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 ShenandoahTaskTerminator* _terminator;
204 ShenandoahHeap* _heap;
205 public:
206 ShenandoahConcurrentTraversalCollectionTask(ShenandoahTaskTerminator* 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 ShenandoahTaskTerminator* _terminator;
225 ShenandoahHeap* _heap;
226 public:
227 ShenandoahFinalTraversalCollectionTask(ShenandoahAllRootScanner* rp, ShenandoahTaskTerminator* 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, ShenandoahTaskTerminator* 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, ShenandoahTaskTerminator* 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(ShenandoahTaskTerminator* 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 ShenandoahTaskTerminator 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 _heap->make_parsable(true);
575
576 if (!_heap->cancelled_gc()) {
577 #if COMPILER2_OR_JVMCI
578 DerivedPointerTable::clear();
579 #endif
580 ShenandoahGCPhase phase_work(ShenandoahPhaseTimings::final_traversal_gc_work);
581 uint nworkers = _heap->workers()->active_workers();
582 task_queues()->reserve(nworkers);
583
584 // Finish traversal
585 ShenandoahAllRootScanner rp(nworkers, ShenandoahPhaseTimings::final_traversal_gc_work);
586 ShenandoahTerminationTracker term(ShenandoahPhaseTimings::final_traversal_gc_termination);
587
588 ShenandoahTaskTerminator terminator(nworkers, task_queues());
589 ShenandoahFinalTraversalCollectionTask task(&rp, &terminator);
590 _heap->workers()->run_task(&task);
591 #if COMPILER2_OR_JVMCI
592 DerivedPointerTable::update_pointers();
593 #endif
594 }
595
596 if (!_heap->cancelled_gc() && _heap->process_references()) {
597 weak_refs_work();
598 }
599
600 if (!_heap->cancelled_gc()) {
601 assert(_task_queues->is_empty(), "queues must be empty after traversal GC");
602 TASKQUEUE_STATS_ONLY(_task_queues->print_taskqueue_stats());
603 TASKQUEUE_STATS_ONLY(_task_queues->reset_taskqueue_stats());
604
605 // No more marking expected
606 _heap->set_concurrent_traversal_in_progress(false);
607 _heap->mark_complete_marking_context();
608
609 _heap->parallel_cleaning(false);
610 fixup_roots();
611
612 _heap->set_has_forwarded_objects(false);
613
614 // Resize metaspace
615 MetaspaceGC::compute_new_size();
616
617 // Need to see that pinned region status is updated: newly pinned regions must not
618 // be trashed. New unpinned regions should be trashed.
619 {
620 ShenandoahGCPhase phase_cleanup(ShenandoahPhaseTimings::traversal_gc_sync_pinned);
621 _heap->sync_pinned_region_status();
622 }
623
624 // Still good? We can now trash the cset, and make final verification
625 {
626 ShenandoahGCPhase phase_cleanup(ShenandoahPhaseTimings::traversal_gc_cleanup);
627 ShenandoahHeapLocker lock(_heap->lock());
628
629 // Trash everything
630 // Clear immediate garbage regions.
631 size_t num_regions = _heap->num_regions();
632
633 ShenandoahHeapRegionSet* traversal_regions = traversal_set();
634 ShenandoahFreeSet* free_regions = _heap->free_set();
635 ShenandoahMarkingContext* const ctx = _heap->marking_context();
636 free_regions->clear();
637 for (size_t i = 0; i < num_regions; i++) {
638 ShenandoahHeapRegion* r = _heap->get_region(i);
639 bool not_allocated = ctx->top_at_mark_start(r) == r->top();
640
641 bool candidate = traversal_regions->is_in(r) && !r->has_live() && not_allocated;
642 if (r->is_humongous_start() && candidate) {
643 // Trash humongous.
644 HeapWord* humongous_obj = r->bottom();
645 assert(!ctx->is_marked(oop(humongous_obj)), "must not be marked");
646 r->make_trash_immediate();
647 while (i + 1 < num_regions && _heap->get_region(i + 1)->is_humongous_continuation()) {
648 i++;
649 r = _heap->get_region(i);
650 assert(r->is_humongous_continuation(), "must be humongous continuation");
651 r->make_trash_immediate();
652 }
653 } else if (!r->is_empty() && candidate) {
654 // Trash regular.
655 assert(!r->is_humongous(), "handled above");
656 assert(!r->is_trash(), "must not already be trashed");
657 r->make_trash_immediate();
658 }
659 }
660 _heap->collection_set()->clear();
661 _heap->free_set()->rebuild();
662 reset();
663 }
664
665 assert(_task_queues->is_empty(), "queues must be empty after traversal GC");
666 assert(!_heap->cancelled_gc(), "must not be cancelled when getting out here");
667
668 if (ShenandoahVerify) {
669 _heap->verifier()->verify_after_traversal();
670 }
671 #ifdef ASSERT
672 else {
673 verify_roots_after_gc();
674 }
675 #endif
676
677 if (VerifyAfterGC) {
678 Universe::verify();
679 }
680 }
681 }
682
683 class ShenandoahVerifyAfterGC : public OopClosure {
684 private:
685 template <class T>
686 void do_oop_work(T* p) {
687 T o = RawAccess<>::oop_load(p);
688 if (!CompressedOops::is_null(o)) {
689 oop obj = CompressedOops::decode_not_null(o);
690 shenandoah_assert_correct(p, obj);
691 shenandoah_assert_not_in_cset_except(p, obj, ShenandoahHeap::heap()->cancelled_gc());
692 shenandoah_assert_not_forwarded(p, obj);
693 }
694 }
695
696 public:
697 void do_oop(narrowOop* p) { do_oop_work(p); }
698 void do_oop(oop* p) { do_oop_work(p); }
699 };
700
701 void ShenandoahTraversalGC::verify_roots_after_gc() {
702 ShenandoahRootVerifier verifier;
703 ShenandoahVerifyAfterGC cl;
704 verifier.oops_do(&cl);
705 }
706
707 class ShenandoahTraversalFixRootsClosure : public OopClosure {
708 private:
709 template <class T>
710 inline void do_oop_work(T* p) {
711 T o = RawAccess<>::oop_load(p);
712 if (!CompressedOops::is_null(o)) {
713 oop obj = CompressedOops::decode_not_null(o);
714 oop forw = ShenandoahBarrierSet::resolve_forwarded_not_null(obj);
715 if (obj != forw) {
716 RawAccess<IS_NOT_NULL>::oop_store(p, forw);
717 }
718 }
719 }
720
721 public:
722 inline void do_oop(oop* p) { do_oop_work(p); }
723 inline void do_oop(narrowOop* p) { do_oop_work(p); }
724 };
725
726 class ShenandoahTraversalFixRootsTask : public AbstractGangTask {
727 private:
728 ShenandoahRootUpdater* _rp;
729
730 public:
731 ShenandoahTraversalFixRootsTask(ShenandoahRootUpdater* rp) :
732 AbstractGangTask("Shenandoah traversal fix roots"),
733 _rp(rp) {
734 assert(ShenandoahHeap::heap()->has_forwarded_objects(), "Must be");
735 }
736
737 void work(uint worker_id) {
738 ShenandoahParallelWorkerSession worker_session(worker_id);
739 ShenandoahTraversalFixRootsClosure cl;
740 ShenandoahForwardedIsAliveClosure is_alive;
741 _rp->roots_do(worker_id, &is_alive, &cl);
742 }
743 };
744
745 void ShenandoahTraversalGC::fixup_roots() {
746 #if COMPILER2_OR_JVMCI
747 DerivedPointerTable::clear();
748 #endif
749 ShenandoahRootUpdater rp(_heap->workers()->active_workers(), ShenandoahPhaseTimings::final_traversal_update_roots);
750 ShenandoahTraversalFixRootsTask update_roots_task(&rp);
751 _heap->workers()->run_task(&update_roots_task);
752 #if COMPILER2_OR_JVMCI
753 DerivedPointerTable::update_pointers();
754 #endif
755 }
756
757 void ShenandoahTraversalGC::reset() {
758 _task_queues->clear();
759 }
760
761 ShenandoahObjToScanQueueSet* ShenandoahTraversalGC::task_queues() {
762 return _task_queues;
763 }
764
765 class ShenandoahTraversalCancelledGCYieldClosure : public YieldClosure {
766 private:
767 ShenandoahHeap* const _heap;
768 public:
769 ShenandoahTraversalCancelledGCYieldClosure() : _heap(ShenandoahHeap::heap()) {};
770 virtual bool should_return() { return _heap->cancelled_gc(); }
771 };
772
773 class ShenandoahTraversalPrecleanCompleteGCClosure : public VoidClosure {
774 public:
775 void do_void() {
776 ShenandoahHeap* sh = ShenandoahHeap::heap();
777 ShenandoahTraversalGC* traversal_gc = sh->traversal_gc();
778 assert(sh->process_references(), "why else would we be here?");
779 ShenandoahTaskTerminator terminator(1, traversal_gc->task_queues());
780 shenandoah_assert_rp_isalive_installed();
781 traversal_gc->main_loop((uint) 0, &terminator, true);
782 }
783 };
784
785 class ShenandoahTraversalKeepAliveUpdateClosure : public OopClosure {
786 private:
787 ShenandoahObjToScanQueue* _queue;
788 Thread* _thread;
789 ShenandoahTraversalGC* _traversal_gc;
790 ShenandoahMarkingContext* const _mark_context;
791
792 template <class T>
793 inline void do_oop_work(T* p) {
794 _traversal_gc->process_oop<T, false /* string dedup */, false /* degen */, true /* atomic update */>(p, _thread, _queue, _mark_context);
795 }
796
797 public:
798 ShenandoahTraversalKeepAliveUpdateClosure(ShenandoahObjToScanQueue* q) :
799 _queue(q), _thread(Thread::current()),
800 _traversal_gc(ShenandoahHeap::heap()->traversal_gc()),
801 _mark_context(ShenandoahHeap::heap()->marking_context()) {}
802
803 void do_oop(narrowOop* p) { do_oop_work(p); }
804 void do_oop(oop* p) { do_oop_work(p); }
805 };
806
807 class ShenandoahTraversalKeepAliveUpdateDegenClosure : public OopClosure {
808 private:
809 ShenandoahObjToScanQueue* _queue;
810 Thread* _thread;
811 ShenandoahTraversalGC* _traversal_gc;
812 ShenandoahMarkingContext* const _mark_context;
813
814 template <class T>
815 inline void do_oop_work(T* p) {
816 _traversal_gc->process_oop<T, false /* string dedup */, true /* degen */, false /* atomic update */>(p, _thread, _queue, _mark_context);
817 }
818
819 public:
820 ShenandoahTraversalKeepAliveUpdateDegenClosure(ShenandoahObjToScanQueue* q) :
821 _queue(q), _thread(Thread::current()),
822 _traversal_gc(ShenandoahHeap::heap()->traversal_gc()),
823 _mark_context(ShenandoahHeap::heap()->marking_context()) {}
824
825 void do_oop(narrowOop* p) { do_oop_work(p); }
826 void do_oop(oop* p) { do_oop_work(p); }
827 };
828
829 class ShenandoahTraversalSingleThreadKeepAliveUpdateClosure : public OopClosure {
830 private:
831 ShenandoahObjToScanQueue* _queue;
832 Thread* _thread;
833 ShenandoahTraversalGC* _traversal_gc;
834 ShenandoahMarkingContext* const _mark_context;
835
836 template <class T>
837 inline void do_oop_work(T* p) {
838 _traversal_gc->process_oop<T, false /* string dedup */, false /* degen */, true /* atomic update */>(p, _thread, _queue, _mark_context);
839 }
840
841 public:
842 ShenandoahTraversalSingleThreadKeepAliveUpdateClosure(ShenandoahObjToScanQueue* q) :
843 _queue(q), _thread(Thread::current()),
844 _traversal_gc(ShenandoahHeap::heap()->traversal_gc()),
845 _mark_context(ShenandoahHeap::heap()->marking_context()) {}
846
847 void do_oop(narrowOop* p) { do_oop_work(p); }
848 void do_oop(oop* p) { do_oop_work(p); }
849 };
850
851 class ShenandoahTraversalSingleThreadKeepAliveUpdateDegenClosure : public OopClosure {
852 private:
853 ShenandoahObjToScanQueue* _queue;
854 Thread* _thread;
855 ShenandoahTraversalGC* _traversal_gc;
856 ShenandoahMarkingContext* const _mark_context;
857
858 template <class T>
859 inline void do_oop_work(T* p) {
860 _traversal_gc->process_oop<T, false /* string dedup */, true /* degen */, false /* atomic update */>(p, _thread, _queue, _mark_context);
861 }
862
863 public:
864 ShenandoahTraversalSingleThreadKeepAliveUpdateDegenClosure(ShenandoahObjToScanQueue* q) :
865 _queue(q), _thread(Thread::current()),
866 _traversal_gc(ShenandoahHeap::heap()->traversal_gc()),
867 _mark_context(ShenandoahHeap::heap()->marking_context()) {}
868
869 void do_oop(narrowOop* p) { do_oop_work(p); }
870 void do_oop(oop* p) { do_oop_work(p); }
871 };
872
873 class ShenandoahTraversalPrecleanTask : public AbstractGangTask {
874 private:
875 ReferenceProcessor* _rp;
876
877 public:
878 ShenandoahTraversalPrecleanTask(ReferenceProcessor* rp) :
879 AbstractGangTask("Precleaning task"),
880 _rp(rp) {}
881
882 void work(uint worker_id) {
883 assert(worker_id == 0, "The code below is single-threaded, only one worker is expected");
884 ShenandoahParallelWorkerSession worker_session(worker_id);
885 ShenandoahSuspendibleThreadSetJoiner stsj(ShenandoahSuspendibleWorkers);
886
887 ShenandoahHeap* sh = ShenandoahHeap::heap();
888
889 ShenandoahObjToScanQueue* q = sh->traversal_gc()->task_queues()->queue(worker_id);
890
891 ShenandoahForwardedIsAliveClosure is_alive;
892 ShenandoahTraversalCancelledGCYieldClosure yield;
893 ShenandoahTraversalPrecleanCompleteGCClosure complete_gc;
894 ShenandoahTraversalKeepAliveUpdateClosure keep_alive(q);
895 ResourceMark rm;
896 _rp->preclean_discovered_references(&is_alive, &keep_alive,
897 &complete_gc, &yield,
898 NULL);
899 }
900 };
901
902 void ShenandoahTraversalGC::preclean_weak_refs() {
903 // Pre-cleaning weak references before diving into STW makes sense at the
904 // end of concurrent mark. This will filter out the references which referents
905 // are alive. Note that ReferenceProcessor already filters out these on reference
906 // discovery, and the bulk of work is done here. This phase processes leftovers
907 // that missed the initial filtering, i.e. when referent was marked alive after
908 // reference was discovered by RP.
909
910 assert(_heap->process_references(), "sanity");
911 assert(!_heap->is_degenerated_gc_in_progress(), "must be in concurrent non-degenerated phase");
912
913 // Shortcut if no references were discovered to avoid winding up threads.
914 ReferenceProcessor* rp = _heap->ref_processor();
915 if (!rp->has_discovered_references()) {
916 return;
917 }
918
919 ReferenceProcessorMTDiscoveryMutator fix_mt_discovery(rp, false);
920
921 shenandoah_assert_rp_isalive_not_installed();
922 ShenandoahForwardedIsAliveClosure is_alive;
923 ReferenceProcessorIsAliveMutator fix_isalive(rp, &is_alive);
924
925 assert(task_queues()->is_empty(), "Should be empty");
926
927 // Execute precleaning in the worker thread: it will give us GCLABs, String dedup
928 // queues and other goodies. When upstream ReferenceProcessor starts supporting
929 // parallel precleans, we can extend this to more threads.
930 ShenandoahPushWorkerScope scope(_heap->workers(), 1, /* check_workers = */ false);
931
932 WorkGang* workers = _heap->workers();
933 uint nworkers = workers->active_workers();
934 assert(nworkers == 1, "This code uses only a single worker");
935 task_queues()->reserve(nworkers);
936
937 ShenandoahTraversalPrecleanTask task(rp);
938 workers->run_task(&task);
939
940 assert(_heap->cancelled_gc() || task_queues()->is_empty(), "Should be empty");
941 }
942
943 // Weak Reference Closures
944 class ShenandoahTraversalDrainMarkingStackClosure: public VoidClosure {
945 uint _worker_id;
946 ShenandoahTaskTerminator* _terminator;
947 bool _reset_terminator;
948
949 public:
950 ShenandoahTraversalDrainMarkingStackClosure(uint worker_id, ShenandoahTaskTerminator* t, bool reset_terminator = false):
951 _worker_id(worker_id),
952 _terminator(t),
953 _reset_terminator(reset_terminator) {
954 }
955
956 void do_void() {
957 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
958
959 ShenandoahHeap* sh = ShenandoahHeap::heap();
960 ShenandoahTraversalGC* traversal_gc = sh->traversal_gc();
961 assert(sh->process_references(), "why else would we be here?");
962 shenandoah_assert_rp_isalive_installed();
963
964 traversal_gc->main_loop(_worker_id, _terminator, false);
965
966 if (_reset_terminator) {
967 _terminator->reset_for_reuse();
968 }
969 }
970 };
971
972 class ShenandoahTraversalSingleThreadedDrainMarkingStackClosure: public VoidClosure {
973 uint _worker_id;
974 ShenandoahTaskTerminator* _terminator;
975 bool _reset_terminator;
976
977 public:
978 ShenandoahTraversalSingleThreadedDrainMarkingStackClosure(uint worker_id, ShenandoahTaskTerminator* t, bool reset_terminator = false):
979 _worker_id(worker_id),
980 _terminator(t),
981 _reset_terminator(reset_terminator) {
982 }
983
984 void do_void() {
985 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
986
987 ShenandoahHeap* sh = ShenandoahHeap::heap();
988 ShenandoahTraversalGC* traversal_gc = sh->traversal_gc();
989 assert(sh->process_references(), "why else would we be here?");
990 shenandoah_assert_rp_isalive_installed();
991
992 traversal_gc->main_loop(_worker_id, _terminator, false);
993
994 if (_reset_terminator) {
995 _terminator->reset_for_reuse();
996 }
997 }
998 };
999
1000 void ShenandoahTraversalGC::weak_refs_work() {
1001 assert(_heap->process_references(), "sanity");
1002
1003 ShenandoahPhaseTimings::Phase phase_root = ShenandoahPhaseTimings::weakrefs;
1004
1005 ShenandoahGCPhase phase(phase_root);
1006
1007 ReferenceProcessor* rp = _heap->ref_processor();
1008
1009 // NOTE: We cannot shortcut on has_discovered_references() here, because
1010 // we will miss marking JNI Weak refs then, see implementation in
1011 // ReferenceProcessor::process_discovered_references.
1012 weak_refs_work_doit();
1013
1014 rp->verify_no_references_recorded();
1015 assert(!rp->discovery_enabled(), "Post condition");
1016
1017 }
1018
1019 class ShenandoahTraversalRefProcTaskProxy : public AbstractGangTask {
1020 private:
1021 AbstractRefProcTaskExecutor::ProcessTask& _proc_task;
1022 ShenandoahTaskTerminator* _terminator;
1023
1024 public:
1025 ShenandoahTraversalRefProcTaskProxy(AbstractRefProcTaskExecutor::ProcessTask& proc_task,
1026 ShenandoahTaskTerminator* t) :
1027 AbstractGangTask("Process reference objects in parallel"),
1028 _proc_task(proc_task),
1029 _terminator(t) {
1030 }
1031
1032 void work(uint worker_id) {
1033 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
1034 ShenandoahHeap* heap = ShenandoahHeap::heap();
1035 ShenandoahTraversalDrainMarkingStackClosure complete_gc(worker_id, _terminator);
1036
1037 ShenandoahForwardedIsAliveClosure is_alive;
1038 if (!heap->is_degenerated_gc_in_progress()) {
1039 ShenandoahTraversalKeepAliveUpdateClosure keep_alive(heap->traversal_gc()->task_queues()->queue(worker_id));
1040 _proc_task.work(worker_id, is_alive, keep_alive, complete_gc);
1041 } else {
1042 ShenandoahTraversalKeepAliveUpdateDegenClosure keep_alive(heap->traversal_gc()->task_queues()->queue(worker_id));
1043 _proc_task.work(worker_id, is_alive, keep_alive, complete_gc);
1044 }
1045 }
1046 };
1047
1048 class ShenandoahTraversalRefProcTaskExecutor : public AbstractRefProcTaskExecutor {
1049 private:
1050 WorkGang* _workers;
1051
1052 public:
1053 ShenandoahTraversalRefProcTaskExecutor(WorkGang* workers) : _workers(workers) {}
1054
1055 // Executes a task using worker threads.
1056 void execute(ProcessTask& task, uint ergo_workers) {
1057 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
1058
1059 ShenandoahHeap* heap = ShenandoahHeap::heap();
1060 ShenandoahTraversalGC* traversal_gc = heap->traversal_gc();
1061 ShenandoahPushWorkerQueuesScope scope(_workers,
1062 traversal_gc->task_queues(),
1063 ergo_workers,
1064 /* do_check = */ false);
1065 uint nworkers = _workers->active_workers();
1066 traversal_gc->task_queues()->reserve(nworkers);
1067 ShenandoahTaskTerminator terminator(nworkers, traversal_gc->task_queues());
1068 ShenandoahTraversalRefProcTaskProxy proc_task_proxy(task, &terminator);
1069 _workers->run_task(&proc_task_proxy);
1070 }
1071 };
1072
1073 void ShenandoahTraversalGC::weak_refs_work_doit() {
1074 ReferenceProcessor* rp = _heap->ref_processor();
1075
1076 ShenandoahPhaseTimings::Phase phase_process = ShenandoahPhaseTimings::weakrefs_process;
1077
1078 shenandoah_assert_rp_isalive_not_installed();
1079 ShenandoahForwardedIsAliveClosure is_alive;
1080 ReferenceProcessorIsAliveMutator fix_isalive(rp, &is_alive);
1081
1082 WorkGang* workers = _heap->workers();
1083 uint nworkers = workers->active_workers();
1084
1085 rp->setup_policy(_heap->soft_ref_policy()->should_clear_all_soft_refs());
1086 rp->set_active_mt_degree(nworkers);
1087
1088 assert(task_queues()->is_empty(), "Should be empty");
1089
1090 // complete_gc and keep_alive closures instantiated here are only needed for
1091 // single-threaded path in RP. They share the queue 0 for tracking work, which
1092 // simplifies implementation. Since RP may decide to call complete_gc several
1093 // times, we need to be able to reuse the terminator.
1094 uint serial_worker_id = 0;
1095 ShenandoahTaskTerminator terminator(1, task_queues());
1096 ShenandoahTraversalSingleThreadedDrainMarkingStackClosure complete_gc(serial_worker_id, &terminator, /* reset_terminator = */ true);
1097 ShenandoahPushWorkerQueuesScope scope(workers, task_queues(), 1, /* do_check = */ false);
1098
1099 ShenandoahTraversalRefProcTaskExecutor executor(workers);
1100
1101 ReferenceProcessorPhaseTimes pt(_heap->gc_timer(), rp->num_queues());
1102 if (!_heap->is_degenerated_gc_in_progress()) {
1103 ShenandoahTraversalSingleThreadKeepAliveUpdateClosure keep_alive(task_queues()->queue(serial_worker_id));
1104 rp->process_discovered_references(&is_alive, &keep_alive,
1105 &complete_gc, &executor,
1106 &pt);
1107 } else {
1108 ShenandoahTraversalSingleThreadKeepAliveUpdateDegenClosure keep_alive(task_queues()->queue(serial_worker_id));
1109 rp->process_discovered_references(&is_alive, &keep_alive,
1110 &complete_gc, &executor,
1111 &pt);
1112 }
1113
1114 pt.print_all_references();
1115 assert(task_queues()->is_empty() || _heap->cancelled_gc(), "Should be empty");
1116 }