1 /*
2 * Copyright (c) 2018, 2020, Red Hat, Inc. All rights reserved.
3 *
4 * This code is free software; you can redistribute it and/or modify it
5 * under the terms of the GNU General Public License version 2 only, as
6 * published by the Free Software Foundation.
7 *
8 * This code is distributed in the hope that it will be useful, but WITHOUT
9 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
10 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
11 * version 2 for more details (a copy is included in the LICENSE file that
12 * accompanied this code).
13 *
14 * You should have received a copy of the GNU General Public License version
15 * 2 along with this work; if not, write to the Free Software Foundation,
16 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
17 *
18 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
19 * or visit www.oracle.com if you need additional information or have any
20 * questions.
21 *
22 */
23
24 #include "precompiled.hpp"
25
26 #include "classfile/classLoaderData.hpp"
27 #include "classfile/classLoaderDataGraph.hpp"
28 #include "gc/shared/referenceProcessor.hpp"
29 #include "gc/shared/referenceProcessorPhaseTimes.hpp"
30 #include "gc/shared/workgroup.hpp"
31 #include "gc/shenandoah/shenandoahBarrierSet.hpp"
32 #include "gc/shenandoah/shenandoahClosures.inline.hpp"
33 #include "gc/shenandoah/shenandoahCodeRoots.hpp"
34 #include "gc/shenandoah/shenandoahCollectionSet.hpp"
35 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
36 #include "gc/shenandoah/shenandoahFreeSet.hpp"
37 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
38 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
39 #include "gc/shenandoah/shenandoahHeapRegionSet.inline.hpp"
40 #include "gc/shenandoah/shenandoahHeuristics.hpp"
41 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"
42 #include "gc/shenandoah/shenandoahOopClosures.inline.hpp"
43 #include "gc/shenandoah/shenandoahPhaseTimings.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/shenandoahTraversalGC.hpp"
48 #include "gc/shenandoah/shenandoahUtils.hpp"
49 #include "gc/shenandoah/shenandoahVerifier.hpp"
50
51 #include "memory/iterator.hpp"
52 #include "memory/metaspace.hpp"
53 #include "memory/resourceArea.hpp"
54 #include "memory/universe.hpp"
55
56 /**
57 * NOTE: We are using the SATB buffer in thread.hpp and satbMarkQueue.hpp, however, it is not an SATB algorithm.
58 * We're using the buffer as generic oop buffer to enqueue new values in concurrent oop stores, IOW, the algorithm
59 * is incremental-update-based.
60 *
61 * NOTE on interaction with TAMS: we want to avoid traversing new objects for
62 * several reasons:
63 * - We will not reclaim them in this cycle anyway, because they are not in the
64 * cset
65 * - It makes up for the bulk of work during final-pause
66 * - It also shortens the concurrent cycle because we don't need to
67 * pointlessly traverse through newly allocated objects.
68 * - As a nice side-effect, it solves the I-U termination problem (mutators
69 * cannot outrun the GC by allocating like crazy)
70 * - It is an easy way to achieve MWF. What MWF does is to also enqueue the
71 * target object of stores if it's new. Treating new objects live implicitely
72 * achieves the same, but without extra barriers. I think the effect of
73 * shortened final-pause (mentioned above) is the main advantage of MWF. In
74 * particular, we will not see the head of a completely new long linked list
75 * in final-pause and end up traversing huge chunks of the heap there.
76 * - We don't need to see/update the fields of new objects either, because they
77 * are either still null, or anything that's been stored into them has been
78 * evacuated+enqueued before (and will thus be treated later).
79 *
80 * We achieve this by setting TAMS for each region, and everything allocated
81 * beyond TAMS will be 'implicitely marked'.
82 *
83 * Gotchas:
84 * - While we want new objects to be implicitely marked, we don't want to count
85 * them alive. Otherwise the next cycle wouldn't pick them up and consider
86 * them for cset. This means that we need to protect such regions from
87 * getting accidentally thrashed at the end of traversal cycle. This is why I
88 * keep track of alloc-regions and check is_alloc_region() in the trashing
89 * code.
90 * - We *need* to traverse through evacuated objects. Those objects are
91 * pre-existing, and any references in them point to interesting objects that
92 * we need to see. We also want to count them as live, because we just
93 * determined that they are alive :-) I achieve this by upping TAMS
94 * concurrently for every gclab/gc-shared alloc before publishing the
95 * evacuated object. This way, the GC threads will not consider such objects
96 * implictely marked, and traverse through them as normal.
97 */
98 class ShenandoahTraversalSATBBufferClosure : public SATBBufferClosure {
99 private:
100 ShenandoahObjToScanQueue* _queue;
101 ShenandoahTraversalGC* _traversal_gc;
102 ShenandoahHeap* const _heap;
103
104 public:
105 ShenandoahTraversalSATBBufferClosure(ShenandoahObjToScanQueue* q) :
106 _queue(q),
107 _heap(ShenandoahHeap::heap())
108 { }
109
110 void do_buffer(void** buffer, size_t size) {
111 for (size_t i = 0; i < size; ++i) {
112 oop* p = (oop*) &buffer[i];
113 oop obj = RawAccess<>::oop_load(p);
114 shenandoah_assert_not_forwarded(p, obj);
115 if (_heap->marking_context()->mark(obj)) {
116 _queue->push(ShenandoahMarkTask(obj));
117 }
118 }
119 }
120 };
121
122 class ShenandoahTraversalSATBThreadsClosure : public ThreadClosure {
123 private:
124 ShenandoahTraversalSATBBufferClosure* _satb_cl;
125
126 public:
127 ShenandoahTraversalSATBThreadsClosure(ShenandoahTraversalSATBBufferClosure* satb_cl) :
128 _satb_cl(satb_cl) {}
129
130 void do_thread(Thread* thread) {
131 ShenandoahThreadLocalData::satb_mark_queue(thread).apply_closure_and_empty(_satb_cl);
132 }
133 };
134
135 // Like CLDToOopClosure, but clears has_modified_oops, so that we can record modified CLDs during traversal
136 // and remark them later during final-traversal.
137 class ShenandoahMarkCLDClosure : public CLDClosure {
138 private:
139 OopClosure* _cl;
140 public:
141 ShenandoahMarkCLDClosure(OopClosure* cl) : _cl(cl) {}
142 void do_cld(ClassLoaderData* cld) {
143 cld->oops_do(_cl, ClassLoaderData::_claim_strong, true);
144 }
145 };
146
147 // Like CLDToOopClosure, but only process modified CLDs
148 class ShenandoahRemarkCLDClosure : public CLDClosure {
149 private:
150 OopClosure* _cl;
151 public:
152 ShenandoahRemarkCLDClosure(OopClosure* cl) : _cl(cl) {}
153 void do_cld(ClassLoaderData* cld) {
154 if (cld->has_modified_oops()) {
155 cld->oops_do(_cl, ClassLoaderData::_claim_strong, true);
156 }
157 }
158 };
159
160 class ShenandoahInitTraversalCollectionTask : public AbstractGangTask {
161 private:
162 ShenandoahCSetRootScanner* _rp;
163 ShenandoahHeap* _heap;
164
165 public:
166 ShenandoahInitTraversalCollectionTask(ShenandoahCSetRootScanner* rp) :
167 AbstractGangTask("Shenandoah Init Traversal Collection"),
168 _rp(rp),
169 _heap(ShenandoahHeap::heap()) {}
170
171 void work(uint worker_id) {
172 ShenandoahParallelWorkerSession worker_session(worker_id);
173
174 ShenandoahObjToScanQueueSet* queues = _heap->traversal_gc()->task_queues();
175 ShenandoahObjToScanQueue* q = queues->queue(worker_id);
176
177 bool process_refs = _heap->process_references();
178 bool unload_classes = _heap->unload_classes();
179 ReferenceProcessor* rp = NULL;
180 if (process_refs) {
181 rp = _heap->ref_processor();
182 }
183
184 // Step 1: Process ordinary GC roots.
185 {
186 ShenandoahTraversalRootsClosure roots_cl(q, rp);
187 ShenandoahMarkCLDClosure cld_cl(&roots_cl);
188 MarkingCodeBlobClosure code_cl(&roots_cl, CodeBlobToOopClosure::FixRelocations);
189 if (unload_classes) {
190 _rp->roots_do(worker_id, &roots_cl, NULL, &code_cl);
191 } else {
192 _rp->roots_do(worker_id, &roots_cl, &cld_cl, &code_cl);
193 }
194 }
195 }
196 };
197
198 class ShenandoahConcurrentTraversalCollectionTask : public AbstractGangTask {
199 private:
200 ShenandoahTaskTerminator* _terminator;
201 ShenandoahHeap* _heap;
202 public:
203 ShenandoahConcurrentTraversalCollectionTask(ShenandoahTaskTerminator* terminator) :
204 AbstractGangTask("Shenandoah Concurrent Traversal Collection"),
205 _terminator(terminator),
206 _heap(ShenandoahHeap::heap()) {}
207
208 void work(uint worker_id) {
209 ShenandoahConcurrentWorkerSession worker_session(worker_id);
210 ShenandoahSuspendibleThreadSetJoiner stsj(ShenandoahSuspendibleWorkers);
211 ShenandoahTraversalGC* traversal_gc = _heap->traversal_gc();
212
213 // Drain all outstanding work in queues.
214 traversal_gc->main_loop(worker_id, _terminator, true);
215 }
216 };
217
218 class ShenandoahFinalTraversalCollectionTask : public AbstractGangTask {
219 private:
220 ShenandoahAllRootScanner* _rp;
221 ShenandoahTaskTerminator* _terminator;
222 ShenandoahHeap* _heap;
223 public:
224 ShenandoahFinalTraversalCollectionTask(ShenandoahAllRootScanner* rp, ShenandoahTaskTerminator* terminator) :
225 AbstractGangTask("Shenandoah Final Traversal Collection"),
226 _rp(rp),
227 _terminator(terminator),
228 _heap(ShenandoahHeap::heap()) {}
229
230 void work(uint worker_id) {
231 ShenandoahParallelWorkerSession worker_session(worker_id);
232
233 ShenandoahTraversalGC* traversal_gc = _heap->traversal_gc();
234
235 ShenandoahObjToScanQueueSet* queues = traversal_gc->task_queues();
236 ShenandoahObjToScanQueue* q = queues->queue(worker_id);
237
238 bool process_refs = _heap->process_references();
239 bool unload_classes = _heap->unload_classes();
240 ReferenceProcessor* rp = NULL;
241 if (process_refs) {
242 rp = _heap->ref_processor();
243 }
244
245 // Step 0: Drain outstanding SATB queues.
246 // NOTE: we piggy-back draining of remaining thread SATB buffers on the final root scan below.
247 ShenandoahTraversalSATBBufferClosure satb_cl(q);
248 {
249 // Process remaining finished SATB buffers.
250 SATBMarkQueueSet& satb_mq_set = ShenandoahBarrierSet::satb_mark_queue_set();
251 while (satb_mq_set.apply_closure_to_completed_buffer(&satb_cl));
252 // Process remaining threads SATB buffers below.
253 }
254
255 // Step 1: Process GC roots.
256 // For oops in code roots, they are marked, evacuated, enqueued for further traversal,
257 // and the references to the oops are updated during init pause. We only need to rescan
258 // on stack code roots, in case of class unloading is enabled. Otherwise, code roots are
259 // scanned during init traversal or degenerated GC will update them at the end.
260 if (!_heap->is_degenerated_gc_in_progress()) {
261 ShenandoahTraversalRootsClosure roots_cl(q, rp);
262 ShenandoahTraversalSATBThreadsClosure tc(&satb_cl);
263 if (unload_classes) {
264 ShenandoahRemarkCLDClosure remark_cld_cl(&roots_cl);
265 MarkingCodeBlobClosure code_cl(&roots_cl, CodeBlobToOopClosure::FixRelocations);
266 _rp->strong_roots_do(worker_id, &roots_cl, &remark_cld_cl, &code_cl, &tc);
267 } else {
268 CLDToOopClosure cld_cl(&roots_cl, ClassLoaderData::_claim_strong);
269 _rp->roots_do(worker_id, &roots_cl, &cld_cl, NULL, &tc);
270 }
271 } else {
272 ShenandoahTraversalDegenClosure roots_cl(q, rp);
273 ShenandoahTraversalSATBThreadsClosure tc(&satb_cl);
274 if (unload_classes) {
275 ShenandoahRemarkCLDClosure remark_cld_cl(&roots_cl);
276 _rp->strong_roots_do(worker_id, &roots_cl, &remark_cld_cl, NULL, &tc);
277 } else {
278 CLDToOopClosure cld_cl(&roots_cl, ClassLoaderData::_claim_strong);
279 _rp->roots_do(worker_id, &roots_cl, &cld_cl, NULL, &tc);
280 }
281 }
282
283 {
284 ShenandoahWorkerTimingsTracker timer(ShenandoahPhaseTimings::FinishQueues, worker_id);
285
286 // Step 3: Finally drain all outstanding work in queues.
287 traversal_gc->main_loop(worker_id, _terminator, false);
288 }
289
290 }
291 };
292
293 ShenandoahTraversalGC::ShenandoahTraversalGC(ShenandoahHeap* heap, size_t num_regions) :
294 _heap(heap),
295 _task_queues(new ShenandoahObjToScanQueueSet(heap->max_workers())),
296 _traversal_set(ShenandoahHeapRegionSet()) {
297
298 // Traversal does not support concurrent code root scanning
299 FLAG_SET_DEFAULT(ShenandoahConcurrentScanCodeRoots, false);
300
301 uint num_queues = heap->max_workers();
302 for (uint i = 0; i < num_queues; ++i) {
303 ShenandoahObjToScanQueue* task_queue = new ShenandoahObjToScanQueue();
304 task_queue->initialize();
305 _task_queues->register_queue(i, task_queue);
306 }
307 }
308
309 ShenandoahTraversalGC::~ShenandoahTraversalGC() {
310 }
311
312 void ShenandoahTraversalGC::prepare_regions() {
313 size_t num_regions = _heap->num_regions();
314 ShenandoahMarkingContext* const ctx = _heap->marking_context();
315 for (size_t i = 0; i < num_regions; i++) {
316 ShenandoahHeapRegion* region = _heap->get_region(i);
317 if (_heap->is_bitmap_slice_committed(region)) {
318 if (_traversal_set.is_in(i)) {
319 ctx->capture_top_at_mark_start(region);
320 region->clear_live_data();
321 assert(ctx->is_bitmap_clear_range(region->bottom(), region->end()), "bitmap for traversal regions must be cleared");
322 } else {
323 // Everything outside the traversal set is always considered live.
324 ctx->reset_top_at_mark_start(region);
325 }
326 } else {
327 // FreeSet may contain uncommitted empty regions, once they are recommitted,
328 // their TAMS may have old values, so reset them here.
329 ctx->reset_top_at_mark_start(region);
330 }
331 }
332 }
333
334 void ShenandoahTraversalGC::prepare() {
335 {
336 ShenandoahGCPhase phase(ShenandoahPhaseTimings::traversal_gc_make_parsable);
337 _heap->make_parsable(true);
338 }
339
340 if (UseTLAB) {
341 ShenandoahGCPhase phase(ShenandoahPhaseTimings::traversal_gc_resize_tlabs);
342 _heap->resize_tlabs();
343 }
344
345 assert(_heap->marking_context()->is_bitmap_clear(), "need clean mark bitmap");
346 assert(!_heap->marking_context()->is_complete(), "should not be complete");
347
348 // About to choose the collection set, make sure we know which regions are pinned.
349 {
350 ShenandoahGCPhase phase_cleanup(ShenandoahPhaseTimings::traversal_gc_prepare_sync_pinned);
351 _heap->sync_pinned_region_status();
352 }
353
354 ShenandoahCollectionSet* collection_set = _heap->collection_set();
355 {
356 ShenandoahHeapLocker lock(_heap->lock());
357
358 collection_set->clear();
359 assert(collection_set->count() == 0, "collection set not clear");
360
361 // Find collection set
362 _heap->heuristics()->choose_collection_set(collection_set);
363 prepare_regions();
364
365 // Rebuild free set
366 _heap->free_set()->rebuild();
367 }
368
369 log_info(gc, ergo)("Collectable Garbage: " SIZE_FORMAT "%s, " SIZE_FORMAT "%s CSet, " SIZE_FORMAT " CSet regions",
370 byte_size_in_proper_unit(collection_set->garbage()), proper_unit_for_byte_size(collection_set->garbage()),
371 byte_size_in_proper_unit(collection_set->live_data()), proper_unit_for_byte_size(collection_set->live_data()),
372 collection_set->count());
373 }
374
375 void ShenandoahTraversalGC::init_traversal_collection() {
376 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "STW traversal GC");
377
378 if (ShenandoahVerify) {
379 _heap->verifier()->verify_before_traversal();
380 }
381
382 if (VerifyBeforeGC) {
383 Universe::verify();
384 }
385
386 {
387 ShenandoahGCPhase phase_prepare(ShenandoahPhaseTimings::traversal_gc_prepare);
388 prepare();
389 }
390
391 _heap->set_concurrent_traversal_in_progress(true);
392 _heap->set_has_forwarded_objects(true);
393
394 bool process_refs = _heap->process_references();
395 if (process_refs) {
396 ReferenceProcessor* rp = _heap->ref_processor();
397 rp->enable_discovery(true /*verify_no_refs*/);
398 rp->setup_policy(_heap->soft_ref_policy()->should_clear_all_soft_refs());
399 }
400
401 {
402 ShenandoahGCPhase phase_work(ShenandoahPhaseTimings::init_traversal_gc_work);
403 assert(_task_queues->is_empty(), "queues must be empty before traversal GC");
404 TASKQUEUE_STATS_ONLY(_task_queues->reset_taskqueue_stats());
405
406 #if COMPILER2_OR_JVMCI
407 DerivedPointerTable::clear();
408 #endif
409
410 {
411 uint nworkers = _heap->workers()->active_workers();
412 task_queues()->reserve(nworkers);
413 ShenandoahCSetRootScanner rp(nworkers, ShenandoahPhaseTimings::init_traversal_gc_work);
414 ShenandoahInitTraversalCollectionTask traversal_task(&rp);
415 _heap->workers()->run_task(&traversal_task);
416 }
417
418 #if COMPILER2_OR_JVMCI
419 DerivedPointerTable::update_pointers();
420 #endif
421 }
422
423 if (ShenandoahPacing) {
424 _heap->pacer()->setup_for_traversal();
425 }
426 }
427
428 void ShenandoahTraversalGC::main_loop(uint w, ShenandoahTaskTerminator* t, bool sts_yield) {
429 ShenandoahObjToScanQueue* q = task_queues()->queue(w);
430
431 // Initialize live data.
432 jushort* ld = _heap->get_liveness_cache(w);
433
434 ReferenceProcessor* rp = NULL;
435 if (_heap->process_references()) {
436 rp = _heap->ref_processor();
437 }
438 {
439 if (!_heap->is_degenerated_gc_in_progress()) {
440 if (_heap->unload_classes()) {
441 if (ShenandoahStringDedup::is_enabled()) {
442 ShenandoahTraversalMetadataDedupClosure cl(q, rp);
443 main_loop_work<ShenandoahTraversalMetadataDedupClosure>(&cl, ld, w, t, sts_yield);
444 } else {
445 ShenandoahTraversalMetadataClosure cl(q, rp);
446 main_loop_work<ShenandoahTraversalMetadataClosure>(&cl, ld, w, t, sts_yield);
447 }
448 } else {
449 if (ShenandoahStringDedup::is_enabled()) {
450 ShenandoahTraversalDedupClosure cl(q, rp);
451 main_loop_work<ShenandoahTraversalDedupClosure>(&cl, ld, w, t, sts_yield);
452 } else {
453 ShenandoahTraversalClosure cl(q, rp);
454 main_loop_work<ShenandoahTraversalClosure>(&cl, ld, w, t, sts_yield);
455 }
456 }
457 } else {
458 if (_heap->unload_classes()) {
459 if (ShenandoahStringDedup::is_enabled()) {
460 ShenandoahTraversalMetadataDedupDegenClosure cl(q, rp);
461 main_loop_work<ShenandoahTraversalMetadataDedupDegenClosure>(&cl, ld, w, t, sts_yield);
462 } else {
463 ShenandoahTraversalMetadataDegenClosure cl(q, rp);
464 main_loop_work<ShenandoahTraversalMetadataDegenClosure>(&cl, ld, w, t, sts_yield);
465 }
466 } else {
467 if (ShenandoahStringDedup::is_enabled()) {
468 ShenandoahTraversalDedupDegenClosure cl(q, rp);
469 main_loop_work<ShenandoahTraversalDedupDegenClosure>(&cl, ld, w, t, sts_yield);
470 } else {
471 ShenandoahTraversalDegenClosure cl(q, rp);
472 main_loop_work<ShenandoahTraversalDegenClosure>(&cl, ld, w, t, sts_yield);
473 }
474 }
475 }
476 }
477
478 _heap->flush_liveness_cache(w);
479 }
480
481 template <class T>
482 void ShenandoahTraversalGC::main_loop_work(T* cl, jushort* live_data, uint worker_id, ShenandoahTaskTerminator* terminator, bool sts_yield) {
483 ShenandoahObjToScanQueueSet* queues = task_queues();
484 ShenandoahObjToScanQueue* q = queues->queue(worker_id);
485 ShenandoahConcurrentMark* conc_mark = _heap->concurrent_mark();
486
487 uintx stride = ShenandoahMarkLoopStride;
488
489 ShenandoahMarkTask task;
490
491 // Process outstanding queues, if any.
492 q = queues->claim_next();
493 while (q != NULL) {
494 if (_heap->check_cancelled_gc_and_yield(sts_yield)) {
495 return;
496 }
497
498 for (uint i = 0; i < stride; i++) {
499 if (q->pop(task)) {
500 conc_mark->do_task<T>(q, cl, live_data, &task);
501 } else {
502 assert(q->is_empty(), "Must be empty");
503 q = queues->claim_next();
504 break;
505 }
506 }
507 }
508
509 if (check_and_handle_cancelled_gc(terminator, sts_yield)) return;
510
511 // Normal loop.
512 q = queues->queue(worker_id);
513
514 ShenandoahTraversalSATBBufferClosure drain_satb(q);
515 SATBMarkQueueSet& satb_mq_set = ShenandoahBarrierSet::satb_mark_queue_set();
516
517 while (true) {
518 if (check_and_handle_cancelled_gc(terminator, sts_yield)) return;
519
520 while (satb_mq_set.completed_buffers_num() > 0) {
521 satb_mq_set.apply_closure_to_completed_buffer(&drain_satb);
522 }
523
524 uint work = 0;
525 for (uint i = 0; i < stride; i++) {
526 if (q->pop(task) ||
527 queues->steal(worker_id, task)) {
528 conc_mark->do_task<T>(q, cl, live_data, &task);
529 work++;
530 } else {
531 break;
532 }
533 }
534
535 if (work == 0) {
536 // No more work, try to terminate
537 ShenandoahSuspendibleThreadSetLeaver stsl(sts_yield && ShenandoahSuspendibleWorkers);
538 ShenandoahTerminatorTerminator tt(_heap);
539
540 if (terminator->offer_termination(&tt)) return;
541 }
542 }
543 }
544
545 bool ShenandoahTraversalGC::check_and_handle_cancelled_gc(ShenandoahTaskTerminator* terminator, bool sts_yield) {
546 if (_heap->cancelled_gc()) {
547 return true;
548 }
549 return false;
550 }
551
552 void ShenandoahTraversalGC::concurrent_traversal_collection() {
553 ShenandoahGCPhase phase_work(ShenandoahPhaseTimings::conc_traversal);
554 if (!_heap->cancelled_gc()) {
555 uint nworkers = _heap->workers()->active_workers();
556 task_queues()->reserve(nworkers);
557
558 ShenandoahTaskTerminator terminator(nworkers, task_queues());
559 ShenandoahConcurrentTraversalCollectionTask task(&terminator);
560 _heap->workers()->run_task(&task);
561 }
562
563 if (!_heap->cancelled_gc() && ShenandoahPreclean && _heap->process_references()) {
564 preclean_weak_refs();
565 }
566 }
567
568 void ShenandoahTraversalGC::final_traversal_collection() {
569 if (!_heap->cancelled_gc()) {
570 #if COMPILER2_OR_JVMCI
571 DerivedPointerTable::clear();
572 #endif
573 ShenandoahGCPhase phase_work(ShenandoahPhaseTimings::final_traversal_gc_work);
574 uint nworkers = _heap->workers()->active_workers();
575 task_queues()->reserve(nworkers);
576
577 // Finish traversal
578 ShenandoahAllRootScanner rp(nworkers, ShenandoahPhaseTimings::final_traversal_gc_work);
579 ShenandoahTaskTerminator terminator(nworkers, task_queues());
580 ShenandoahFinalTraversalCollectionTask task(&rp, &terminator);
581 _heap->workers()->run_task(&task);
582 #if COMPILER2_OR_JVMCI
583 DerivedPointerTable::update_pointers();
584 #endif
585 }
586
587 if (!_heap->cancelled_gc() && _heap->process_references()) {
588 weak_refs_work();
589 }
590
591 if (!_heap->cancelled_gc()) {
592 assert(_task_queues->is_empty(), "queues must be empty after traversal GC");
593 TASKQUEUE_STATS_ONLY(_task_queues->print_taskqueue_stats());
594 TASKQUEUE_STATS_ONLY(_task_queues->reset_taskqueue_stats());
595
596 // No more marking expected
597 _heap->set_concurrent_traversal_in_progress(false);
598 _heap->mark_complete_marking_context();
599
600 // A rare case, TLAB/GCLAB is initialized from an empty region without
601 // any live data, the region can be trashed and may be uncommitted in later code,
602 // that results the TLAB/GCLAB not usable. Retire them here.
603 _heap->make_parsable(true);
604
605 _heap->parallel_cleaning(false);
606 fixup_roots();
607
608 _heap->set_has_forwarded_objects(false);
609
610 // Resize metaspace
611 MetaspaceGC::compute_new_size();
612
613 // Need to see that pinned region status is updated: newly pinned regions must not
614 // be trashed. New unpinned regions should be trashed.
615 {
616 ShenandoahGCPhase phase_cleanup(ShenandoahPhaseTimings::traversal_gc_sync_pinned);
617 _heap->sync_pinned_region_status();
618 }
619
620 // Still good? We can now trash the cset, and make final verification
621 {
622 ShenandoahGCPhase phase_cleanup(ShenandoahPhaseTimings::traversal_gc_cleanup);
623 ShenandoahHeapLocker lock(_heap->lock());
624
625 // Trash everything
626 // Clear immediate garbage regions.
627 size_t num_regions = _heap->num_regions();
628
629 ShenandoahHeapRegionSet* traversal_regions = traversal_set();
630 ShenandoahFreeSet* free_regions = _heap->free_set();
631 ShenandoahMarkingContext* const ctx = _heap->marking_context();
632 free_regions->clear();
633 for (size_t i = 0; i < num_regions; i++) {
634 ShenandoahHeapRegion* r = _heap->get_region(i);
635 bool not_allocated = ctx->top_at_mark_start(r) == r->top();
636
637 bool candidate = traversal_regions->is_in(r) && !r->has_live() && not_allocated;
638 if (r->is_humongous_start() && candidate) {
639 // Trash humongous.
640 HeapWord* humongous_obj = r->bottom();
641 assert(!ctx->is_marked(oop(humongous_obj)), "must not be marked");
642 r->make_trash_immediate();
643 while (i + 1 < num_regions && _heap->get_region(i + 1)->is_humongous_continuation()) {
644 i++;
645 r = _heap->get_region(i);
646 assert(r->is_humongous_continuation(), "must be humongous continuation");
647 r->make_trash_immediate();
648 }
649 } else if (!r->is_empty() && candidate) {
650 // Trash regular.
651 assert(!r->is_humongous(), "handled above");
652 assert(!r->is_trash(), "must not already be trashed");
653 r->make_trash_immediate();
654 }
655 }
656 _heap->collection_set()->clear();
657 _heap->free_set()->rebuild();
658 reset();
659 }
660
661 assert(_task_queues->is_empty(), "queues must be empty after traversal GC");
662 assert(!_heap->cancelled_gc(), "must not be cancelled when getting out here");
663
664 if (ShenandoahVerify) {
665 _heap->verifier()->verify_after_traversal();
666 }
667 #ifdef ASSERT
668 else {
669 verify_roots_after_gc();
670 }
671 #endif
672
673 if (VerifyAfterGC) {
674 Universe::verify();
675 }
676 }
677 }
678
679 class ShenandoahVerifyAfterGC : public OopClosure {
680 private:
681 template <class T>
682 void do_oop_work(T* p) {
683 T o = RawAccess<>::oop_load(p);
684 if (!CompressedOops::is_null(o)) {
685 oop obj = CompressedOops::decode_not_null(o);
686 shenandoah_assert_correct(p, obj);
687 shenandoah_assert_not_in_cset_except(p, obj, ShenandoahHeap::heap()->cancelled_gc());
688 shenandoah_assert_not_forwarded(p, obj);
689 }
690 }
691
692 public:
693 void do_oop(narrowOop* p) { do_oop_work(p); }
694 void do_oop(oop* p) { do_oop_work(p); }
695 };
696
697 void ShenandoahTraversalGC::verify_roots_after_gc() {
698 ShenandoahRootVerifier verifier;
699 ShenandoahVerifyAfterGC cl;
700 verifier.oops_do(&cl);
701 }
702
703 class ShenandoahTraversalFixRootsClosure : public OopClosure {
704 private:
705 template <class T>
706 inline void do_oop_work(T* p) {
707 T o = RawAccess<>::oop_load(p);
708 if (!CompressedOops::is_null(o)) {
709 oop obj = CompressedOops::decode_not_null(o);
710 oop forw = ShenandoahBarrierSet::resolve_forwarded_not_null(obj);
711 if (obj != forw) {
712 RawAccess<IS_NOT_NULL>::oop_store(p, forw);
713 }
714 }
715 }
716
717 public:
718 inline void do_oop(oop* p) { do_oop_work(p); }
719 inline void do_oop(narrowOop* p) { do_oop_work(p); }
720 };
721
722 class ShenandoahTraversalFixRootsTask : public AbstractGangTask {
723 private:
724 ShenandoahRootUpdater* _rp;
725
726 public:
727 ShenandoahTraversalFixRootsTask(ShenandoahRootUpdater* rp) :
728 AbstractGangTask("Shenandoah traversal fix roots"),
729 _rp(rp) {
730 assert(ShenandoahHeap::heap()->has_forwarded_objects(), "Must be");
731 }
732
733 void work(uint worker_id) {
734 ShenandoahParallelWorkerSession worker_session(worker_id);
735 ShenandoahTraversalFixRootsClosure cl;
736 ShenandoahForwardedIsAliveClosure is_alive;
737 _rp->roots_do(worker_id, &is_alive, &cl);
738 }
739 };
740
741 void ShenandoahTraversalGC::fixup_roots() {
742 #if COMPILER2_OR_JVMCI
743 DerivedPointerTable::clear();
744 #endif
745 ShenandoahRootUpdater rp(_heap->workers()->active_workers(), ShenandoahPhaseTimings::final_traversal_update_roots);
746 ShenandoahTraversalFixRootsTask update_roots_task(&rp);
747 _heap->workers()->run_task(&update_roots_task);
748 #if COMPILER2_OR_JVMCI
749 DerivedPointerTable::update_pointers();
750 #endif
751 }
752
753 void ShenandoahTraversalGC::reset() {
754 _task_queues->clear();
755 }
756
757 ShenandoahObjToScanQueueSet* ShenandoahTraversalGC::task_queues() {
758 return _task_queues;
759 }
760
761 class ShenandoahTraversalCancelledGCYieldClosure : public YieldClosure {
762 private:
763 ShenandoahHeap* const _heap;
764 public:
765 ShenandoahTraversalCancelledGCYieldClosure() : _heap(ShenandoahHeap::heap()) {};
766 virtual bool should_return() { return _heap->cancelled_gc(); }
767 };
768
769 class ShenandoahTraversalPrecleanCompleteGCClosure : public VoidClosure {
770 public:
771 void do_void() {
772 ShenandoahHeap* sh = ShenandoahHeap::heap();
773 ShenandoahTraversalGC* traversal_gc = sh->traversal_gc();
774 assert(sh->process_references(), "why else would we be here?");
775 ShenandoahTaskTerminator terminator(1, traversal_gc->task_queues());
776 shenandoah_assert_rp_isalive_installed();
777 traversal_gc->main_loop((uint) 0, &terminator, true);
778 }
779 };
780
781 class ShenandoahTraversalKeepAliveUpdateClosure : public OopClosure {
782 private:
783 ShenandoahObjToScanQueue* _queue;
784 Thread* _thread;
785 ShenandoahTraversalGC* _traversal_gc;
786 ShenandoahMarkingContext* const _mark_context;
787
788 template <class T>
789 inline void do_oop_work(T* p) {
790 _traversal_gc->process_oop<T, false /* string dedup */, false /* degen */, true /* atomic update */>(p, _thread, _queue, _mark_context);
791 }
792
793 public:
794 ShenandoahTraversalKeepAliveUpdateClosure(ShenandoahObjToScanQueue* q) :
795 _queue(q), _thread(Thread::current()),
796 _traversal_gc(ShenandoahHeap::heap()->traversal_gc()),
797 _mark_context(ShenandoahHeap::heap()->marking_context()) {}
798
799 void do_oop(narrowOop* p) { do_oop_work(p); }
800 void do_oop(oop* p) { do_oop_work(p); }
801 };
802
803 class ShenandoahTraversalKeepAliveUpdateDegenClosure : public OopClosure {
804 private:
805 ShenandoahObjToScanQueue* _queue;
806 Thread* _thread;
807 ShenandoahTraversalGC* _traversal_gc;
808 ShenandoahMarkingContext* const _mark_context;
809
810 template <class T>
811 inline void do_oop_work(T* p) {
812 _traversal_gc->process_oop<T, false /* string dedup */, true /* degen */, false /* atomic update */>(p, _thread, _queue, _mark_context);
813 }
814
815 public:
816 ShenandoahTraversalKeepAliveUpdateDegenClosure(ShenandoahObjToScanQueue* q) :
817 _queue(q), _thread(Thread::current()),
818 _traversal_gc(ShenandoahHeap::heap()->traversal_gc()),
819 _mark_context(ShenandoahHeap::heap()->marking_context()) {}
820
821 void do_oop(narrowOop* p) { do_oop_work(p); }
822 void do_oop(oop* p) { do_oop_work(p); }
823 };
824
825 class ShenandoahTraversalSingleThreadKeepAliveUpdateClosure : public OopClosure {
826 private:
827 ShenandoahObjToScanQueue* _queue;
828 Thread* _thread;
829 ShenandoahTraversalGC* _traversal_gc;
830 ShenandoahMarkingContext* const _mark_context;
831
832 template <class T>
833 inline void do_oop_work(T* p) {
834 _traversal_gc->process_oop<T, false /* string dedup */, false /* degen */, true /* atomic update */>(p, _thread, _queue, _mark_context);
835 }
836
837 public:
838 ShenandoahTraversalSingleThreadKeepAliveUpdateClosure(ShenandoahObjToScanQueue* q) :
839 _queue(q), _thread(Thread::current()),
840 _traversal_gc(ShenandoahHeap::heap()->traversal_gc()),
841 _mark_context(ShenandoahHeap::heap()->marking_context()) {}
842
843 void do_oop(narrowOop* p) { do_oop_work(p); }
844 void do_oop(oop* p) { do_oop_work(p); }
845 };
846
847 class ShenandoahTraversalSingleThreadKeepAliveUpdateDegenClosure : public OopClosure {
848 private:
849 ShenandoahObjToScanQueue* _queue;
850 Thread* _thread;
851 ShenandoahTraversalGC* _traversal_gc;
852 ShenandoahMarkingContext* const _mark_context;
853
854 template <class T>
855 inline void do_oop_work(T* p) {
856 _traversal_gc->process_oop<T, false /* string dedup */, true /* degen */, false /* atomic update */>(p, _thread, _queue, _mark_context);
857 }
858
859 public:
860 ShenandoahTraversalSingleThreadKeepAliveUpdateDegenClosure(ShenandoahObjToScanQueue* q) :
861 _queue(q), _thread(Thread::current()),
862 _traversal_gc(ShenandoahHeap::heap()->traversal_gc()),
863 _mark_context(ShenandoahHeap::heap()->marking_context()) {}
864
865 void do_oop(narrowOop* p) { do_oop_work(p); }
866 void do_oop(oop* p) { do_oop_work(p); }
867 };
868
869 class ShenandoahTraversalPrecleanTask : public AbstractGangTask {
870 private:
871 ReferenceProcessor* _rp;
872
873 public:
874 ShenandoahTraversalPrecleanTask(ReferenceProcessor* rp) :
875 AbstractGangTask("Precleaning task"),
876 _rp(rp) {}
877
878 void work(uint worker_id) {
879 assert(worker_id == 0, "The code below is single-threaded, only one worker is expected");
880 ShenandoahParallelWorkerSession worker_session(worker_id);
881 ShenandoahSuspendibleThreadSetJoiner stsj(ShenandoahSuspendibleWorkers);
882
883 ShenandoahHeap* sh = ShenandoahHeap::heap();
884
885 ShenandoahObjToScanQueue* q = sh->traversal_gc()->task_queues()->queue(worker_id);
886
887 ShenandoahForwardedIsAliveClosure is_alive;
888 ShenandoahTraversalCancelledGCYieldClosure yield;
889 ShenandoahTraversalPrecleanCompleteGCClosure complete_gc;
890 ShenandoahTraversalKeepAliveUpdateClosure keep_alive(q);
891 ResourceMark rm;
892 _rp->preclean_discovered_references(&is_alive, &keep_alive,
893 &complete_gc, &yield,
894 NULL);
895 }
896 };
897
898 void ShenandoahTraversalGC::preclean_weak_refs() {
899 // Pre-cleaning weak references before diving into STW makes sense at the
900 // end of concurrent mark. This will filter out the references which referents
901 // are alive. Note that ReferenceProcessor already filters out these on reference
902 // discovery, and the bulk of work is done here. This phase processes leftovers
903 // that missed the initial filtering, i.e. when referent was marked alive after
904 // reference was discovered by RP.
905
906 assert(_heap->process_references(), "sanity");
907 assert(!_heap->is_degenerated_gc_in_progress(), "must be in concurrent non-degenerated phase");
908
909 // Shortcut if no references were discovered to avoid winding up threads.
910 ReferenceProcessor* rp = _heap->ref_processor();
911 if (!rp->has_discovered_references()) {
912 return;
913 }
914
915 ReferenceProcessorMTDiscoveryMutator fix_mt_discovery(rp, false);
916
917 shenandoah_assert_rp_isalive_not_installed();
918 ShenandoahForwardedIsAliveClosure is_alive;
919 ReferenceProcessorIsAliveMutator fix_isalive(rp, &is_alive);
920
921 assert(task_queues()->is_empty(), "Should be empty");
922
923 // Execute precleaning in the worker thread: it will give us GCLABs, String dedup
924 // queues and other goodies. When upstream ReferenceProcessor starts supporting
925 // parallel precleans, we can extend this to more threads.
926 ShenandoahPushWorkerScope scope(_heap->workers(), 1, /* check_workers = */ false);
927
928 WorkGang* workers = _heap->workers();
929 uint nworkers = workers->active_workers();
930 assert(nworkers == 1, "This code uses only a single worker");
931 task_queues()->reserve(nworkers);
932
933 ShenandoahTraversalPrecleanTask task(rp);
934 workers->run_task(&task);
935
936 assert(_heap->cancelled_gc() || task_queues()->is_empty(), "Should be empty");
937 }
938
939 // Weak Reference Closures
940 class ShenandoahTraversalDrainMarkingStackClosure: public VoidClosure {
941 uint _worker_id;
942 ShenandoahTaskTerminator* _terminator;
943 bool _reset_terminator;
944
945 public:
946 ShenandoahTraversalDrainMarkingStackClosure(uint worker_id, ShenandoahTaskTerminator* t, bool reset_terminator = false):
947 _worker_id(worker_id),
948 _terminator(t),
949 _reset_terminator(reset_terminator) {
950 }
951
952 void do_void() {
953 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
954
955 ShenandoahHeap* sh = ShenandoahHeap::heap();
956 ShenandoahTraversalGC* traversal_gc = sh->traversal_gc();
957 assert(sh->process_references(), "why else would we be here?");
958 shenandoah_assert_rp_isalive_installed();
959
960 traversal_gc->main_loop(_worker_id, _terminator, false);
961
962 if (_reset_terminator) {
963 _terminator->reset_for_reuse();
964 }
965 }
966 };
967
968 class ShenandoahTraversalSingleThreadedDrainMarkingStackClosure: public VoidClosure {
969 uint _worker_id;
970 ShenandoahTaskTerminator* _terminator;
971 bool _reset_terminator;
972
973 public:
974 ShenandoahTraversalSingleThreadedDrainMarkingStackClosure(uint worker_id, ShenandoahTaskTerminator* t, bool reset_terminator = false):
975 _worker_id(worker_id),
976 _terminator(t),
977 _reset_terminator(reset_terminator) {
978 }
979
980 void do_void() {
981 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
982
983 ShenandoahHeap* sh = ShenandoahHeap::heap();
984 ShenandoahTraversalGC* traversal_gc = sh->traversal_gc();
985 assert(sh->process_references(), "why else would we be here?");
986 shenandoah_assert_rp_isalive_installed();
987
988 traversal_gc->main_loop(_worker_id, _terminator, false);
989
990 if (_reset_terminator) {
991 _terminator->reset_for_reuse();
992 }
993 }
994 };
995
996 void ShenandoahTraversalGC::weak_refs_work() {
997 assert(_heap->process_references(), "sanity");
998
999 ShenandoahPhaseTimings::Phase phase_root = ShenandoahPhaseTimings::weakrefs;
1000
1001 ShenandoahGCPhase phase(phase_root);
1002
1003 ReferenceProcessor* rp = _heap->ref_processor();
1004
1005 // NOTE: We cannot shortcut on has_discovered_references() here, because
1006 // we will miss marking JNI Weak refs then, see implementation in
1007 // ReferenceProcessor::process_discovered_references.
1008 weak_refs_work_doit();
1009
1010 rp->verify_no_references_recorded();
1011 assert(!rp->discovery_enabled(), "Post condition");
1012
1013 }
1014
1015 class ShenandoahTraversalRefProcTaskProxy : public AbstractGangTask {
1016 private:
1017 AbstractRefProcTaskExecutor::ProcessTask& _proc_task;
1018 ShenandoahTaskTerminator* _terminator;
1019
1020 public:
1021 ShenandoahTraversalRefProcTaskProxy(AbstractRefProcTaskExecutor::ProcessTask& proc_task,
1022 ShenandoahTaskTerminator* t) :
1023 AbstractGangTask("Process reference objects in parallel"),
1024 _proc_task(proc_task),
1025 _terminator(t) {
1026 }
1027
1028 void work(uint worker_id) {
1029 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
1030 ShenandoahHeap* heap = ShenandoahHeap::heap();
1031 ShenandoahTraversalDrainMarkingStackClosure complete_gc(worker_id, _terminator);
1032
1033 ShenandoahForwardedIsAliveClosure is_alive;
1034 if (!heap->is_degenerated_gc_in_progress()) {
1035 ShenandoahTraversalKeepAliveUpdateClosure keep_alive(heap->traversal_gc()->task_queues()->queue(worker_id));
1036 _proc_task.work(worker_id, is_alive, keep_alive, complete_gc);
1037 } else {
1038 ShenandoahTraversalKeepAliveUpdateDegenClosure keep_alive(heap->traversal_gc()->task_queues()->queue(worker_id));
1039 _proc_task.work(worker_id, is_alive, keep_alive, complete_gc);
1040 }
1041 }
1042 };
1043
1044 class ShenandoahTraversalRefProcTaskExecutor : public AbstractRefProcTaskExecutor {
1045 private:
1046 WorkGang* _workers;
1047
1048 public:
1049 ShenandoahTraversalRefProcTaskExecutor(WorkGang* workers) : _workers(workers) {}
1050
1051 // Executes a task using worker threads.
1052 void execute(ProcessTask& task, uint ergo_workers) {
1053 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
1054
1055 ShenandoahHeap* heap = ShenandoahHeap::heap();
1056 ShenandoahTraversalGC* traversal_gc = heap->traversal_gc();
1057 ShenandoahPushWorkerQueuesScope scope(_workers,
1058 traversal_gc->task_queues(),
1059 ergo_workers,
1060 /* do_check = */ false);
1061 uint nworkers = _workers->active_workers();
1062 traversal_gc->task_queues()->reserve(nworkers);
1063 ShenandoahTaskTerminator terminator(nworkers, traversal_gc->task_queues());
1064 ShenandoahTraversalRefProcTaskProxy proc_task_proxy(task, &terminator);
1065 _workers->run_task(&proc_task_proxy);
1066 }
1067 };
1068
1069 void ShenandoahTraversalGC::weak_refs_work_doit() {
1070 ReferenceProcessor* rp = _heap->ref_processor();
1071
1072 ShenandoahPhaseTimings::Phase phase_process = ShenandoahPhaseTimings::weakrefs_process;
1073
1074 shenandoah_assert_rp_isalive_not_installed();
1075 ShenandoahForwardedIsAliveClosure is_alive;
1076 ReferenceProcessorIsAliveMutator fix_isalive(rp, &is_alive);
1077
1078 WorkGang* workers = _heap->workers();
1079 uint nworkers = workers->active_workers();
1080
1081 rp->setup_policy(_heap->soft_ref_policy()->should_clear_all_soft_refs());
1082 rp->set_active_mt_degree(nworkers);
1083
1084 assert(task_queues()->is_empty(), "Should be empty");
1085
1086 // complete_gc and keep_alive closures instantiated here are only needed for
1087 // single-threaded path in RP. They share the queue 0 for tracking work, which
1088 // simplifies implementation. Since RP may decide to call complete_gc several
1089 // times, we need to be able to reuse the terminator.
1090 uint serial_worker_id = 0;
1091 ShenandoahTaskTerminator terminator(1, task_queues());
1092 ShenandoahTraversalSingleThreadedDrainMarkingStackClosure complete_gc(serial_worker_id, &terminator, /* reset_terminator = */ true);
1093 ShenandoahPushWorkerQueuesScope scope(workers, task_queues(), 1, /* do_check = */ false);
1094
1095 ShenandoahTraversalRefProcTaskExecutor executor(workers);
1096
1097 ReferenceProcessorPhaseTimes pt(_heap->gc_timer(), rp->num_queues());
1098 if (!_heap->is_degenerated_gc_in_progress()) {
1099 ShenandoahTraversalSingleThreadKeepAliveUpdateClosure keep_alive(task_queues()->queue(serial_worker_id));
1100 rp->process_discovered_references(&is_alive, &keep_alive,
1101 &complete_gc, &executor,
1102 &pt);
1103 } else {
1104 ShenandoahTraversalSingleThreadKeepAliveUpdateDegenClosure keep_alive(task_queues()->queue(serial_worker_id));
1105 rp->process_discovered_references(&is_alive, &keep_alive,
1106 &complete_gc, &executor,
1107 &pt);
1108 }
1109
1110 pt.print_all_references();
1111 assert(task_queues()->is_empty() || _heap->cancelled_gc(), "Should be empty");
1112 }