1 /*
2 * Copyright (c) 2001, 2016, 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 "gc/cms/compactibleFreeListSpace.hpp"
27 #include "gc/cms/concurrentMarkSweepGeneration.hpp"
28 #include "gc/cms/parNewGeneration.inline.hpp"
29 #include "gc/cms/parOopClosures.inline.hpp"
30 #include "gc/serial/defNewGeneration.inline.hpp"
31 #include "gc/shared/adaptiveSizePolicy.hpp"
32 #include "gc/shared/ageTable.inline.hpp"
33 #include "gc/shared/copyFailedInfo.hpp"
34 #include "gc/shared/gcHeapSummary.hpp"
35 #include "gc/shared/gcTimer.hpp"
36 #include "gc/shared/gcTrace.hpp"
37 #include "gc/shared/gcTraceTime.inline.hpp"
38 #include "gc/shared/genCollectedHeap.hpp"
39 #include "gc/shared/genOopClosures.inline.hpp"
40 #include "gc/shared/generation.hpp"
41 #include "gc/shared/plab.inline.hpp"
42 #include "gc/shared/preservedMarks.inline.hpp"
43 #include "gc/shared/referencePolicy.hpp"
44 #include "gc/shared/space.hpp"
45 #include "gc/shared/spaceDecorator.hpp"
46 #include "gc/shared/strongRootsScope.hpp"
47 #include "gc/shared/taskqueue.inline.hpp"
48 #include "gc/shared/workgroup.hpp"
49 #include "logging/log.hpp"
50 #include "memory/resourceArea.hpp"
51 #include "oops/objArrayOop.hpp"
52 #include "oops/oop.inline.hpp"
53 #include "runtime/atomic.inline.hpp"
54 #include "runtime/handles.hpp"
55 #include "runtime/handles.inline.hpp"
56 #include "runtime/java.hpp"
57 #include "runtime/thread.inline.hpp"
58 #include "utilities/copy.hpp"
59 #include "utilities/globalDefinitions.hpp"
60 #include "utilities/stack.inline.hpp"
61
62 ParScanThreadState::ParScanThreadState(Space* to_space_,
63 ParNewGeneration* young_gen_,
64 Generation* old_gen_,
65 int thread_num_,
66 ObjToScanQueueSet* work_queue_set_,
67 Stack<oop, mtGC>* overflow_stacks_,
68 PreservedMarks* preserved_marks_,
69 size_t desired_plab_sz_,
70 ParallelTaskTerminator& term_) :
71 _to_space(to_space_),
72 _old_gen(old_gen_),
73 _young_gen(young_gen_),
74 _thread_num(thread_num_),
75 _work_queue(work_queue_set_->queue(thread_num_)),
76 _to_space_full(false),
77 _overflow_stack(overflow_stacks_ ? overflow_stacks_ + thread_num_ : NULL),
78 _preserved_marks(preserved_marks_),
79 _ageTable(false), // false ==> not the global age table, no perf data.
80 _to_space_alloc_buffer(desired_plab_sz_),
81 _to_space_closure(young_gen_, this),
82 _old_gen_closure(young_gen_, this),
83 _to_space_root_closure(young_gen_, this),
84 _old_gen_root_closure(young_gen_, this),
85 _older_gen_closure(young_gen_, this),
86 _evacuate_followers(this, &_to_space_closure, &_old_gen_closure,
87 &_to_space_root_closure, young_gen_, &_old_gen_root_closure,
88 work_queue_set_, &term_),
89 _is_alive_closure(young_gen_),
90 _scan_weak_ref_closure(young_gen_, this),
91 _keep_alive_closure(&_scan_weak_ref_closure),
92 _strong_roots_time(0.0),
93 _term_time(0.0)
94 {
95 #if TASKQUEUE_STATS
96 _term_attempts = 0;
97 _overflow_refills = 0;
98 _overflow_refill_objs = 0;
99 #endif // TASKQUEUE_STATS
100
101 _survivor_chunk_array = (ChunkArray*) old_gen()->get_data_recorder(thread_num());
102 _hash_seed = 17; // Might want to take time-based random value.
103 _start = os::elapsedTime();
104 _old_gen_closure.set_generation(old_gen_);
105 _old_gen_root_closure.set_generation(old_gen_);
106 }
107
108 void ParScanThreadState::record_survivor_plab(HeapWord* plab_start,
109 size_t plab_word_size) {
110 ChunkArray* sca = survivor_chunk_array();
111 if (sca != NULL) {
112 // A non-null SCA implies that we want the PLAB data recorded.
113 sca->record_sample(plab_start, plab_word_size);
114 }
115 }
116
117 bool ParScanThreadState::should_be_partially_scanned(oop new_obj, oop old_obj) const {
118 return new_obj->is_objArray() &&
119 arrayOop(new_obj)->length() > ParGCArrayScanChunk &&
120 new_obj != old_obj;
121 }
122
123 void ParScanThreadState::scan_partial_array_and_push_remainder(oop old) {
124 assert(old->is_objArray(), "must be obj array");
125 assert(old->is_forwarded(), "must be forwarded");
126 assert(GenCollectedHeap::heap()->is_in_reserved(old), "must be in heap.");
127 assert(!old_gen()->is_in(old), "must be in young generation.");
128
129 objArrayOop obj = objArrayOop(old->forwardee());
130 // Process ParGCArrayScanChunk elements now
131 // and push the remainder back onto queue
132 int start = arrayOop(old)->length();
133 int end = obj->length();
134 int remainder = end - start;
135 assert(start <= end, "just checking");
136 if (remainder > 2 * ParGCArrayScanChunk) {
137 // Test above combines last partial chunk with a full chunk
138 end = start + ParGCArrayScanChunk;
139 arrayOop(old)->set_length(end);
140 // Push remainder.
141 bool ok = work_queue()->push(old);
142 assert(ok, "just popped, push must be okay");
143 } else {
144 // Restore length so that it can be used if there
145 // is a promotion failure and forwarding pointers
146 // must be removed.
147 arrayOop(old)->set_length(end);
148 }
149
150 // process our set of indices (include header in first chunk)
151 // should make sure end is even (aligned to HeapWord in case of compressed oops)
152 if ((HeapWord *)obj < young_old_boundary()) {
153 // object is in to_space
154 obj->oop_iterate_range(&_to_space_closure, start, end);
155 } else {
156 // object is in old generation
157 obj->oop_iterate_range(&_old_gen_closure, start, end);
158 }
159 }
160
161 void ParScanThreadState::trim_queues(int max_size) {
162 ObjToScanQueue* queue = work_queue();
163 do {
164 while (queue->size() > (juint)max_size) {
165 oop obj_to_scan;
166 if (queue->pop_local(obj_to_scan)) {
167 if ((HeapWord *)obj_to_scan < young_old_boundary()) {
168 if (obj_to_scan->is_objArray() &&
169 obj_to_scan->is_forwarded() &&
170 obj_to_scan->forwardee() != obj_to_scan) {
171 scan_partial_array_and_push_remainder(obj_to_scan);
172 } else {
173 // object is in to_space
174 obj_to_scan->oop_iterate(&_to_space_closure);
175 }
176 } else {
177 // object is in old generation
178 obj_to_scan->oop_iterate(&_old_gen_closure);
179 }
180 }
181 }
182 // For the case of compressed oops, we have a private, non-shared
183 // overflow stack, so we eagerly drain it so as to more evenly
184 // distribute load early. Note: this may be good to do in
185 // general rather than delay for the final stealing phase.
186 // If applicable, we'll transfer a set of objects over to our
187 // work queue, allowing them to be stolen and draining our
188 // private overflow stack.
189 } while (ParGCTrimOverflow && young_gen()->take_from_overflow_list(this));
190 }
191
192 bool ParScanThreadState::take_from_overflow_stack() {
193 assert(ParGCUseLocalOverflow, "Else should not call");
194 assert(young_gen()->overflow_list() == NULL, "Error");
195 ObjToScanQueue* queue = work_queue();
196 Stack<oop, mtGC>* const of_stack = overflow_stack();
197 const size_t num_overflow_elems = of_stack->size();
198 const size_t space_available = queue->max_elems() - queue->size();
199 const size_t num_take_elems = MIN3(space_available / 4,
200 ParGCDesiredObjsFromOverflowList,
201 num_overflow_elems);
202 // Transfer the most recent num_take_elems from the overflow
203 // stack to our work queue.
204 for (size_t i = 0; i != num_take_elems; i++) {
205 oop cur = of_stack->pop();
206 oop obj_to_push = cur->forwardee();
207 assert(GenCollectedHeap::heap()->is_in_reserved(cur), "Should be in heap");
208 assert(!old_gen()->is_in_reserved(cur), "Should be in young gen");
209 assert(GenCollectedHeap::heap()->is_in_reserved(obj_to_push), "Should be in heap");
210 if (should_be_partially_scanned(obj_to_push, cur)) {
211 assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned");
212 obj_to_push = cur;
213 }
214 bool ok = queue->push(obj_to_push);
215 assert(ok, "Should have succeeded");
216 }
217 assert(young_gen()->overflow_list() == NULL, "Error");
218 return num_take_elems > 0; // was something transferred?
219 }
220
221 void ParScanThreadState::push_on_overflow_stack(oop p) {
222 assert(ParGCUseLocalOverflow, "Else should not call");
223 overflow_stack()->push(p);
224 assert(young_gen()->overflow_list() == NULL, "Error");
225 }
226
227 HeapWord* ParScanThreadState::alloc_in_to_space_slow(size_t word_sz) {
228 // If the object is small enough, try to reallocate the buffer.
229 HeapWord* obj = NULL;
230 if (!_to_space_full) {
231 PLAB* const plab = to_space_alloc_buffer();
232 Space* const sp = to_space();
233 if (word_sz * 100 < ParallelGCBufferWastePct * plab->word_sz()) {
234 // Is small enough; abandon this buffer and start a new one.
235 plab->retire();
236 size_t buf_size = plab->word_sz();
237 HeapWord* buf_space = sp->par_allocate(buf_size);
238 if (buf_space == NULL) {
239 const size_t min_bytes =
240 PLAB::min_size() << LogHeapWordSize;
241 size_t free_bytes = sp->free();
242 while(buf_space == NULL && free_bytes >= min_bytes) {
243 buf_size = free_bytes >> LogHeapWordSize;
244 assert(buf_size == (size_t)align_object_size(buf_size), "Invariant");
245 buf_space = sp->par_allocate(buf_size);
246 free_bytes = sp->free();
247 }
248 }
249 if (buf_space != NULL) {
250 plab->set_buf(buf_space, buf_size);
251 record_survivor_plab(buf_space, buf_size);
252 obj = plab->allocate_aligned(word_sz, SurvivorAlignmentInBytes);
253 // Note that we cannot compare buf_size < word_sz below
254 // because of AlignmentReserve (see PLAB::allocate()).
255 assert(obj != NULL || plab->words_remaining() < word_sz,
256 "Else should have been able to allocate");
257 // It's conceivable that we may be able to use the
258 // buffer we just grabbed for subsequent small requests
259 // even if not for this one.
260 } else {
261 // We're used up.
262 _to_space_full = true;
263 }
264 } else {
265 // Too large; allocate the object individually.
266 obj = sp->par_allocate(word_sz);
267 }
268 }
269 return obj;
270 }
271
272 void ParScanThreadState::undo_alloc_in_to_space(HeapWord* obj, size_t word_sz) {
273 to_space_alloc_buffer()->undo_allocation(obj, word_sz);
274 }
275
276 void ParScanThreadState::print_promotion_failure_size() {
277 if (_promotion_failed_info.has_failed()) {
278 log_trace(gc, promotion)(" (%d: promotion failure size = " SIZE_FORMAT ") ",
279 _thread_num, _promotion_failed_info.first_size());
280 }
281 }
282
283 class ParScanThreadStateSet: private ResourceArray {
284 public:
285 // Initializes states for the specified number of threads;
286 ParScanThreadStateSet(int num_threads,
287 Space& to_space,
288 ParNewGeneration& young_gen,
289 Generation& old_gen,
290 ObjToScanQueueSet& queue_set,
291 Stack<oop, mtGC>* overflow_stacks_,
292 PreservedMarksSet& preserved_marks_set,
293 size_t desired_plab_sz,
294 ParallelTaskTerminator& term);
295
296 ~ParScanThreadStateSet() { TASKQUEUE_STATS_ONLY(reset_stats()); }
297
298 inline ParScanThreadState& thread_state(int i);
299
300 void trace_promotion_failed(const YoungGCTracer* gc_tracer);
301 void reset(uint active_workers, bool promotion_failed);
302 void flush();
303
304 #if TASKQUEUE_STATS
305 static void
306 print_termination_stats_hdr(outputStream* const st);
307 void print_termination_stats();
308 static void
309 print_taskqueue_stats_hdr(outputStream* const st);
310 void print_taskqueue_stats();
311 void reset_stats();
312 #endif // TASKQUEUE_STATS
313
314 private:
315 ParallelTaskTerminator& _term;
316 ParNewGeneration& _young_gen;
317 Generation& _old_gen;
318 public:
319 bool is_valid(int id) const { return id < length(); }
320 ParallelTaskTerminator* terminator() { return &_term; }
321 };
322
323 ParScanThreadStateSet::ParScanThreadStateSet(int num_threads,
324 Space& to_space,
325 ParNewGeneration& young_gen,
326 Generation& old_gen,
327 ObjToScanQueueSet& queue_set,
328 Stack<oop, mtGC>* overflow_stacks,
329 PreservedMarksSet& preserved_marks_set,
330 size_t desired_plab_sz,
331 ParallelTaskTerminator& term)
332 : ResourceArray(sizeof(ParScanThreadState), num_threads),
333 _young_gen(young_gen),
334 _old_gen(old_gen),
335 _term(term)
336 {
337 assert(num_threads > 0, "sanity check!");
338 assert(ParGCUseLocalOverflow == (overflow_stacks != NULL),
339 "overflow_stack allocation mismatch");
340 // Initialize states.
341 for (int i = 0; i < num_threads; ++i) {
342 new ((ParScanThreadState*)_data + i)
343 ParScanThreadState(&to_space, &young_gen, &old_gen, i, &queue_set,
344 overflow_stacks, preserved_marks_set.get(i),
345 desired_plab_sz, term);
346 }
347 }
348
349 inline ParScanThreadState& ParScanThreadStateSet::thread_state(int i) {
350 assert(i >= 0 && i < length(), "sanity check!");
351 return ((ParScanThreadState*)_data)[i];
352 }
353
354 void ParScanThreadStateSet::trace_promotion_failed(const YoungGCTracer* gc_tracer) {
355 for (int i = 0; i < length(); ++i) {
356 if (thread_state(i).promotion_failed()) {
357 gc_tracer->report_promotion_failed(thread_state(i).promotion_failed_info());
358 thread_state(i).promotion_failed_info().reset();
359 }
360 }
361 }
362
363 void ParScanThreadStateSet::reset(uint active_threads, bool promotion_failed) {
364 _term.reset_for_reuse(active_threads);
365 if (promotion_failed) {
366 for (int i = 0; i < length(); ++i) {
367 thread_state(i).print_promotion_failure_size();
368 }
369 }
370 }
371
372 #if TASKQUEUE_STATS
373 void ParScanThreadState::reset_stats() {
374 taskqueue_stats().reset();
375 _term_attempts = 0;
376 _overflow_refills = 0;
377 _overflow_refill_objs = 0;
378 }
379
380 void ParScanThreadStateSet::reset_stats() {
381 for (int i = 0; i < length(); ++i) {
382 thread_state(i).reset_stats();
383 }
384 }
385
386 void ParScanThreadStateSet::print_termination_stats_hdr(outputStream* const st) {
387 st->print_raw_cr("GC Termination Stats");
388 st->print_raw_cr(" elapsed --strong roots-- -------termination-------");
389 st->print_raw_cr("thr ms ms % ms % attempts");
390 st->print_raw_cr("--- --------- --------- ------ --------- ------ --------");
391 }
392
393 void ParScanThreadStateSet::print_termination_stats() {
394 LogHandle(gc, task, stats) log;
395 if (!log.is_debug()) {
396 return;
397 }
398
399 ResourceMark rm;
400 outputStream* st = log.debug_stream();
401
402 print_termination_stats_hdr(st);
403
404 for (int i = 0; i < length(); ++i) {
405 const ParScanThreadState & pss = thread_state(i);
406 const double elapsed_ms = pss.elapsed_time() * 1000.0;
407 const double s_roots_ms = pss.strong_roots_time() * 1000.0;
408 const double term_ms = pss.term_time() * 1000.0;
409 st->print_cr("%3d %9.2f %9.2f %6.2f %9.2f %6.2f " SIZE_FORMAT_W(8),
410 i, elapsed_ms, s_roots_ms, s_roots_ms * 100 / elapsed_ms,
411 term_ms, term_ms * 100 / elapsed_ms, pss.term_attempts());
412 }
413 }
414
415 // Print stats related to work queue activity.
416 void ParScanThreadStateSet::print_taskqueue_stats_hdr(outputStream* const st) {
417 st->print_raw_cr("GC Task Stats");
418 st->print_raw("thr "); TaskQueueStats::print_header(1, st); st->cr();
419 st->print_raw("--- "); TaskQueueStats::print_header(2, st); st->cr();
420 }
421
422 void ParScanThreadStateSet::print_taskqueue_stats() {
423 if (!log_develop_is_enabled(Trace, gc, task, stats)) {
424 return;
425 }
426 LogHandle(gc, task, stats) log;
427 ResourceMark rm;
428 outputStream* st = log.trace_stream();
429 print_taskqueue_stats_hdr(st);
430
431 TaskQueueStats totals;
432 for (int i = 0; i < length(); ++i) {
433 const ParScanThreadState & pss = thread_state(i);
434 const TaskQueueStats & stats = pss.taskqueue_stats();
435 st->print("%3d ", i); stats.print(st); st->cr();
436 totals += stats;
437
438 if (pss.overflow_refills() > 0) {
439 st->print_cr(" " SIZE_FORMAT_W(10) " overflow refills "
440 SIZE_FORMAT_W(10) " overflow objects",
441 pss.overflow_refills(), pss.overflow_refill_objs());
442 }
443 }
444 st->print("tot "); totals.print(st); st->cr();
445
446 DEBUG_ONLY(totals.verify());
447 }
448 #endif // TASKQUEUE_STATS
449
450 void ParScanThreadStateSet::flush() {
451 // Work in this loop should be kept as lightweight as
452 // possible since this might otherwise become a bottleneck
453 // to scaling. Should we add heavy-weight work into this
454 // loop, consider parallelizing the loop into the worker threads.
455 for (int i = 0; i < length(); ++i) {
456 ParScanThreadState& par_scan_state = thread_state(i);
457
458 // Flush stats related to To-space PLAB activity and
459 // retire the last buffer.
460 par_scan_state.to_space_alloc_buffer()->flush_and_retire_stats(_young_gen.plab_stats());
461
462 // Every thread has its own age table. We need to merge
463 // them all into one.
464 AgeTable *local_table = par_scan_state.age_table();
465 _young_gen.age_table()->merge(local_table);
466
467 // Inform old gen that we're done.
468 _old_gen.par_promote_alloc_done(i);
469 _old_gen.par_oop_since_save_marks_iterate_done(i);
470 }
471
472 if (UseConcMarkSweepGC) {
473 // We need to call this even when ResizeOldPLAB is disabled
474 // so as to avoid breaking some asserts. While we may be able
475 // to avoid this by reorganizing the code a bit, I am loathe
476 // to do that unless we find cases where ergo leads to bad
477 // performance.
478 CompactibleFreeListSpaceLAB::compute_desired_plab_size();
479 }
480 }
481
482 ParScanClosure::ParScanClosure(ParNewGeneration* g,
483 ParScanThreadState* par_scan_state) :
484 OopsInKlassOrGenClosure(g), _par_scan_state(par_scan_state), _g(g) {
485 _boundary = _g->reserved().end();
486 }
487
488 void ParScanWithBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, true, false); }
489 void ParScanWithBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, false); }
490
491 void ParScanWithoutBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, false, false); }
492 void ParScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, false); }
493
494 void ParRootScanWithBarrierTwoGensClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, true, true); }
495 void ParRootScanWithBarrierTwoGensClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, true); }
496
497 void ParRootScanWithoutBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, false, true); }
498 void ParRootScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, true); }
499
500 ParScanWeakRefClosure::ParScanWeakRefClosure(ParNewGeneration* g,
501 ParScanThreadState* par_scan_state)
502 : ScanWeakRefClosure(g), _par_scan_state(par_scan_state)
503 {}
504
505 void ParScanWeakRefClosure::do_oop(oop* p) { ParScanWeakRefClosure::do_oop_work(p); }
506 void ParScanWeakRefClosure::do_oop(narrowOop* p) { ParScanWeakRefClosure::do_oop_work(p); }
507
508 #ifdef WIN32
509 #pragma warning(disable: 4786) /* identifier was truncated to '255' characters in the browser information */
510 #endif
511
512 ParEvacuateFollowersClosure::ParEvacuateFollowersClosure(
513 ParScanThreadState* par_scan_state_,
514 ParScanWithoutBarrierClosure* to_space_closure_,
515 ParScanWithBarrierClosure* old_gen_closure_,
516 ParRootScanWithoutBarrierClosure* to_space_root_closure_,
517 ParNewGeneration* par_gen_,
518 ParRootScanWithBarrierTwoGensClosure* old_gen_root_closure_,
519 ObjToScanQueueSet* task_queues_,
520 ParallelTaskTerminator* terminator_) :
521
522 _par_scan_state(par_scan_state_),
523 _to_space_closure(to_space_closure_),
524 _old_gen_closure(old_gen_closure_),
525 _to_space_root_closure(to_space_root_closure_),
526 _old_gen_root_closure(old_gen_root_closure_),
527 _par_gen(par_gen_),
528 _task_queues(task_queues_),
529 _terminator(terminator_)
530 {}
531
532 void ParEvacuateFollowersClosure::do_void() {
533 ObjToScanQueue* work_q = par_scan_state()->work_queue();
534
535 while (true) {
536 // Scan to-space and old-gen objs until we run out of both.
537 oop obj_to_scan;
538 par_scan_state()->trim_queues(0);
539
540 // We have no local work, attempt to steal from other threads.
541
542 // Attempt to steal work from promoted.
543 if (task_queues()->steal(par_scan_state()->thread_num(),
544 par_scan_state()->hash_seed(),
545 obj_to_scan)) {
546 bool res = work_q->push(obj_to_scan);
547 assert(res, "Empty queue should have room for a push.");
548
549 // If successful, goto Start.
550 continue;
551
552 // Try global overflow list.
553 } else if (par_gen()->take_from_overflow_list(par_scan_state())) {
554 continue;
555 }
556
557 // Otherwise, offer termination.
558 par_scan_state()->start_term_time();
559 if (terminator()->offer_termination()) break;
560 par_scan_state()->end_term_time();
561 }
562 assert(par_gen()->_overflow_list == NULL && par_gen()->_num_par_pushes == 0,
563 "Broken overflow list?");
564 // Finish the last termination pause.
565 par_scan_state()->end_term_time();
566 }
567
568 ParNewGenTask::ParNewGenTask(ParNewGeneration* young_gen,
569 Generation* old_gen,
570 HeapWord* young_old_boundary,
571 ParScanThreadStateSet* state_set,
572 StrongRootsScope* strong_roots_scope) :
573 AbstractGangTask("ParNewGeneration collection"),
574 _young_gen(young_gen), _old_gen(old_gen),
575 _young_old_boundary(young_old_boundary),
576 _state_set(state_set),
577 _strong_roots_scope(strong_roots_scope)
578 {}
579
580 void ParNewGenTask::work(uint worker_id) {
581 GenCollectedHeap* gch = GenCollectedHeap::heap();
582 // Since this is being done in a separate thread, need new resource
583 // and handle marks.
584 ResourceMark rm;
585 HandleMark hm;
586
587 ParScanThreadState& par_scan_state = _state_set->thread_state(worker_id);
588 assert(_state_set->is_valid(worker_id), "Should not have been called");
589
590 par_scan_state.set_young_old_boundary(_young_old_boundary);
591
592 KlassScanClosure klass_scan_closure(&par_scan_state.to_space_root_closure(),
593 gch->rem_set()->klass_rem_set());
594 CLDToKlassAndOopClosure cld_scan_closure(&klass_scan_closure,
595 &par_scan_state.to_space_root_closure(),
596 false);
597
598 par_scan_state.start_strong_roots();
599 gch->gen_process_roots(_strong_roots_scope,
600 GenCollectedHeap::YoungGen,
601 true, // Process younger gens, if any, as strong roots.
602 GenCollectedHeap::SO_ScavengeCodeCache,
603 GenCollectedHeap::StrongAndWeakRoots,
604 &par_scan_state.to_space_root_closure(),
605 &par_scan_state.older_gen_closure(),
606 &cld_scan_closure);
607
608 par_scan_state.end_strong_roots();
609
610 // "evacuate followers".
611 par_scan_state.evacuate_followers_closure().do_void();
612 }
613
614 ParNewGeneration::ParNewGeneration(ReservedSpace rs, size_t initial_byte_size)
615 : DefNewGeneration(rs, initial_byte_size, "PCopy"),
616 _overflow_list(NULL),
617 _is_alive_closure(this),
618 _plab_stats(YoungPLABSize, PLABWeight)
619 {
620 NOT_PRODUCT(_overflow_counter = ParGCWorkQueueOverflowInterval;)
621 NOT_PRODUCT(_num_par_pushes = 0;)
622 _task_queues = new ObjToScanQueueSet(ParallelGCThreads);
623 guarantee(_task_queues != NULL, "task_queues allocation failure.");
624
625 for (uint i = 0; i < ParallelGCThreads; i++) {
626 ObjToScanQueue *q = new ObjToScanQueue();
627 guarantee(q != NULL, "work_queue Allocation failure.");
628 _task_queues->register_queue(i, q);
629 }
630
631 for (uint i = 0; i < ParallelGCThreads; i++) {
632 _task_queues->queue(i)->initialize();
633 }
634
635 _overflow_stacks = NULL;
636 if (ParGCUseLocalOverflow) {
637 // typedef to workaround NEW_C_HEAP_ARRAY macro, which can not deal with ','
638 typedef Stack<oop, mtGC> GCOopStack;
639
640 _overflow_stacks = NEW_C_HEAP_ARRAY(GCOopStack, ParallelGCThreads, mtGC);
641 for (size_t i = 0; i < ParallelGCThreads; ++i) {
642 new (_overflow_stacks + i) Stack<oop, mtGC>();
643 }
644 }
645
646 if (UsePerfData) {
647 EXCEPTION_MARK;
648 ResourceMark rm;
649
650 const char* cname =
651 PerfDataManager::counter_name(_gen_counters->name_space(), "threads");
652 PerfDataManager::create_constant(SUN_GC, cname, PerfData::U_None,
653 ParallelGCThreads, CHECK);
654 }
655 }
656
657 // ParNewGeneration::
658 ParKeepAliveClosure::ParKeepAliveClosure(ParScanWeakRefClosure* cl) :
659 DefNewGeneration::KeepAliveClosure(cl), _par_cl(cl) {}
660
661 template <class T>
662 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop_work(T* p) {
663 #ifdef ASSERT
664 {
665 assert(!oopDesc::is_null(*p), "expected non-null ref");
666 oop obj = oopDesc::load_decode_heap_oop_not_null(p);
667 // We never expect to see a null reference being processed
668 // as a weak reference.
669 assert(obj->is_oop(), "expected an oop while scanning weak refs");
670 }
671 #endif // ASSERT
672
673 _par_cl->do_oop_nv(p);
674
675 if (GenCollectedHeap::heap()->is_in_reserved(p)) {
676 oop obj = oopDesc::load_decode_heap_oop_not_null(p);
677 _rs->write_ref_field_gc_par(p, obj);
678 }
679 }
680
681 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(oop* p) { ParKeepAliveClosure::do_oop_work(p); }
682 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(narrowOop* p) { ParKeepAliveClosure::do_oop_work(p); }
683
684 // ParNewGeneration::
685 KeepAliveClosure::KeepAliveClosure(ScanWeakRefClosure* cl) :
686 DefNewGeneration::KeepAliveClosure(cl) {}
687
688 template <class T>
689 void /*ParNewGeneration::*/KeepAliveClosure::do_oop_work(T* p) {
690 #ifdef ASSERT
691 {
692 assert(!oopDesc::is_null(*p), "expected non-null ref");
693 oop obj = oopDesc::load_decode_heap_oop_not_null(p);
694 // We never expect to see a null reference being processed
695 // as a weak reference.
696 assert(obj->is_oop(), "expected an oop while scanning weak refs");
697 }
698 #endif // ASSERT
699
700 _cl->do_oop_nv(p);
701
702 if (GenCollectedHeap::heap()->is_in_reserved(p)) {
703 oop obj = oopDesc::load_decode_heap_oop_not_null(p);
704 _rs->write_ref_field_gc_par(p, obj);
705 }
706 }
707
708 void /*ParNewGeneration::*/KeepAliveClosure::do_oop(oop* p) { KeepAliveClosure::do_oop_work(p); }
709 void /*ParNewGeneration::*/KeepAliveClosure::do_oop(narrowOop* p) { KeepAliveClosure::do_oop_work(p); }
710
711 template <class T> void ScanClosureWithParBarrier::do_oop_work(T* p) {
712 T heap_oop = oopDesc::load_heap_oop(p);
713 if (!oopDesc::is_null(heap_oop)) {
714 oop obj = oopDesc::decode_heap_oop_not_null(heap_oop);
715 if ((HeapWord*)obj < _boundary) {
716 assert(!_g->to()->is_in_reserved(obj), "Scanning field twice?");
717 oop new_obj = obj->is_forwarded()
718 ? obj->forwardee()
719 : _g->DefNewGeneration::copy_to_survivor_space(obj);
720 oopDesc::encode_store_heap_oop_not_null(p, new_obj);
721 }
722 if (_gc_barrier) {
723 // If p points to a younger generation, mark the card.
724 if ((HeapWord*)obj < _gen_boundary) {
725 _rs->write_ref_field_gc_par(p, obj);
726 }
727 }
728 }
729 }
730
731 void ScanClosureWithParBarrier::do_oop(oop* p) { ScanClosureWithParBarrier::do_oop_work(p); }
732 void ScanClosureWithParBarrier::do_oop(narrowOop* p) { ScanClosureWithParBarrier::do_oop_work(p); }
733
734 class ParNewRefProcTaskProxy: public AbstractGangTask {
735 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
736 public:
737 ParNewRefProcTaskProxy(ProcessTask& task,
738 ParNewGeneration& young_gen,
739 Generation& old_gen,
740 HeapWord* young_old_boundary,
741 ParScanThreadStateSet& state_set);
742
743 private:
744 virtual void work(uint worker_id);
745 private:
746 ParNewGeneration& _young_gen;
747 ProcessTask& _task;
748 Generation& _old_gen;
749 HeapWord* _young_old_boundary;
750 ParScanThreadStateSet& _state_set;
751 };
752
753 ParNewRefProcTaskProxy::ParNewRefProcTaskProxy(ProcessTask& task,
754 ParNewGeneration& young_gen,
755 Generation& old_gen,
756 HeapWord* young_old_boundary,
757 ParScanThreadStateSet& state_set)
758 : AbstractGangTask("ParNewGeneration parallel reference processing"),
759 _young_gen(young_gen),
760 _task(task),
761 _old_gen(old_gen),
762 _young_old_boundary(young_old_boundary),
763 _state_set(state_set)
764 { }
765
766 void ParNewRefProcTaskProxy::work(uint worker_id) {
767 ResourceMark rm;
768 HandleMark hm;
769 ParScanThreadState& par_scan_state = _state_set.thread_state(worker_id);
770 par_scan_state.set_young_old_boundary(_young_old_boundary);
771 _task.work(worker_id, par_scan_state.is_alive_closure(),
772 par_scan_state.keep_alive_closure(),
773 par_scan_state.evacuate_followers_closure());
774 }
775
776 class ParNewRefEnqueueTaskProxy: public AbstractGangTask {
777 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
778 EnqueueTask& _task;
779
780 public:
781 ParNewRefEnqueueTaskProxy(EnqueueTask& task)
782 : AbstractGangTask("ParNewGeneration parallel reference enqueue"),
783 _task(task)
784 { }
785
786 virtual void work(uint worker_id) {
787 _task.work(worker_id);
788 }
789 };
790
791 void ParNewRefProcTaskExecutor::execute(ProcessTask& task) {
792 GenCollectedHeap* gch = GenCollectedHeap::heap();
793 WorkGang* workers = gch->workers();
794 assert(workers != NULL, "Need parallel worker threads.");
795 _state_set.reset(workers->active_workers(), _young_gen.promotion_failed());
796 ParNewRefProcTaskProxy rp_task(task, _young_gen, _old_gen,
797 _young_gen.reserved().end(), _state_set);
798 workers->run_task(&rp_task);
799 _state_set.reset(0 /* bad value in debug if not reset */,
800 _young_gen.promotion_failed());
801 }
802
803 void ParNewRefProcTaskExecutor::execute(EnqueueTask& task) {
804 GenCollectedHeap* gch = GenCollectedHeap::heap();
805 WorkGang* workers = gch->workers();
806 assert(workers != NULL, "Need parallel worker threads.");
807 ParNewRefEnqueueTaskProxy enq_task(task);
808 workers->run_task(&enq_task);
809 }
810
811 void ParNewRefProcTaskExecutor::set_single_threaded_mode() {
812 _state_set.flush();
813 GenCollectedHeap* gch = GenCollectedHeap::heap();
814 gch->save_marks();
815 }
816
817 ScanClosureWithParBarrier::
818 ScanClosureWithParBarrier(ParNewGeneration* g, bool gc_barrier) :
819 ScanClosure(g, gc_barrier)
820 { }
821
822 EvacuateFollowersClosureGeneral::
823 EvacuateFollowersClosureGeneral(GenCollectedHeap* gch,
824 OopsInGenClosure* cur,
825 OopsInGenClosure* older) :
826 _gch(gch),
827 _scan_cur_or_nonheap(cur), _scan_older(older)
828 { }
829
830 void EvacuateFollowersClosureGeneral::do_void() {
831 do {
832 // Beware: this call will lead to closure applications via virtual
833 // calls.
834 _gch->oop_since_save_marks_iterate(GenCollectedHeap::YoungGen,
835 _scan_cur_or_nonheap,
836 _scan_older);
837 } while (!_gch->no_allocs_since_save_marks());
838 }
839
840 // A Generation that does parallel young-gen collection.
841
842 void ParNewGeneration::handle_promotion_failed(GenCollectedHeap* gch, ParScanThreadStateSet& thread_state_set) {
843 assert(_promo_failure_scan_stack.is_empty(), "post condition");
844 _promo_failure_scan_stack.clear(true); // Clear cached segments.
845
846 remove_forwarding_pointers();
847 log_info(gc, promotion)("Promotion failed");
848 // All the spaces are in play for mark-sweep.
849 swap_spaces(); // Make life simpler for CMS || rescan; see 6483690.
850 from()->set_next_compaction_space(to());
851 gch->set_incremental_collection_failed();
852 // Inform the next generation that a promotion failure occurred.
853 _old_gen->promotion_failure_occurred();
854
855 // Trace promotion failure in the parallel GC threads
856 thread_state_set.trace_promotion_failed(gc_tracer());
857 // Single threaded code may have reported promotion failure to the global state
858 if (_promotion_failed_info.has_failed()) {
859 _gc_tracer.report_promotion_failed(_promotion_failed_info);
860 }
861 // Reset the PromotionFailureALot counters.
862 NOT_PRODUCT(gch->reset_promotion_should_fail();)
863 }
864
865 void ParNewGeneration::collect(bool full,
866 bool clear_all_soft_refs,
867 size_t size,
868 bool is_tlab) {
869 assert(full || size > 0, "otherwise we don't want to collect");
870
871 GenCollectedHeap* gch = GenCollectedHeap::heap();
872
873 _gc_timer->register_gc_start();
874
875 AdaptiveSizePolicy* size_policy = gch->gen_policy()->size_policy();
876 WorkGang* workers = gch->workers();
877 assert(workers != NULL, "Need workgang for parallel work");
878 uint active_workers =
879 AdaptiveSizePolicy::calc_active_workers(workers->total_workers(),
880 workers->active_workers(),
881 Threads::number_of_non_daemon_threads());
882 workers->set_active_workers(active_workers);
883 _old_gen = gch->old_gen();
884
885 // If the next generation is too full to accommodate worst-case promotion
886 // from this generation, pass on collection; let the next generation
887 // do it.
888 if (!collection_attempt_is_safe()) {
889 gch->set_incremental_collection_failed(); // slight lie, in that we did not even attempt one
890 return;
891 }
892 assert(to()->is_empty(), "Else not collection_attempt_is_safe");
893
894 _gc_tracer.report_gc_start(gch->gc_cause(), _gc_timer->gc_start());
895 gch->trace_heap_before_gc(gc_tracer());
896
897 init_assuming_no_promotion_failure();
898
899 if (UseAdaptiveSizePolicy) {
900 set_survivor_overflow(false);
901 size_policy->minor_collection_begin();
902 }
903
904 GCTraceTime(Trace, gc) t1("ParNew", NULL, gch->gc_cause());
905
906 age_table()->clear();
907 to()->clear(SpaceDecorator::Mangle);
908
909 gch->save_marks();
910
911 // Set the correct parallelism (number of queues) in the reference processor
912 ref_processor()->set_active_mt_degree(active_workers);
913
914 // Need to initialize the preserved marks before the ThreadStateSet c'tor.
915 _preserved_marks_set.init(active_workers);
916
917 // Always set the terminator for the active number of workers
918 // because only those workers go through the termination protocol.
919 ParallelTaskTerminator _term(active_workers, task_queues());
920 ParScanThreadStateSet thread_state_set(active_workers,
921 *to(), *this, *_old_gen, *task_queues(),
922 _overflow_stacks, _preserved_marks_set,
923 desired_plab_sz(), _term);
924
925 thread_state_set.reset(active_workers, promotion_failed());
926
927 {
928 StrongRootsScope srs(active_workers);
929
930 ParNewGenTask tsk(this, _old_gen, reserved().end(), &thread_state_set, &srs);
931 gch->rem_set()->prepare_for_younger_refs_iterate(true);
932 // It turns out that even when we're using 1 thread, doing the work in a
933 // separate thread causes wide variance in run times. We can't help this
934 // in the multi-threaded case, but we special-case n=1 here to get
935 // repeatable measurements of the 1-thread overhead of the parallel code.
936 if (active_workers > 1) {
937 workers->run_task(&tsk);
938 } else {
939 tsk.work(0);
940 }
941 }
942
943 thread_state_set.reset(0 /* Bad value in debug if not reset */,
944 promotion_failed());
945
946 // Trace and reset failed promotion info.
947 if (promotion_failed()) {
948 thread_state_set.trace_promotion_failed(gc_tracer());
949 }
950
951 // Process (weak) reference objects found during scavenge.
952 ReferenceProcessor* rp = ref_processor();
953 IsAliveClosure is_alive(this);
954 ScanWeakRefClosure scan_weak_ref(this);
955 KeepAliveClosure keep_alive(&scan_weak_ref);
956 ScanClosure scan_without_gc_barrier(this, false);
957 ScanClosureWithParBarrier scan_with_gc_barrier(this, true);
958 set_promo_failure_scan_stack_closure(&scan_without_gc_barrier);
959 EvacuateFollowersClosureGeneral evacuate_followers(gch,
960 &scan_without_gc_barrier, &scan_with_gc_barrier);
961 rp->setup_policy(clear_all_soft_refs);
962 // Can the mt_degree be set later (at run_task() time would be best)?
963 rp->set_active_mt_degree(active_workers);
964 ReferenceProcessorStats stats;
965 if (rp->processing_is_mt()) {
966 ParNewRefProcTaskExecutor task_executor(*this, *_old_gen, thread_state_set);
967 stats = rp->process_discovered_references(&is_alive, &keep_alive,
968 &evacuate_followers, &task_executor,
969 _gc_timer);
970 } else {
971 thread_state_set.flush();
972 gch->save_marks();
973 stats = rp->process_discovered_references(&is_alive, &keep_alive,
974 &evacuate_followers, NULL,
975 _gc_timer);
976 }
977 _gc_tracer.report_gc_reference_stats(stats);
978 _gc_tracer.report_tenuring_threshold(tenuring_threshold());
979
980 if (!promotion_failed()) {
981 // Swap the survivor spaces.
982 eden()->clear(SpaceDecorator::Mangle);
983 from()->clear(SpaceDecorator::Mangle);
984 if (ZapUnusedHeapArea) {
985 // This is now done here because of the piece-meal mangling which
986 // can check for valid mangling at intermediate points in the
987 // collection(s). When a young collection fails to collect
988 // sufficient space resizing of the young generation can occur
989 // and redistribute the spaces in the young generation. Mangle
990 // here so that unzapped regions don't get distributed to
991 // other spaces.
992 to()->mangle_unused_area();
993 }
994 swap_spaces();
995
996 // A successful scavenge should restart the GC time limit count which is
997 // for full GC's.
998 size_policy->reset_gc_overhead_limit_count();
999
1000 assert(to()->is_empty(), "to space should be empty now");
1001
1002 adjust_desired_tenuring_threshold();
1003 } else {
1004 handle_promotion_failed(gch, thread_state_set);
1005 }
1006 _preserved_marks_set.reclaim();
1007 // set new iteration safe limit for the survivor spaces
1008 from()->set_concurrent_iteration_safe_limit(from()->top());
1009 to()->set_concurrent_iteration_safe_limit(to()->top());
1010
1011 if (ResizePLAB) {
1012 plab_stats()->adjust_desired_plab_sz();
1013 }
1014
1015 TASKQUEUE_STATS_ONLY(thread_state_set.print_termination_stats());
1016 TASKQUEUE_STATS_ONLY(thread_state_set.print_taskqueue_stats());
1017
1018 if (UseAdaptiveSizePolicy) {
1019 size_policy->minor_collection_end(gch->gc_cause());
1020 size_policy->avg_survived()->sample(from()->used());
1021 }
1022
1023 // We need to use a monotonically non-decreasing time in ms
1024 // or we will see time-warp warnings and os::javaTimeMillis()
1025 // does not guarantee monotonicity.
1026 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
1027 update_time_of_last_gc(now);
1028
1029 rp->set_enqueuing_is_done(true);
1030 if (rp->processing_is_mt()) {
1031 ParNewRefProcTaskExecutor task_executor(*this, *_old_gen, thread_state_set);
1032 rp->enqueue_discovered_references(&task_executor);
1033 } else {
1034 rp->enqueue_discovered_references(NULL);
1035 }
1036 rp->verify_no_references_recorded();
1037
1038 gch->trace_heap_after_gc(gc_tracer());
1039
1040 _gc_timer->register_gc_end();
1041
1042 _gc_tracer.report_gc_end(_gc_timer->gc_end(), _gc_timer->time_partitions());
1043 }
1044
1045 size_t ParNewGeneration::desired_plab_sz() {
1046 return _plab_stats.desired_plab_sz(GenCollectedHeap::heap()->workers()->active_workers());
1047 }
1048
1049 static int sum;
1050 void ParNewGeneration::waste_some_time() {
1051 for (int i = 0; i < 100; i++) {
1052 sum += i;
1053 }
1054 }
1055
1056 static const oop ClaimedForwardPtr = cast_to_oop<intptr_t>(0x4);
1057
1058 // Because of concurrency, there are times where an object for which
1059 // "is_forwarded()" is true contains an "interim" forwarding pointer
1060 // value. Such a value will soon be overwritten with a real value.
1061 // This method requires "obj" to have a forwarding pointer, and waits, if
1062 // necessary for a real one to be inserted, and returns it.
1063
1064 oop ParNewGeneration::real_forwardee(oop obj) {
1065 oop forward_ptr = obj->forwardee();
1066 if (forward_ptr != ClaimedForwardPtr) {
1067 return forward_ptr;
1068 } else {
1069 return real_forwardee_slow(obj);
1070 }
1071 }
1072
1073 oop ParNewGeneration::real_forwardee_slow(oop obj) {
1074 // Spin-read if it is claimed but not yet written by another thread.
1075 oop forward_ptr = obj->forwardee();
1076 while (forward_ptr == ClaimedForwardPtr) {
1077 waste_some_time();
1078 assert(obj->is_forwarded(), "precondition");
1079 forward_ptr = obj->forwardee();
1080 }
1081 return forward_ptr;
1082 }
1083
1084 // Multiple GC threads may try to promote an object. If the object
1085 // is successfully promoted, a forwarding pointer will be installed in
1086 // the object in the young generation. This method claims the right
1087 // to install the forwarding pointer before it copies the object,
1088 // thus avoiding the need to undo the copy as in
1089 // copy_to_survivor_space_avoiding_with_undo.
1090
1091 oop ParNewGeneration::copy_to_survivor_space(ParScanThreadState* par_scan_state,
1092 oop old,
1093 size_t sz,
1094 markOop m) {
1095 // In the sequential version, this assert also says that the object is
1096 // not forwarded. That might not be the case here. It is the case that
1097 // the caller observed it to be not forwarded at some time in the past.
1098 assert(is_in_reserved(old), "shouldn't be scavenging this oop");
1099
1100 // The sequential code read "old->age()" below. That doesn't work here,
1101 // since the age is in the mark word, and that might be overwritten with
1102 // a forwarding pointer by a parallel thread. So we must save the mark
1103 // word in a local and then analyze it.
1104 oopDesc dummyOld;
1105 dummyOld.set_mark(m);
1106 assert(!dummyOld.is_forwarded(),
1107 "should not be called with forwarding pointer mark word.");
1108
1109 oop new_obj = NULL;
1110 oop forward_ptr;
1111
1112 // Try allocating obj in to-space (unless too old)
1113 if (dummyOld.age() < tenuring_threshold()) {
1114 new_obj = (oop)par_scan_state->alloc_in_to_space(sz);
1115 if (new_obj == NULL) {
1116 set_survivor_overflow(true);
1117 }
1118 }
1119
1120 if (new_obj == NULL) {
1121 // Either to-space is full or we decided to promote try allocating obj tenured
1122
1123 // Attempt to install a null forwarding pointer (atomically),
1124 // to claim the right to install the real forwarding pointer.
1125 forward_ptr = old->forward_to_atomic(ClaimedForwardPtr);
1126 if (forward_ptr != NULL) {
1127 // someone else beat us to it.
1128 return real_forwardee(old);
1129 }
1130
1131 if (!_promotion_failed) {
1132 new_obj = _old_gen->par_promote(par_scan_state->thread_num(),
1133 old, m, sz);
1134 }
1135
1136 if (new_obj == NULL) {
1137 // promotion failed, forward to self
1138 _promotion_failed = true;
1139 new_obj = old;
1140
1141 par_scan_state->preserved_marks()->push_if_necessary(old, m);
1142 par_scan_state->register_promotion_failure(sz);
1143 }
1144
1145 old->forward_to(new_obj);
1146 forward_ptr = NULL;
1147 } else {
1148 // Is in to-space; do copying ourselves.
1149 Copy::aligned_disjoint_words((HeapWord*)old, (HeapWord*)new_obj, sz);
1150 assert(GenCollectedHeap::heap()->is_in_reserved(new_obj), "illegal forwarding pointer value.");
1151 forward_ptr = old->forward_to_atomic(new_obj);
1152 // Restore the mark word copied above.
1153 new_obj->set_mark(m);
1154 // Increment age if obj still in new generation
1155 new_obj->incr_age();
1156 par_scan_state->age_table()->add(new_obj, sz);
1157 }
1158 assert(new_obj != NULL, "just checking");
1159
1160 // This code must come after the CAS test, or it will print incorrect
1161 // information.
1162 log_develop_trace(gc, scavenge)("{%s %s " PTR_FORMAT " -> " PTR_FORMAT " (%d)}",
1163 is_in_reserved(new_obj) ? "copying" : "tenuring",
1164 new_obj->klass()->internal_name(), p2i(old), p2i(new_obj), new_obj->size());
1165
1166 if (forward_ptr == NULL) {
1167 oop obj_to_push = new_obj;
1168 if (par_scan_state->should_be_partially_scanned(obj_to_push, old)) {
1169 // Length field used as index of next element to be scanned.
1170 // Real length can be obtained from real_forwardee()
1171 arrayOop(old)->set_length(0);
1172 obj_to_push = old;
1173 assert(obj_to_push->is_forwarded() && obj_to_push->forwardee() != obj_to_push,
1174 "push forwarded object");
1175 }
1176 // Push it on one of the queues of to-be-scanned objects.
1177 bool simulate_overflow = false;
1178 NOT_PRODUCT(
1179 if (ParGCWorkQueueOverflowALot && should_simulate_overflow()) {
1180 // simulate a stack overflow
1181 simulate_overflow = true;
1182 }
1183 )
1184 if (simulate_overflow || !par_scan_state->work_queue()->push(obj_to_push)) {
1185 // Add stats for overflow pushes.
1186 log_develop_trace(gc)("Queue Overflow");
1187 push_on_overflow_list(old, par_scan_state);
1188 TASKQUEUE_STATS_ONLY(par_scan_state->taskqueue_stats().record_overflow(0));
1189 }
1190
1191 return new_obj;
1192 }
1193
1194 // Oops. Someone beat us to it. Undo the allocation. Where did we
1195 // allocate it?
1196 if (is_in_reserved(new_obj)) {
1197 // Must be in to_space.
1198 assert(to()->is_in_reserved(new_obj), "Checking");
1199 if (forward_ptr == ClaimedForwardPtr) {
1200 // Wait to get the real forwarding pointer value.
1201 forward_ptr = real_forwardee(old);
1202 }
1203 par_scan_state->undo_alloc_in_to_space((HeapWord*)new_obj, sz);
1204 }
1205
1206 return forward_ptr;
1207 }
1208
1209 #ifndef PRODUCT
1210 // It's OK to call this multi-threaded; the worst thing
1211 // that can happen is that we'll get a bunch of closely
1212 // spaced simulated overflows, but that's OK, in fact
1213 // probably good as it would exercise the overflow code
1214 // under contention.
1215 bool ParNewGeneration::should_simulate_overflow() {
1216 if (_overflow_counter-- <= 0) { // just being defensive
1217 _overflow_counter = ParGCWorkQueueOverflowInterval;
1218 return true;
1219 } else {
1220 return false;
1221 }
1222 }
1223 #endif
1224
1225 // In case we are using compressed oops, we need to be careful.
1226 // If the object being pushed is an object array, then its length
1227 // field keeps track of the "grey boundary" at which the next
1228 // incremental scan will be done (see ParGCArrayScanChunk).
1229 // When using compressed oops, this length field is kept in the
1230 // lower 32 bits of the erstwhile klass word and cannot be used
1231 // for the overflow chaining pointer (OCP below). As such the OCP
1232 // would itself need to be compressed into the top 32-bits in this
1233 // case. Unfortunately, see below, in the event that we have a
1234 // promotion failure, the node to be pushed on the list can be
1235 // outside of the Java heap, so the heap-based pointer compression
1236 // would not work (we would have potential aliasing between C-heap
1237 // and Java-heap pointers). For this reason, when using compressed
1238 // oops, we simply use a worker-thread-local, non-shared overflow
1239 // list in the form of a growable array, with a slightly different
1240 // overflow stack draining strategy. If/when we start using fat
1241 // stacks here, we can go back to using (fat) pointer chains
1242 // (although some performance comparisons would be useful since
1243 // single global lists have their own performance disadvantages
1244 // as we were made painfully aware not long ago, see 6786503).
1245 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
1246 void ParNewGeneration::push_on_overflow_list(oop from_space_obj, ParScanThreadState* par_scan_state) {
1247 assert(is_in_reserved(from_space_obj), "Should be from this generation");
1248 if (ParGCUseLocalOverflow) {
1249 // In the case of compressed oops, we use a private, not-shared
1250 // overflow stack.
1251 par_scan_state->push_on_overflow_stack(from_space_obj);
1252 } else {
1253 assert(!UseCompressedOops, "Error");
1254 // if the object has been forwarded to itself, then we cannot
1255 // use the klass pointer for the linked list. Instead we have
1256 // to allocate an oopDesc in the C-Heap and use that for the linked list.
1257 // XXX This is horribly inefficient when a promotion failure occurs
1258 // and should be fixed. XXX FIX ME !!!
1259 #ifndef PRODUCT
1260 Atomic::inc_ptr(&_num_par_pushes);
1261 assert(_num_par_pushes > 0, "Tautology");
1262 #endif
1263 if (from_space_obj->forwardee() == from_space_obj) {
1264 oopDesc* listhead = NEW_C_HEAP_ARRAY(oopDesc, 1, mtGC);
1265 listhead->forward_to(from_space_obj);
1266 from_space_obj = listhead;
1267 }
1268 oop observed_overflow_list = _overflow_list;
1269 oop cur_overflow_list;
1270 do {
1271 cur_overflow_list = observed_overflow_list;
1272 if (cur_overflow_list != BUSY) {
1273 from_space_obj->set_klass_to_list_ptr(cur_overflow_list);
1274 } else {
1275 from_space_obj->set_klass_to_list_ptr(NULL);
1276 }
1277 observed_overflow_list =
1278 (oop)Atomic::cmpxchg_ptr(from_space_obj, &_overflow_list, cur_overflow_list);
1279 } while (cur_overflow_list != observed_overflow_list);
1280 }
1281 }
1282
1283 bool ParNewGeneration::take_from_overflow_list(ParScanThreadState* par_scan_state) {
1284 bool res;
1285
1286 if (ParGCUseLocalOverflow) {
1287 res = par_scan_state->take_from_overflow_stack();
1288 } else {
1289 assert(!UseCompressedOops, "Error");
1290 res = take_from_overflow_list_work(par_scan_state);
1291 }
1292 return res;
1293 }
1294
1295
1296 // *NOTE*: The overflow list manipulation code here and
1297 // in CMSCollector:: are very similar in shape,
1298 // except that in the CMS case we thread the objects
1299 // directly into the list via their mark word, and do
1300 // not need to deal with special cases below related
1301 // to chunking of object arrays and promotion failure
1302 // handling.
1303 // CR 6797058 has been filed to attempt consolidation of
1304 // the common code.
1305 // Because of the common code, if you make any changes in
1306 // the code below, please check the CMS version to see if
1307 // similar changes might be needed.
1308 // See CMSCollector::par_take_from_overflow_list() for
1309 // more extensive documentation comments.
1310 bool ParNewGeneration::take_from_overflow_list_work(ParScanThreadState* par_scan_state) {
1311 ObjToScanQueue* work_q = par_scan_state->work_queue();
1312 // How many to take?
1313 size_t objsFromOverflow = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
1314 (size_t)ParGCDesiredObjsFromOverflowList);
1315
1316 assert(!UseCompressedOops, "Error");
1317 assert(par_scan_state->overflow_stack() == NULL, "Error");
1318 if (_overflow_list == NULL) return false;
1319
1320 // Otherwise, there was something there; try claiming the list.
1321 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
1322 // Trim off a prefix of at most objsFromOverflow items
1323 Thread* tid = Thread::current();
1324 size_t spin_count = ParallelGCThreads;
1325 size_t sleep_time_millis = MAX2((size_t)1, objsFromOverflow/100);
1326 for (size_t spin = 0; prefix == BUSY && spin < spin_count; spin++) {
1327 // someone grabbed it before we did ...
1328 // ... we spin for a short while...
1329 os::sleep(tid, sleep_time_millis, false);
1330 if (_overflow_list == NULL) {
1331 // nothing left to take
1332 return false;
1333 } else if (_overflow_list != BUSY) {
1334 // try and grab the prefix
1335 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
1336 }
1337 }
1338 if (prefix == NULL || prefix == BUSY) {
1339 // Nothing to take or waited long enough
1340 if (prefix == NULL) {
1341 // Write back the NULL in case we overwrote it with BUSY above
1342 // and it is still the same value.
1343 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
1344 }
1345 return false;
1346 }
1347 assert(prefix != NULL && prefix != BUSY, "Error");
1348 size_t i = 1;
1349 oop cur = prefix;
1350 while (i < objsFromOverflow && cur->klass_or_null() != NULL) {
1351 i++; cur = cur->list_ptr_from_klass();
1352 }
1353
1354 // Reattach remaining (suffix) to overflow list
1355 if (cur->klass_or_null() == NULL) {
1356 // Write back the NULL in lieu of the BUSY we wrote
1357 // above and it is still the same value.
1358 if (_overflow_list == BUSY) {
1359 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
1360 }
1361 } else {
1362 assert(cur->klass_or_null() != (Klass*)(address)BUSY, "Error");
1363 oop suffix = cur->list_ptr_from_klass(); // suffix will be put back on global list
1364 cur->set_klass_to_list_ptr(NULL); // break off suffix
1365 // It's possible that the list is still in the empty(busy) state
1366 // we left it in a short while ago; in that case we may be
1367 // able to place back the suffix.
1368 oop observed_overflow_list = _overflow_list;
1369 oop cur_overflow_list = observed_overflow_list;
1370 bool attached = false;
1371 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
1372 observed_overflow_list =
1373 (oop) Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list);
1374 if (cur_overflow_list == observed_overflow_list) {
1375 attached = true;
1376 break;
1377 } else cur_overflow_list = observed_overflow_list;
1378 }
1379 if (!attached) {
1380 // Too bad, someone else got in in between; we'll need to do a splice.
1381 // Find the last item of suffix list
1382 oop last = suffix;
1383 while (last->klass_or_null() != NULL) {
1384 last = last->list_ptr_from_klass();
1385 }
1386 // Atomically prepend suffix to current overflow list
1387 observed_overflow_list = _overflow_list;
1388 do {
1389 cur_overflow_list = observed_overflow_list;
1390 if (cur_overflow_list != BUSY) {
1391 // Do the splice ...
1392 last->set_klass_to_list_ptr(cur_overflow_list);
1393 } else { // cur_overflow_list == BUSY
1394 last->set_klass_to_list_ptr(NULL);
1395 }
1396 observed_overflow_list =
1397 (oop)Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list);
1398 } while (cur_overflow_list != observed_overflow_list);
1399 }
1400 }
1401
1402 // Push objects on prefix list onto this thread's work queue
1403 assert(prefix != NULL && prefix != BUSY, "program logic");
1404 cur = prefix;
1405 ssize_t n = 0;
1406 while (cur != NULL) {
1407 oop obj_to_push = cur->forwardee();
1408 oop next = cur->list_ptr_from_klass();
1409 cur->set_klass(obj_to_push->klass());
1410 // This may be an array object that is self-forwarded. In that case, the list pointer
1411 // space, cur, is not in the Java heap, but rather in the C-heap and should be freed.
1412 if (!is_in_reserved(cur)) {
1413 // This can become a scaling bottleneck when there is work queue overflow coincident
1414 // with promotion failure.
1415 oopDesc* f = cur;
1416 FREE_C_HEAP_ARRAY(oopDesc, f);
1417 } else if (par_scan_state->should_be_partially_scanned(obj_to_push, cur)) {
1418 assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned");
1419 obj_to_push = cur;
1420 }
1421 bool ok = work_q->push(obj_to_push);
1422 assert(ok, "Should have succeeded");
1423 cur = next;
1424 n++;
1425 }
1426 TASKQUEUE_STATS_ONLY(par_scan_state->note_overflow_refill(n));
1427 #ifndef PRODUCT
1428 assert(_num_par_pushes >= n, "Too many pops?");
1429 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
1430 #endif
1431 return true;
1432 }
1433 #undef BUSY
1434
1435 void ParNewGeneration::ref_processor_init() {
1436 if (_ref_processor == NULL) {
1437 // Allocate and initialize a reference processor
1438 _ref_processor =
1439 new ReferenceProcessor(_reserved, // span
1440 ParallelRefProcEnabled && (ParallelGCThreads > 1), // mt processing
1441 ParallelGCThreads, // mt processing degree
1442 refs_discovery_is_mt(), // mt discovery
1443 ParallelGCThreads, // mt discovery degree
1444 refs_discovery_is_atomic(), // atomic_discovery
1445 NULL); // is_alive_non_header
1446 }
1447 }
1448
1449 const char* ParNewGeneration::name() const {
1450 return "par new generation";
1451 }