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