1 /*
2 * Copyright (c) 2018, 2020, Red Hat, Inc. 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
27 #include "classfile/classLoaderData.hpp"
28 #include "classfile/classLoaderDataGraph.hpp"
29 #include "gc/shared/referenceProcessor.hpp"
30 #include "gc/shared/referenceProcessorPhaseTimes.hpp"
31 #include "gc/shared/workgroup.hpp"
32 #include "gc/shenandoah/shenandoahBarrierSet.hpp"
33 #include "gc/shenandoah/shenandoahClosures.inline.hpp"
34 #include "gc/shenandoah/shenandoahCodeRoots.hpp"
35 #include "gc/shenandoah/shenandoahCollectionSet.hpp"
36 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
37 #include "gc/shenandoah/shenandoahFreeSet.hpp"
38 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
39 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
40 #include "gc/shenandoah/shenandoahHeapRegionSet.inline.hpp"
41 #include "gc/shenandoah/shenandoahHeuristics.hpp"
42 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"
43 #include "gc/shenandoah/shenandoahOopClosures.inline.hpp"
44 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
45 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
46 #include "gc/shenandoah/shenandoahStringDedup.hpp"
47 #include "gc/shenandoah/shenandoahTaskqueue.inline.hpp"
48 #include "gc/shenandoah/shenandoahTraversalGC.hpp"
49 #include "gc/shenandoah/shenandoahUtils.hpp"
50 #include "gc/shenandoah/shenandoahVerifier.hpp"
51
52 #include "memory/iterator.hpp"
53 #include "memory/metaspace.hpp"
54 #include "memory/resourceArea.hpp"
55 #include "memory/universe.hpp"
56
57 /**
58 * NOTE: We are using the SATB buffer in thread.hpp and satbMarkQueue.hpp, however, it is not an SATB algorithm.
59 * We're using the buffer as generic oop buffer to enqueue new values in concurrent oop stores, IOW, the algorithm
60 * is incremental-update-based.
61 *
62 * NOTE on interaction with TAMS: we want to avoid traversing new objects for
63 * several reasons:
64 * - We will not reclaim them in this cycle anyway, because they are not in the
65 * cset
66 * - It makes up for the bulk of work during final-pause
67 * - It also shortens the concurrent cycle because we don't need to
68 * pointlessly traverse through newly allocated objects.
69 * - As a nice side-effect, it solves the I-U termination problem (mutators
70 * cannot outrun the GC by allocating like crazy)
71 * - It is an easy way to achieve MWF. What MWF does is to also enqueue the
72 * target object of stores if it's new. Treating new objects live implicitely
73 * achieves the same, but without extra barriers. I think the effect of
74 * shortened final-pause (mentioned above) is the main advantage of MWF. In
75 * particular, we will not see the head of a completely new long linked list
76 * in final-pause and end up traversing huge chunks of the heap there.
77 * - We don't need to see/update the fields of new objects either, because they
78 * are either still null, or anything that's been stored into them has been
79 * evacuated+enqueued before (and will thus be treated later).
80 *
81 * We achieve this by setting TAMS for each region, and everything allocated
82 * beyond TAMS will be 'implicitely marked'.
83 *
84 * Gotchas:
85 * - While we want new objects to be implicitely marked, we don't want to count
86 * them alive. Otherwise the next cycle wouldn't pick them up and consider
87 * them for cset. This means that we need to protect such regions from
88 * getting accidentally thrashed at the end of traversal cycle. This is why I
89 * keep track of alloc-regions and check is_alloc_region() in the trashing
90 * code.
91 * - We *need* to traverse through evacuated objects. Those objects are
92 * pre-existing, and any references in them point to interesting objects that
93 * we need to see. We also want to count them as live, because we just
94 * determined that they are alive :-) I achieve this by upping TAMS
95 * concurrently for every gclab/gc-shared alloc before publishing the
96 * evacuated object. This way, the GC threads will not consider such objects
97 * implictely marked, and traverse through them as normal.
98 */
99 class ShenandoahTraversalSATBBufferClosure : public SATBBufferClosure {
100 private:
101 ShenandoahObjToScanQueue* _queue;
102 ShenandoahTraversalGC* _traversal_gc;
103 ShenandoahHeap* const _heap;
104
105 public:
106 ShenandoahTraversalSATBBufferClosure(ShenandoahObjToScanQueue* q) :
107 _queue(q),
108 _heap(ShenandoahHeap::heap())
109 { }
110
111 void do_buffer(void** buffer, size_t size) {
112 for (size_t i = 0; i < size; ++i) {
113 oop* p = (oop*) &buffer[i];
114 oop obj = RawAccess<>::oop_load(p);
115 shenandoah_assert_not_forwarded(p, obj);
116 if (_heap->marking_context()->mark(obj)) {
117 _queue->push(ShenandoahMarkTask(obj));
118 }
119 }
120 }
121 };
122
123 class ShenandoahTraversalSATBThreadsClosure : public ThreadClosure {
124 private:
125 ShenandoahTraversalSATBBufferClosure* _satb_cl;
126
127 public:
128 ShenandoahTraversalSATBThreadsClosure(ShenandoahTraversalSATBBufferClosure* satb_cl) :
129 _satb_cl(satb_cl) {}
130
131 void do_thread(Thread* thread) {
132 ShenandoahThreadLocalData::satb_mark_queue(thread).apply_closure_and_empty(_satb_cl);
133 }
134 };
135
136 // Like CLDToOopClosure, but clears has_modified_oops, so that we can record modified CLDs during traversal
137 // and remark them later during final-traversal.
138 class ShenandoahMarkCLDClosure : public CLDClosure {
139 private:
140 OopClosure* _cl;
141 public:
142 ShenandoahMarkCLDClosure(OopClosure* cl) : _cl(cl) {}
143 void do_cld(ClassLoaderData* cld) {
144 cld->oops_do(_cl, ClassLoaderData::_claim_strong, true);
145 }
146 };
147
148 // Like CLDToOopClosure, but only process modified CLDs
149 class ShenandoahRemarkCLDClosure : public CLDClosure {
150 private:
151 OopClosure* _cl;
152 public:
153 ShenandoahRemarkCLDClosure(OopClosure* cl) : _cl(cl) {}
154 void do_cld(ClassLoaderData* cld) {
155 if (cld->has_modified_oops()) {
156 cld->oops_do(_cl, ClassLoaderData::_claim_strong, true);
157 }
158 }
159 };
160
161 class ShenandoahInitTraversalCollectionTask : public AbstractGangTask {
162 private:
163 ShenandoahCSetRootScanner* _rp;
164 ShenandoahHeap* _heap;
165 ShenandoahCsetCodeRootsIterator* _cset_coderoots;
166 ShenandoahStringDedupRoots _dedup_roots;
167
168 public:
169 ShenandoahInitTraversalCollectionTask(ShenandoahCSetRootScanner* rp) :
170 AbstractGangTask("Shenandoah Init Traversal Collection"),
171 _rp(rp),
172 _heap(ShenandoahHeap::heap()) {}
173
174 void work(uint worker_id) {
175 ShenandoahParallelWorkerSession worker_session(worker_id);
176
177 ShenandoahObjToScanQueueSet* queues = _heap->traversal_gc()->task_queues();
178 ShenandoahObjToScanQueue* q = queues->queue(worker_id);
179
180 bool process_refs = _heap->process_references();
181 bool unload_classes = _heap->unload_classes();
182 ReferenceProcessor* rp = NULL;
183 if (process_refs) {
184 rp = _heap->ref_processor();
185 }
186
187 // Step 1: Process ordinary GC roots.
188 {
189 ShenandoahTraversalRootsClosure roots_cl(q, rp);
190 ShenandoahMarkCLDClosure cld_cl(&roots_cl);
191 MarkingCodeBlobClosure code_cl(&roots_cl, CodeBlobToOopClosure::FixRelocations);
192 if (unload_classes) {
193 _rp->roots_do(worker_id, &roots_cl, NULL, &code_cl);
194 } else {
195 _rp->roots_do(worker_id, &roots_cl, &cld_cl, &code_cl);
196 }
197 }
198 }
199 };
200
201 class ShenandoahConcurrentTraversalCollectionTask : public AbstractGangTask {
202 private:
203 TaskTerminator* _terminator;
204 ShenandoahHeap* _heap;
205 public:
206 ShenandoahConcurrentTraversalCollectionTask(TaskTerminator* terminator) :
207 AbstractGangTask("Shenandoah Concurrent Traversal Collection"),
208 _terminator(terminator),
209 _heap(ShenandoahHeap::heap()) {}
210
211 void work(uint worker_id) {
212 ShenandoahConcurrentWorkerSession worker_session(worker_id);
213 ShenandoahSuspendibleThreadSetJoiner stsj(ShenandoahSuspendibleWorkers);
214 ShenandoahTraversalGC* traversal_gc = _heap->traversal_gc();
215
216 // Drain all outstanding work in queues.
217 traversal_gc->main_loop(worker_id, _terminator, true);
218 }
219 };
220
221 class ShenandoahFinalTraversalCollectionTask : public AbstractGangTask {
222 private:
223 ShenandoahAllRootScanner* _rp;
224 TaskTerminator* _terminator;
225 ShenandoahHeap* _heap;
226 public:
227 ShenandoahFinalTraversalCollectionTask(ShenandoahAllRootScanner* rp, TaskTerminator* terminator) :
228 AbstractGangTask("Shenandoah Final Traversal Collection"),
229 _rp(rp),
230 _terminator(terminator),
231 _heap(ShenandoahHeap::heap()) {}
232
233 void work(uint worker_id) {
234 ShenandoahParallelWorkerSession worker_session(worker_id);
235
236 ShenandoahTraversalGC* traversal_gc = _heap->traversal_gc();
237
238 ShenandoahObjToScanQueueSet* queues = traversal_gc->task_queues();
239 ShenandoahObjToScanQueue* q = queues->queue(worker_id);
240
241 bool process_refs = _heap->process_references();
242 bool unload_classes = _heap->unload_classes();
243 ReferenceProcessor* rp = NULL;
244 if (process_refs) {
245 rp = _heap->ref_processor();
246 }
247
248 // Step 0: Drain outstanding SATB queues.
249 // NOTE: we piggy-back draining of remaining thread SATB buffers on the final root scan below.
250 ShenandoahTraversalSATBBufferClosure satb_cl(q);
251 {
252 // Process remaining finished SATB buffers.
253 SATBMarkQueueSet& satb_mq_set = ShenandoahBarrierSet::satb_mark_queue_set();
254 while (satb_mq_set.apply_closure_to_completed_buffer(&satb_cl));
255 // Process remaining threads SATB buffers below.
256 }
257
258 // Step 1: Process GC roots.
259 // For oops in code roots, they are marked, evacuated, enqueued for further traversal,
260 // and the references to the oops are updated during init pause. New nmethods are handled
261 // in similar way during nmethod-register process. Therefore, we don't need to rescan code
262 // roots here.
263 if (!_heap->is_degenerated_gc_in_progress()) {
264 ShenandoahTraversalRootsClosure roots_cl(q, rp);
265 ShenandoahTraversalSATBThreadsClosure tc(&satb_cl);
266 if (unload_classes) {
267 ShenandoahRemarkCLDClosure remark_cld_cl(&roots_cl);
268 _rp->strong_roots_do(worker_id, &roots_cl, &remark_cld_cl, NULL, &tc);
269 } else {
270 CLDToOopClosure cld_cl(&roots_cl, ClassLoaderData::_claim_strong);
271 _rp->roots_do(worker_id, &roots_cl, &cld_cl, NULL, &tc);
272 }
273 } else {
274 ShenandoahTraversalDegenClosure roots_cl(q, rp);
275 ShenandoahTraversalSATBThreadsClosure tc(&satb_cl);
276 if (unload_classes) {
277 ShenandoahRemarkCLDClosure remark_cld_cl(&roots_cl);
278 _rp->strong_roots_do(worker_id, &roots_cl, &remark_cld_cl, NULL, &tc);
279 } else {
280 CLDToOopClosure cld_cl(&roots_cl, ClassLoaderData::_claim_strong);
281 _rp->roots_do(worker_id, &roots_cl, &cld_cl, NULL, &tc);
282 }
283 }
284
285 {
286 ShenandoahWorkerTimingsTracker timer(ShenandoahPhaseTimings::FinishQueues, worker_id);
287
288 // Step 3: Finally drain all outstanding work in queues.
289 traversal_gc->main_loop(worker_id, _terminator, false);
290 }
291
292 }
293 };
294
295 ShenandoahTraversalGC::ShenandoahTraversalGC(ShenandoahHeap* heap, size_t num_regions) :
296 _heap(heap),
297 _task_queues(new ShenandoahObjToScanQueueSet(heap->max_workers())),
298 _traversal_set(ShenandoahHeapRegionSet()) {
299
300 // Traversal does not support concurrent code root scanning
301 FLAG_SET_DEFAULT(ShenandoahConcurrentScanCodeRoots, false);
302
303 uint num_queues = heap->max_workers();
304 for (uint i = 0; i < num_queues; ++i) {
305 ShenandoahObjToScanQueue* task_queue = new ShenandoahObjToScanQueue();
306 task_queue->initialize();
307 _task_queues->register_queue(i, task_queue);
308 }
309 }
310
311 ShenandoahTraversalGC::~ShenandoahTraversalGC() {
312 }
313
314 void ShenandoahTraversalGC::prepare_regions() {
315 size_t num_regions = _heap->num_regions();
316 ShenandoahMarkingContext* const ctx = _heap->marking_context();
317 for (size_t i = 0; i < num_regions; i++) {
318 ShenandoahHeapRegion* region = _heap->get_region(i);
319 if (_heap->is_bitmap_slice_committed(region)) {
320 if (_traversal_set.is_in(i)) {
321 ctx->capture_top_at_mark_start(region);
322 region->clear_live_data();
323 assert(ctx->is_bitmap_clear_range(region->bottom(), region->end()), "bitmap for traversal regions must be cleared");
324 } else {
325 // Everything outside the traversal set is always considered live.
326 ctx->reset_top_at_mark_start(region);
327 }
328 } else {
329 // FreeSet may contain uncommitted empty regions, once they are recommitted,
330 // their TAMS may have old values, so reset them here.
331 ctx->reset_top_at_mark_start(region);
332 }
333 }
334 }
335
336 void ShenandoahTraversalGC::prepare() {
337 {
338 ShenandoahGCPhase phase(ShenandoahPhaseTimings::traversal_gc_make_parsable);
339 _heap->make_parsable(true);
340 }
341
342 if (UseTLAB) {
343 ShenandoahGCPhase phase(ShenandoahPhaseTimings::traversal_gc_resize_tlabs);
344 _heap->resize_tlabs();
345 }
346
347 assert(_heap->marking_context()->is_bitmap_clear(), "need clean mark bitmap");
348 assert(!_heap->marking_context()->is_complete(), "should not be complete");
349
350 // About to choose the collection set, make sure we know which regions are pinned.
351 {
352 ShenandoahGCPhase phase_cleanup(ShenandoahPhaseTimings::traversal_gc_prepare_sync_pinned);
353 _heap->sync_pinned_region_status();
354 }
355
356 ShenandoahCollectionSet* collection_set = _heap->collection_set();
357 {
358 ShenandoahHeapLocker lock(_heap->lock());
359
360 collection_set->clear();
361 assert(collection_set->count() == 0, "collection set not clear");
362
363 // Find collection set
364 _heap->heuristics()->choose_collection_set(collection_set);
365 prepare_regions();
366
367 // Rebuild free set
368 _heap->free_set()->rebuild();
369 }
370
371 log_info(gc, ergo)("Collectable Garbage: " SIZE_FORMAT "%s, " SIZE_FORMAT "%s CSet, " SIZE_FORMAT " CSet regions",
372 byte_size_in_proper_unit(collection_set->garbage()), proper_unit_for_byte_size(collection_set->garbage()),
373 byte_size_in_proper_unit(collection_set->live_data()), proper_unit_for_byte_size(collection_set->live_data()),
374 collection_set->count());
375 }
376
377 void ShenandoahTraversalGC::init_traversal_collection() {
378 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "STW traversal GC");
379
380 if (ShenandoahVerify) {
381 _heap->verifier()->verify_before_traversal();
382 }
383
384 if (VerifyBeforeGC) {
385 Universe::verify();
386 }
387
388 {
389 ShenandoahGCPhase phase_prepare(ShenandoahPhaseTimings::traversal_gc_prepare);
390 prepare();
391 }
392
393 _heap->set_concurrent_traversal_in_progress(true);
394 _heap->set_has_forwarded_objects(true);
395
396 bool process_refs = _heap->process_references();
397 if (process_refs) {
398 ReferenceProcessor* rp = _heap->ref_processor();
399 rp->enable_discovery(true /*verify_no_refs*/);
400 rp->setup_policy(_heap->soft_ref_policy()->should_clear_all_soft_refs());
401 }
402
403 {
404 ShenandoahGCPhase phase_work(ShenandoahPhaseTimings::init_traversal_gc_work);
405 assert(_task_queues->is_empty(), "queues must be empty before traversal GC");
406 TASKQUEUE_STATS_ONLY(_task_queues->reset_taskqueue_stats());
407
408 #if COMPILER2_OR_JVMCI
409 DerivedPointerTable::clear();
410 #endif
411
412 {
413 uint nworkers = _heap->workers()->active_workers();
414 task_queues()->reserve(nworkers);
415 ShenandoahCSetRootScanner rp(nworkers, ShenandoahPhaseTimings::init_traversal_gc_work);
416 ShenandoahInitTraversalCollectionTask traversal_task(&rp);
417 _heap->workers()->run_task(&traversal_task);
418 }
419
420 #if COMPILER2_OR_JVMCI
421 DerivedPointerTable::update_pointers();
422 #endif
423 }
424
425 if (ShenandoahPacing) {
426 _heap->pacer()->setup_for_traversal();
427 }
428 }
429
430 void ShenandoahTraversalGC::main_loop(uint w, TaskTerminator* t, bool sts_yield) {
431 ShenandoahObjToScanQueue* q = task_queues()->queue(w);
432
433 // Initialize live data.
434 jushort* ld = _heap->get_liveness_cache(w);
435
436 ReferenceProcessor* rp = NULL;
437 if (_heap->process_references()) {
438 rp = _heap->ref_processor();
439 }
440 {
441 if (!_heap->is_degenerated_gc_in_progress()) {
442 if (_heap->unload_classes()) {
443 if (ShenandoahStringDedup::is_enabled()) {
444 ShenandoahTraversalMetadataDedupClosure cl(q, rp);
445 main_loop_work<ShenandoahTraversalMetadataDedupClosure>(&cl, ld, w, t, sts_yield);
446 } else {
447 ShenandoahTraversalMetadataClosure cl(q, rp);
448 main_loop_work<ShenandoahTraversalMetadataClosure>(&cl, ld, w, t, sts_yield);
449 }
450 } else {
451 if (ShenandoahStringDedup::is_enabled()) {
452 ShenandoahTraversalDedupClosure cl(q, rp);
453 main_loop_work<ShenandoahTraversalDedupClosure>(&cl, ld, w, t, sts_yield);
454 } else {
455 ShenandoahTraversalClosure cl(q, rp);
456 main_loop_work<ShenandoahTraversalClosure>(&cl, ld, w, t, sts_yield);
457 }
458 }
459 } else {
460 if (_heap->unload_classes()) {
461 if (ShenandoahStringDedup::is_enabled()) {
462 ShenandoahTraversalMetadataDedupDegenClosure cl(q, rp);
463 main_loop_work<ShenandoahTraversalMetadataDedupDegenClosure>(&cl, ld, w, t, sts_yield);
464 } else {
465 ShenandoahTraversalMetadataDegenClosure cl(q, rp);
466 main_loop_work<ShenandoahTraversalMetadataDegenClosure>(&cl, ld, w, t, sts_yield);
467 }
468 } else {
469 if (ShenandoahStringDedup::is_enabled()) {
470 ShenandoahTraversalDedupDegenClosure cl(q, rp);
471 main_loop_work<ShenandoahTraversalDedupDegenClosure>(&cl, ld, w, t, sts_yield);
472 } else {
473 ShenandoahTraversalDegenClosure cl(q, rp);
474 main_loop_work<ShenandoahTraversalDegenClosure>(&cl, ld, w, t, sts_yield);
475 }
476 }
477 }
478 }
479
480 _heap->flush_liveness_cache(w);
481 }
482
483 template <class T>
484 void ShenandoahTraversalGC::main_loop_work(T* cl, jushort* live_data, uint worker_id, TaskTerminator* terminator, bool sts_yield) {
485 ShenandoahObjToScanQueueSet* queues = task_queues();
486 ShenandoahObjToScanQueue* q = queues->queue(worker_id);
487 ShenandoahConcurrentMark* conc_mark = _heap->concurrent_mark();
488
489 uintx stride = ShenandoahMarkLoopStride;
490
491 ShenandoahMarkTask task;
492
493 // Process outstanding queues, if any.
494 q = queues->claim_next();
495 while (q != NULL) {
496 if (_heap->check_cancelled_gc_and_yield(sts_yield)) {
497 return;
498 }
499
500 for (uint i = 0; i < stride; i++) {
501 if (q->pop(task)) {
502 conc_mark->do_task<T>(q, cl, live_data, &task);
503 } else {
504 assert(q->is_empty(), "Must be empty");
505 q = queues->claim_next();
506 break;
507 }
508 }
509 }
510
511 if (check_and_handle_cancelled_gc(terminator, sts_yield)) return;
512
513 // Normal loop.
514 q = queues->queue(worker_id);
515
516 ShenandoahTraversalSATBBufferClosure drain_satb(q);
517 SATBMarkQueueSet& satb_mq_set = ShenandoahBarrierSet::satb_mark_queue_set();
518
519 while (true) {
520 if (check_and_handle_cancelled_gc(terminator, sts_yield)) return;
521
522 while (satb_mq_set.completed_buffers_num() > 0) {
523 satb_mq_set.apply_closure_to_completed_buffer(&drain_satb);
524 }
525
526 uint work = 0;
527 for (uint i = 0; i < stride; i++) {
528 if (q->pop(task) ||
529 queues->steal(worker_id, task)) {
530 conc_mark->do_task<T>(q, cl, live_data, &task);
531 work++;
532 } else {
533 break;
534 }
535 }
536
537 if (work == 0) {
538 // No more work, try to terminate
539 ShenandoahSuspendibleThreadSetLeaver stsl(sts_yield && ShenandoahSuspendibleWorkers);
540 ShenandoahTerminatorTerminator tt(_heap);
541
542 if (terminator->offer_termination(&tt)) return;
543 }
544 }
545 }
546
547 bool ShenandoahTraversalGC::check_and_handle_cancelled_gc(TaskTerminator* terminator, bool sts_yield) {
548 if (_heap->cancelled_gc()) {
549 return true;
550 }
551 return false;
552 }
553
554 void ShenandoahTraversalGC::concurrent_traversal_collection() {
555 ShenandoahGCPhase phase_work(ShenandoahPhaseTimings::conc_traversal);
556 if (!_heap->cancelled_gc()) {
557 uint nworkers = _heap->workers()->active_workers();
558 task_queues()->reserve(nworkers);
559
560 TaskTerminator terminator(nworkers, task_queues());
561 ShenandoahConcurrentTraversalCollectionTask task(&terminator);
562 _heap->workers()->run_task(&task);
563 }
564
565 if (!_heap->cancelled_gc() && ShenandoahPreclean && _heap->process_references()) {
566 preclean_weak_refs();
567 }
568 }
569
570 void ShenandoahTraversalGC::final_traversal_collection() {
571 if (!_heap->cancelled_gc()) {
572 #if COMPILER2_OR_JVMCI
573 DerivedPointerTable::clear();
574 #endif
575 ShenandoahGCPhase phase_work(ShenandoahPhaseTimings::final_traversal_gc_work);
576 uint nworkers = _heap->workers()->active_workers();
577 task_queues()->reserve(nworkers);
578
579 // Finish traversal
580 ShenandoahAllRootScanner rp(nworkers, ShenandoahPhaseTimings::final_traversal_gc_work);
581 TaskTerminator terminator(nworkers, task_queues());
582 ShenandoahFinalTraversalCollectionTask task(&rp, &terminator);
583 _heap->workers()->run_task(&task);
584 #if COMPILER2_OR_JVMCI
585 DerivedPointerTable::update_pointers();
586 #endif
587 }
588
589 if (!_heap->cancelled_gc() && _heap->process_references()) {
590 weak_refs_work();
591 }
592
593 if (!_heap->cancelled_gc()) {
594 assert(_task_queues->is_empty(), "queues must be empty after traversal GC");
595 TASKQUEUE_STATS_ONLY(_task_queues->print_taskqueue_stats());
596 TASKQUEUE_STATS_ONLY(_task_queues->reset_taskqueue_stats());
597
598 // No more marking expected
599 _heap->set_concurrent_traversal_in_progress(false);
600 _heap->mark_complete_marking_context();
601
602 // A rare case, TLAB/GCLAB is initialized from an empty region without
603 // any live data, the region can be trashed and may be uncommitted in later code,
604 // that results the TLAB/GCLAB not usable. Retire them here.
605 _heap->make_parsable(true);
606
607 // Do this fixup before the call to parallel_cleaning to ensure that all
608 // forwarded objects (including those that are no longer in the cset) are
609 // updated by the time we do weak root processing.
610 fixup_roots();
611 _heap->parallel_cleaning(false);
612
613 _heap->set_has_forwarded_objects(false);
614
615 // Resize metaspace
616 MetaspaceGC::compute_new_size();
617
618 // Need to see that pinned region status is updated: newly pinned regions must not
619 // be trashed. New unpinned regions should be trashed.
620 {
621 ShenandoahGCPhase phase_cleanup(ShenandoahPhaseTimings::traversal_gc_sync_pinned);
622 _heap->sync_pinned_region_status();
623 }
624
625 // Still good? We can now trash the cset, and make final verification
626 {
627 ShenandoahGCPhase phase_cleanup(ShenandoahPhaseTimings::traversal_gc_cleanup);
628 ShenandoahHeapLocker lock(_heap->lock());
629
630 // Trash everything
631 // Clear immediate garbage regions.
632 size_t num_regions = _heap->num_regions();
633
634 ShenandoahHeapRegionSet* traversal_regions = traversal_set();
635 ShenandoahFreeSet* free_regions = _heap->free_set();
636 ShenandoahMarkingContext* const ctx = _heap->marking_context();
637 free_regions->clear();
638 for (size_t i = 0; i < num_regions; i++) {
639 ShenandoahHeapRegion* r = _heap->get_region(i);
640 bool not_allocated = ctx->top_at_mark_start(r) == r->top();
641
642 bool candidate = traversal_regions->is_in(r) && !r->has_live() && not_allocated;
643 if (r->is_humongous_start() && candidate) {
644 // Trash humongous.
645 HeapWord* humongous_obj = r->bottom();
646 assert(!ctx->is_marked(oop(humongous_obj)), "must not be marked");
647 r->make_trash_immediate();
648 while (i + 1 < num_regions && _heap->get_region(i + 1)->is_humongous_continuation()) {
649 i++;
650 r = _heap->get_region(i);
651 assert(r->is_humongous_continuation(), "must be humongous continuation");
652 r->make_trash_immediate();
653 }
654 } else if (!r->is_empty() && candidate) {
655 // Trash regular.
656 assert(!r->is_humongous(), "handled above");
657 assert(!r->is_trash(), "must not already be trashed");
658 r->make_trash_immediate();
659 }
660 }
661 _heap->collection_set()->clear();
662 _heap->free_set()->rebuild();
663 reset();
664 }
665
666 assert(_task_queues->is_empty(), "queues must be empty after traversal GC");
667 assert(!_heap->cancelled_gc(), "must not be cancelled when getting out here");
668
669 if (ShenandoahVerify) {
670 _heap->verifier()->verify_after_traversal();
671 }
672 #ifdef ASSERT
673 else {
674 verify_roots_after_gc();
675 }
676 #endif
677
678 if (VerifyAfterGC) {
679 Universe::verify();
680 }
681 }
682 }
683
684 class ShenandoahVerifyAfterGC : public OopClosure {
685 private:
686 template <class T>
687 void do_oop_work(T* p) {
688 T o = RawAccess<>::oop_load(p);
689 if (!CompressedOops::is_null(o)) {
690 oop obj = CompressedOops::decode_not_null(o);
691 shenandoah_assert_correct(p, obj);
692 shenandoah_assert_not_in_cset_except(p, obj, ShenandoahHeap::heap()->cancelled_gc());
693 shenandoah_assert_not_forwarded(p, obj);
694 }
695 }
696
697 public:
698 void do_oop(narrowOop* p) { do_oop_work(p); }
699 void do_oop(oop* p) { do_oop_work(p); }
700 };
701
702 void ShenandoahTraversalGC::verify_roots_after_gc() {
703 ShenandoahRootVerifier verifier;
704 ShenandoahVerifyAfterGC cl;
705 verifier.oops_do(&cl);
706 }
707
708 class ShenandoahTraversalFixRootsClosure : public OopClosure {
709 private:
710 template <class T>
711 inline void do_oop_work(T* p) {
712 T o = RawAccess<>::oop_load(p);
713 if (!CompressedOops::is_null(o)) {
714 oop obj = CompressedOops::decode_not_null(o);
715 oop forw = ShenandoahBarrierSet::resolve_forwarded_not_null(obj);
716 if (obj != forw) {
717 RawAccess<IS_NOT_NULL>::oop_store(p, forw);
718 }
719 }
720 }
721
722 public:
723 inline void do_oop(oop* p) { do_oop_work(p); }
724 inline void do_oop(narrowOop* p) { do_oop_work(p); }
725 };
726
727 class ShenandoahTraversalFixRootsTask : public AbstractGangTask {
728 private:
729 ShenandoahRootUpdater* _rp;
730
731 public:
732 ShenandoahTraversalFixRootsTask(ShenandoahRootUpdater* rp) :
733 AbstractGangTask("Shenandoah traversal fix roots"),
734 _rp(rp) {
735 assert(ShenandoahHeap::heap()->has_forwarded_objects(), "Must be");
736 }
737
738 void work(uint worker_id) {
739 ShenandoahParallelWorkerSession worker_session(worker_id);
740 ShenandoahTraversalFixRootsClosure cl;
741 ShenandoahForwardedIsAliveClosure is_alive;
742 _rp->roots_do(worker_id, &is_alive, &cl);
743 }
744 };
745
746 void ShenandoahTraversalGC::fixup_roots() {
747 #if COMPILER2_OR_JVMCI
748 DerivedPointerTable::clear();
749 #endif
750 ShenandoahRootUpdater rp(_heap->workers()->active_workers(), ShenandoahPhaseTimings::final_traversal_update_roots);
751 ShenandoahTraversalFixRootsTask update_roots_task(&rp);
752 _heap->workers()->run_task(&update_roots_task);
753 #if COMPILER2_OR_JVMCI
754 DerivedPointerTable::update_pointers();
755 #endif
756 }
757
758 void ShenandoahTraversalGC::reset() {
759 _task_queues->clear();
760 }
761
762 ShenandoahObjToScanQueueSet* ShenandoahTraversalGC::task_queues() {
763 return _task_queues;
764 }
765
766 class ShenandoahTraversalCancelledGCYieldClosure : public YieldClosure {
767 private:
768 ShenandoahHeap* const _heap;
769 public:
770 ShenandoahTraversalCancelledGCYieldClosure() : _heap(ShenandoahHeap::heap()) {};
771 virtual bool should_return() { return _heap->cancelled_gc(); }
772 };
773
774 class ShenandoahTraversalPrecleanCompleteGCClosure : public VoidClosure {
775 public:
776 void do_void() {
777 ShenandoahHeap* sh = ShenandoahHeap::heap();
778 ShenandoahTraversalGC* traversal_gc = sh->traversal_gc();
779 assert(sh->process_references(), "why else would we be here?");
780 TaskTerminator terminator(1, traversal_gc->task_queues());
781 shenandoah_assert_rp_isalive_installed();
782 traversal_gc->main_loop((uint) 0, &terminator, true);
783 }
784 };
785
786 class ShenandoahTraversalKeepAliveUpdateClosure : public OopClosure {
787 private:
788 ShenandoahObjToScanQueue* _queue;
789 Thread* _thread;
790 ShenandoahTraversalGC* _traversal_gc;
791 ShenandoahMarkingContext* const _mark_context;
792
793 template <class T>
794 inline void do_oop_work(T* p) {
795 _traversal_gc->process_oop<T, false /* string dedup */, false /* degen */, true /* atomic update */>(p, _thread, _queue, _mark_context);
796 }
797
798 public:
799 ShenandoahTraversalKeepAliveUpdateClosure(ShenandoahObjToScanQueue* q) :
800 _queue(q), _thread(Thread::current()),
801 _traversal_gc(ShenandoahHeap::heap()->traversal_gc()),
802 _mark_context(ShenandoahHeap::heap()->marking_context()) {}
803
804 void do_oop(narrowOop* p) { do_oop_work(p); }
805 void do_oop(oop* p) { do_oop_work(p); }
806 };
807
808 class ShenandoahTraversalKeepAliveUpdateDegenClosure : public OopClosure {
809 private:
810 ShenandoahObjToScanQueue* _queue;
811 Thread* _thread;
812 ShenandoahTraversalGC* _traversal_gc;
813 ShenandoahMarkingContext* const _mark_context;
814
815 template <class T>
816 inline void do_oop_work(T* p) {
817 _traversal_gc->process_oop<T, false /* string dedup */, true /* degen */, false /* atomic update */>(p, _thread, _queue, _mark_context);
818 }
819
820 public:
821 ShenandoahTraversalKeepAliveUpdateDegenClosure(ShenandoahObjToScanQueue* q) :
822 _queue(q), _thread(Thread::current()),
823 _traversal_gc(ShenandoahHeap::heap()->traversal_gc()),
824 _mark_context(ShenandoahHeap::heap()->marking_context()) {}
825
826 void do_oop(narrowOop* p) { do_oop_work(p); }
827 void do_oop(oop* p) { do_oop_work(p); }
828 };
829
830 class ShenandoahTraversalSingleThreadKeepAliveUpdateClosure : public OopClosure {
831 private:
832 ShenandoahObjToScanQueue* _queue;
833 Thread* _thread;
834 ShenandoahTraversalGC* _traversal_gc;
835 ShenandoahMarkingContext* const _mark_context;
836
837 template <class T>
838 inline void do_oop_work(T* p) {
839 _traversal_gc->process_oop<T, false /* string dedup */, false /* degen */, true /* atomic update */>(p, _thread, _queue, _mark_context);
840 }
841
842 public:
843 ShenandoahTraversalSingleThreadKeepAliveUpdateClosure(ShenandoahObjToScanQueue* q) :
844 _queue(q), _thread(Thread::current()),
845 _traversal_gc(ShenandoahHeap::heap()->traversal_gc()),
846 _mark_context(ShenandoahHeap::heap()->marking_context()) {}
847
848 void do_oop(narrowOop* p) { do_oop_work(p); }
849 void do_oop(oop* p) { do_oop_work(p); }
850 };
851
852 class ShenandoahTraversalSingleThreadKeepAliveUpdateDegenClosure : public OopClosure {
853 private:
854 ShenandoahObjToScanQueue* _queue;
855 Thread* _thread;
856 ShenandoahTraversalGC* _traversal_gc;
857 ShenandoahMarkingContext* const _mark_context;
858
859 template <class T>
860 inline void do_oop_work(T* p) {
861 _traversal_gc->process_oop<T, false /* string dedup */, true /* degen */, false /* atomic update */>(p, _thread, _queue, _mark_context);
862 }
863
864 public:
865 ShenandoahTraversalSingleThreadKeepAliveUpdateDegenClosure(ShenandoahObjToScanQueue* q) :
866 _queue(q), _thread(Thread::current()),
867 _traversal_gc(ShenandoahHeap::heap()->traversal_gc()),
868 _mark_context(ShenandoahHeap::heap()->marking_context()) {}
869
870 void do_oop(narrowOop* p) { do_oop_work(p); }
871 void do_oop(oop* p) { do_oop_work(p); }
872 };
873
874 class ShenandoahTraversalPrecleanTask : public AbstractGangTask {
875 private:
876 ReferenceProcessor* _rp;
877
878 public:
879 ShenandoahTraversalPrecleanTask(ReferenceProcessor* rp) :
880 AbstractGangTask("Precleaning task"),
881 _rp(rp) {}
882
883 void work(uint worker_id) {
884 assert(worker_id == 0, "The code below is single-threaded, only one worker is expected");
885 ShenandoahParallelWorkerSession worker_session(worker_id);
886 ShenandoahSuspendibleThreadSetJoiner stsj(ShenandoahSuspendibleWorkers);
887
888 ShenandoahHeap* sh = ShenandoahHeap::heap();
889
890 ShenandoahObjToScanQueue* q = sh->traversal_gc()->task_queues()->queue(worker_id);
891
892 ShenandoahForwardedIsAliveClosure is_alive;
893 ShenandoahTraversalCancelledGCYieldClosure yield;
894 ShenandoahTraversalPrecleanCompleteGCClosure complete_gc;
895 ShenandoahTraversalKeepAliveUpdateClosure keep_alive(q);
896 ResourceMark rm;
897 _rp->preclean_discovered_references(&is_alive, &keep_alive,
898 &complete_gc, &yield,
899 NULL);
900 }
901 };
902
903 void ShenandoahTraversalGC::preclean_weak_refs() {
904 // Pre-cleaning weak references before diving into STW makes sense at the
905 // end of concurrent mark. This will filter out the references which referents
906 // are alive. Note that ReferenceProcessor already filters out these on reference
907 // discovery, and the bulk of work is done here. This phase processes leftovers
908 // that missed the initial filtering, i.e. when referent was marked alive after
909 // reference was discovered by RP.
910
911 assert(_heap->process_references(), "sanity");
912 assert(!_heap->is_degenerated_gc_in_progress(), "must be in concurrent non-degenerated phase");
913
914 // Shortcut if no references were discovered to avoid winding up threads.
915 ReferenceProcessor* rp = _heap->ref_processor();
916 if (!rp->has_discovered_references()) {
917 return;
918 }
919
920 ReferenceProcessorMTDiscoveryMutator fix_mt_discovery(rp, false);
921
922 shenandoah_assert_rp_isalive_not_installed();
923 ShenandoahForwardedIsAliveClosure is_alive;
924 ReferenceProcessorIsAliveMutator fix_isalive(rp, &is_alive);
925
926 assert(task_queues()->is_empty(), "Should be empty");
927
928 // Execute precleaning in the worker thread: it will give us GCLABs, String dedup
929 // queues and other goodies. When upstream ReferenceProcessor starts supporting
930 // parallel precleans, we can extend this to more threads.
931 ShenandoahPushWorkerScope scope(_heap->workers(), 1, /* check_workers = */ false);
932
933 WorkGang* workers = _heap->workers();
934 uint nworkers = workers->active_workers();
935 assert(nworkers == 1, "This code uses only a single worker");
936 task_queues()->reserve(nworkers);
937
938 ShenandoahTraversalPrecleanTask task(rp);
939 workers->run_task(&task);
940
941 assert(_heap->cancelled_gc() || task_queues()->is_empty(), "Should be empty");
942 }
943
944 // Weak Reference Closures
945 class ShenandoahTraversalDrainMarkingStackClosure: public VoidClosure {
946 uint _worker_id;
947 TaskTerminator* _terminator;
948 bool _reset_terminator;
949
950 public:
951 ShenandoahTraversalDrainMarkingStackClosure(uint worker_id, TaskTerminator* t, bool reset_terminator = false):
952 _worker_id(worker_id),
953 _terminator(t),
954 _reset_terminator(reset_terminator) {
955 }
956
957 void do_void() {
958 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
959
960 ShenandoahHeap* sh = ShenandoahHeap::heap();
961 ShenandoahTraversalGC* traversal_gc = sh->traversal_gc();
962 assert(sh->process_references(), "why else would we be here?");
963 shenandoah_assert_rp_isalive_installed();
964
965 traversal_gc->main_loop(_worker_id, _terminator, false);
966
967 if (_reset_terminator) {
968 _terminator->reset_for_reuse();
969 }
970 }
971 };
972
973 class ShenandoahTraversalSingleThreadedDrainMarkingStackClosure: public VoidClosure {
974 uint _worker_id;
975 TaskTerminator* _terminator;
976 bool _reset_terminator;
977
978 public:
979 ShenandoahTraversalSingleThreadedDrainMarkingStackClosure(uint worker_id, TaskTerminator* t, bool reset_terminator = false):
980 _worker_id(worker_id),
981 _terminator(t),
982 _reset_terminator(reset_terminator) {
983 }
984
985 void do_void() {
986 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
987
988 ShenandoahHeap* sh = ShenandoahHeap::heap();
989 ShenandoahTraversalGC* traversal_gc = sh->traversal_gc();
990 assert(sh->process_references(), "why else would we be here?");
991 shenandoah_assert_rp_isalive_installed();
992
993 traversal_gc->main_loop(_worker_id, _terminator, false);
994
995 if (_reset_terminator) {
996 _terminator->reset_for_reuse();
997 }
998 }
999 };
1000
1001 void ShenandoahTraversalGC::weak_refs_work() {
1002 assert(_heap->process_references(), "sanity");
1003
1004 ShenandoahPhaseTimings::Phase phase_root = ShenandoahPhaseTimings::weakrefs;
1005
1006 ShenandoahGCPhase phase(phase_root);
1007
1008 ReferenceProcessor* rp = _heap->ref_processor();
1009
1010 // NOTE: We cannot shortcut on has_discovered_references() here, because
1011 // we will miss marking JNI Weak refs then, see implementation in
1012 // ReferenceProcessor::process_discovered_references.
1013 weak_refs_work_doit();
1014
1015 rp->verify_no_references_recorded();
1016 assert(!rp->discovery_enabled(), "Post condition");
1017
1018 }
1019
1020 class ShenandoahTraversalRefProcTaskProxy : public AbstractGangTask {
1021 private:
1022 AbstractRefProcTaskExecutor::ProcessTask& _proc_task;
1023 TaskTerminator* _terminator;
1024
1025 public:
1026 ShenandoahTraversalRefProcTaskProxy(AbstractRefProcTaskExecutor::ProcessTask& proc_task,
1027 TaskTerminator* t) :
1028 AbstractGangTask("Process reference objects in parallel"),
1029 _proc_task(proc_task),
1030 _terminator(t) {
1031 }
1032
1033 void work(uint worker_id) {
1034 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
1035 ShenandoahHeap* heap = ShenandoahHeap::heap();
1036 ShenandoahTraversalDrainMarkingStackClosure complete_gc(worker_id, _terminator);
1037
1038 ShenandoahForwardedIsAliveClosure is_alive;
1039 if (!heap->is_degenerated_gc_in_progress()) {
1040 ShenandoahTraversalKeepAliveUpdateClosure keep_alive(heap->traversal_gc()->task_queues()->queue(worker_id));
1041 _proc_task.work(worker_id, is_alive, keep_alive, complete_gc);
1042 } else {
1043 ShenandoahTraversalKeepAliveUpdateDegenClosure keep_alive(heap->traversal_gc()->task_queues()->queue(worker_id));
1044 _proc_task.work(worker_id, is_alive, keep_alive, complete_gc);
1045 }
1046 }
1047 };
1048
1049 class ShenandoahTraversalRefProcTaskExecutor : public AbstractRefProcTaskExecutor {
1050 private:
1051 WorkGang* _workers;
1052
1053 public:
1054 ShenandoahTraversalRefProcTaskExecutor(WorkGang* workers) : _workers(workers) {}
1055
1056 // Executes a task using worker threads.
1057 void execute(ProcessTask& task, uint ergo_workers) {
1058 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
1059
1060 ShenandoahHeap* heap = ShenandoahHeap::heap();
1061 ShenandoahTraversalGC* traversal_gc = heap->traversal_gc();
1062 ShenandoahPushWorkerQueuesScope scope(_workers,
1063 traversal_gc->task_queues(),
1064 ergo_workers,
1065 /* do_check = */ false);
1066 uint nworkers = _workers->active_workers();
1067 traversal_gc->task_queues()->reserve(nworkers);
1068 TaskTerminator terminator(nworkers, traversal_gc->task_queues());
1069 ShenandoahTraversalRefProcTaskProxy proc_task_proxy(task, &terminator);
1070 _workers->run_task(&proc_task_proxy);
1071 }
1072 };
1073
1074 void ShenandoahTraversalGC::weak_refs_work_doit() {
1075 ReferenceProcessor* rp = _heap->ref_processor();
1076
1077 ShenandoahPhaseTimings::Phase phase_process = ShenandoahPhaseTimings::weakrefs_process;
1078
1079 shenandoah_assert_rp_isalive_not_installed();
1080 ShenandoahForwardedIsAliveClosure is_alive;
1081 ReferenceProcessorIsAliveMutator fix_isalive(rp, &is_alive);
1082
1083 WorkGang* workers = _heap->workers();
1084 uint nworkers = workers->active_workers();
1085
1086 rp->setup_policy(_heap->soft_ref_policy()->should_clear_all_soft_refs());
1087 rp->set_active_mt_degree(nworkers);
1088
1089 assert(task_queues()->is_empty(), "Should be empty");
1090
1091 // complete_gc and keep_alive closures instantiated here are only needed for
1092 // single-threaded path in RP. They share the queue 0 for tracking work, which
1093 // simplifies implementation. Since RP may decide to call complete_gc several
1094 // times, we need to be able to reuse the terminator.
1095 uint serial_worker_id = 0;
1096 TaskTerminator terminator(1, task_queues());
1097 ShenandoahTraversalSingleThreadedDrainMarkingStackClosure complete_gc(serial_worker_id, &terminator, /* reset_terminator = */ true);
1098 ShenandoahPushWorkerQueuesScope scope(workers, task_queues(), 1, /* do_check = */ false);
1099
1100 ShenandoahTraversalRefProcTaskExecutor executor(workers);
1101
1102 ReferenceProcessorPhaseTimes pt(_heap->gc_timer(), rp->num_queues());
1103 if (!_heap->is_degenerated_gc_in_progress()) {
1104 ShenandoahTraversalSingleThreadKeepAliveUpdateClosure keep_alive(task_queues()->queue(serial_worker_id));
1105 rp->process_discovered_references(&is_alive, &keep_alive,
1106 &complete_gc, &executor,
1107 &pt);
1108 } else {
1109 ShenandoahTraversalSingleThreadKeepAliveUpdateDegenClosure keep_alive(task_queues()->queue(serial_worker_id));
1110 rp->process_discovered_references(&is_alive, &keep_alive,
1111 &complete_gc, &executor,
1112 &pt);
1113 }
1114
1115 pt.print_all_references();
1116 assert(task_queues()->is_empty() || _heap->cancelled_gc(), "Should be empty");
1117 }