_overflow = true;
7780 }
7781 )
7782 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7783 if (PrintCMSStatistics != 0) {
7784 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7785 SIZE_FORMAT, _markStack->capacity());
7786 }
7787 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7788 handle_stack_overflow(addr);
7789 }
7790 }
7791 // anything including and to the right of _finger
7792 // will be scanned as we iterate over the remainder of the
7793 // bit map
7794 do_yield_check();
7795 }
7796 }
7797
7798 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7799 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7800
7801 void Par_PushOrMarkClosure::do_oop(oop obj) {
7802 // Ignore mark word because we are running concurrent with mutators.
7803 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7804 HeapWord* addr = (HeapWord*)obj;
7805 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7806 // Oop lies in _span and isn't yet grey or black
7807 // We read the global_finger (volatile read) strictly after marking oop
7808 bool res = _bit_map->par_mark(addr); // now grey
7809 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7810 // Should we push this marked oop on our stack?
7811 // -- if someone else marked it, nothing to do
7812 // -- if target oop is above global finger nothing to do
7813 // -- if target oop is in chunk and above local finger
7814 // then nothing to do
7815 // -- else push on work queue
7816 if ( !res // someone else marked it, they will deal with it
7817 || (addr >= *gfa) // will be scanned in a later task
7818 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7819 return;
7820 }
7821 // the bit map iteration has already either passed, or
7822 // sampled, this bit in the bit map; we'll need to
7823 // use the marking stack to scan this oop's oops.
7824 bool simulate_overflow = false;
7825 NOT_PRODUCT(
7826 if (CMSMarkStackOverflowALot &&
7827 _collector->simulate_overflow()) {
7828 // simulate a stack overflow
7829 simulate_overflow = true;
7830 }
7831 )
7832 if (simulate_overflow ||
7833 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7834 // stack overflow
7835 if (PrintCMSStatistics != 0) {
7836 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7837 SIZE_FORMAT, _overflow_stack->capacity());
7838 }
7839 // We cannot assert that the overflow stack is full because
7840 // it may have been emptied since.
7841 assert(simulate_overflow ||
7842 _work_queue->size() == _work_queue->max_elems(),
7843 "Else push should have succeeded");
7844 handle_stack_overflow(addr);
7845 }
7846 do_yield_check();
7847 }
7848 }
7849
7850 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7851 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7852
7853 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7854 MemRegion span,
7855 ReferenceProcessor* rp,
7856 CMSBitMap* bit_map,
7857 CMSBitMap* mod_union_table,
7858 CMSMarkStack* mark_stack,
7859 bool concurrent_precleaning):
7860 MetadataAwareOopClosure(rp),
7861 _collector(collector),
7862 _span(span),
7863 _bit_map(bit_map),
7864 _mod_union_table(mod_union_table),
7865 _mark_stack(mark_stack),
7866 _concurrent_precleaning(concurrent_precleaning)
7867 {
7868 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7869 }
7870
7871 // Grey object rescan during pre-cleaning and second checkpoint phases --
7872 // the non-parallel version (the parallel version appears further below.)
7873 void PushAndMarkClosure::do_oop(oop obj) {
7874 // Ignore mark word verification. If during concurrent precleaning,
7875 // the object monitor may be locked. If during the checkpoint
7876 // phases, the object may already have been reached by a different
7877 // path and may be at the end of the global overflow list (so
7878 // the mark word may be NULL).
7879 assert(obj->is_oop_or_null(true /* ignore mark word */),
7880 "expected an oop or NULL");
7881 HeapWord* addr = (HeapWord*)obj;
7882 // Check if oop points into the CMS generation
7883 // and is not marked
7884 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7885 // a white object ...
7886 _bit_map->mark(addr); // ... now grey
7887 // push on the marking stack (grey set)
7888 bool simulate_overflow = false;
7889 NOT_PRODUCT(
7890 if (CMSMarkStackOverflowALot &&
7891 _collector->simulate_overflow()) {
7892 // simulate a stack overflow
7893 simulate_overflow = true;
7894 }
7895 )
7896 if (simulate_overflow || !_mark_stack->push(obj)) {
7897 if (_concurrent_precleaning) {
7898 // During precleaning we can just dirty the appropriate card(s)
7899 // in the mod union table, thus ensuring that the object remains
7900 // in the grey set and continue. In the case of object arrays
7901 // we need to dirty all of the cards that the object spans,
7902 // since the rescan of object arrays will be limited to the
7903 // dirty cards.
7904 // Note that no one can be interfering with us in this action
7905 // of dirtying the mod union table, so no locking or atomics
7906 // are required.
7907 if (obj->is_objArray()) {
7908 size_t sz = obj->size();
7909 HeapWord* end_card_addr = (HeapWord*)round_to(
7910 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7911 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7912 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7913 _mod_union_table->mark_range(redirty_range);
7914 } else {
7915 _mod_union_table->mark(addr);
7916 }
7917 _collector->_ser_pmc_preclean_ovflw++;
7918 } else {
7919 // During the remark phase, we need to remember this oop
7920 // in the overflow list.
7921 _collector->push_on_overflow_list(obj);
7922 _collector->_ser_pmc_remark_ovflw++;
7923 }
7924 }
7925 }
7926 }
7927
7928 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7929 MemRegion span,
7930 ReferenceProcessor* rp,
7931 CMSBitMap* bit_map,
7932 OopTaskQueue* work_queue):
7933 MetadataAwareOopClosure(rp),
7934 _collector(collector),
7935 _span(span),
7936 _bit_map(bit_map),
7937 _work_queue(work_queue)
7938 {
7939 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7940 }
7941
7942 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7943 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7944
7945 // Grey object rescan during second checkpoint phase --
7946 // the parallel version.
7947 void Par_PushAndMarkClosure::do_oop(oop obj) {
7948 // In the assert below, we ignore the mark word because
7949 // this oop may point to an already visited object that is
7950 // on the overflow stack (in which case the mark word has
7951 // been hijacked for chaining into the overflow stack --
7952 // if this is the last object in the overflow stack then
7953 // its mark word will be NULL). Because this object may
7954 // have been subsequently popped off the global overflow
7955 // stack, and the mark word possibly restored to the prototypical
7956 // value, by the time we get to examined this failing assert in
7957 // the debugger, is_oop_or_null(false) may subsequently start
7958 // to hold.
7959 assert(obj->is_oop_or_null(true),
7960 "expected an oop or NULL");
7961 HeapWord* addr = (HeapWord*)obj;
7962 // Check if oop points into the CMS generation
7963 // and is not marked
7964 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7965 // a white object ...
7966 // If we manage to "claim" the object, by being the
7967 // first thread to mark it, then we push it on our
7968 // marking stack
7969 if (_bit_map->par_mark(addr)) { // ... now grey
7970 // push on work queue (grey set)
7971 bool simulate_overflow = false;
7972 NOT_PRODUCT(
7973 if (CMSMarkStackOverflowALot &&
7974 _collector->par_simulate_overflow()) {
7975 // simulate a stack overflow
7976 simulate_overflow = true;
7977 }
7978 )
7979 if (simulate_overflow || !_work_queue->push(obj)) {
7980 _collector->par_push_on_overflow_list(obj);
7981 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7982 }
7983 } // Else, some other thread got there first
7984 }
7985 }
7986
7987 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7988 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7989
7990 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7991 Mutex* bml = _collector->bitMapLock();
7992 assert_lock_strong(bml);
7993 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7994 "CMS thread should hold CMS token");
7995
7996 bml->unlock();
7997 ConcurrentMarkSweepThread::desynchronize(true);
7998
7999 ConcurrentMarkSweepThread::acknowledge_yield_request();
8000
8001 _collector->stopTimer();
8002 if (PrintCMSStatistics != 0) {
8003 _collector->incrementYields();
8004 }
8005 _collector->icms_wait();
8006
8007 // See the comment in coordinator_yield()
8008 for (unsigned i = 0; i < CMSYieldSleepCount &&
8009 ConcurrentMarkSweepThread::should_yield() &&
8010 !CMSCollector::foregroundGCIsActive(); ++i) {
8011 os::sleep(Thread::current(), 1, false);
8012 ConcurrentMarkSweepThread::acknowledge_yield_request();
8013 }
8014
8015 ConcurrentMarkSweepThread::synchronize(true);
8016 bml->lock();
8017
8018 _collector->startTimer();
8019 }
8020
8021 bool CMSPrecleanRefsYieldClosure::should_return() {
8022 if (ConcurrentMarkSweepThread::should_yield()) {
8023 do_yield_work();
8024 }
8025 return _collector->foregroundGCIsActive();
8026 }
8027
8028 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
8029 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
8030 "mr should be aligned to start at a card boundary");
8031 // We'd like to assert:
8032 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
8033 // "mr should be a range of cards");
8034 // However, that would be too strong in one case -- the last
8035 // partition ends at _unallocated_block which, in general, can be
8036 // an arbitrary boundary, not necessarily card aligned.
8037 if (PrintCMSStatistics != 0) {
8038 _num_dirty_cards +=
8039 mr.word_size()/CardTableModRefBS::card_size_in_words;
8040 }
8041 _space->object_iterate_mem(mr, &_scan_cl);
8042 }
8043
8044 SweepClosure::SweepClosure(CMSCollector* collector,
8045 ConcurrentMarkSweepGeneration* g,
8046 CMSBitMap* bitMap, bool should_yield) :
8047 _collector(collector),
8048 _g(g),
8049 _sp(g->cmsSpace()),
8050 _limit(_sp->sweep_limit()),
8051 _freelistLock(_sp->freelistLock()),
8052 _bitMap(bitMap),
8053 _yield(should_yield),
8054 _inFreeRange(false), // No free range at beginning of sweep
8055 _freeRangeInFreeLists(false), // No free range at beginning of sweep
8056 _lastFreeRangeCoalesced(false),
8057 _freeFinger(g->used_region().start())
8058 {
8059 NOT_PRODUCT(
8060 _numObjectsFreed = 0;
8061 _numWordsFreed = 0;
8062 _numObjectsLive = 0;
8063 _numWordsLive = 0;
8064 _numObjectsAlreadyFree = 0;
8065 _numWordsAlreadyFree = 0;
8066 _last_fc = NULL;
8067
8068 _sp->initializeIndexedFreeListArrayReturnedBytes();
8069 _sp->dictionary()->initialize_dict_returned_bytes();
8070 )
8071 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8072 "sweep _limit out of bounds");
8073 if (CMSTraceSweeper) {
8074 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
8075 _limit);
8076 }
8077 }
8078
8079 void SweepClosure::print_on(outputStream* st) const {
8080 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
8081 _sp->bottom(), _sp->end());
8082 tty->print_cr("_limit = " PTR_FORMAT, _limit);
8083 tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
8084 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
8085 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
8086 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
8087 }
8088
8089 #ifndef PRODUCT
8090 // Assertion checking only: no useful work in product mode --
8091 // however, if any of the flags below become product flags,
8092 // you may need to review this code to see if it needs to be
8093 // enabled in product mode.
8094 SweepClosure::~SweepClosure() {
8095 assert_lock_strong(_freelistLock);
8096 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8097 "sweep _limit out of bounds");
8098 if (inFreeRange()) {
8099 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
8100 print();
8101 ShouldNotReachHere();
8102 }
8103 if (Verbose && PrintGC) {
8104 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
8105 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
8106 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
8107 SIZE_FORMAT" bytes "
8108 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
8109 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
8110 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
8111 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
8112 * sizeof(HeapWord);
8113 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
8114
8115 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
8116 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
8117 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
8118 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
8119 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
8120 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
8121 indexListReturnedBytes);
8122 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
8123 dict_returned_bytes);
8124 }
8125 }
8126 if (CMSTraceSweeper) {
8127 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
8128 _limit);
8129 }
8130 }
8131 #endif // PRODUCT
8132
8133 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
8134 bool freeRangeInFreeLists) {
8135 if (CMSTraceSweeper) {
8136 gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
8137 freeFinger, freeRangeInFreeLists);
8138 }
8139 assert(!inFreeRange(), "Trampling existing free range");
8140 set_inFreeRange(true);
8141 set_lastFreeRangeCoalesced(false);
8142
8143 set_freeFinger(freeFinger);
8144 set_freeRangeInFreeLists(freeRangeInFreeLists);
8145 if (CMSTestInFreeList) {
8146 if (freeRangeInFreeLists) {
8147 FreeChunk* fc = (FreeChunk*) freeFinger;
8148 assert(fc->is_free(), "A chunk on the free list should be free.");
8149 assert(fc->size() > 0, "Free range should have a size");
8150 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
8151 }
8152 }
8153 }
8154
8155 // Note that the sweeper runs concurrently with mutators. Thus,
8156 // it is possible for direct allocation in this generation to happen
8157 // in the middle of the sweep. Note that the sweeper also coalesces
8158 // contiguous free blocks. Thus, unless the sweeper and the allocator
8159 // synchronize appropriately freshly allocated blocks may get swept up.
8160 // This is accomplished by the sweeper locking the free lists while
8161 // it is sweeping. Thus blocks that are determined to be free are
8162 // indeed free. There is however one additional complication:
8163 // blocks that have been allocated since the final checkpoint and
8164 // mark, will not have been marked and so would be treated as
8165 // unreachable and swept up. To prevent this, the allocator marks
8166 // the bit map when allocating during the sweep phase. This leads,
8167 // however, to a further complication -- objects may have been allocated
8168 // but not yet initialized -- in the sense that the header isn't yet
8169 // installed. The sweeper can not then determine the size of the block
8170 // in order to skip over it. To deal with this case, we use a technique
8171 // (due to Printezis) to encode such uninitialized block sizes in the
8172 // bit map. Since the bit map uses a bit per every HeapWord, but the
8173 // CMS generation has a minimum object size of 3 HeapWords, it follows
8174 // that "normal marks" won't be adjacent in the bit map (there will
8175 // always be at least two 0 bits between successive 1 bits). We make use
8176 // of these "unused" bits to represent uninitialized blocks -- the bit
8177 // corresponding to the start of the uninitialized object and the next
8178 // bit are both set. Finally, a 1 bit marks the end of the object that
8179 // started with the two consecutive 1 bits to indicate its potentially
8180 // uninitialized state.
8181
8182 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
8183 FreeChunk* fc = (FreeChunk*)addr;
8184 size_t res;
8185
8186 // Check if we are done sweeping. Below we check "addr >= _limit" rather
8187 // than "addr == _limit" because although _limit was a block boundary when
8188 // we started the sweep, it may no longer be one because heap expansion
8189 // may have caused us to coalesce the block ending at the address _limit
8190 // with a newly expanded chunk (this happens when _limit was set to the
8191 // previous _end of the space), so we may have stepped past _limit:
8192 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
8193 if (addr >= _limit) { // we have swept up to or past the limit: finish up
8194 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8195 "sweep _limit out of bounds");
8196 assert(addr < _sp->end(), "addr out of bounds");
8197 // Flush any free range we might be holding as a single
8198 // coalesced chunk to the appropriate free list.
8199 if (inFreeRange()) {
8200 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
8201 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
8202 flush_cur_free_chunk(freeFinger(),
8203 pointer_delta(addr, freeFinger()));
8204 if (CMSTraceSweeper) {
8205 gclog_or_tty->print("Sweep: last chunk: ");
8206 gclog_or_tty->print("put_free_blk " PTR_FORMAT " ("SIZE_FORMAT") "
8207 "[coalesced:%d]\n",
8208 freeFinger(), pointer_delta(addr, freeFinger()),
8209 lastFreeRangeCoalesced() ? 1 : 0);
8210 }
8211 }
8212
8213 // help the iterator loop finish
8214 return pointer_delta(_sp->end(), addr);
8215 }
8216
8217 assert(addr < _limit, "sweep invariant");
8218 // check if we should yield
8219 do_yield_check(addr);
8220 if (fc->is_free()) {
8221 // Chunk that is already free
8222 res = fc->size();
8223 do_already_free_chunk(fc);
8224 debug_only(_sp->verifyFreeLists());
8225 // If we flush the chunk at hand in lookahead_and_flush()
8226 // and it's coalesced with a preceding chunk, then the
8227 // process of "mangling" the payload of the coalesced block
8228 // will cause erasure of the size information from the
8229 // (erstwhile) header of all the coalesced blocks but the
8230 // first, so the first disjunct in the assert will not hold
8231 // in that specific case (in which case the second disjunct
8232 // will hold).
8233 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
8234 "Otherwise the size info doesn't change at this step");
8235 NOT_PRODUCT(
8236 _numObjectsAlreadyFree++;
8237 _numWordsAlreadyFree += res;
8238 )
8239 NOT_PRODUCT(_last_fc = fc;)
8240 } else if (!_bitMap->isMarked(addr)) {
8241 // Chunk is fresh garbage
8242 res = do_garbage_chunk(fc);
8243 debug_only(_sp->verifyFreeLists());
8244 NOT_PRODUCT(
8245 _numObjectsFreed++;
8246 _numWordsFreed += res;
8247 )
8248 } else {
8249 // Chunk that is alive.
8250 res = do_live_chunk(fc);
8251 debug_only(_sp->verifyFreeLists());
8252 NOT_PRODUCT(
8253 _numObjectsLive++;
8254 _numWordsLive += res;
8255 )
8256 }
8257 return res;
8258 }
8259
8260 // For the smart allocation, record following
8261 // split deaths - a free chunk is removed from its free list because
8262 // it is being split into two or more chunks.
8263 // split birth - a free chunk is being added to its free list because
8264 // a larger free chunk has been split and resulted in this free chunk.
8265 // coal death - a free chunk is being removed from its free list because
8266 // it is being coalesced into a large free chunk.
8267 // coal birth - a free chunk is being added to its free list because
8268 // it was created when two or more free chunks where coalesced into
8269 // this free chunk.
8270 //
8271 // These statistics are used to determine the desired number of free
8272 // chunks of a given size. The desired number is chosen to be relative
8273 // to the end of a CMS sweep. The desired number at the end of a sweep
8274 // is the
8275 // count-at-end-of-previous-sweep (an amount that was enough)
8276 // - count-at-beginning-of-current-sweep (the excess)
8277 // + split-births (gains in this size during interval)
8278 // - split-deaths (demands on this size during interval)
8279 // where the interval is from the end of one sweep to the end of the
8280 // next.
8281 //
8282 // When sweeping the sweeper maintains an accumulated chunk which is
8283 // the chunk that is made up of chunks that have been coalesced. That
8284 // will be termed the left-hand chunk. A new chunk of garbage that
8285 // is being considered for coalescing will be referred to as the
8286 // right-hand chunk.
8287 //
8288 // When making a decision on whether to coalesce a right-hand chunk with
8289 // the current left-hand chunk, the current count vs. the desired count
8290 // of the left-hand chunk is considered. Also if the right-hand chunk
8291 // is near the large chunk at the end of the heap (see
8292 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8293 // left-hand chunk is coalesced.
8294 //
8295 // When making a decision about whether to split a chunk, the desired count
8296 // vs. the current count of the candidate to be split is also considered.
8297 // If the candidate is underpopulated (currently fewer chunks than desired)
8298 // a chunk of an overpopulated (currently more chunks than desired) size may
8299 // be chosen. The "hint" associated with a free list, if non-null, points
8300 // to a free list which may be overpopulated.
8301 //
8302
8303 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
8304 const size_t size = fc->size();
8305 // Chunks that cannot be coalesced are not in the
8306 // free lists.
8307 if (CMSTestInFreeList && !fc->cantCoalesce()) {
8308 assert(_sp->verify_chunk_in_free_list(fc),
8309 "free chunk should be in free lists");
8310 }
8311 // a chunk that is already free, should not have been
8312 // marked in the bit map
8313 HeapWord* const addr = (HeapWord*) fc;
8314 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8315 // Verify that the bit map has no bits marked between
8316 // addr and purported end of this block.
8317 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8318
8319 // Some chunks cannot be coalesced under any circumstances.
8320 // See the definition of cantCoalesce().
8321 if (!fc->cantCoalesce()) {
8322 // This chunk can potentially be coalesced.
8323 if (_sp->adaptive_freelists()) {
8324 // All the work is done in
8325 do_post_free_or_garbage_chunk(fc, size);
8326 } else { // Not adaptive free lists
8327 // this is a free chunk that can potentially be coalesced by the sweeper;
8328 if (!inFreeRange()) {
8329 // if the next chunk is a free block that can't be coalesced
8330 // it doesn't make sense to remove this chunk from the free lists
8331 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8332 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
8333 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
8334 nextChunk->is_free() && // ... which is free...
8335 nextChunk->cantCoalesce()) { // ... but can't be coalesced
8336 // nothing to do
8337 } else {
8338 // Potentially the start of a new free range:
8339 // Don't eagerly remove it from the free lists.
8340 // No need to remove it if it will just be put
8341 // back again. (Also from a pragmatic point of view
8342 // if it is a free block in a region that is beyond
8343 // any allocated blocks, an assertion will fail)
8344 // Remember the start of a free run.
8345 initialize_free_range(addr, true);
8346 // end - can coalesce with next chunk
8347 }
8348 } else {
8349 // the midst of a free range, we are coalescing
8350 print_free_block_coalesced(fc);
8351 if (CMSTraceSweeper) {
8352 gclog_or_tty->print(" -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", fc, size);
8353 }
8354 // remove it from the free lists
8355 _sp->removeFreeChunkFromFreeLists(fc);
8356 set_lastFreeRangeCoalesced(true);
8357 // If the chunk is being coalesced and the current free range is
8358 // in the free lists, remove the current free range so that it
8359 // will be returned to the free lists in its entirety - all
8360 // the coalesced pieces included.
8361 if (freeRangeInFreeLists()) {
8362 FreeChunk* ffc = (FreeChunk*) freeFinger();
8363 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8364 "Size of free range is inconsistent with chunk size.");
8365 if (CMSTestInFreeList) {
8366 assert(_sp->verify_chunk_in_free_list(ffc),
8367 "free range is not in free lists");
8368 }
8369 _sp->removeFreeChunkFromFreeLists(ffc);
8370 set_freeRangeInFreeLists(false);
8371 }
8372 }
8373 }
8374 // Note that if the chunk is not coalescable (the else arm
8375 // below), we unconditionally flush, without needing to do
8376 // a "lookahead," as we do below.
8377 if (inFreeRange()) lookahead_and_flush(fc, size);
8378 } else {
8379 // Code path common to both original and adaptive free lists.
8380
8381 // cant coalesce with previous block; this should be treated
8382 // as the end of a free run if any
8383 if (inFreeRange()) {
8384 // we kicked some butt; time to pick up the garbage
8385 assert(freeFinger() < addr, "freeFinger points too high");
8386 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8387 }
8388 // else, nothing to do, just continue
8389 }
8390 }
8391
8392 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
8393 // This is a chunk of garbage. It is not in any free list.
8394 // Add it to a free list or let it possibly be coalesced into
8395 // a larger chunk.
8396 HeapWord* const addr = (HeapWord*) fc;
8397 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8398
8399 if (_sp->adaptive_freelists()) {
8400 // Verify that the bit map has no bits marked between
8401 // addr and purported end of just dead object.
8402 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8403
8404 do_post_free_or_garbage_chunk(fc, size);
8405 } else {
8406 if (!inFreeRange()) {
8407 // start of a new free range
8408 assert(size > 0, "A free range should have a size");
8409 initialize_free_range(addr, false);
8410 } else {
8411 // this will be swept up when we hit the end of the
8412 // free range
8413 if (CMSTraceSweeper) {
8414 gclog_or_tty->print(" -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", fc, size);
8415 }
8416 // If the chunk is being coalesced and the current free range is
8417 // in the free lists, remove the current free range so that it
8418 // will be returned to the free lists in its entirety - all
8419 // the coalesced pieces included.
8420 if (freeRangeInFreeLists()) {
8421 FreeChunk* ffc = (FreeChunk*)freeFinger();
8422 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8423 "Size of free range is inconsistent with chunk size.");
8424 if (CMSTestInFreeList) {
8425 assert(_sp->verify_chunk_in_free_list(ffc),
8426 "free range is not in free lists");
8427 }
8428 _sp->removeFreeChunkFromFreeLists(ffc);
8429 set_freeRangeInFreeLists(false);
8430 }
8431 set_lastFreeRangeCoalesced(true);
8432 }
8433 // this will be swept up when we hit the end of the free range
8434
8435 // Verify that the bit map has no bits marked between
8436 // addr and purported end of just dead object.
8437 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8438 }
8439 assert(_limit >= addr + size,
8440 "A freshly garbage chunk can't possibly straddle over _limit");
8441 if (inFreeRange()) lookahead_and_flush(fc, size);
8442 return size;
8443 }
8444
8445 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
8446 HeapWord* addr = (HeapWord*) fc;
8447 // The sweeper has just found a live object. Return any accumulated
8448 // left hand chunk to the free lists.
8449 if (inFreeRange()) {
8450 assert(freeFinger() < addr, "freeFinger points too high");
8451 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8452 }
8453
8454 // This object is live: we'd normally expect this to be
8455 // an oop, and like to assert the following:
8456 // assert(oop(addr)->is_oop(), "live block should be an oop");
8457 // However, as we commented above, this may be an object whose
8458 // header hasn't yet been initialized.
8459 size_t size;
8460 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8461 if (_bitMap->isMarked(addr + 1)) {
8462 // Determine the size from the bit map, rather than trying to
8463 // compute it from the object header.
8464 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8465 size = pointer_delta(nextOneAddr + 1, addr);
8466 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8467 "alignment problem");
8468
8469 #ifdef ASSERT
8470 if (oop(addr)->klass_or_null() != NULL) {
8471 // Ignore mark word because we are running concurrent with mutators
8472 assert(oop(addr)->is_oop(true), "live block should be an oop");
8473 assert(size ==
8474 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8475 "P-mark and computed size do not agree");
8476 }
8477 #endif
8478
8479 } else {
8480 // This should be an initialized object that's alive.
8481 assert(oop(addr)->klass_or_null() != NULL,
8482 "Should be an initialized object");
8483 // Ignore mark word because we are running concurrent with mutators
8484 assert(oop(addr)->is_oop(true), "live block should be an oop");
8485 // Verify that the bit map has no bits marked between
8486 // addr and purported end of this block.
8487 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8488 assert(size >= 3, "Necessary for Printezis marks to work");
8489 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8490 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8491 }
8492 return size;
8493 }
8494
8495 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
8496 size_t chunkSize) {
8497 // do_post_free_or_garbage_chunk() should only be called in the case
8498 // of the adaptive free list allocator.
8499 const bool fcInFreeLists = fc->is_free();
8500 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8501 assert((HeapWord*)fc <= _limit, "sweep invariant");
8502 if (CMSTestInFreeList && fcInFreeLists) {
8503 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
8504 }
8505
8506 if (CMSTraceSweeper) {
8507 gclog_or_tty->print_cr(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", fc, chunkSize);
8508 }
8509
8510 HeapWord* const fc_addr = (HeapWord*) fc;
8511
8512 bool coalesce;
8513 const size_t left = pointer_delta(fc_addr, freeFinger());
8514 const size_t right = chunkSize;
8515 switch (FLSCoalescePolicy) {
8516 // numeric value forms a coalition aggressiveness metric
8517 case 0: { // never coalesce
8518 coalesce = false;
8519 break;
8520 }
8521 case 1: { // coalesce if left & right chunks on overpopulated lists
8522 coalesce = _sp->coalOverPopulated(left) &&
8523 _sp->coalOverPopulated(right);
8524 break;
8525 }
8526 case 2: { // coalesce if left chunk on overpopulated list (default)
8527 coalesce = _sp->coalOverPopulated(left);
8528 break;
8529 }
8530 case 3: { // coalesce if left OR right chunk on overpopulated list
8531 coalesce = _sp->coalOverPopulated(left) ||
8532 _sp->coalOverPopulated(right);
8533 break;
8534 }
8535 case 4: { // always coalesce
8536 coalesce = true;
8537 break;
8538 }
8539 default:
8540 ShouldNotReachHere();
8541 }
8542
8543 // Should the current free range be coalesced?
8544 // If the chunk is in a free range and either we decided to coalesce above
8545 // or the chunk is near the large block at the end of the heap
8546 // (isNearLargestChunk() returns true), then coalesce this chunk.
8547 const bool doCoalesce = inFreeRange()
8548 && (coalesce || _g->isNearLargestChunk(fc_addr));
8549 if (doCoalesce) {
8550 // Coalesce the current free range on the left with the new
8551 // chunk on the right. If either is on a free list,
8552 // it must be removed from the list and stashed in the closure.
8553 if (freeRangeInFreeLists()) {
8554 FreeChunk* const ffc = (FreeChunk*)freeFinger();
8555 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
8556 "Size of free range is inconsistent with chunk size.");
8557 if (CMSTestInFreeList) {
8558 assert(_sp->verify_chunk_in_free_list(ffc),
8559 "Chunk is not in free lists");
8560 }
8561 _sp->coalDeath(ffc->size());
8562 _sp->removeFreeChunkFromFreeLists(ffc);
8563 set_freeRangeInFreeLists(false);
8564 }
8565 if (fcInFreeLists) {
8566 _sp->coalDeath(chunkSize);
8567 assert(fc->size() == chunkSize,
8568 "The chunk has the wrong size or is not in the free lists");
8569 _sp->removeFreeChunkFromFreeLists(fc);
8570 }
8571 set_lastFreeRangeCoalesced(true);
8572 print_free_block_coalesced(fc);
8573 } else { // not in a free range and/or should not coalesce
8574 // Return the current free range and start a new one.
8575 if (inFreeRange()) {
8576 // In a free range but cannot coalesce with the right hand chunk.
8577 // Put the current free range into the free lists.
8578 flush_cur_free_chunk(freeFinger(),
8579 pointer_delta(fc_addr, freeFinger()));
8580 }
8581 // Set up for new free range. Pass along whether the right hand
8582 // chunk is in the free lists.
8583 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8584 }
8585 }
8586
8587 // Lookahead flush:
8588 // If we are tracking a free range, and this is the last chunk that
8589 // we'll look at because its end crosses past _limit, we'll preemptively
8590 // flush it along with any free range we may be holding on to. Note that
8591 // this can be the case only for an already free or freshly garbage
8592 // chunk. If this block is an object, it can never straddle
8593 // over _limit. The "straddling" occurs when _limit is set at
8594 // the previous end of the space when this cycle started, and
8595 // a subsequent heap expansion caused the previously co-terminal
8596 // free block to be coalesced with the newly expanded portion,
8597 // thus rendering _limit a non-block-boundary making it dangerous
8598 // for the sweeper to step over and examine.
8599 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
8600 assert(inFreeRange(), "Should only be called if currently in a free range.");
8601 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
8602 assert(_sp->used_region().contains(eob - 1),
8603 err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
8604 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
8605 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
8606 eob, eob-1, _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
8607 if (eob >= _limit) {
8608 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
8609 if (CMSTraceSweeper) {
8610 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
8611 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
8612 "[" PTR_FORMAT "," PTR_FORMAT ")",
8613 _limit, fc, eob, _sp->bottom(), _sp->end());
8614 }
8615 // Return the storage we are tracking back into the free lists.
8616 if (CMSTraceSweeper) {
8617 gclog_or_tty->print_cr("Flushing ... ");
8618 }
8619 assert(freeFinger() < eob, "Error");
8620 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8621 }
8622 }
8623
8624 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8625 assert(inFreeRange(), "Should only be called if currently in a free range.");
8626 assert(size > 0,
8627 "A zero sized chunk cannot be added to the free lists.");
8628 if (!freeRangeInFreeLists()) {
8629 if (CMSTestInFreeList) {
8630 FreeChunk* fc = (FreeChunk*) chunk;
8631 fc->set_size(size);
8632 assert(!_sp->verify_chunk_in_free_list(fc),
8633 "chunk should not be in free lists yet");
8634 }
8635 if (CMSTraceSweeper) {
8636 gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
8637 chunk, size);
8638 }
8639 // A new free range is going to be starting. The current
8640 // free range has not been added to the free lists yet or
8641 // was removed so add it back.
8642 // If the current free range was coalesced, then the death
8643 // of the free range was recorded. Record a birth now.
8644 if (lastFreeRangeCoalesced()) {
8645 _sp->coalBirth(size);
8646 }
8647 _sp->addChunkAndRepairOffsetTable(chunk, size,
8648 lastFreeRangeCoalesced());
8649 } else if (CMSTraceSweeper) {
8650 gclog_or_tty->print_cr("Already in free list: nothing to flush");
8651 }
8652 set_inFreeRange(false);
8653 set_freeRangeInFreeLists(false);
8654 }
8655
8656 // We take a break if we've been at this for a while,
8657 // so as to avoid monopolizing the locks involved.
8658 void SweepClosure::do_yield_work(HeapWord* addr) {
8659 // Return current free chunk being used for coalescing (if any)
8660 // to the appropriate freelist. After yielding, the next
8661 // free block encountered will start a coalescing range of
8662 // free blocks. If the next free block is adjacent to the
8663 // chunk just flushed, they will need to wait for the next
8664 // sweep to be coalesced.
8665 if (inFreeRange()) {
8666 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8667 }
8668
8669 // First give up the locks, then yield, then re-lock.
8670 // We should probably use a constructor/destructor idiom to
8671 // do this unlock/lock or modify the MutexUnlocker class to
8672 // serve our purpose. XXX
8673 assert_lock_strong(_bitMap->lock());
8674 assert_lock_strong(_freelistLock);
8675 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8676 "CMS thread should hold CMS token");
8677 _bitMap->lock()->unlock();
8678 _freelistLock->unlock();
8679 ConcurrentMarkSweepThread::desynchronize(true);
8680 ConcurrentMarkSweepThread::acknowledge_yield_request();
8681 _collector->stopTimer();
8682 if (PrintCMSStatistics != 0) {
8683 _collector->incrementYields();
8684 }
8685 _collector->icms_wait();
8686
8687 // See the comment in coordinator_yield()
8688 for (unsigned i = 0; i < CMSYieldSleepCount &&
8689 ConcurrentMarkSweepThread::should_yield() &&
8690 !CMSCollector::foregroundGCIsActive(); ++i) {
8691 os::sleep(Thread::current(), 1, false);
8692 ConcurrentMarkSweepThread::acknowledge_yield_request();
8693 }
8694
8695 ConcurrentMarkSweepThread::synchronize(true);
8696 _freelistLock->lock();
8697 _bitMap->lock()->lock_without_safepoint_check();
8698 _collector->startTimer();
8699 }
8700
8701 #ifndef PRODUCT
8702 // This is actually very useful in a product build if it can
8703 // be called from the debugger. Compile it into the product
8704 // as needed.
8705 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8706 return debug_cms_space->verify_chunk_in_free_list(fc);
8707 }
8708 #endif
8709
8710 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8711 if (CMSTraceSweeper) {
8712 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8713 fc, fc->size());
8714 }
8715 }
8716
8717 // CMSIsAliveClosure
8718 bool CMSIsAliveClosure::do_object_b(oop obj) {
8719 HeapWord* addr = (HeapWord*)obj;
8720 return addr != NULL &&
8721 (!_span.contains(addr) || _bit_map->isMarked(addr));
8722 }
8723
8724
8725 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8726 MemRegion span,
8727 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8728 bool cpc):
8729 _collector(collector),
8730 _span(span),
8731 _bit_map(bit_map),
8732 _mark_stack(mark_stack),
8733 _concurrent_precleaning(cpc) {
8734 assert(!_span.is_empty(), "Empty span could spell trouble");
8735 }
8736
8737
8738 // CMSKeepAliveClosure: the serial version
8739 void CMSKeepAliveClosure::do_oop(oop obj) {
8740 HeapWord* addr = (HeapWord*)obj;
8741 if (_span.contains(addr) &&
8742 !_bit_map->isMarked(addr)) {
8743 _bit_map->mark(addr);
8744 bool simulate_overflow = false;
8745 NOT_PRODUCT(
8746 if (CMSMarkStackOverflowALot &&
8747 _collector->simulate_overflow()) {
8748 // simulate a stack overflow
8749 simulate_overflow = true;
8750 }
8751 )
8752 if (simulate_overflow || !_mark_stack->push(obj)) {
8753 if (_concurrent_precleaning) {
8754 // We dirty the overflown object and let the remark
8755 // phase deal with it.
8756 assert(_collector->overflow_list_is_empty(), "Error");
8757 // In the case of object arrays, we need to dirty all of
8758 // the cards that the object spans. No locking or atomics
8759 // are needed since no one else can be mutating the mod union
8760 // table.
8761 if (obj->is_objArray()) {
8762 size_t sz = obj->size();
8763 HeapWord* end_card_addr =
8764 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8765 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8766 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8767 _collector->_modUnionTable.mark_range(redirty_range);
8768 } else {
8769 _collector->_modUnionTable.mark(addr);
8770 }
8771 _collector->_ser_kac_preclean_ovflw++;
8772 } else {
8773 _collector->push_on_overflow_list(obj);
8774 _collector->_ser_kac_ovflw++;
8775 }
8776 }
8777 }
8778 }
8779
8780 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8781 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8782
8783 // CMSParKeepAliveClosure: a parallel version of the above.
8784 // The work queues are private to each closure (thread),
8785 // but (may be) available for stealing by other threads.
8786 void CMSParKeepAliveClosure::do_oop(oop obj) {
8787 HeapWord* addr = (HeapWord*)obj;
8788 if (_span.contains(addr) &&
8789 !_bit_map->isMarked(addr)) {
8790 // In general, during recursive tracing, several threads
8791 // may be concurrently getting here; the first one to
8792 // "tag" it, claims it.
8793 if (_bit_map->par_mark(addr)) {
8794 bool res = _work_queue->push(obj);
8795 assert(res, "Low water mark should be much less than capacity");
8796 // Do a recursive trim in the hope that this will keep
8797 // stack usage lower, but leave some oops for potential stealers
8798 trim_queue(_low_water_mark);
8799 } // Else, another thread got there first
8800 }
8801 }
8802
8803 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8804 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8805
8806 void CMSParKeepAliveClosure::trim_queue(uint max) {
8807 while (_work_queue->size() > max) {
8808 oop new_oop;
8809 if (_work_queue->pop_local(new_oop)) {
8810 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8811 assert(_bit_map->isMarked((HeapWord*)new_oop),
8812 "no white objects on this stack!");
8813 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8814 // iterate over the oops in this oop, marking and pushing
8815 // the ones in CMS heap (i.e. in _span).
8816 new_oop->oop_iterate(&_mark_and_push);
8817 }
8818 }
8819 }
8820
8821 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8822 CMSCollector* collector,
8823 MemRegion span, CMSBitMap* bit_map,
8824 OopTaskQueue* work_queue):
8825 _collector(collector),
8826 _span(span),
8827 _bit_map(bit_map),
8828 _work_queue(work_queue) { }
8829
8830 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8831 HeapWord* addr = (HeapWord*)obj;
8832 if (_span.contains(addr) &&
8833 !_bit_map->isMarked(addr)) {
8834 if (_bit_map->par_mark(addr)) {
8835 bool simulate_overflow = false;
8836 NOT_PRODUCT(
8837 if (CMSMarkStackOverflowALot &&
8838 _collector->par_simulate_overflow()) {
8839 // simulate a stack overflow
8840 simulate_overflow = true;
8841 }
8842 )
8843 if (simulate_overflow || !_work_queue->push(obj)) {
8844 _collector->par_push_on_overflow_list(obj);
8845 _collector->_par_kac_ovflw++;
8846 }
8847 } // Else another thread got there already
8848 }
8849 }
8850
8851 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8852 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8853
8854 //////////////////////////////////////////////////////////////////
8855 // CMSExpansionCause /////////////////////////////
8856 //////////////////////////////////////////////////////////////////
8857 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8858 switch (cause) {
8859 case _no_expansion:
8860 return "No expansion";
8861 case _satisfy_free_ratio:
8862 return "Free ratio";
8863 case _satisfy_promotion:
8864 return "Satisfy promotion";
8865 case _satisfy_allocation:
8866 return "allocation";
8867 case _allocate_par_lab:
8868 return "Par LAB";
8869 case _allocate_par_spooling_space:
8870 return "Par Spooling Space";
8871 case _adaptive_size_policy:
8872 return "Ergonomics";
8873 default:
8874 return "unknown";
8875 }
8876 }
8877
8878 void CMSDrainMarkingStackClosure::do_void() {
8879 // the max number to take from overflow list at a time
8880 const size_t num = _mark_stack->capacity()/4;
8881 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8882 "Overflow list should be NULL during concurrent phases");
8883 while (!_mark_stack->isEmpty() ||
8884 // if stack is empty, check the overflow list
8885 _collector->take_from_overflow_list(num, _mark_stack)) {
8886 oop obj = _mark_stack->pop();
8887 HeapWord* addr = (HeapWord*)obj;
8888 assert(_span.contains(addr), "Should be within span");
8889 assert(_bit_map->isMarked(addr), "Should be marked");
8890 assert(obj->is_oop(), "Should be an oop");
8891 obj->oop_iterate(_keep_alive);
8892 }
8893 }
8894
8895 void CMSParDrainMarkingStackClosure::do_void() {
8896 // drain queue
8897 trim_queue(0);
8898 }
8899
8900 // Trim our work_queue so its length is below max at return
8901 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8902 while (_work_queue->size() > max) {
8903 oop new_oop;
8904 if (_work_queue->pop_local(new_oop)) {
8905 assert(new_oop->is_oop(), "Expected an oop");
8906 assert(_bit_map->isMarked((HeapWord*)new_oop),
8907 "no white objects on this stack!");
8908 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8909 // iterate over the oops in this oop, marking and pushing
8910 // the ones in CMS heap (i.e. in _span).
8911 new_oop->oop_iterate(&_mark_and_push);
8912 }
8913 }
8914 }
8915
8916 ////////////////////////////////////////////////////////////////////
8917 // Support for Marking Stack Overflow list handling and related code
8918 ////////////////////////////////////////////////////////////////////
8919 // Much of the following code is similar in shape and spirit to the
8920 // code used in ParNewGC. We should try and share that code
8921 // as much as possible in the future.
8922
8923 #ifndef PRODUCT
8924 // Debugging support for CMSStackOverflowALot
8925
8926 // It's OK to call this multi-threaded; the worst thing
8927 // that can happen is that we'll get a bunch of closely
8928 // spaced simulated overflows, but that's OK, in fact
8929 // probably good as it would exercise the overflow code
8930 // under contention.
8931 bool CMSCollector::simulate_overflow() {
8932 if (_overflow_counter-- <= 0) { // just being defensive
8933 _overflow_counter = CMSMarkStackOverflowInterval;
8934 return true;
8935 } else {
8936 return false;
8937 }
8938 }
8939
8940 bool CMSCollector::par_simulate_overflow() {
8941 return simulate_overflow();
8942 }
8943 #endif
8944
8945 // Single-threaded
8946 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8947 assert(stack->isEmpty(), "Expected precondition");
8948 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8949 size_t i = num;
8950 oop cur = _overflow_list;
8951 const markOop proto = markOopDesc::prototype();
8952 NOT_PRODUCT(ssize_t n = 0;)
8953 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8954 next = oop(cur->mark());
8955 cur->set_mark(proto); // until proven otherwise
8956 assert(cur->is_oop(), "Should be an oop");
8957 bool res = stack->push(cur);
8958 assert(res, "Bit off more than can chew?");
8959 NOT_PRODUCT(n++;)
8960 }
8961 _overflow_list = cur;
8962 #ifndef PRODUCT
8963 assert(_num_par_pushes >= n, "Too many pops?");
8964 _num_par_pushes -=n;
8965 #endif
8966 return !stack->isEmpty();
8967 }
8968
8969 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
8970 // (MT-safe) Get a prefix of at most "num" from the list.
8971 // The overflow list is chained through the mark word of
8972 // each object in the list. We fetch the entire list,
8973 // break off a prefix of the right size and return the
8974 // remainder. If other threads try to take objects from
8975 // the overflow list at that time, they will wait for
8976 // some time to see if data becomes available. If (and
8977 // only if) another thread places one or more object(s)
8978 // on the global list before we have returned the suffix
8979 // to the global list, we will walk down our local list
8980 // to find its end and append the global list to
8981 // our suffix before returning it. This suffix walk can
8982 // prove to be expensive (quadratic in the amount of traffic)
8983 // when there are many objects in the overflow list and
8984 // there is much producer-consumer contention on the list.
8985 // *NOTE*: The overflow list manipulation code here and
8986 // in ParNewGeneration:: are very similar in shape,
8987 // except that in the ParNew case we use the old (from/eden)
8988 // copy of the object to thread the list via its klass word.
8989 // Because of the common code, if you make any changes in
8990 // the code below, please check the ParNew version to see if
8991 // similar changes might be needed.
8992 // CR 6797058 has been filed to consolidate the common code.
8993 bool CMSCollector::par_take_from_overflow_list(size_t num,
8994 OopTaskQueue* work_q,
8995 int no_of_gc_threads) {
8996 assert(work_q->size() == 0, "First empty local work queue");
8997 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8998 if (_overflow_list == NULL) {
8999 return false;
9000 }
9001 // Grab the entire list; we'll put back a suffix
9002 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
9003 Thread* tid = Thread::current();
9004 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
9005 // set to ParallelGCThreads.
9006 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
9007 size_t sleep_time_millis = MAX2((size_t)1, num/100);
9008 // If the list is busy, we spin for a short while,
9009 // sleeping between attempts to get the list.
9010 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
9011 os::sleep(tid, sleep_time_millis, false);
9012 if (_overflow_list == NULL) {
9013 // Nothing left to take
9014 return false;
9015 } else if (_overflow_list != BUSY) {
9016 // Try and grab the prefix
9017 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
9018 }
9019 }
9020 // If the list was found to be empty, or we spun long
9021 // enough, we give up and return empty-handed. If we leave
9022 // the list in the BUSY state below, it must be the case that
9023 // some other thread holds the overflow list and will set it
9024 // to a non-BUSY state in the future.
9025 if (prefix == NULL || prefix == BUSY) {
9026 // Nothing to take or waited long enough
9027 if (prefix == NULL) {
9028 // Write back the NULL in case we overwrote it with BUSY above
9029 // and it is still the same value.
9030 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
9031 }
9032 return false;
9033 }
9034 assert(prefix != NULL && prefix != BUSY, "Error");
9035 size_t i = num;
9036 oop cur = prefix;
9037 // Walk down the first "num" objects, unless we reach the end.
9038 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
9039 if (cur->mark() == NULL) {
9040 // We have "num" or fewer elements in the list, so there
9041 // is nothing to return to the global list.
9042 // Write back the NULL in lieu of the BUSY we wrote
9043 // above, if it is still the same value.
9044 if (_overflow_list == BUSY) {
9045 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
9046 }
9047 } else {
9048 // Chop off the suffix and return it to the global list.
9049 assert(cur->mark() != BUSY, "Error");
9050 oop suffix_head = cur->mark(); // suffix will be put back on global list
9051 cur->set_mark(NULL); // break off suffix
9052 // It's possible that the list is still in the empty(busy) state
9053 // we left it in a short while ago; in that case we may be
9054 // able to place back the suffix without incurring the cost
9055 // of a walk down the list.
9056 oop observed_overflow_list = _overflow_list;
9057 oop cur_overflow_list = observed_overflow_list;
9058 bool attached = false;
9059 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
9060 observed_overflow_list =
9061 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9062 if (cur_overflow_list == observed_overflow_list) {
9063 attached = true;
9064 break;
9065 } else cur_overflow_list = observed_overflow_list;
9066 }
9067 if (!attached) {
9068 // Too bad, someone else sneaked in (at least) an element; we'll need
9069 // to do a splice. Find tail of suffix so we can prepend suffix to global
9070 // list.
9071 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
9072 oop suffix_tail = cur;
9073 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
9074 "Tautology");
9075 observed_overflow_list = _overflow_list;
9076 do {
9077 cur_overflow_list = observed_overflow_list;
9078 if (cur_overflow_list != BUSY) {
9079 // Do the splice ...
9080 suffix_tail->set_mark(markOop(cur_overflow_list));
9081 } else { // cur_overflow_list == BUSY
9082 suffix_tail->set_mark(NULL);
9083 }
9084 // ... and try to place spliced list back on overflow_list ...
9085 observed_overflow_list =
9086 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9087 } while (cur_overflow_list != observed_overflow_list);
9088 // ... until we have succeeded in doing so.
9089 }
9090 }
9091
9092 // Push the prefix elements on work_q
9093 assert(prefix != NULL, "control point invariant");
9094 const markOop proto = markOopDesc::prototype();
9095 oop next;
9096 NOT_PRODUCT(ssize_t n = 0;)
9097 for (cur = prefix; cur != NULL; cur = next) {
9098 next = oop(cur->mark());
9099 cur->set_mark(proto); // until proven otherwise
9100 assert(cur->is_oop(), "Should be an oop");
9101 bool res = work_q->push(cur);
9102 assert(res, "Bit off more than we can chew?");
9103 NOT_PRODUCT(n++;)
9104 }
9105 #ifndef PRODUCT
9106 assert(_num_par_pushes >= n, "Too many pops?");
9107 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
9108 #endif
9109 return true;
9110 }
9111
9112 // Single-threaded
9113 void CMSCollector::push_on_overflow_list(oop p) {
9114 NOT_PRODUCT(_num_par_pushes++;)
9115 assert(p->is_oop(), "Not an oop");
9116 preserve_mark_if_necessary(p);
9117 p->set_mark((markOop)_overflow_list);
9118 _overflow_list = p;
9119 }
9120
9121 // Multi-threaded; use CAS to prepend to overflow list
9122 void CMSCollector::par_push_on_overflow_list(oop p) {
9123 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
9124 assert(p->is_oop(), "Not an oop");
9125 par_preserve_mark_if_necessary(p);
9126 oop observed_overflow_list = _overflow_list;
9127 oop cur_overflow_list;
9128 do {
9129 cur_overflow_list = observed_overflow_list;
9130 if (cur_overflow_list != BUSY) {
9131 p->set_mark(markOop(cur_overflow_list));
9132 } else {
9133 p->set_mark(NULL);
9134 }
9135 observed_overflow_list =
9136 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
9137 } while (cur_overflow_list != observed_overflow_list);
9138 }
9139 #undef BUSY
9140
9141 // Single threaded
9142 // General Note on GrowableArray: pushes may silently fail
9143 // because we are (temporarily) out of C-heap for expanding
9144 // the stack. The problem is quite ubiquitous and affects
9145 // a lot of code in the JVM. The prudent thing for GrowableArray
9146 // to do (for now) is to exit with an error. However, that may
9147 // be too draconian in some cases because the caller may be
9148 // able to recover without much harm. For such cases, we
9149 // should probably introduce a "soft_push" method which returns
9150 // an indication of success or failure with the assumption that
9151 // the caller may be able to recover from a failure; code in
9152 // the VM can then be changed, incrementally, to deal with such
9153 // failures where possible, thus, incrementally hardening the VM
9154 // in such low resource situations.
9155 void CMSCollector::preserve_mark_work(oop p, markOop m) {
9156 _preserved_oop_stack.push(p);
9157 _preserved_mark_stack.push(m);
9158 assert(m == p->mark(), "Mark word changed");
9159 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9160 "bijection");
9161 }
9162
9163 // Single threaded
9164 void CMSCollector::preserve_mark_if_necessary(oop p) {
9165 markOop m = p->mark();
9166 if (m->must_be_preserved(p)) {
9167 preserve_mark_work(p, m);
9168 }
9169 }
9170
9171 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
9172 markOop m = p->mark();
9173 if (m->must_be_preserved(p)) {
9174 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
9175 // Even though we read the mark word without holding
9176 // the lock, we are assured that it will not change
9177 // because we "own" this oop, so no other thread can
9178 // be trying to push it on the overflow list; see
9179 // the assertion in preserve_mark_work() that checks
9180 // that m == p->mark().
9181 preserve_mark_work(p, m);
9182 }
9183 }
9184
9185 // We should be able to do this multi-threaded,
9186 // a chunk of stack being a task (this is
9187 // correct because each oop only ever appears
9188 // once in the overflow list. However, it's
9189 // not very easy to completely overlap this with
9190 // other operations, so will generally not be done
9191 // until all work's been completed. Because we
9192 // expect the preserved oop stack (set) to be small,
9193 // it's probably fine to do this single-threaded.
9194 // We can explore cleverer concurrent/overlapped/parallel
9195 // processing of preserved marks if we feel the
9196 // need for this in the future. Stack overflow should
9197 // be so rare in practice and, when it happens, its
9198 // effect on performance so great that this will
9199 // likely just be in the noise anyway.
9200 void CMSCollector::restore_preserved_marks_if_any() {
9201 assert(SafepointSynchronize::is_at_safepoint(),
9202 "world should be stopped");
9203 assert(Thread::current()->is_ConcurrentGC_thread() ||
9204 Thread::current()->is_VM_thread(),
9205 "should be single-threaded");
9206 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9207 "bijection");
9208
9209 while (!_preserved_oop_stack.is_empty()) {
9210 oop p = _preserved_oop_stack.pop();
9211 assert(p->is_oop(), "Should be an oop");
9212 assert(_span.contains(p), "oop should be in _span");
9213 assert(p->mark() == markOopDesc::prototype(),
9214 "Set when taken from overflow list");
9215 markOop m = _preserved_mark_stack.pop();
9216 p->set_mark(m);
9217 }
9218 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
9219 "stacks were cleared above");
9220 }
9221
9222 #ifndef PRODUCT
9223 bool CMSCollector::no_preserved_marks() const {
9224 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
9225 }
9226 #endif
9227
9228 // Transfer some number of overflown objects to usual marking
9229 // stack. Return true if some objects were transferred.
9230 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9231 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9232 (size_t)ParGCDesiredObjsFromOverflowList);
9233
9234 bool res = _collector->take_from_overflow_list(num, _mark_stack);
9235 assert(_collector->overflow_list_is_empty() || res,
9236 "If list is not empty, we should have taken something");
9237 assert(!res || !_mark_stack->isEmpty(),
9238 "If we took something, it should now be on our stack");
9239 return res;
9240 }
9241
9242 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9243 size_t res = _sp->block_size_no_stall(addr, _collector);
9244 if (_sp->block_is_obj(addr)) {
9245 if (_live_bit_map->isMarked(addr)) {
9246 // It can't have been dead in a previous cycle
9247 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9248 } else {
9249 _dead_bit_map->mark(addr); // mark the dead object
9250 }
9251 }
9252 // Could be 0, if the block size could not be computed without stalling.
9253 return res;
9254 }
9255
9256 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
9257
9258 switch (phase) {
9259 case CMSCollector::InitialMarking:
9260 initialize(true /* fullGC */ ,
9261 cause /* cause of the GC */,
9262 true /* recordGCBeginTime */,
9263 true /* recordPreGCUsage */,
9264 false /* recordPeakUsage */,
9265 false /* recordPostGCusage */,
9266 true /* recordAccumulatedGCTime */,
9267 false /* recordGCEndTime */,
9268 false /* countCollection */ );
9269 break;
9270
9271 case CMSCollector::FinalMarking:
9272 initialize(true /* fullGC */ ,
9273 cause /* cause of the GC */,
9274 false /* recordGCBeginTime */,
9275 false /* recordPreGCUsage */,
9276 false /* recordPeakUsage */,
9277 false /* recordPostGCusage */,
9278 true /* recordAccumulatedGCTime */,
9279 false /* recordGCEndTime */,
9280 false /* countCollection */ );
9281 break;
9282
9283 case CMSCollector::Sweeping:
9284 initialize(true /* fullGC */ ,
9285 cause /* cause of the GC */,
9286 false /* recordGCBeginTime */,
9287 false /* recordPreGCUsage */,
9288 true /* recordPeakUsage */,
9289 true /* recordPostGCusage */,
9290 false /* recordAccumulatedGCTime */,
9291 true /* recordGCEndTime */,
9292 true /* countCollection */ );
9293 break;
9294
9295 default:
9296 ShouldNotReachHere();
9297 }
9298 }