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 "compiler/oopMap.hpp"
28 #include "gc/shared/continuationGCSupport.hpp"
29 #include "gc/shared/gcTraceTime.inline.hpp"
30 #include "gc/shared/preservedMarks.inline.hpp"
31 #include "gc/shared/tlab_globals.hpp"
32 #include "gc/shared/workerThread.hpp"
33 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
34 #include "gc/shenandoah/shenandoahConcurrentGC.hpp"
35 #include "gc/shenandoah/shenandoahCollectionSet.hpp"
36 #include "gc/shenandoah/shenandoahFreeSet.hpp"
37 #include "gc/shenandoah/shenandoahFullGC.hpp"
38 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
39 #include "gc/shenandoah/shenandoahMark.inline.hpp"
40 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
41 #include "gc/shenandoah/shenandoahHeapRegionSet.hpp"
42 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
43 #include "gc/shenandoah/shenandoahHeapRegion.inline.hpp"
44 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"
45 #include "gc/shenandoah/shenandoahMetrics.hpp"
46 #include "gc/shenandoah/shenandoahOopClosures.inline.hpp"
47 #include "gc/shenandoah/shenandoahReferenceProcessor.hpp"
48 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
49 #include "gc/shenandoah/shenandoahSTWMark.hpp"
50 #include "gc/shenandoah/shenandoahUtils.hpp"
204 // Coming out of Full GC, we would not have any forwarded objects.
205 // This also prevents resolves with fwdptr from kicking in while adjusting pointers in phase3.
206 heap->set_has_forwarded_objects(false);
207
208 heap->set_full_gc_move_in_progress(true);
209
210 // Setup workers for the rest
211 OrderAccess::fence();
212
213 // Initialize worker slices
214 ShenandoahHeapRegionSet** worker_slices = NEW_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, heap->max_workers(), mtGC);
215 for (uint i = 0; i < heap->max_workers(); i++) {
216 worker_slices[i] = new ShenandoahHeapRegionSet();
217 }
218
219 {
220 // The rest of code performs region moves, where region status is undefined
221 // until all phases run together.
222 ShenandoahHeapLocker lock(heap->lock());
223
224 phase2_calculate_target_addresses(worker_slices);
225
226 OrderAccess::fence();
227
228 phase3_update_references();
229
230 phase4_compact_objects(worker_slices);
231 }
232
233 {
234 // Epilogue
235 _preserved_marks->restore(heap->workers());
236 _preserved_marks->reclaim();
237 }
238
239 // Resize metaspace
240 MetaspaceGC::compute_new_size();
241
242 // Free worker slices
243 for (uint i = 0; i < heap->max_workers(); i++) {
244 delete worker_slices[i];
245 }
246 FREE_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, worker_slices);
247
248 heap->set_full_gc_move_in_progress(false);
249 heap->set_full_gc_in_progress(false);
250
251 if (ShenandoahVerify) {
252 heap->verifier()->verify_after_fullgc();
253 }
254
255 if (VerifyAfterGC) {
256 Universe::verify();
278 void ShenandoahFullGC::phase1_mark_heap() {
279 GCTraceTime(Info, gc, phases) time("Phase 1: Mark live objects", _gc_timer);
280 ShenandoahGCPhase mark_phase(ShenandoahPhaseTimings::full_gc_mark);
281
282 ShenandoahHeap* heap = ShenandoahHeap::heap();
283
284 ShenandoahPrepareForMarkClosure cl;
285 heap->heap_region_iterate(&cl);
286
287 heap->set_unload_classes(heap->heuristics()->can_unload_classes());
288
289 ShenandoahReferenceProcessor* rp = heap->ref_processor();
290 // enable ("weak") refs discovery
291 rp->set_soft_reference_policy(true); // forcefully purge all soft references
292
293 ShenandoahSTWMark mark(true /*full_gc*/);
294 mark.mark();
295 heap->parallel_cleaning(true /* full_gc */);
296 }
297
298 class ShenandoahPrepareForCompactionObjectClosure : public ObjectClosure {
299 private:
300 PreservedMarks* const _preserved_marks;
301 ShenandoahHeap* const _heap;
302 GrowableArray<ShenandoahHeapRegion*>& _empty_regions;
303 int _empty_regions_pos;
304 ShenandoahHeapRegion* _to_region;
305 ShenandoahHeapRegion* _from_region;
306 HeapWord* _compact_point;
307
308 public:
309 ShenandoahPrepareForCompactionObjectClosure(PreservedMarks* preserved_marks,
310 GrowableArray<ShenandoahHeapRegion*>& empty_regions,
311 ShenandoahHeapRegion* to_region) :
312 _preserved_marks(preserved_marks),
313 _heap(ShenandoahHeap::heap()),
314 _empty_regions(empty_regions),
315 _empty_regions_pos(0),
316 _to_region(to_region),
317 _from_region(nullptr),
347 ShenandoahHeapRegion* new_to_region;
348 if (_empty_regions_pos < _empty_regions.length()) {
349 new_to_region = _empty_regions.at(_empty_regions_pos);
350 _empty_regions_pos++;
351 } else {
352 // Out of empty region? Compact within the same region.
353 new_to_region = _from_region;
354 }
355
356 assert(new_to_region != _to_region, "must not reuse same to-region");
357 assert(new_to_region != nullptr, "must not be null");
358 _to_region = new_to_region;
359 _compact_point = _to_region->bottom();
360 }
361
362 // Object fits into current region, record new location, if object does not move:
363 assert(_compact_point + obj_size <= _to_region->end(), "must fit");
364 shenandoah_assert_not_forwarded(nullptr, p);
365 if (_compact_point != cast_from_oop<HeapWord*>(p)) {
366 _preserved_marks->push_if_necessary(p, p->mark());
367 p->forward_to(cast_to_oop(_compact_point));
368 }
369 _compact_point += obj_size;
370 }
371 };
372
373 class ShenandoahPrepareForCompactionTask : public WorkerTask {
374 private:
375 PreservedMarksSet* const _preserved_marks;
376 ShenandoahHeap* const _heap;
377 ShenandoahHeapRegionSet** const _worker_slices;
378
379 public:
380 ShenandoahPrepareForCompactionTask(PreservedMarksSet *preserved_marks, ShenandoahHeapRegionSet **worker_slices) :
381 WorkerTask("Shenandoah Prepare For Compaction"),
382 _preserved_marks(preserved_marks),
383 _heap(ShenandoahHeap::heap()), _worker_slices(worker_slices) {
384 }
385
386 static bool is_candidate_region(ShenandoahHeapRegion* r) {
387 // Empty region: get it into the slice to defragment the slice itself.
388 // We could have skipped this without violating correctness, but we really
389 // want to compact all live regions to the start of the heap, which sometimes
390 // means moving them into the fully empty regions.
391 if (r->is_empty()) return true;
392
393 // Can move the region, and this is not the humongous region. Humongous
394 // moves are special cased here, because their moves are handled separately.
395 return r->is_stw_move_allowed() && !r->is_humongous();
396 }
397
398 void work(uint worker_id) {
399 ShenandoahParallelWorkerSession worker_session(worker_id);
400 ShenandoahHeapRegionSet* slice = _worker_slices[worker_id];
401 ShenandoahHeapRegionSetIterator it(slice);
402 ShenandoahHeapRegion* from_region = it.next();
403 // No work?
404 if (from_region == nullptr) {
405 return;
406 }
407
408 // Sliding compaction. Walk all regions in the slice, and compact them.
409 // Remember empty regions and reuse them as needed.
410 ResourceMark rm;
411
412 GrowableArray<ShenandoahHeapRegion*> empty_regions((int)_heap->num_regions());
413
414 ShenandoahPrepareForCompactionObjectClosure cl(_preserved_marks->get(worker_id), empty_regions, from_region);
415
416 while (from_region != nullptr) {
417 assert(is_candidate_region(from_region), "Sanity");
418
419 cl.set_from_region(from_region);
420 if (from_region->has_live()) {
421 _heap->marked_object_iterate(from_region, &cl);
422 }
423
424 // Compacted the region to somewhere else? From-region is empty then.
425 if (!cl.is_compact_same_region()) {
426 empty_regions.append(from_region);
427 }
428 from_region = it.next();
429 }
430 cl.finish_region();
431
432 // Mark all remaining regions as empty
433 for (int pos = cl.empty_regions_pos(); pos < empty_regions.length(); ++pos) {
434 ShenandoahHeapRegion* r = empty_regions.at(pos);
435 r->set_new_top(r->bottom());
436 }
437 }
438 };
439
440 void ShenandoahFullGC::calculate_target_humongous_objects() {
441 ShenandoahHeap* heap = ShenandoahHeap::heap();
442
443 // Compute the new addresses for humongous objects. We need to do this after addresses
444 // for regular objects are calculated, and we know what regions in heap suffix are
445 // available for humongous moves.
446 //
447 // Scan the heap backwards, because we are compacting humongous regions towards the end.
448 // Maintain the contiguous compaction window in [to_begin; to_end), so that we can slide
449 // humongous start there.
450 //
451 // The complication is potential non-movable regions during the scan. If such region is
452 // detected, then sliding restarts towards that non-movable region.
453
454 size_t to_begin = heap->num_regions();
455 size_t to_end = heap->num_regions();
456
457 for (size_t c = heap->num_regions(); c > 0; c--) {
458 ShenandoahHeapRegion *r = heap->get_region(c - 1);
459 if (r->is_humongous_continuation() || (r->new_top() == r->bottom())) {
460 // To-region candidate: record this, and continue scan
461 to_begin = r->index();
462 continue;
463 }
464
465 if (r->is_humongous_start() && r->is_stw_move_allowed()) {
466 // From-region candidate: movable humongous region
467 oop old_obj = cast_to_oop(r->bottom());
468 size_t words_size = old_obj->size();
469 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
470
471 size_t start = to_end - num_regions;
472
473 if (start >= to_begin && start != r->index()) {
474 // Fits into current window, and the move is non-trivial. Record the move then, and continue scan.
475 _preserved_marks->get(0)->push_if_necessary(old_obj, old_obj->mark());
476 old_obj->forward_to(cast_to_oop(heap->get_region(start)->bottom()));
477 to_end = start;
478 continue;
479 }
480 }
481
482 // Failed to fit. Scan starting from current region.
483 to_begin = r->index();
484 to_end = r->index();
485 }
486 }
487
488 class ShenandoahEnsureHeapActiveClosure: public ShenandoahHeapRegionClosure {
489 private:
490 ShenandoahHeap* const _heap;
491
492 public:
493 ShenandoahEnsureHeapActiveClosure() : _heap(ShenandoahHeap::heap()) {}
494 void heap_region_do(ShenandoahHeapRegion* r) {
495 if (r->is_trash()) {
496 r->recycle();
497 }
498 if (r->is_cset()) {
499 r->make_regular_bypass();
500 }
501 if (r->is_empty_uncommitted()) {
502 r->make_committed_bypass();
503 }
504 assert (r->is_committed(), "only committed regions in heap now, see region " SIZE_FORMAT, r->index());
505
506 // Record current region occupancy: this communicates empty regions are free
507 // to the rest of Full GC code.
705 heap->heap_region_iterate(&ecl);
706 }
707
708 // Compute the new addresses for regular objects
709 {
710 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_regular);
711
712 distribute_slices(worker_slices);
713
714 ShenandoahPrepareForCompactionTask task(_preserved_marks, worker_slices);
715 heap->workers()->run_task(&task);
716 }
717
718 // Compute the new addresses for humongous objects
719 {
720 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_humong);
721 calculate_target_humongous_objects();
722 }
723 }
724
725 class ShenandoahAdjustPointersClosure : public MetadataVisitingOopIterateClosure {
726 private:
727 ShenandoahHeap* const _heap;
728 ShenandoahMarkingContext* const _ctx;
729
730 template <class T>
731 inline void do_oop_work(T* p) {
732 T o = RawAccess<>::oop_load(p);
733 if (!CompressedOops::is_null(o)) {
734 oop obj = CompressedOops::decode_not_null(o);
735 assert(_ctx->is_marked(obj), "must be marked");
736 if (obj->is_forwarded()) {
737 oop forw = obj->forwardee();
738 RawAccess<IS_NOT_NULL>::oop_store(p, forw);
739 }
740 }
741 }
742
743 public:
744 ShenandoahAdjustPointersClosure() :
745 _heap(ShenandoahHeap::heap()),
746 _ctx(ShenandoahHeap::heap()->complete_marking_context()) {}
747
748 void do_oop(oop* p) { do_oop_work(p); }
749 void do_oop(narrowOop* p) { do_oop_work(p); }
750 void do_method(Method* m) {}
751 void do_nmethod(nmethod* nm) {}
752 };
753
754 class ShenandoahAdjustPointersObjectClosure : public ObjectClosure {
755 private:
756 ShenandoahHeap* const _heap;
757 ShenandoahAdjustPointersClosure _cl;
758
759 public:
760 ShenandoahAdjustPointersObjectClosure() :
761 _heap(ShenandoahHeap::heap()) {
762 }
763 void do_object(oop p) {
764 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
765 p->oop_iterate(&_cl);
766 }
767 };
768
769 class ShenandoahAdjustPointersTask : public WorkerTask {
770 private:
771 ShenandoahHeap* const _heap;
772 ShenandoahRegionIterator _regions;
773
774 public:
775 ShenandoahAdjustPointersTask() :
776 WorkerTask("Shenandoah Adjust Pointers"),
777 _heap(ShenandoahHeap::heap()) {
778 }
779
780 void work(uint worker_id) {
781 ShenandoahParallelWorkerSession worker_session(worker_id);
782 ShenandoahAdjustPointersObjectClosure obj_cl;
783 ShenandoahHeapRegion* r = _regions.next();
784 while (r != nullptr) {
785 if (!r->is_humongous_continuation() && r->has_live()) {
786 _heap->marked_object_iterate(r, &obj_cl);
787 }
788 r = _regions.next();
789 }
790 }
791 };
792
793 class ShenandoahAdjustRootPointersTask : public WorkerTask {
794 private:
795 ShenandoahRootAdjuster* _rp;
796 PreservedMarksSet* _preserved_marks;
797 public:
798 ShenandoahAdjustRootPointersTask(ShenandoahRootAdjuster* rp, PreservedMarksSet* preserved_marks) :
799 WorkerTask("Shenandoah Adjust Root Pointers"),
800 _rp(rp),
801 _preserved_marks(preserved_marks) {}
802
803 void work(uint worker_id) {
804 ShenandoahParallelWorkerSession worker_session(worker_id);
805 ShenandoahAdjustPointersClosure cl;
806 _rp->roots_do(worker_id, &cl);
807 _preserved_marks->get(worker_id)->adjust_during_full_gc();
808 }
809 };
810
811 void ShenandoahFullGC::phase3_update_references() {
812 GCTraceTime(Info, gc, phases) time("Phase 3: Adjust pointers", _gc_timer);
813 ShenandoahGCPhase adjust_pointer_phase(ShenandoahPhaseTimings::full_gc_adjust_pointers);
814
815 ShenandoahHeap* heap = ShenandoahHeap::heap();
816
817 WorkerThreads* workers = heap->workers();
818 uint nworkers = workers->active_workers();
819 {
820 #if COMPILER2_OR_JVMCI
821 DerivedPointerTable::clear();
822 #endif
823 ShenandoahRootAdjuster rp(nworkers, ShenandoahPhaseTimings::full_gc_adjust_roots);
824 ShenandoahAdjustRootPointersTask task(&rp, _preserved_marks);
825 workers->run_task(&task);
826 #if COMPILER2_OR_JVMCI
827 DerivedPointerTable::update_pointers();
828 #endif
829 }
830
831 ShenandoahAdjustPointersTask adjust_pointers_task;
832 workers->run_task(&adjust_pointers_task);
833 }
834
835 class ShenandoahCompactObjectsClosure : public ObjectClosure {
836 private:
837 ShenandoahHeap* const _heap;
838 uint const _worker_id;
839
840 public:
841 ShenandoahCompactObjectsClosure(uint worker_id) :
842 _heap(ShenandoahHeap::heap()), _worker_id(worker_id) {}
843
844 void do_object(oop p) {
845 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
846 size_t size = p->size();
847 if (p->is_forwarded()) {
848 HeapWord* compact_from = cast_from_oop<HeapWord*>(p);
849 HeapWord* compact_to = cast_from_oop<HeapWord*>(p->forwardee());
850 assert(compact_from != compact_to, "Forwarded object should move");
851 Copy::aligned_conjoint_words(compact_from, compact_to, size);
852 oop new_obj = cast_to_oop(compact_to);
853
854 ContinuationGCSupport::relativize_stack_chunk(new_obj);
855 new_obj->init_mark();
856 }
857 }
858 };
859
860 class ShenandoahCompactObjectsTask : public WorkerTask {
861 private:
862 ShenandoahHeap* const _heap;
863 ShenandoahHeapRegionSet** const _worker_slices;
864
865 public:
866 ShenandoahCompactObjectsTask(ShenandoahHeapRegionSet** worker_slices) :
867 WorkerTask("Shenandoah Compact Objects"),
868 _heap(ShenandoahHeap::heap()),
869 _worker_slices(worker_slices) {
870 }
871
872 void work(uint worker_id) {
873 ShenandoahParallelWorkerSession worker_session(worker_id);
874 ShenandoahHeapRegionSetIterator slice(_worker_slices[worker_id]);
875
876 ShenandoahCompactObjectsClosure cl(worker_id);
877 ShenandoahHeapRegion* r = slice.next();
878 while (r != nullptr) {
879 assert(!r->is_humongous(), "must not get humongous regions here");
880 if (r->has_live()) {
881 _heap->marked_object_iterate(r, &cl);
882 }
883 r->set_top(r->new_top());
884 r = slice.next();
885 }
886 }
887 };
888
889 class ShenandoahPostCompactClosure : public ShenandoahHeapRegionClosure {
890 private:
891 ShenandoahHeap* const _heap;
892 size_t _live;
893
894 public:
895 ShenandoahPostCompactClosure() : _heap(ShenandoahHeap::heap()), _live(0) {
896 _heap->free_set()->clear();
897 }
898
899 void heap_region_do(ShenandoahHeapRegion* r) {
900 assert (!r->is_cset(), "cset regions should have been demoted already");
901
902 // Need to reset the complete-top-at-mark-start pointer here because
903 // the complete marking bitmap is no longer valid. This ensures
904 // size-based iteration in marked_object_iterate().
905 // NOTE: See blurb at ShenandoahMCResetCompleteBitmapTask on why we need to skip
906 // pinned regions.
922 if (r->is_regular() && live == 0) {
923 r->make_trash();
924 }
925
926 // Recycle all trash regions
927 if (r->is_trash()) {
928 live = 0;
929 r->recycle();
930 }
931
932 r->set_live_data(live);
933 r->reset_alloc_metadata();
934 _live += live;
935 }
936
937 size_t get_live() {
938 return _live;
939 }
940 };
941
942 void ShenandoahFullGC::compact_humongous_objects() {
943 // Compact humongous regions, based on their fwdptr objects.
944 //
945 // This code is serial, because doing the in-slice parallel sliding is tricky. In most cases,
946 // humongous regions are already compacted, and do not require further moves, which alleviates
947 // sliding costs. We may consider doing this in parallel in future.
948
949 ShenandoahHeap* heap = ShenandoahHeap::heap();
950
951 for (size_t c = heap->num_regions(); c > 0; c--) {
952 ShenandoahHeapRegion* r = heap->get_region(c - 1);
953 if (r->is_humongous_start()) {
954 oop old_obj = cast_to_oop(r->bottom());
955 if (!old_obj->is_forwarded()) {
956 // No need to move the object, it stays at the same slot
957 continue;
958 }
959 size_t words_size = old_obj->size();
960 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
961
962 size_t old_start = r->index();
963 size_t old_end = old_start + num_regions - 1;
964 size_t new_start = heap->heap_region_index_containing(old_obj->forwardee());
965 size_t new_end = new_start + num_regions - 1;
966 assert(old_start != new_start, "must be real move");
967 assert(r->is_stw_move_allowed(), "Region " SIZE_FORMAT " should be movable", r->index());
968
969 Copy::aligned_conjoint_words(r->bottom(), heap->get_region(new_start)->bottom(), words_size);
970 ContinuationGCSupport::relativize_stack_chunk(cast_to_oop<HeapWord*>(r->bottom()));
971
972 oop new_obj = cast_to_oop(heap->get_region(new_start)->bottom());
973 new_obj->init_mark();
974
975 {
976 for (size_t c = old_start; c <= old_end; c++) {
977 ShenandoahHeapRegion* r = heap->get_region(c);
978 r->make_regular_bypass();
979 r->set_top(r->bottom());
980 }
981
982 for (size_t c = new_start; c <= new_end; c++) {
983 ShenandoahHeapRegion* r = heap->get_region(c);
984 if (c == new_start) {
985 r->make_humongous_start_bypass();
986 } else {
987 r->make_humongous_cont_bypass();
988 }
989
990 // Trailing region may be non-full, record the remainder there
991 size_t remainder = words_size & ShenandoahHeapRegion::region_size_words_mask();
992 if ((c == new_end) && (remainder != 0)) {
993 r->set_top(r->bottom() + remainder);
994 } else {
995 r->set_top(r->end());
996 }
997
998 r->reset_alloc_metadata();
999 }
1000 }
1001 }
1002 }
1003 }
1004
1005 // This is slightly different to ShHeap::reset_next_mark_bitmap:
1006 // we need to remain able to walk pinned regions.
1007 // Since pinned region do not move and don't get compacted, we will get holes with
1008 // unreachable objects in them (which may have pointers to unloaded Klasses and thus
1009 // cannot be iterated over using oop->size(). The only way to safely iterate over those is using
1010 // a valid marking bitmap and valid TAMS pointer. This class only resets marking
1011 // bitmaps for un-pinned regions, and later we only reset TAMS for unpinned regions.
1012 class ShenandoahMCResetCompleteBitmapTask : public WorkerTask {
1013 private:
1014 ShenandoahRegionIterator _regions;
1015
1016 public:
1017 ShenandoahMCResetCompleteBitmapTask() :
1018 WorkerTask("Shenandoah Reset Bitmap") {
1019 }
1020
1021 void work(uint worker_id) {
1022 ShenandoahParallelWorkerSession worker_session(worker_id);
1023 ShenandoahHeapRegion* region = _regions.next();
1024 ShenandoahHeap* heap = ShenandoahHeap::heap();
|
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 "compiler/oopMap.hpp"
28 #include "gc/shared/continuationGCSupport.hpp"
29 #include "gc/shared/gcTraceTime.inline.hpp"
30 #include "gc/shared/preservedMarks.inline.hpp"
31 #include "gc/shared/slidingForwarding.inline.hpp"
32 #include "gc/shared/tlab_globals.hpp"
33 #include "gc/shared/workerThread.hpp"
34 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
35 #include "gc/shenandoah/shenandoahConcurrentGC.hpp"
36 #include "gc/shenandoah/shenandoahCollectionSet.hpp"
37 #include "gc/shenandoah/shenandoahFreeSet.hpp"
38 #include "gc/shenandoah/shenandoahFullGC.hpp"
39 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
40 #include "gc/shenandoah/shenandoahMark.inline.hpp"
41 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
42 #include "gc/shenandoah/shenandoahHeapRegionSet.hpp"
43 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
44 #include "gc/shenandoah/shenandoahHeapRegion.inline.hpp"
45 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"
46 #include "gc/shenandoah/shenandoahMetrics.hpp"
47 #include "gc/shenandoah/shenandoahOopClosures.inline.hpp"
48 #include "gc/shenandoah/shenandoahReferenceProcessor.hpp"
49 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
50 #include "gc/shenandoah/shenandoahSTWMark.hpp"
51 #include "gc/shenandoah/shenandoahUtils.hpp"
205 // Coming out of Full GC, we would not have any forwarded objects.
206 // This also prevents resolves with fwdptr from kicking in while adjusting pointers in phase3.
207 heap->set_has_forwarded_objects(false);
208
209 heap->set_full_gc_move_in_progress(true);
210
211 // Setup workers for the rest
212 OrderAccess::fence();
213
214 // Initialize worker slices
215 ShenandoahHeapRegionSet** worker_slices = NEW_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, heap->max_workers(), mtGC);
216 for (uint i = 0; i < heap->max_workers(); i++) {
217 worker_slices[i] = new ShenandoahHeapRegionSet();
218 }
219
220 {
221 // The rest of code performs region moves, where region status is undefined
222 // until all phases run together.
223 ShenandoahHeapLocker lock(heap->lock());
224
225 SlidingForwarding::begin();
226
227 phase2_calculate_target_addresses(worker_slices);
228
229 OrderAccess::fence();
230
231 phase3_update_references();
232
233 phase4_compact_objects(worker_slices);
234 }
235
236 {
237 // Epilogue
238 _preserved_marks->restore(heap->workers());
239 _preserved_marks->reclaim();
240 SlidingForwarding::end();
241 }
242
243 // Resize metaspace
244 MetaspaceGC::compute_new_size();
245
246 // Free worker slices
247 for (uint i = 0; i < heap->max_workers(); i++) {
248 delete worker_slices[i];
249 }
250 FREE_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, worker_slices);
251
252 heap->set_full_gc_move_in_progress(false);
253 heap->set_full_gc_in_progress(false);
254
255 if (ShenandoahVerify) {
256 heap->verifier()->verify_after_fullgc();
257 }
258
259 if (VerifyAfterGC) {
260 Universe::verify();
282 void ShenandoahFullGC::phase1_mark_heap() {
283 GCTraceTime(Info, gc, phases) time("Phase 1: Mark live objects", _gc_timer);
284 ShenandoahGCPhase mark_phase(ShenandoahPhaseTimings::full_gc_mark);
285
286 ShenandoahHeap* heap = ShenandoahHeap::heap();
287
288 ShenandoahPrepareForMarkClosure cl;
289 heap->heap_region_iterate(&cl);
290
291 heap->set_unload_classes(heap->heuristics()->can_unload_classes());
292
293 ShenandoahReferenceProcessor* rp = heap->ref_processor();
294 // enable ("weak") refs discovery
295 rp->set_soft_reference_policy(true); // forcefully purge all soft references
296
297 ShenandoahSTWMark mark(true /*full_gc*/);
298 mark.mark();
299 heap->parallel_cleaning(true /* full_gc */);
300 }
301
302 template <bool ALT_FWD>
303 class ShenandoahPrepareForCompactionObjectClosure : public ObjectClosure {
304 private:
305 PreservedMarks* const _preserved_marks;
306 ShenandoahHeap* const _heap;
307 GrowableArray<ShenandoahHeapRegion*>& _empty_regions;
308 int _empty_regions_pos;
309 ShenandoahHeapRegion* _to_region;
310 ShenandoahHeapRegion* _from_region;
311 HeapWord* _compact_point;
312
313 public:
314 ShenandoahPrepareForCompactionObjectClosure(PreservedMarks* preserved_marks,
315 GrowableArray<ShenandoahHeapRegion*>& empty_regions,
316 ShenandoahHeapRegion* to_region) :
317 _preserved_marks(preserved_marks),
318 _heap(ShenandoahHeap::heap()),
319 _empty_regions(empty_regions),
320 _empty_regions_pos(0),
321 _to_region(to_region),
322 _from_region(nullptr),
352 ShenandoahHeapRegion* new_to_region;
353 if (_empty_regions_pos < _empty_regions.length()) {
354 new_to_region = _empty_regions.at(_empty_regions_pos);
355 _empty_regions_pos++;
356 } else {
357 // Out of empty region? Compact within the same region.
358 new_to_region = _from_region;
359 }
360
361 assert(new_to_region != _to_region, "must not reuse same to-region");
362 assert(new_to_region != nullptr, "must not be null");
363 _to_region = new_to_region;
364 _compact_point = _to_region->bottom();
365 }
366
367 // Object fits into current region, record new location, if object does not move:
368 assert(_compact_point + obj_size <= _to_region->end(), "must fit");
369 shenandoah_assert_not_forwarded(nullptr, p);
370 if (_compact_point != cast_from_oop<HeapWord*>(p)) {
371 _preserved_marks->push_if_necessary(p, p->mark());
372 SlidingForwarding::forward_to<ALT_FWD>(p, cast_to_oop(_compact_point));
373 }
374 _compact_point += obj_size;
375 }
376 };
377
378 class ShenandoahPrepareForCompactionTask : public WorkerTask {
379 private:
380 PreservedMarksSet* const _preserved_marks;
381 ShenandoahHeap* const _heap;
382 ShenandoahHeapRegionSet** const _worker_slices;
383
384 public:
385 ShenandoahPrepareForCompactionTask(PreservedMarksSet *preserved_marks, ShenandoahHeapRegionSet **worker_slices) :
386 WorkerTask("Shenandoah Prepare For Compaction"),
387 _preserved_marks(preserved_marks),
388 _heap(ShenandoahHeap::heap()), _worker_slices(worker_slices) {
389 }
390
391 static bool is_candidate_region(ShenandoahHeapRegion* r) {
392 // Empty region: get it into the slice to defragment the slice itself.
393 // We could have skipped this without violating correctness, but we really
394 // want to compact all live regions to the start of the heap, which sometimes
395 // means moving them into the fully empty regions.
396 if (r->is_empty()) return true;
397
398 // Can move the region, and this is not the humongous region. Humongous
399 // moves are special cased here, because their moves are handled separately.
400 return r->is_stw_move_allowed() && !r->is_humongous();
401 }
402
403 void work(uint worker_id) {
404 if (UseAltGCForwarding) {
405 work_impl<true>(worker_id);
406 } else {
407 work_impl<false>(worker_id);
408 }
409 }
410
411 private:
412 template <bool ALT_FWD>
413 void work_impl(uint worker_id) {
414 ShenandoahParallelWorkerSession worker_session(worker_id);
415 ShenandoahHeapRegionSet* slice = _worker_slices[worker_id];
416 ShenandoahHeapRegionSetIterator it(slice);
417 ShenandoahHeapRegion* from_region = it.next();
418 // No work?
419 if (from_region == nullptr) {
420 return;
421 }
422
423 // Sliding compaction. Walk all regions in the slice, and compact them.
424 // Remember empty regions and reuse them as needed.
425 ResourceMark rm;
426
427 GrowableArray<ShenandoahHeapRegion*> empty_regions((int)_heap->num_regions());
428
429 ShenandoahPrepareForCompactionObjectClosure<ALT_FWD> cl(_preserved_marks->get(worker_id), empty_regions, from_region);
430
431 while (from_region != nullptr) {
432 assert(is_candidate_region(from_region), "Sanity");
433
434 cl.set_from_region(from_region);
435 if (from_region->has_live()) {
436 _heap->marked_object_iterate(from_region, &cl);
437 }
438
439 // Compacted the region to somewhere else? From-region is empty then.
440 if (!cl.is_compact_same_region()) {
441 empty_regions.append(from_region);
442 }
443 from_region = it.next();
444 }
445 cl.finish_region();
446
447 // Mark all remaining regions as empty
448 for (int pos = cl.empty_regions_pos(); pos < empty_regions.length(); ++pos) {
449 ShenandoahHeapRegion* r = empty_regions.at(pos);
450 r->set_new_top(r->bottom());
451 }
452 }
453 };
454
455 template <bool ALT_FWD>
456 void ShenandoahFullGC::calculate_target_humongous_objects_impl() {
457 ShenandoahHeap* heap = ShenandoahHeap::heap();
458
459 // Compute the new addresses for humongous objects. We need to do this after addresses
460 // for regular objects are calculated, and we know what regions in heap suffix are
461 // available for humongous moves.
462 //
463 // Scan the heap backwards, because we are compacting humongous regions towards the end.
464 // Maintain the contiguous compaction window in [to_begin; to_end), so that we can slide
465 // humongous start there.
466 //
467 // The complication is potential non-movable regions during the scan. If such region is
468 // detected, then sliding restarts towards that non-movable region.
469
470 size_t to_begin = heap->num_regions();
471 size_t to_end = heap->num_regions();
472
473 for (size_t c = heap->num_regions(); c > 0; c--) {
474 ShenandoahHeapRegion *r = heap->get_region(c - 1);
475 if (r->is_humongous_continuation() || (r->new_top() == r->bottom())) {
476 // To-region candidate: record this, and continue scan
477 to_begin = r->index();
478 continue;
479 }
480
481 if (r->is_humongous_start() && r->is_stw_move_allowed()) {
482 // From-region candidate: movable humongous region
483 oop old_obj = cast_to_oop(r->bottom());
484 size_t words_size = old_obj->size();
485 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
486
487 size_t start = to_end - num_regions;
488
489 if (start >= to_begin && start != r->index()) {
490 // Fits into current window, and the move is non-trivial. Record the move then, and continue scan.
491 _preserved_marks->get(0)->push_if_necessary(old_obj, old_obj->mark());
492 SlidingForwarding::forward_to<ALT_FWD>(old_obj, cast_to_oop(heap->get_region(start)->bottom()));
493 to_end = start;
494 continue;
495 }
496 }
497
498 // Failed to fit. Scan starting from current region.
499 to_begin = r->index();
500 to_end = r->index();
501 }
502 }
503
504 void ShenandoahFullGC::calculate_target_humongous_objects() {
505 if (UseAltGCForwarding) {
506 calculate_target_humongous_objects_impl<true>();
507 } else {
508 calculate_target_humongous_objects_impl<false>();
509 }
510 }
511
512 class ShenandoahEnsureHeapActiveClosure: public ShenandoahHeapRegionClosure {
513 private:
514 ShenandoahHeap* const _heap;
515
516 public:
517 ShenandoahEnsureHeapActiveClosure() : _heap(ShenandoahHeap::heap()) {}
518 void heap_region_do(ShenandoahHeapRegion* r) {
519 if (r->is_trash()) {
520 r->recycle();
521 }
522 if (r->is_cset()) {
523 r->make_regular_bypass();
524 }
525 if (r->is_empty_uncommitted()) {
526 r->make_committed_bypass();
527 }
528 assert (r->is_committed(), "only committed regions in heap now, see region " SIZE_FORMAT, r->index());
529
530 // Record current region occupancy: this communicates empty regions are free
531 // to the rest of Full GC code.
729 heap->heap_region_iterate(&ecl);
730 }
731
732 // Compute the new addresses for regular objects
733 {
734 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_regular);
735
736 distribute_slices(worker_slices);
737
738 ShenandoahPrepareForCompactionTask task(_preserved_marks, worker_slices);
739 heap->workers()->run_task(&task);
740 }
741
742 // Compute the new addresses for humongous objects
743 {
744 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_humong);
745 calculate_target_humongous_objects();
746 }
747 }
748
749 template <bool ALT_FWD>
750 class ShenandoahAdjustPointersClosure : public MetadataVisitingOopIterateClosure {
751 private:
752 ShenandoahHeap* const _heap;
753 ShenandoahMarkingContext* const _ctx;
754
755 template <class T>
756 inline void do_oop_work(T* p) {
757 T o = RawAccess<>::oop_load(p);
758 if (!CompressedOops::is_null(o)) {
759 oop obj = CompressedOops::decode_not_null(o);
760 assert(_ctx->is_marked(obj), "must be marked");
761 if (SlidingForwarding::is_forwarded(obj)) {
762 oop forw = SlidingForwarding::forwardee<ALT_FWD>(obj);
763 RawAccess<IS_NOT_NULL>::oop_store(p, forw);
764 }
765 }
766 }
767
768 public:
769 ShenandoahAdjustPointersClosure() :
770 _heap(ShenandoahHeap::heap()),
771 _ctx(ShenandoahHeap::heap()->complete_marking_context()) {}
772
773 void do_oop(oop* p) { do_oop_work(p); }
774 void do_oop(narrowOop* p) { do_oop_work(p); }
775 void do_method(Method* m) {}
776 void do_nmethod(nmethod* nm) {}
777 };
778
779 template <bool ALT_FWD>
780 class ShenandoahAdjustPointersObjectClosure : public ObjectClosure {
781 private:
782 ShenandoahHeap* const _heap;
783 ShenandoahAdjustPointersClosure<ALT_FWD> _cl;
784
785 public:
786 ShenandoahAdjustPointersObjectClosure() :
787 _heap(ShenandoahHeap::heap()) {
788 }
789 void do_object(oop p) {
790 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
791 p->oop_iterate(&_cl);
792 }
793 };
794
795 class ShenandoahAdjustPointersTask : public WorkerTask {
796 private:
797 ShenandoahHeap* const _heap;
798 ShenandoahRegionIterator _regions;
799
800 public:
801 ShenandoahAdjustPointersTask() :
802 WorkerTask("Shenandoah Adjust Pointers"),
803 _heap(ShenandoahHeap::heap()) {
804 }
805
806 private:
807 template <bool ALT_FWD>
808 void work_impl(uint worker_id) {
809 ShenandoahParallelWorkerSession worker_session(worker_id);
810 ShenandoahAdjustPointersObjectClosure<ALT_FWD> obj_cl;
811 ShenandoahHeapRegion* r = _regions.next();
812 while (r != nullptr) {
813 if (!r->is_humongous_continuation() && r->has_live()) {
814 _heap->marked_object_iterate(r, &obj_cl);
815 }
816 r = _regions.next();
817 }
818 }
819
820 public:
821 void work(uint worker_id) {
822 if (UseAltGCForwarding) {
823 work_impl<true>(worker_id);
824 } else {
825 work_impl<false>(worker_id);
826 }
827 }
828 };
829
830 class ShenandoahAdjustRootPointersTask : public WorkerTask {
831 private:
832 ShenandoahRootAdjuster* _rp;
833 PreservedMarksSet* _preserved_marks;
834
835 public:
836 ShenandoahAdjustRootPointersTask(ShenandoahRootAdjuster* rp, PreservedMarksSet* preserved_marks) :
837 WorkerTask("Shenandoah Adjust Root Pointers"),
838 _rp(rp),
839 _preserved_marks(preserved_marks) {}
840
841 private:
842 template <bool ALT_FWD>
843 void work_impl(uint worker_id) {
844 ShenandoahParallelWorkerSession worker_session(worker_id);
845 ShenandoahAdjustPointersClosure<ALT_FWD> cl;
846 _rp->roots_do(worker_id, &cl);
847 _preserved_marks->get(worker_id)->adjust_during_full_gc();
848 }
849
850 public:
851 void work(uint worker_id) {
852 if (UseAltGCForwarding) {
853 work_impl<true>(worker_id);
854 } else {
855 work_impl<false>(worker_id);
856 }
857 }
858 };
859
860 void ShenandoahFullGC::phase3_update_references() {
861 GCTraceTime(Info, gc, phases) time("Phase 3: Adjust pointers", _gc_timer);
862 ShenandoahGCPhase adjust_pointer_phase(ShenandoahPhaseTimings::full_gc_adjust_pointers);
863
864 ShenandoahHeap* heap = ShenandoahHeap::heap();
865
866 WorkerThreads* workers = heap->workers();
867 uint nworkers = workers->active_workers();
868 {
869 #if COMPILER2_OR_JVMCI
870 DerivedPointerTable::clear();
871 #endif
872 ShenandoahRootAdjuster rp(nworkers, ShenandoahPhaseTimings::full_gc_adjust_roots);
873 ShenandoahAdjustRootPointersTask task(&rp, _preserved_marks);
874 workers->run_task(&task);
875 #if COMPILER2_OR_JVMCI
876 DerivedPointerTable::update_pointers();
877 #endif
878 }
879
880 ShenandoahAdjustPointersTask adjust_pointers_task;
881 workers->run_task(&adjust_pointers_task);
882 }
883
884 template <bool ALT_FWD>
885 class ShenandoahCompactObjectsClosure : public ObjectClosure {
886 private:
887 ShenandoahHeap* const _heap;
888 uint const _worker_id;
889
890 public:
891 ShenandoahCompactObjectsClosure(uint worker_id) :
892 _heap(ShenandoahHeap::heap()), _worker_id(worker_id) {}
893
894 void do_object(oop p) {
895 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
896 size_t size = p->size();
897 if (SlidingForwarding::is_forwarded(p)) {
898 HeapWord* compact_from = cast_from_oop<HeapWord*>(p);
899 HeapWord* compact_to = cast_from_oop<HeapWord*>(SlidingForwarding::forwardee<ALT_FWD>(p));
900 assert(compact_from != compact_to, "Forwarded object should move");
901 Copy::aligned_conjoint_words(compact_from, compact_to, size);
902 oop new_obj = cast_to_oop(compact_to);
903
904 ContinuationGCSupport::relativize_stack_chunk(new_obj);
905 new_obj->init_mark();
906 }
907 }
908 };
909
910 class ShenandoahCompactObjectsTask : public WorkerTask {
911 private:
912 ShenandoahHeap* const _heap;
913 ShenandoahHeapRegionSet** const _worker_slices;
914
915 public:
916 ShenandoahCompactObjectsTask(ShenandoahHeapRegionSet** worker_slices) :
917 WorkerTask("Shenandoah Compact Objects"),
918 _heap(ShenandoahHeap::heap()),
919 _worker_slices(worker_slices) {
920 }
921
922 private:
923 template <bool ALT_FWD>
924 void work_impl(uint worker_id) {
925 ShenandoahParallelWorkerSession worker_session(worker_id);
926 ShenandoahHeapRegionSetIterator slice(_worker_slices[worker_id]);
927
928 ShenandoahCompactObjectsClosure<ALT_FWD> cl(worker_id);
929 ShenandoahHeapRegion* r = slice.next();
930 while (r != nullptr) {
931 assert(!r->is_humongous(), "must not get humongous regions here");
932 if (r->has_live()) {
933 _heap->marked_object_iterate(r, &cl);
934 }
935 r->set_top(r->new_top());
936 r = slice.next();
937 }
938 }
939
940 public:
941 void work(uint worker_id) {
942 if (UseAltGCForwarding) {
943 work_impl<true>(worker_id);
944 } else {
945 work_impl<false>(worker_id);
946 }
947 }
948 };
949
950 class ShenandoahPostCompactClosure : public ShenandoahHeapRegionClosure {
951 private:
952 ShenandoahHeap* const _heap;
953 size_t _live;
954
955 public:
956 ShenandoahPostCompactClosure() : _heap(ShenandoahHeap::heap()), _live(0) {
957 _heap->free_set()->clear();
958 }
959
960 void heap_region_do(ShenandoahHeapRegion* r) {
961 assert (!r->is_cset(), "cset regions should have been demoted already");
962
963 // Need to reset the complete-top-at-mark-start pointer here because
964 // the complete marking bitmap is no longer valid. This ensures
965 // size-based iteration in marked_object_iterate().
966 // NOTE: See blurb at ShenandoahMCResetCompleteBitmapTask on why we need to skip
967 // pinned regions.
983 if (r->is_regular() && live == 0) {
984 r->make_trash();
985 }
986
987 // Recycle all trash regions
988 if (r->is_trash()) {
989 live = 0;
990 r->recycle();
991 }
992
993 r->set_live_data(live);
994 r->reset_alloc_metadata();
995 _live += live;
996 }
997
998 size_t get_live() {
999 return _live;
1000 }
1001 };
1002
1003 template <bool ALT_FWD>
1004 void ShenandoahFullGC::compact_humongous_objects_impl() {
1005 // Compact humongous regions, based on their fwdptr objects.
1006 //
1007 // This code is serial, because doing the in-slice parallel sliding is tricky. In most cases,
1008 // humongous regions are already compacted, and do not require further moves, which alleviates
1009 // sliding costs. We may consider doing this in parallel in future.
1010
1011 ShenandoahHeap* heap = ShenandoahHeap::heap();
1012
1013 for (size_t c = heap->num_regions(); c > 0; c--) {
1014 ShenandoahHeapRegion* r = heap->get_region(c - 1);
1015 if (r->is_humongous_start()) {
1016 oop old_obj = cast_to_oop(r->bottom());
1017 if (SlidingForwarding::is_not_forwarded(old_obj)) {
1018 // No need to move the object, it stays at the same slot
1019 continue;
1020 }
1021 size_t words_size = old_obj->size();
1022 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
1023
1024 size_t old_start = r->index();
1025 size_t old_end = old_start + num_regions - 1;
1026 size_t new_start = heap->heap_region_index_containing(SlidingForwarding::forwardee<ALT_FWD>(old_obj));
1027 size_t new_end = new_start + num_regions - 1;
1028 assert(old_start != new_start, "must be real move");
1029 assert(r->is_stw_move_allowed(), "Region " SIZE_FORMAT " should be movable", r->index());
1030
1031 Copy::aligned_conjoint_words(r->bottom(), heap->get_region(new_start)->bottom(), words_size);
1032 ContinuationGCSupport::relativize_stack_chunk(cast_to_oop<HeapWord*>(r->bottom()));
1033
1034 oop new_obj = cast_to_oop(heap->get_region(new_start)->bottom());
1035 new_obj->init_mark();
1036
1037 {
1038 for (size_t c = old_start; c <= old_end; c++) {
1039 ShenandoahHeapRegion* r = heap->get_region(c);
1040 r->make_regular_bypass();
1041 r->set_top(r->bottom());
1042 }
1043
1044 for (size_t c = new_start; c <= new_end; c++) {
1045 ShenandoahHeapRegion* r = heap->get_region(c);
1046 if (c == new_start) {
1047 r->make_humongous_start_bypass();
1048 } else {
1049 r->make_humongous_cont_bypass();
1050 }
1051
1052 // Trailing region may be non-full, record the remainder there
1053 size_t remainder = words_size & ShenandoahHeapRegion::region_size_words_mask();
1054 if ((c == new_end) && (remainder != 0)) {
1055 r->set_top(r->bottom() + remainder);
1056 } else {
1057 r->set_top(r->end());
1058 }
1059
1060 r->reset_alloc_metadata();
1061 }
1062 }
1063 }
1064 }
1065 }
1066
1067 void ShenandoahFullGC::compact_humongous_objects() {
1068 if (UseAltGCForwarding) {
1069 compact_humongous_objects_impl<true>();
1070 } else {
1071 compact_humongous_objects_impl<false>();
1072 }
1073 }
1074
1075 // This is slightly different to ShHeap::reset_next_mark_bitmap:
1076 // we need to remain able to walk pinned regions.
1077 // Since pinned region do not move and don't get compacted, we will get holes with
1078 // unreachable objects in them (which may have pointers to unloaded Klasses and thus
1079 // cannot be iterated over using oop->size(). The only way to safely iterate over those is using
1080 // a valid marking bitmap and valid TAMS pointer. This class only resets marking
1081 // bitmaps for un-pinned regions, and later we only reset TAMS for unpinned regions.
1082 class ShenandoahMCResetCompleteBitmapTask : public WorkerTask {
1083 private:
1084 ShenandoahRegionIterator _regions;
1085
1086 public:
1087 ShenandoahMCResetCompleteBitmapTask() :
1088 WorkerTask("Shenandoah Reset Bitmap") {
1089 }
1090
1091 void work(uint worker_id) {
1092 ShenandoahParallelWorkerSession worker_session(worker_id);
1093 ShenandoahHeapRegion* region = _regions.next();
1094 ShenandoahHeap* heap = ShenandoahHeap::heap();
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