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/shenandoahRootProcessor.inline.hpp"
45 #include "gc/shenandoah/shenandoahStringDedup.hpp"
46 #include "gc/shenandoah/shenandoahTaskqueue.inline.hpp"
47 #include "gc/shenandoah/shenandoahTimingTracker.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 ShenandoahWorkerTimings *worker_times = _heap->phase_timings()->worker_times();
287 ShenandoahWorkerTimingsTracker timer(worker_times, ShenandoahPhaseTimings::FinishQueues, worker_id);
288
289 // Step 3: Finally drain all outstanding work in queues.
290 traversal_gc->main_loop(worker_id, _terminator, false);
291 }
292
293 }
294 };
295
296 ShenandoahTraversalGC::ShenandoahTraversalGC(ShenandoahHeap* heap, size_t num_regions) :
297 _heap(heap),
298 _task_queues(new ShenandoahObjToScanQueueSet(heap->max_workers())),
299 _traversal_set(ShenandoahHeapRegionSet()) {
300
301 // Traversal does not support concurrent code root scanning
302 FLAG_SET_DEFAULT(ShenandoahConcurrentScanCodeRoots, false);
303
304 uint num_queues = heap->max_workers();
305 for (uint i = 0; i < num_queues; ++i) {
306 ShenandoahObjToScanQueue* task_queue = new ShenandoahObjToScanQueue();
307 task_queue->initialize();
308 _task_queues->register_queue(i, task_queue);
309 }
310 }
311
312 ShenandoahTraversalGC::~ShenandoahTraversalGC() {
313 }
314
315 void ShenandoahTraversalGC::prepare_regions() {
316 size_t num_regions = _heap->num_regions();
317 ShenandoahMarkingContext* const ctx = _heap->marking_context();
318 for (size_t i = 0; i < num_regions; i++) {
319 ShenandoahHeapRegion* region = _heap->get_region(i);
320 if (_heap->is_bitmap_slice_committed(region)) {
321 if (_traversal_set.is_in(i)) {
322 ctx->capture_top_at_mark_start(region);
323 region->clear_live_data();
324 assert(ctx->is_bitmap_clear_range(region->bottom(), region->end()), "bitmap for traversal regions must be cleared");
325 } else {
326 // Everything outside the traversal set is always considered live.
327 ctx->reset_top_at_mark_start(region);
328 }
329 } else {
330 // FreeSet may contain uncommitted empty regions, once they are recommitted,
331 // their TAMS may have old values, so reset them here.
332 ctx->reset_top_at_mark_start(region);
333 }
334 }
335 }
336
337 void ShenandoahTraversalGC::prepare() {
338 {
339 ShenandoahGCPhase phase(ShenandoahPhaseTimings::traversal_gc_make_parsable);
340 _heap->make_parsable(true);
341 }
342
343 if (UseTLAB) {
344 ShenandoahGCPhase phase(ShenandoahPhaseTimings::traversal_gc_resize_tlabs);
345 _heap->resize_tlabs();
346 }
347
348 assert(_heap->marking_context()->is_bitmap_clear(), "need clean mark bitmap");
349 assert(!_heap->marking_context()->is_complete(), "should not be complete");
350
351 // About to choose the collection set, make sure we know which regions are pinned.
352 {
353 ShenandoahGCPhase phase_cleanup(ShenandoahPhaseTimings::traversal_gc_prepare_sync_pinned);
354 _heap->sync_pinned_region_status();
355 }
356
357 ShenandoahCollectionSet* collection_set = _heap->collection_set();
358 {
359 ShenandoahHeapLocker lock(_heap->lock());
360
361 collection_set->clear();
362 assert(collection_set->count() == 0, "collection set not clear");
363
364 // Find collection set
365 _heap->heuristics()->choose_collection_set(collection_set);
366 prepare_regions();
367
368 // Rebuild free set
369 _heap->free_set()->rebuild();
370 }
371
372 log_info(gc, ergo)("Collectable Garbage: " SIZE_FORMAT "%s, " SIZE_FORMAT "%s CSet, " SIZE_FORMAT " CSet regions",
373 byte_size_in_proper_unit(collection_set->garbage()), proper_unit_for_byte_size(collection_set->garbage()),
374 byte_size_in_proper_unit(collection_set->live_data()), proper_unit_for_byte_size(collection_set->live_data()),
375 collection_set->count());
376 }
377
378 void ShenandoahTraversalGC::init_traversal_collection() {
379 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "STW traversal GC");
380
381 if (ShenandoahVerify) {
382 _heap->verifier()->verify_before_traversal();
383 }
384
385 if (VerifyBeforeGC) {
386 Universe::verify();
387 }
388
389 {
390 ShenandoahGCPhase phase_prepare(ShenandoahPhaseTimings::traversal_gc_prepare);
391 prepare();
392 }
393
394 _heap->set_concurrent_traversal_in_progress(true);
395 _heap->set_has_forwarded_objects(true);
396
397 bool process_refs = _heap->process_references();
398 if (process_refs) {
399 ReferenceProcessor* rp = _heap->ref_processor();
400 rp->enable_discovery(true /*verify_no_refs*/);
401 rp->setup_policy(_heap->soft_ref_policy()->should_clear_all_soft_refs());
402 }
403
404 {
405 ShenandoahGCPhase phase_work(ShenandoahPhaseTimings::init_traversal_gc_work);
406 assert(_task_queues->is_empty(), "queues must be empty before traversal GC");
407 TASKQUEUE_STATS_ONLY(_task_queues->reset_taskqueue_stats());
408
409 #if COMPILER2_OR_JVMCI
410 DerivedPointerTable::clear();
411 #endif
412
413 {
414 uint nworkers = _heap->workers()->active_workers();
415 task_queues()->reserve(nworkers);
416 ShenandoahCSetRootScanner rp(nworkers, ShenandoahPhaseTimings::init_traversal_gc_work);
417 ShenandoahInitTraversalCollectionTask traversal_task(&rp);
418 _heap->workers()->run_task(&traversal_task);
419 }
420
421 #if COMPILER2_OR_JVMCI
422 DerivedPointerTable::update_pointers();
423 #endif
424 }
425
426 if (ShenandoahPacing) {
427 _heap->pacer()->setup_for_traversal();
428 }
429 }
430
431 void ShenandoahTraversalGC::main_loop(uint w, TaskTerminator* t, bool sts_yield) {
432 ShenandoahObjToScanQueue* q = task_queues()->queue(w);
433
434 // Initialize live data.
435 jushort* ld = _heap->get_liveness_cache(w);
436
437 ReferenceProcessor* rp = NULL;
438 if (_heap->process_references()) {
439 rp = _heap->ref_processor();
440 }
441 {
442 if (!_heap->is_degenerated_gc_in_progress()) {
443 if (_heap->unload_classes()) {
444 if (ShenandoahStringDedup::is_enabled()) {
445 ShenandoahTraversalMetadataDedupClosure cl(q, rp);
446 main_loop_work<ShenandoahTraversalMetadataDedupClosure>(&cl, ld, w, t, sts_yield);
447 } else {
448 ShenandoahTraversalMetadataClosure cl(q, rp);
449 main_loop_work<ShenandoahTraversalMetadataClosure>(&cl, ld, w, t, sts_yield);
450 }
451 } else {
452 if (ShenandoahStringDedup::is_enabled()) {
453 ShenandoahTraversalDedupClosure cl(q, rp);
454 main_loop_work<ShenandoahTraversalDedupClosure>(&cl, ld, w, t, sts_yield);
455 } else {
456 ShenandoahTraversalClosure cl(q, rp);
457 main_loop_work<ShenandoahTraversalClosure>(&cl, ld, w, t, sts_yield);
458 }
459 }
460 } else {
461 if (_heap->unload_classes()) {
462 if (ShenandoahStringDedup::is_enabled()) {
463 ShenandoahTraversalMetadataDedupDegenClosure cl(q, rp);
464 main_loop_work<ShenandoahTraversalMetadataDedupDegenClosure>(&cl, ld, w, t, sts_yield);
465 } else {
466 ShenandoahTraversalMetadataDegenClosure cl(q, rp);
467 main_loop_work<ShenandoahTraversalMetadataDegenClosure>(&cl, ld, w, t, sts_yield);
468 }
469 } else {
470 if (ShenandoahStringDedup::is_enabled()) {
471 ShenandoahTraversalDedupDegenClosure cl(q, rp);
472 main_loop_work<ShenandoahTraversalDedupDegenClosure>(&cl, ld, w, t, sts_yield);
473 } else {
474 ShenandoahTraversalDegenClosure cl(q, rp);
475 main_loop_work<ShenandoahTraversalDegenClosure>(&cl, ld, w, t, sts_yield);
476 }
477 }
478 }
479 }
480
481 _heap->flush_liveness_cache(w);
482 }
483
484 template <class T>
485 void ShenandoahTraversalGC::main_loop_work(T* cl, jushort* live_data, uint worker_id, TaskTerminator* terminator, bool sts_yield) {
486 ShenandoahObjToScanQueueSet* queues = task_queues();
487 ShenandoahObjToScanQueue* q = queues->queue(worker_id);
488 ShenandoahConcurrentMark* conc_mark = _heap->concurrent_mark();
489
490 uintx stride = ShenandoahMarkLoopStride;
491
492 ShenandoahMarkTask task;
493
494 // Process outstanding queues, if any.
495 q = queues->claim_next();
496 while (q != NULL) {
497 if (_heap->check_cancelled_gc_and_yield(sts_yield)) {
498 return;
499 }
500
501 for (uint i = 0; i < stride; i++) {
502 if (q->pop(task)) {
503 conc_mark->do_task<T>(q, cl, live_data, &task);
504 } else {
505 assert(q->is_empty(), "Must be empty");
506 q = queues->claim_next();
507 break;
508 }
509 }
510 }
511
512 if (check_and_handle_cancelled_gc(terminator, sts_yield)) return;
513
514 // Normal loop.
515 q = queues->queue(worker_id);
516
517 ShenandoahTraversalSATBBufferClosure drain_satb(q);
518 SATBMarkQueueSet& satb_mq_set = ShenandoahBarrierSet::satb_mark_queue_set();
519
520 while (true) {
521 if (check_and_handle_cancelled_gc(terminator, sts_yield)) return;
522
523 while (satb_mq_set.completed_buffers_num() > 0) {
524 satb_mq_set.apply_closure_to_completed_buffer(&drain_satb);
525 }
526
527 uint work = 0;
528 for (uint i = 0; i < stride; i++) {
529 if (q->pop(task) ||
530 queues->steal(worker_id, task)) {
531 conc_mark->do_task<T>(q, cl, live_data, &task);
532 work++;
533 } else {
534 break;
535 }
536 }
537
538 if (work == 0) {
539 // No more work, try to terminate
540 ShenandoahSuspendibleThreadSetLeaver stsl(sts_yield && ShenandoahSuspendibleWorkers);
541 ShenandoahTerminationTimingsTracker term_tracker(worker_id);
542 ShenandoahTerminatorTerminator tt(_heap);
543
544 if (terminator->offer_termination(&tt)) return;
545 }
546 }
547 }
548
549 bool ShenandoahTraversalGC::check_and_handle_cancelled_gc(TaskTerminator* terminator, bool sts_yield) {
550 if (_heap->cancelled_gc()) {
551 return true;
552 }
553 return false;
554 }
555
556 void ShenandoahTraversalGC::concurrent_traversal_collection() {
557 ShenandoahGCPhase phase_work(ShenandoahPhaseTimings::conc_traversal);
558 if (!_heap->cancelled_gc()) {
559 uint nworkers = _heap->workers()->active_workers();
560 task_queues()->reserve(nworkers);
561 ShenandoahTerminationTracker tracker(ShenandoahPhaseTimings::conc_traversal_termination);
562
563 TaskTerminator terminator(nworkers, task_queues());
564 ShenandoahConcurrentTraversalCollectionTask task(&terminator);
565 _heap->workers()->run_task(&task);
566 }
567
568 if (!_heap->cancelled_gc() && ShenandoahPreclean && _heap->process_references()) {
569 preclean_weak_refs();
570 }
571 }
572
573 void ShenandoahTraversalGC::final_traversal_collection() {
574 if (!_heap->cancelled_gc()) {
575 #if COMPILER2_OR_JVMCI
576 DerivedPointerTable::clear();
577 #endif
578 ShenandoahGCPhase phase_work(ShenandoahPhaseTimings::final_traversal_gc_work);
579 uint nworkers = _heap->workers()->active_workers();
580 task_queues()->reserve(nworkers);
581
582 // Finish traversal
583 ShenandoahAllRootScanner rp(nworkers, ShenandoahPhaseTimings::final_traversal_gc_work);
584 ShenandoahTerminationTracker term(ShenandoahPhaseTimings::final_traversal_gc_termination);
585
586 TaskTerminator terminator(nworkers, task_queues());
587 ShenandoahFinalTraversalCollectionTask task(&rp, &terminator);
588 _heap->workers()->run_task(&task);
589 #if COMPILER2_OR_JVMCI
590 DerivedPointerTable::update_pointers();
591 #endif
592 }
593
594 if (!_heap->cancelled_gc() && _heap->process_references()) {
595 weak_refs_work();
596 }
597
598 if (!_heap->cancelled_gc()) {
599 assert(_task_queues->is_empty(), "queues must be empty after traversal GC");
600 TASKQUEUE_STATS_ONLY(_task_queues->print_taskqueue_stats());
601 TASKQUEUE_STATS_ONLY(_task_queues->reset_taskqueue_stats());
602
603 // No more marking expected
604 _heap->set_concurrent_traversal_in_progress(false);
605 _heap->mark_complete_marking_context();
606
607 // A rare case, TLAB/GCLAB is initialized from an empty region without
608 // any live data, the region can be trashed and may be uncommitted in later code,
609 // that results the TLAB/GCLAB not usable. Retire them here.
610 _heap->make_parsable(true);
611
612 _heap->parallel_cleaning(false);
613 fixup_roots();
614
615 _heap->set_has_forwarded_objects(false);
616
617 // Resize metaspace
618 MetaspaceGC::compute_new_size();
619
620 // Need to see that pinned region status is updated: newly pinned regions must not
621 // be trashed. New unpinned regions should be trashed.
622 {
623 ShenandoahGCPhase phase_cleanup(ShenandoahPhaseTimings::traversal_gc_sync_pinned);
624 _heap->sync_pinned_region_status();
625 }
626
627 // Still good? We can now trash the cset, and make final verification
628 {
629 ShenandoahGCPhase phase_cleanup(ShenandoahPhaseTimings::traversal_gc_cleanup);
630 ShenandoahHeapLocker lock(_heap->lock());
631
632 // Trash everything
633 // Clear immediate garbage regions.
634 size_t num_regions = _heap->num_regions();
635
636 ShenandoahHeapRegionSet* traversal_regions = traversal_set();
637 ShenandoahFreeSet* free_regions = _heap->free_set();
638 ShenandoahMarkingContext* const ctx = _heap->marking_context();
639 free_regions->clear();
640 for (size_t i = 0; i < num_regions; i++) {
641 ShenandoahHeapRegion* r = _heap->get_region(i);
642 bool not_allocated = ctx->top_at_mark_start(r) == r->top();
643
644 bool candidate = traversal_regions->is_in(r) && !r->has_live() && not_allocated;
645 if (r->is_humongous_start() && candidate) {
646 // Trash humongous.
647 HeapWord* humongous_obj = r->bottom();
648 assert(!ctx->is_marked(oop(humongous_obj)), "must not be marked");
649 r->make_trash_immediate();
650 while (i + 1 < num_regions && _heap->get_region(i + 1)->is_humongous_continuation()) {
651 i++;
652 r = _heap->get_region(i);
653 assert(r->is_humongous_continuation(), "must be humongous continuation");
654 r->make_trash_immediate();
655 }
656 } else if (!r->is_empty() && candidate) {
657 // Trash regular.
658 assert(!r->is_humongous(), "handled above");
659 assert(!r->is_trash(), "must not already be trashed");
660 r->make_trash_immediate();
661 }
662 }
663 _heap->collection_set()->clear();
664 _heap->free_set()->rebuild();
665 reset();
666 }
667
668 assert(_task_queues->is_empty(), "queues must be empty after traversal GC");
669 assert(!_heap->cancelled_gc(), "must not be cancelled when getting out here");
670
671 if (ShenandoahVerify) {
672 _heap->verifier()->verify_after_traversal();
673 }
674 #ifdef ASSERT
675 else {
676 verify_roots_after_gc();
677 }
678 #endif
679
680 if (VerifyAfterGC) {
681 Universe::verify();
682 }
683 }
684 }
685
686 class ShenandoahVerifyAfterGC : public OopClosure {
687 private:
688 template <class T>
689 void do_oop_work(T* p) {
690 T o = RawAccess<>::oop_load(p);
691 if (!CompressedOops::is_null(o)) {
692 oop obj = CompressedOops::decode_not_null(o);
693 shenandoah_assert_correct(p, obj);
694 shenandoah_assert_not_in_cset_except(p, obj, ShenandoahHeap::heap()->cancelled_gc());
695 shenandoah_assert_not_forwarded(p, obj);
696 }
697 }
698
699 public:
700 void do_oop(narrowOop* p) { do_oop_work(p); }
701 void do_oop(oop* p) { do_oop_work(p); }
702 };
703
704 void ShenandoahTraversalGC::verify_roots_after_gc() {
705 ShenandoahRootVerifier verifier;
706 ShenandoahVerifyAfterGC cl;
707 verifier.oops_do(&cl);
708 }
709
710 class ShenandoahTraversalFixRootsClosure : public OopClosure {
711 private:
712 template <class T>
713 inline void do_oop_work(T* p) {
714 T o = RawAccess<>::oop_load(p);
715 if (!CompressedOops::is_null(o)) {
716 oop obj = CompressedOops::decode_not_null(o);
717 oop forw = ShenandoahBarrierSet::resolve_forwarded_not_null(obj);
718 if (obj != forw) {
719 RawAccess<IS_NOT_NULL>::oop_store(p, forw);
720 }
721 }
722 }
723
724 public:
725 inline void do_oop(oop* p) { do_oop_work(p); }
726 inline void do_oop(narrowOop* p) { do_oop_work(p); }
727 };
728
729 class ShenandoahTraversalFixRootsTask : public AbstractGangTask {
730 private:
731 ShenandoahRootUpdater* _rp;
732
733 public:
734 ShenandoahTraversalFixRootsTask(ShenandoahRootUpdater* rp) :
735 AbstractGangTask("Shenandoah traversal fix roots"),
736 _rp(rp) {
737 assert(ShenandoahHeap::heap()->has_forwarded_objects(), "Must be");
738 }
739
740 void work(uint worker_id) {
741 ShenandoahParallelWorkerSession worker_session(worker_id);
742 ShenandoahTraversalFixRootsClosure cl;
743 ShenandoahForwardedIsAliveClosure is_alive;
744 _rp->roots_do(worker_id, &is_alive, &cl);
745 }
746 };
747
748 void ShenandoahTraversalGC::fixup_roots() {
749 #if COMPILER2_OR_JVMCI
750 DerivedPointerTable::clear();
751 #endif
752 ShenandoahRootUpdater rp(_heap->workers()->active_workers(), ShenandoahPhaseTimings::final_traversal_update_roots);
753 ShenandoahTraversalFixRootsTask update_roots_task(&rp);
754 _heap->workers()->run_task(&update_roots_task);
755 #if COMPILER2_OR_JVMCI
756 DerivedPointerTable::update_pointers();
757 #endif
758 }
759
760 void ShenandoahTraversalGC::reset() {
761 _task_queues->clear();
762 }
763
764 ShenandoahObjToScanQueueSet* ShenandoahTraversalGC::task_queues() {
765 return _task_queues;
766 }
767
768 class ShenandoahTraversalCancelledGCYieldClosure : public YieldClosure {
769 private:
770 ShenandoahHeap* const _heap;
771 public:
772 ShenandoahTraversalCancelledGCYieldClosure() : _heap(ShenandoahHeap::heap()) {};
773 virtual bool should_return() { return _heap->cancelled_gc(); }
774 };
775
776 class ShenandoahTraversalPrecleanCompleteGCClosure : public VoidClosure {
777 public:
778 void do_void() {
779 ShenandoahHeap* sh = ShenandoahHeap::heap();
780 ShenandoahTraversalGC* traversal_gc = sh->traversal_gc();
781 assert(sh->process_references(), "why else would we be here?");
782 TaskTerminator terminator(1, traversal_gc->task_queues());
783 shenandoah_assert_rp_isalive_installed();
784 traversal_gc->main_loop((uint) 0, &terminator, true);
785 }
786 };
787
788 class ShenandoahTraversalKeepAliveUpdateClosure : public OopClosure {
789 private:
790 ShenandoahObjToScanQueue* _queue;
791 Thread* _thread;
792 ShenandoahTraversalGC* _traversal_gc;
793 ShenandoahMarkingContext* const _mark_context;
794
795 template <class T>
796 inline void do_oop_work(T* p) {
797 _traversal_gc->process_oop<T, false /* string dedup */, false /* degen */, true /* atomic update */>(p, _thread, _queue, _mark_context);
798 }
799
800 public:
801 ShenandoahTraversalKeepAliveUpdateClosure(ShenandoahObjToScanQueue* q) :
802 _queue(q), _thread(Thread::current()),
803 _traversal_gc(ShenandoahHeap::heap()->traversal_gc()),
804 _mark_context(ShenandoahHeap::heap()->marking_context()) {}
805
806 void do_oop(narrowOop* p) { do_oop_work(p); }
807 void do_oop(oop* p) { do_oop_work(p); }
808 };
809
810 class ShenandoahTraversalKeepAliveUpdateDegenClosure : public OopClosure {
811 private:
812 ShenandoahObjToScanQueue* _queue;
813 Thread* _thread;
814 ShenandoahTraversalGC* _traversal_gc;
815 ShenandoahMarkingContext* const _mark_context;
816
817 template <class T>
818 inline void do_oop_work(T* p) {
819 _traversal_gc->process_oop<T, false /* string dedup */, true /* degen */, false /* atomic update */>(p, _thread, _queue, _mark_context);
820 }
821
822 public:
823 ShenandoahTraversalKeepAliveUpdateDegenClosure(ShenandoahObjToScanQueue* q) :
824 _queue(q), _thread(Thread::current()),
825 _traversal_gc(ShenandoahHeap::heap()->traversal_gc()),
826 _mark_context(ShenandoahHeap::heap()->marking_context()) {}
827
828 void do_oop(narrowOop* p) { do_oop_work(p); }
829 void do_oop(oop* p) { do_oop_work(p); }
830 };
831
832 class ShenandoahTraversalSingleThreadKeepAliveUpdateClosure : public OopClosure {
833 private:
834 ShenandoahObjToScanQueue* _queue;
835 Thread* _thread;
836 ShenandoahTraversalGC* _traversal_gc;
837 ShenandoahMarkingContext* const _mark_context;
838
839 template <class T>
840 inline void do_oop_work(T* p) {
841 _traversal_gc->process_oop<T, false /* string dedup */, false /* degen */, true /* atomic update */>(p, _thread, _queue, _mark_context);
842 }
843
844 public:
845 ShenandoahTraversalSingleThreadKeepAliveUpdateClosure(ShenandoahObjToScanQueue* q) :
846 _queue(q), _thread(Thread::current()),
847 _traversal_gc(ShenandoahHeap::heap()->traversal_gc()),
848 _mark_context(ShenandoahHeap::heap()->marking_context()) {}
849
850 void do_oop(narrowOop* p) { do_oop_work(p); }
851 void do_oop(oop* p) { do_oop_work(p); }
852 };
853
854 class ShenandoahTraversalSingleThreadKeepAliveUpdateDegenClosure : public OopClosure {
855 private:
856 ShenandoahObjToScanQueue* _queue;
857 Thread* _thread;
858 ShenandoahTraversalGC* _traversal_gc;
859 ShenandoahMarkingContext* const _mark_context;
860
861 template <class T>
862 inline void do_oop_work(T* p) {
863 _traversal_gc->process_oop<T, false /* string dedup */, true /* degen */, false /* atomic update */>(p, _thread, _queue, _mark_context);
864 }
865
866 public:
867 ShenandoahTraversalSingleThreadKeepAliveUpdateDegenClosure(ShenandoahObjToScanQueue* q) :
868 _queue(q), _thread(Thread::current()),
869 _traversal_gc(ShenandoahHeap::heap()->traversal_gc()),
870 _mark_context(ShenandoahHeap::heap()->marking_context()) {}
871
872 void do_oop(narrowOop* p) { do_oop_work(p); }
873 void do_oop(oop* p) { do_oop_work(p); }
874 };
875
876 class ShenandoahTraversalPrecleanTask : public AbstractGangTask {
877 private:
878 ReferenceProcessor* _rp;
879
880 public:
881 ShenandoahTraversalPrecleanTask(ReferenceProcessor* rp) :
882 AbstractGangTask("Precleaning task"),
883 _rp(rp) {}
884
885 void work(uint worker_id) {
886 assert(worker_id == 0, "The code below is single-threaded, only one worker is expected");
887 ShenandoahParallelWorkerSession worker_session(worker_id);
888 ShenandoahSuspendibleThreadSetJoiner stsj(ShenandoahSuspendibleWorkers);
889
890 ShenandoahHeap* sh = ShenandoahHeap::heap();
891
892 ShenandoahObjToScanQueue* q = sh->traversal_gc()->task_queues()->queue(worker_id);
893
894 ShenandoahForwardedIsAliveClosure is_alive;
895 ShenandoahTraversalCancelledGCYieldClosure yield;
896 ShenandoahTraversalPrecleanCompleteGCClosure complete_gc;
897 ShenandoahTraversalKeepAliveUpdateClosure keep_alive(q);
898 ResourceMark rm;
899 _rp->preclean_discovered_references(&is_alive, &keep_alive,
900 &complete_gc, &yield,
901 NULL);
902 }
903 };
904
905 void ShenandoahTraversalGC::preclean_weak_refs() {
906 // Pre-cleaning weak references before diving into STW makes sense at the
907 // end of concurrent mark. This will filter out the references which referents
908 // are alive. Note that ReferenceProcessor already filters out these on reference
909 // discovery, and the bulk of work is done here. This phase processes leftovers
910 // that missed the initial filtering, i.e. when referent was marked alive after
911 // reference was discovered by RP.
912
913 assert(_heap->process_references(), "sanity");
914 assert(!_heap->is_degenerated_gc_in_progress(), "must be in concurrent non-degenerated phase");
915
916 // Shortcut if no references were discovered to avoid winding up threads.
917 ReferenceProcessor* rp = _heap->ref_processor();
918 if (!rp->has_discovered_references()) {
919 return;
920 }
921
922 ReferenceProcessorMTDiscoveryMutator fix_mt_discovery(rp, false);
923
924 shenandoah_assert_rp_isalive_not_installed();
925 ShenandoahForwardedIsAliveClosure is_alive;
926 ReferenceProcessorIsAliveMutator fix_isalive(rp, &is_alive);
927
928 assert(task_queues()->is_empty(), "Should be empty");
929
930 // Execute precleaning in the worker thread: it will give us GCLABs, String dedup
931 // queues and other goodies. When upstream ReferenceProcessor starts supporting
932 // parallel precleans, we can extend this to more threads.
933 ShenandoahPushWorkerScope scope(_heap->workers(), 1, /* check_workers = */ false);
934
935 WorkGang* workers = _heap->workers();
936 uint nworkers = workers->active_workers();
937 assert(nworkers == 1, "This code uses only a single worker");
938 task_queues()->reserve(nworkers);
939
940 ShenandoahTraversalPrecleanTask task(rp);
941 workers->run_task(&task);
942
943 assert(_heap->cancelled_gc() || task_queues()->is_empty(), "Should be empty");
944 }
945
946 // Weak Reference Closures
947 class ShenandoahTraversalDrainMarkingStackClosure: public VoidClosure {
948 uint _worker_id;
949 TaskTerminator* _terminator;
950 bool _reset_terminator;
951
952 public:
953 ShenandoahTraversalDrainMarkingStackClosure(uint worker_id, TaskTerminator* t, bool reset_terminator = false):
954 _worker_id(worker_id),
955 _terminator(t),
956 _reset_terminator(reset_terminator) {
957 }
958
959 void do_void() {
960 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
961
962 ShenandoahHeap* sh = ShenandoahHeap::heap();
963 ShenandoahTraversalGC* traversal_gc = sh->traversal_gc();
964 assert(sh->process_references(), "why else would we be here?");
965 shenandoah_assert_rp_isalive_installed();
966
967 traversal_gc->main_loop(_worker_id, _terminator, false);
968
969 if (_reset_terminator) {
970 _terminator->reset_for_reuse();
971 }
972 }
973 };
974
975 class ShenandoahTraversalSingleThreadedDrainMarkingStackClosure: public VoidClosure {
976 uint _worker_id;
977 TaskTerminator* _terminator;
978 bool _reset_terminator;
979
980 public:
981 ShenandoahTraversalSingleThreadedDrainMarkingStackClosure(uint worker_id, TaskTerminator* t, bool reset_terminator = false):
982 _worker_id(worker_id),
983 _terminator(t),
984 _reset_terminator(reset_terminator) {
985 }
986
987 void do_void() {
988 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
989
990 ShenandoahHeap* sh = ShenandoahHeap::heap();
991 ShenandoahTraversalGC* traversal_gc = sh->traversal_gc();
992 assert(sh->process_references(), "why else would we be here?");
993 shenandoah_assert_rp_isalive_installed();
994
995 traversal_gc->main_loop(_worker_id, _terminator, false);
996
997 if (_reset_terminator) {
998 _terminator->reset_for_reuse();
999 }
1000 }
1001 };
1002
1003 void ShenandoahTraversalGC::weak_refs_work() {
1004 assert(_heap->process_references(), "sanity");
1005
1006 ShenandoahPhaseTimings::Phase phase_root = ShenandoahPhaseTimings::weakrefs;
1007
1008 ShenandoahGCPhase phase(phase_root);
1009
1010 ReferenceProcessor* rp = _heap->ref_processor();
1011
1012 // NOTE: We cannot shortcut on has_discovered_references() here, because
1013 // we will miss marking JNI Weak refs then, see implementation in
1014 // ReferenceProcessor::process_discovered_references.
1015 weak_refs_work_doit();
1016
1017 rp->verify_no_references_recorded();
1018 assert(!rp->discovery_enabled(), "Post condition");
1019
1020 }
1021
1022 class ShenandoahTraversalRefProcTaskProxy : public AbstractGangTask {
1023 private:
1024 AbstractRefProcTaskExecutor::ProcessTask& _proc_task;
1025 TaskTerminator* _terminator;
1026
1027 public:
1028 ShenandoahTraversalRefProcTaskProxy(AbstractRefProcTaskExecutor::ProcessTask& proc_task,
1029 TaskTerminator* t) :
1030 AbstractGangTask("Process reference objects in parallel"),
1031 _proc_task(proc_task),
1032 _terminator(t) {
1033 }
1034
1035 void work(uint worker_id) {
1036 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
1037 ShenandoahHeap* heap = ShenandoahHeap::heap();
1038 ShenandoahTraversalDrainMarkingStackClosure complete_gc(worker_id, _terminator);
1039
1040 ShenandoahForwardedIsAliveClosure is_alive;
1041 if (!heap->is_degenerated_gc_in_progress()) {
1042 ShenandoahTraversalKeepAliveUpdateClosure keep_alive(heap->traversal_gc()->task_queues()->queue(worker_id));
1043 _proc_task.work(worker_id, is_alive, keep_alive, complete_gc);
1044 } else {
1045 ShenandoahTraversalKeepAliveUpdateDegenClosure keep_alive(heap->traversal_gc()->task_queues()->queue(worker_id));
1046 _proc_task.work(worker_id, is_alive, keep_alive, complete_gc);
1047 }
1048 }
1049 };
1050
1051 class ShenandoahTraversalRefProcTaskExecutor : public AbstractRefProcTaskExecutor {
1052 private:
1053 WorkGang* _workers;
1054
1055 public:
1056 ShenandoahTraversalRefProcTaskExecutor(WorkGang* workers) : _workers(workers) {}
1057
1058 // Executes a task using worker threads.
1059 void execute(ProcessTask& task, uint ergo_workers) {
1060 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
1061
1062 ShenandoahHeap* heap = ShenandoahHeap::heap();
1063 ShenandoahTraversalGC* traversal_gc = heap->traversal_gc();
1064 ShenandoahPushWorkerQueuesScope scope(_workers,
1065 traversal_gc->task_queues(),
1066 ergo_workers,
1067 /* do_check = */ false);
1068 uint nworkers = _workers->active_workers();
1069 traversal_gc->task_queues()->reserve(nworkers);
1070 TaskTerminator terminator(nworkers, traversal_gc->task_queues());
1071 ShenandoahTraversalRefProcTaskProxy proc_task_proxy(task, &terminator);
1072 _workers->run_task(&proc_task_proxy);
1073 }
1074 };
1075
1076 void ShenandoahTraversalGC::weak_refs_work_doit() {
1077 ReferenceProcessor* rp = _heap->ref_processor();
1078
1079 ShenandoahPhaseTimings::Phase phase_process = ShenandoahPhaseTimings::weakrefs_process;
1080
1081 shenandoah_assert_rp_isalive_not_installed();
1082 ShenandoahForwardedIsAliveClosure is_alive;
1083 ReferenceProcessorIsAliveMutator fix_isalive(rp, &is_alive);
1084
1085 WorkGang* workers = _heap->workers();
1086 uint nworkers = workers->active_workers();
1087
1088 rp->setup_policy(_heap->soft_ref_policy()->should_clear_all_soft_refs());
1089 rp->set_active_mt_degree(nworkers);
1090
1091 assert(task_queues()->is_empty(), "Should be empty");
1092
1093 // complete_gc and keep_alive closures instantiated here are only needed for
1094 // single-threaded path in RP. They share the queue 0 for tracking work, which
1095 // simplifies implementation. Since RP may decide to call complete_gc several
1096 // times, we need to be able to reuse the terminator.
1097 uint serial_worker_id = 0;
1098 TaskTerminator terminator(1, task_queues());
1099 ShenandoahTraversalSingleThreadedDrainMarkingStackClosure complete_gc(serial_worker_id, &terminator, /* reset_terminator = */ true);
1100 ShenandoahPushWorkerQueuesScope scope(workers, task_queues(), 1, /* do_check = */ false);
1101
1102 ShenandoahTraversalRefProcTaskExecutor executor(workers);
1103
1104 ReferenceProcessorPhaseTimes pt(_heap->gc_timer(), rp->num_queues());
1105 if (!_heap->is_degenerated_gc_in_progress()) {
1106 ShenandoahTraversalSingleThreadKeepAliveUpdateClosure keep_alive(task_queues()->queue(serial_worker_id));
1107 rp->process_discovered_references(&is_alive, &keep_alive,
1108 &complete_gc, &executor,
1109 &pt);
1110 } else {
1111 ShenandoahTraversalSingleThreadKeepAliveUpdateDegenClosure keep_alive(task_queues()->queue(serial_worker_id));
1112 rp->process_discovered_references(&is_alive, &keep_alive,
1113 &complete_gc, &executor,
1114 &pt);
1115 }
1116
1117 pt.print_all_references();
1118 assert(task_queues()->is_empty() || _heap->cancelled_gc(), "Should be empty");
1119 }