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src/hotspot/share/gc/shenandoah/shenandoahFullGC.cpp

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  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 "compiler/oopMap.hpp"
  28 #include "gc/shared/gcTraceTime.inline.hpp"
  29 #include "gc/shared/preservedMarks.inline.hpp"

  30 #include "gc/shared/tlab_globals.hpp"
  31 #include "gc/shared/workerThread.hpp"
  32 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
  33 #include "gc/shenandoah/shenandoahConcurrentGC.hpp"
  34 #include "gc/shenandoah/shenandoahCollectionSet.hpp"
  35 #include "gc/shenandoah/shenandoahFreeSet.hpp"
  36 #include "gc/shenandoah/shenandoahFullGC.hpp"
  37 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
  38 #include "gc/shenandoah/shenandoahMark.inline.hpp"
  39 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
  40 #include "gc/shenandoah/shenandoahHeapRegionSet.hpp"
  41 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
  42 #include "gc/shenandoah/shenandoahHeapRegion.inline.hpp"
  43 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"
  44 #include "gc/shenandoah/shenandoahMetrics.hpp"
  45 #include "gc/shenandoah/shenandoahOopClosures.inline.hpp"
  46 #include "gc/shenandoah/shenandoahReferenceProcessor.hpp"
  47 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
  48 #include "gc/shenandoah/shenandoahSTWMark.hpp"
  49 #include "gc/shenandoah/shenandoahUtils.hpp"

 165 
 166     // c. Update roots if this full GC is due to evac-oom, which may carry from-space pointers in roots.
 167     if (has_forwarded_objects) {
 168       update_roots(true /*full_gc*/);
 169     }
 170 
 171     // d. Reset the bitmaps for new marking
 172     heap->reset_mark_bitmap();
 173     assert(heap->marking_context()->is_bitmap_clear(), "sanity");
 174     assert(!heap->marking_context()->is_complete(), "sanity");
 175 
 176     // e. Abandon reference discovery and clear all discovered references.
 177     ShenandoahReferenceProcessor* rp = heap->ref_processor();
 178     rp->abandon_partial_discovery();
 179 
 180     // f. Sync pinned region status from the CP marks
 181     heap->sync_pinned_region_status();
 182 
 183     // The rest of prologue:
 184     _preserved_marks->init(heap->workers()->active_workers());

 185 
 186     assert(heap->has_forwarded_objects() == has_forwarded_objects, "This should not change");
 187   }
 188 
 189   if (UseTLAB) {
 190     heap->gclabs_retire(ResizeTLAB);
 191     heap->tlabs_retire(ResizeTLAB);
 192   }
 193 
 194   OrderAccess::fence();
 195 
 196   phase1_mark_heap();
 197 
 198   // Once marking is done, which may have fixed up forwarded objects, we can drop it.
 199   // Coming out of Full GC, we would not have any forwarded objects.
 200   // This also prevents resolves with fwdptr from kicking in while adjusting pointers in phase3.
 201   heap->set_has_forwarded_objects(false);
 202 
 203   heap->set_full_gc_move_in_progress(true);
 204 

 275   ShenandoahGCPhase mark_phase(ShenandoahPhaseTimings::full_gc_mark);
 276 
 277   ShenandoahHeap* heap = ShenandoahHeap::heap();
 278 
 279   ShenandoahPrepareForMarkClosure cl;
 280   heap->heap_region_iterate(&cl);
 281 
 282   heap->set_unload_classes(heap->heuristics()->can_unload_classes());
 283 
 284   ShenandoahReferenceProcessor* rp = heap->ref_processor();
 285   // enable ("weak") refs discovery
 286   rp->set_soft_reference_policy(true); // forcefully purge all soft references
 287 
 288   ShenandoahSTWMark mark(true /*full_gc*/);
 289   mark.mark();
 290   heap->parallel_cleaning(true /* full_gc */);
 291 }
 292 
 293 class ShenandoahPrepareForCompactionObjectClosure : public ObjectClosure {
 294 private:
 295   PreservedMarks*          const _preserved_marks;
 296   ShenandoahHeap*          const _heap;

 297   GrowableArray<ShenandoahHeapRegion*>& _empty_regions;
 298   int _empty_regions_pos;
 299   ShenandoahHeapRegion*          _to_region;
 300   ShenandoahHeapRegion*          _from_region;
 301   HeapWord* _compact_point;
 302 
 303 public:
 304   ShenandoahPrepareForCompactionObjectClosure(PreservedMarks* preserved_marks,
 305                                               GrowableArray<ShenandoahHeapRegion*>& empty_regions,
 306                                               ShenandoahHeapRegion* to_region) :
 307     _preserved_marks(preserved_marks),

 308     _heap(ShenandoahHeap::heap()),
 309     _empty_regions(empty_regions),
 310     _empty_regions_pos(0),
 311     _to_region(to_region),
 312     _from_region(NULL),
 313     _compact_point(to_region->bottom()) {}
 314 
 315   void set_from_region(ShenandoahHeapRegion* from_region) {
 316     _from_region = from_region;
 317   }
 318 
 319   void finish_region() {
 320     assert(_to_region != NULL, "should not happen");
 321     _to_region->set_new_top(_compact_point);
 322   }
 323 
 324   bool is_compact_same_region() {
 325     return _from_region == _to_region;
 326   }
 327 

 341       // Object doesn't fit. Pick next empty region and start compacting there.
 342       ShenandoahHeapRegion* new_to_region;
 343       if (_empty_regions_pos < _empty_regions.length()) {
 344         new_to_region = _empty_regions.at(_empty_regions_pos);
 345         _empty_regions_pos++;
 346       } else {
 347         // Out of empty region? Compact within the same region.
 348         new_to_region = _from_region;
 349       }
 350 
 351       assert(new_to_region != _to_region, "must not reuse same to-region");
 352       assert(new_to_region != NULL, "must not be NULL");
 353       _to_region = new_to_region;
 354       _compact_point = _to_region->bottom();
 355     }
 356 
 357     // Object fits into current region, record new location:
 358     assert(_compact_point + obj_size <= _to_region->end(), "must fit");
 359     shenandoah_assert_not_forwarded(NULL, p);
 360     _preserved_marks->push_if_necessary(p, p->mark());
 361     p->forward_to(cast_to_oop(_compact_point));
 362     _compact_point += obj_size;
 363   }
 364 };
 365 
 366 class ShenandoahPrepareForCompactionTask : public WorkerTask {
 367 private:
 368   PreservedMarksSet*        const _preserved_marks;
 369   ShenandoahHeap*           const _heap;
 370   ShenandoahHeapRegionSet** const _worker_slices;
 371 
 372 public:
 373   ShenandoahPrepareForCompactionTask(PreservedMarksSet *preserved_marks, ShenandoahHeapRegionSet **worker_slices) :
 374     WorkerTask("Shenandoah Prepare For Compaction"),
 375     _preserved_marks(preserved_marks),
 376     _heap(ShenandoahHeap::heap()), _worker_slices(worker_slices) {
 377   }
 378 
 379   static bool is_candidate_region(ShenandoahHeapRegion* r) {
 380     // Empty region: get it into the slice to defragment the slice itself.
 381     // We could have skipped this without violating correctness, but we really

 415       }
 416 
 417       // Compacted the region to somewhere else? From-region is empty then.
 418       if (!cl.is_compact_same_region()) {
 419         empty_regions.append(from_region);
 420       }
 421       from_region = it.next();
 422     }
 423     cl.finish_region();
 424 
 425     // Mark all remaining regions as empty
 426     for (int pos = cl.empty_regions_pos(); pos < empty_regions.length(); ++pos) {
 427       ShenandoahHeapRegion* r = empty_regions.at(pos);
 428       r->set_new_top(r->bottom());
 429     }
 430   }
 431 };
 432 
 433 void ShenandoahFullGC::calculate_target_humongous_objects() {
 434   ShenandoahHeap* heap = ShenandoahHeap::heap();

 435 
 436   // Compute the new addresses for humongous objects. We need to do this after addresses
 437   // for regular objects are calculated, and we know what regions in heap suffix are
 438   // available for humongous moves.
 439   //
 440   // Scan the heap backwards, because we are compacting humongous regions towards the end.
 441   // Maintain the contiguous compaction window in [to_begin; to_end), so that we can slide
 442   // humongous start there.
 443   //
 444   // The complication is potential non-movable regions during the scan. If such region is
 445   // detected, then sliding restarts towards that non-movable region.
 446 
 447   size_t to_begin = heap->num_regions();
 448   size_t to_end = heap->num_regions();
 449 
 450   for (size_t c = heap->num_regions(); c > 0; c--) {
 451     ShenandoahHeapRegion *r = heap->get_region(c - 1);
 452     if (r->is_humongous_continuation() || (r->new_top() == r->bottom())) {
 453       // To-region candidate: record this, and continue scan
 454       to_begin = r->index();
 455       continue;
 456     }
 457 
 458     if (r->is_humongous_start() && r->is_stw_move_allowed()) {
 459       // From-region candidate: movable humongous region
 460       oop old_obj = cast_to_oop(r->bottom());
 461       size_t words_size = old_obj->size();
 462       size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
 463 
 464       size_t start = to_end - num_regions;
 465 
 466       if (start >= to_begin && start != r->index()) {
 467         // Fits into current window, and the move is non-trivial. Record the move then, and continue scan.
 468         _preserved_marks->get(0)->push_if_necessary(old_obj, old_obj->mark());
 469         old_obj->forward_to(cast_to_oop(heap->get_region(start)->bottom()));
 470         to_end = start;
 471         continue;
 472       }
 473     }
 474 
 475     // Failed to fit. Scan starting from current region.
 476     to_begin = r->index();
 477     to_end = r->index();
 478   }
 479 }
 480 
 481 class ShenandoahEnsureHeapActiveClosure: public ShenandoahHeapRegionClosure {
 482 private:
 483   ShenandoahHeap* const _heap;
 484 
 485 public:
 486   ShenandoahEnsureHeapActiveClosure() : _heap(ShenandoahHeap::heap()) {}
 487   void heap_region_do(ShenandoahHeapRegion* r) {
 488     if (r->is_trash()) {
 489       r->recycle();

 700 
 701   // Compute the new addresses for regular objects
 702   {
 703     ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_regular);
 704 
 705     distribute_slices(worker_slices);
 706 
 707     ShenandoahPrepareForCompactionTask task(_preserved_marks, worker_slices);
 708     heap->workers()->run_task(&task);
 709   }
 710 
 711   // Compute the new addresses for humongous objects
 712   {
 713     ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_humong);
 714     calculate_target_humongous_objects();
 715   }
 716 }
 717 
 718 class ShenandoahAdjustPointersClosure : public MetadataVisitingOopIterateClosure {
 719 private:
 720   ShenandoahHeap* const _heap;

 721   ShenandoahMarkingContext* const _ctx;
 722 
 723   template <class T>
 724   inline void do_oop_work(T* p) {
 725     T o = RawAccess<>::oop_load(p);
 726     if (!CompressedOops::is_null(o)) {
 727       oop obj = CompressedOops::decode_not_null(o);
 728       assert(_ctx->is_marked(obj), "must be marked");
 729       if (obj->is_forwarded()) {
 730         oop forw = obj->forwardee();
 731         RawAccess<IS_NOT_NULL>::oop_store(p, forw);
 732       }
 733     }
 734   }
 735 
 736 public:
 737   ShenandoahAdjustPointersClosure() :
 738     _heap(ShenandoahHeap::heap()),

 739     _ctx(ShenandoahHeap::heap()->complete_marking_context()) {}
 740 
 741   void do_oop(oop* p)       { do_oop_work(p); }
 742   void do_oop(narrowOop* p) { do_oop_work(p); }
 743 };
 744 
 745 class ShenandoahAdjustPointersObjectClosure : public ObjectClosure {
 746 private:
 747   ShenandoahHeap* const _heap;
 748   ShenandoahAdjustPointersClosure _cl;
 749 
 750 public:
 751   ShenandoahAdjustPointersObjectClosure() :
 752     _heap(ShenandoahHeap::heap()) {
 753   }
 754   void do_object(oop p) {
 755     assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
 756     p->oop_iterate(&_cl);
 757   }
 758 };

 778       }
 779       r = _regions.next();
 780     }
 781   }
 782 };
 783 
 784 class ShenandoahAdjustRootPointersTask : public WorkerTask {
 785 private:
 786   ShenandoahRootAdjuster* _rp;
 787   PreservedMarksSet* _preserved_marks;
 788 public:
 789   ShenandoahAdjustRootPointersTask(ShenandoahRootAdjuster* rp, PreservedMarksSet* preserved_marks) :
 790     WorkerTask("Shenandoah Adjust Root Pointers"),
 791     _rp(rp),
 792     _preserved_marks(preserved_marks) {}
 793 
 794   void work(uint worker_id) {
 795     ShenandoahParallelWorkerSession worker_session(worker_id);
 796     ShenandoahAdjustPointersClosure cl;
 797     _rp->roots_do(worker_id, &cl);
 798     _preserved_marks->get(worker_id)->adjust_during_full_gc();

 799   }
 800 };
 801 
 802 void ShenandoahFullGC::phase3_update_references() {
 803   GCTraceTime(Info, gc, phases) time("Phase 3: Adjust pointers", _gc_timer);
 804   ShenandoahGCPhase adjust_pointer_phase(ShenandoahPhaseTimings::full_gc_adjust_pointers);
 805 
 806   ShenandoahHeap* heap = ShenandoahHeap::heap();
 807 
 808   WorkerThreads* workers = heap->workers();
 809   uint nworkers = workers->active_workers();
 810   {
 811 #if COMPILER2_OR_JVMCI
 812     DerivedPointerTable::clear();
 813 #endif
 814     ShenandoahRootAdjuster rp(nworkers, ShenandoahPhaseTimings::full_gc_adjust_roots);
 815     ShenandoahAdjustRootPointersTask task(&rp, _preserved_marks);
 816     workers->run_task(&task);
 817 #if COMPILER2_OR_JVMCI
 818     DerivedPointerTable::update_pointers();
 819 #endif
 820   }
 821 
 822   ShenandoahAdjustPointersTask adjust_pointers_task;
 823   workers->run_task(&adjust_pointers_task);
 824 }
 825 
 826 class ShenandoahCompactObjectsClosure : public ObjectClosure {
 827 private:
 828   ShenandoahHeap* const _heap;
 829   uint            const _worker_id;

 830 
 831 public:
 832   ShenandoahCompactObjectsClosure(uint worker_id) :
 833     _heap(ShenandoahHeap::heap()), _worker_id(worker_id) {}
 834 
 835   void do_object(oop p) {
 836     assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
 837     size_t size = p->size();
 838     if (p->is_forwarded()) {
 839       HeapWord* compact_from = cast_from_oop<HeapWord*>(p);
 840       HeapWord* compact_to = cast_from_oop<HeapWord*>(p->forwardee());
 841       Copy::aligned_conjoint_words(compact_from, compact_to, size);
 842       oop new_obj = cast_to_oop(compact_to);
 843       new_obj->init_mark();
 844     }
 845   }
 846 };
 847 
 848 class ShenandoahCompactObjectsTask : public WorkerTask {
 849 private:
 850   ShenandoahHeap* const _heap;
 851   ShenandoahHeapRegionSet** const _worker_slices;
 852 
 853 public:
 854   ShenandoahCompactObjectsTask(ShenandoahHeapRegionSet** worker_slices) :
 855     WorkerTask("Shenandoah Compact Objects"),
 856     _heap(ShenandoahHeap::heap()),
 857     _worker_slices(worker_slices) {
 858   }
 859 
 860   void work(uint worker_id) {

 915     }
 916 
 917     r->set_live_data(live);
 918     r->reset_alloc_metadata();
 919     _live += live;
 920   }
 921 
 922   size_t get_live() {
 923     return _live;
 924   }
 925 };
 926 
 927 void ShenandoahFullGC::compact_humongous_objects() {
 928   // Compact humongous regions, based on their fwdptr objects.
 929   //
 930   // This code is serial, because doing the in-slice parallel sliding is tricky. In most cases,
 931   // humongous regions are already compacted, and do not require further moves, which alleviates
 932   // sliding costs. We may consider doing this in parallel in future.
 933 
 934   ShenandoahHeap* heap = ShenandoahHeap::heap();

 935 
 936   for (size_t c = heap->num_regions(); c > 0; c--) {
 937     ShenandoahHeapRegion* r = heap->get_region(c - 1);
 938     if (r->is_humongous_start()) {
 939       oop old_obj = cast_to_oop(r->bottom());
 940       if (!old_obj->is_forwarded()) {
 941         // No need to move the object, it stays at the same slot
 942         continue;
 943       }
 944       size_t words_size = old_obj->size();
 945       size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
 946 
 947       size_t old_start = r->index();
 948       size_t old_end   = old_start + num_regions - 1;
 949       size_t new_start = heap->heap_region_index_containing(old_obj->forwardee());
 950       size_t new_end   = new_start + num_regions - 1;
 951       assert(old_start != new_start, "must be real move");
 952       assert(r->is_stw_move_allowed(), "Region " SIZE_FORMAT " should be movable", r->index());
 953 
 954       Copy::aligned_conjoint_words(heap->get_region(old_start)->bottom(),
 955                                    heap->get_region(new_start)->bottom(),
 956                                    words_size);
 957 
 958       oop new_obj = cast_to_oop(heap->get_region(new_start)->bottom());
 959       new_obj->init_mark();
 960 
 961       {
 962         for (size_t c = old_start; c <= old_end; c++) {
 963           ShenandoahHeapRegion* r = heap->get_region(c);
 964           r->make_regular_bypass();
 965           r->set_top(r->bottom());
 966         }
 967 
 968         for (size_t c = new_start; c <= new_end; c++) {
 969           ShenandoahHeapRegion* r = heap->get_region(c);

  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 "compiler/oopMap.hpp"
  28 #include "gc/shared/gcTraceTime.inline.hpp"
  29 #include "gc/shared/preservedMarks.inline.hpp"
  30 #include "gc/shared/slidingForwarding.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"

 166 
 167     // c. Update roots if this full GC is due to evac-oom, which may carry from-space pointers in roots.
 168     if (has_forwarded_objects) {
 169       update_roots(true /*full_gc*/);
 170     }
 171 
 172     // d. Reset the bitmaps for new marking
 173     heap->reset_mark_bitmap();
 174     assert(heap->marking_context()->is_bitmap_clear(), "sanity");
 175     assert(!heap->marking_context()->is_complete(), "sanity");
 176 
 177     // e. Abandon reference discovery and clear all discovered references.
 178     ShenandoahReferenceProcessor* rp = heap->ref_processor();
 179     rp->abandon_partial_discovery();
 180 
 181     // f. Sync pinned region status from the CP marks
 182     heap->sync_pinned_region_status();
 183 
 184     // The rest of prologue:
 185     _preserved_marks->init(heap->workers()->active_workers());
 186     heap->forwarding()->clear();
 187 
 188     assert(heap->has_forwarded_objects() == has_forwarded_objects, "This should not change");
 189   }
 190 
 191   if (UseTLAB) {
 192     heap->gclabs_retire(ResizeTLAB);
 193     heap->tlabs_retire(ResizeTLAB);
 194   }
 195 
 196   OrderAccess::fence();
 197 
 198   phase1_mark_heap();
 199 
 200   // Once marking is done, which may have fixed up forwarded objects, we can drop it.
 201   // Coming out of Full GC, we would not have any forwarded objects.
 202   // This also prevents resolves with fwdptr from kicking in while adjusting pointers in phase3.
 203   heap->set_has_forwarded_objects(false);
 204 
 205   heap->set_full_gc_move_in_progress(true);
 206 

 277   ShenandoahGCPhase mark_phase(ShenandoahPhaseTimings::full_gc_mark);
 278 
 279   ShenandoahHeap* heap = ShenandoahHeap::heap();
 280 
 281   ShenandoahPrepareForMarkClosure cl;
 282   heap->heap_region_iterate(&cl);
 283 
 284   heap->set_unload_classes(heap->heuristics()->can_unload_classes());
 285 
 286   ShenandoahReferenceProcessor* rp = heap->ref_processor();
 287   // enable ("weak") refs discovery
 288   rp->set_soft_reference_policy(true); // forcefully purge all soft references
 289 
 290   ShenandoahSTWMark mark(true /*full_gc*/);
 291   mark.mark();
 292   heap->parallel_cleaning(true /* full_gc */);
 293 }
 294 
 295 class ShenandoahPrepareForCompactionObjectClosure : public ObjectClosure {
 296 private:
 297   PreservedMarks*    const _preserved_marks;
 298   SlidingForwarding* const _forwarding;
 299   ShenandoahHeap*    const _heap;
 300   GrowableArray<ShenandoahHeapRegion*>& _empty_regions;
 301   int _empty_regions_pos;
 302   ShenandoahHeapRegion*          _to_region;
 303   ShenandoahHeapRegion*          _from_region;
 304   HeapWord* _compact_point;
 305 
 306 public:
 307   ShenandoahPrepareForCompactionObjectClosure(PreservedMarks* preserved_marks,
 308                                               GrowableArray<ShenandoahHeapRegion*>& empty_regions,
 309                                               ShenandoahHeapRegion* to_region) :
 310     _preserved_marks(preserved_marks),
 311     _forwarding(ShenandoahHeap::heap()->forwarding()),
 312     _heap(ShenandoahHeap::heap()),
 313     _empty_regions(empty_regions),
 314     _empty_regions_pos(0),
 315     _to_region(to_region),
 316     _from_region(NULL),
 317     _compact_point(to_region->bottom()) {}
 318 
 319   void set_from_region(ShenandoahHeapRegion* from_region) {
 320     _from_region = from_region;
 321   }
 322 
 323   void finish_region() {
 324     assert(_to_region != NULL, "should not happen");
 325     _to_region->set_new_top(_compact_point);
 326   }
 327 
 328   bool is_compact_same_region() {
 329     return _from_region == _to_region;
 330   }
 331 

 345       // Object doesn't fit. Pick next empty region and start compacting there.
 346       ShenandoahHeapRegion* new_to_region;
 347       if (_empty_regions_pos < _empty_regions.length()) {
 348         new_to_region = _empty_regions.at(_empty_regions_pos);
 349         _empty_regions_pos++;
 350       } else {
 351         // Out of empty region? Compact within the same region.
 352         new_to_region = _from_region;
 353       }
 354 
 355       assert(new_to_region != _to_region, "must not reuse same to-region");
 356       assert(new_to_region != NULL, "must not be NULL");
 357       _to_region = new_to_region;
 358       _compact_point = _to_region->bottom();
 359     }
 360 
 361     // Object fits into current region, record new location:
 362     assert(_compact_point + obj_size <= _to_region->end(), "must fit");
 363     shenandoah_assert_not_forwarded(NULL, p);
 364     _preserved_marks->push_if_necessary(p, p->mark());
 365     _forwarding->forward_to(p, cast_to_oop(_compact_point));
 366     _compact_point += obj_size;
 367   }
 368 };
 369 
 370 class ShenandoahPrepareForCompactionTask : public WorkerTask {
 371 private:
 372   PreservedMarksSet*        const _preserved_marks;
 373   ShenandoahHeap*           const _heap;
 374   ShenandoahHeapRegionSet** const _worker_slices;
 375 
 376 public:
 377   ShenandoahPrepareForCompactionTask(PreservedMarksSet *preserved_marks, ShenandoahHeapRegionSet **worker_slices) :
 378     WorkerTask("Shenandoah Prepare For Compaction"),
 379     _preserved_marks(preserved_marks),
 380     _heap(ShenandoahHeap::heap()), _worker_slices(worker_slices) {
 381   }
 382 
 383   static bool is_candidate_region(ShenandoahHeapRegion* r) {
 384     // Empty region: get it into the slice to defragment the slice itself.
 385     // We could have skipped this without violating correctness, but we really

 419       }
 420 
 421       // Compacted the region to somewhere else? From-region is empty then.
 422       if (!cl.is_compact_same_region()) {
 423         empty_regions.append(from_region);
 424       }
 425       from_region = it.next();
 426     }
 427     cl.finish_region();
 428 
 429     // Mark all remaining regions as empty
 430     for (int pos = cl.empty_regions_pos(); pos < empty_regions.length(); ++pos) {
 431       ShenandoahHeapRegion* r = empty_regions.at(pos);
 432       r->set_new_top(r->bottom());
 433     }
 434   }
 435 };
 436 
 437 void ShenandoahFullGC::calculate_target_humongous_objects() {
 438   ShenandoahHeap* heap = ShenandoahHeap::heap();
 439   SlidingForwarding* forwarding = heap->forwarding();
 440 
 441   // Compute the new addresses for humongous objects. We need to do this after addresses
 442   // for regular objects are calculated, and we know what regions in heap suffix are
 443   // available for humongous moves.
 444   //
 445   // Scan the heap backwards, because we are compacting humongous regions towards the end.
 446   // Maintain the contiguous compaction window in [to_begin; to_end), so that we can slide
 447   // humongous start there.
 448   //
 449   // The complication is potential non-movable regions during the scan. If such region is
 450   // detected, then sliding restarts towards that non-movable region.
 451 
 452   size_t to_begin = heap->num_regions();
 453   size_t to_end = heap->num_regions();
 454 
 455   for (size_t c = heap->num_regions(); c > 0; c--) {
 456     ShenandoahHeapRegion *r = heap->get_region(c - 1);
 457     if (r->is_humongous_continuation() || (r->new_top() == r->bottom())) {
 458       // To-region candidate: record this, and continue scan
 459       to_begin = r->index();
 460       continue;
 461     }
 462 
 463     if (r->is_humongous_start() && r->is_stw_move_allowed()) {
 464       // From-region candidate: movable humongous region
 465       oop old_obj = cast_to_oop(r->bottom());
 466       size_t words_size = old_obj->size();
 467       size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
 468 
 469       size_t start = to_end - num_regions;
 470 
 471       if (start >= to_begin && start != r->index()) {
 472         // Fits into current window, and the move is non-trivial. Record the move then, and continue scan.
 473         _preserved_marks->get(0)->push_if_necessary(old_obj, old_obj->mark());
 474         forwarding->forward_to(old_obj, cast_to_oop(heap->get_region(start)->bottom()));
 475         to_end = start;
 476         continue;
 477       }
 478     }
 479 
 480     // Failed to fit. Scan starting from current region.
 481     to_begin = r->index();
 482     to_end = r->index();
 483   }
 484 }
 485 
 486 class ShenandoahEnsureHeapActiveClosure: public ShenandoahHeapRegionClosure {
 487 private:
 488   ShenandoahHeap* const _heap;
 489 
 490 public:
 491   ShenandoahEnsureHeapActiveClosure() : _heap(ShenandoahHeap::heap()) {}
 492   void heap_region_do(ShenandoahHeapRegion* r) {
 493     if (r->is_trash()) {
 494       r->recycle();

 705 
 706   // Compute the new addresses for regular objects
 707   {
 708     ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_regular);
 709 
 710     distribute_slices(worker_slices);
 711 
 712     ShenandoahPrepareForCompactionTask task(_preserved_marks, worker_slices);
 713     heap->workers()->run_task(&task);
 714   }
 715 
 716   // Compute the new addresses for humongous objects
 717   {
 718     ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_humong);
 719     calculate_target_humongous_objects();
 720   }
 721 }
 722 
 723 class ShenandoahAdjustPointersClosure : public MetadataVisitingOopIterateClosure {
 724 private:
 725   ShenandoahHeap*           const _heap;
 726   const SlidingForwarding*  const _forwarding;
 727   ShenandoahMarkingContext* const _ctx;
 728 
 729   template <class T>
 730   inline void do_oop_work(T* p) {
 731     T o = RawAccess<>::oop_load(p);
 732     if (!CompressedOops::is_null(o)) {
 733       oop obj = CompressedOops::decode_not_null(o);
 734       assert(_ctx->is_marked(obj), "must be marked");
 735       if (obj->is_forwarded()) {
 736         oop forw = _forwarding->forwardee(obj);
 737         RawAccess<IS_NOT_NULL>::oop_store(p, forw);
 738       }
 739     }
 740   }
 741 
 742 public:
 743   ShenandoahAdjustPointersClosure() :
 744     _heap(ShenandoahHeap::heap()),
 745     _forwarding(_heap->forwarding()),
 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 };
 751 
 752 class ShenandoahAdjustPointersObjectClosure : public ObjectClosure {
 753 private:
 754   ShenandoahHeap* const _heap;
 755   ShenandoahAdjustPointersClosure _cl;
 756 
 757 public:
 758   ShenandoahAdjustPointersObjectClosure() :
 759     _heap(ShenandoahHeap::heap()) {
 760   }
 761   void do_object(oop p) {
 762     assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
 763     p->oop_iterate(&_cl);
 764   }
 765 };

 785       }
 786       r = _regions.next();
 787     }
 788   }
 789 };
 790 
 791 class ShenandoahAdjustRootPointersTask : public WorkerTask {
 792 private:
 793   ShenandoahRootAdjuster* _rp;
 794   PreservedMarksSet* _preserved_marks;
 795 public:
 796   ShenandoahAdjustRootPointersTask(ShenandoahRootAdjuster* rp, PreservedMarksSet* preserved_marks) :
 797     WorkerTask("Shenandoah Adjust Root Pointers"),
 798     _rp(rp),
 799     _preserved_marks(preserved_marks) {}
 800 
 801   void work(uint worker_id) {
 802     ShenandoahParallelWorkerSession worker_session(worker_id);
 803     ShenandoahAdjustPointersClosure cl;
 804     _rp->roots_do(worker_id, &cl);
 805     const SlidingForwarding* const forwarding = ShenandoahHeap::heap()->forwarding();
 806     _preserved_marks->get(worker_id)->adjust_during_full_gc(forwarding);
 807   }
 808 };
 809 
 810 void ShenandoahFullGC::phase3_update_references() {
 811   GCTraceTime(Info, gc, phases) time("Phase 3: Adjust pointers", _gc_timer);
 812   ShenandoahGCPhase adjust_pointer_phase(ShenandoahPhaseTimings::full_gc_adjust_pointers);
 813 
 814   ShenandoahHeap* heap = ShenandoahHeap::heap();
 815 
 816   WorkerThreads* workers = heap->workers();
 817   uint nworkers = workers->active_workers();
 818   {
 819 #if COMPILER2_OR_JVMCI
 820     DerivedPointerTable::clear();
 821 #endif
 822     ShenandoahRootAdjuster rp(nworkers, ShenandoahPhaseTimings::full_gc_adjust_roots);
 823     ShenandoahAdjustRootPointersTask task(&rp, _preserved_marks);
 824     workers->run_task(&task);
 825 #if COMPILER2_OR_JVMCI
 826     DerivedPointerTable::update_pointers();
 827 #endif
 828   }
 829 
 830   ShenandoahAdjustPointersTask adjust_pointers_task;
 831   workers->run_task(&adjust_pointers_task);
 832 }
 833 
 834 class ShenandoahCompactObjectsClosure : public ObjectClosure {
 835 private:
 836   ShenandoahHeap*          const _heap;
 837   const SlidingForwarding* const _forwarding;
 838   uint                     const _worker_id;
 839 
 840 public:
 841   ShenandoahCompactObjectsClosure(uint worker_id) :
 842     _heap(ShenandoahHeap::heap()), _forwarding(_heap->forwarding()), _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*>(_forwarding->forwardee(p));
 850       Copy::aligned_conjoint_words(compact_from, compact_to, size);
 851       oop new_obj = cast_to_oop(compact_to);
 852       new_obj->init_mark();
 853     }
 854   }
 855 };
 856 
 857 class ShenandoahCompactObjectsTask : public WorkerTask {
 858 private:
 859   ShenandoahHeap* const _heap;
 860   ShenandoahHeapRegionSet** const _worker_slices;
 861 
 862 public:
 863   ShenandoahCompactObjectsTask(ShenandoahHeapRegionSet** worker_slices) :
 864     WorkerTask("Shenandoah Compact Objects"),
 865     _heap(ShenandoahHeap::heap()),
 866     _worker_slices(worker_slices) {
 867   }
 868 
 869   void work(uint worker_id) {

 924     }
 925 
 926     r->set_live_data(live);
 927     r->reset_alloc_metadata();
 928     _live += live;
 929   }
 930 
 931   size_t get_live() {
 932     return _live;
 933   }
 934 };
 935 
 936 void ShenandoahFullGC::compact_humongous_objects() {
 937   // Compact humongous regions, based on their fwdptr objects.
 938   //
 939   // This code is serial, because doing the in-slice parallel sliding is tricky. In most cases,
 940   // humongous regions are already compacted, and do not require further moves, which alleviates
 941   // sliding costs. We may consider doing this in parallel in future.
 942 
 943   ShenandoahHeap* heap = ShenandoahHeap::heap();
 944   const SlidingForwarding* const forwarding = heap->forwarding();
 945 
 946   for (size_t c = heap->num_regions(); c > 0; c--) {
 947     ShenandoahHeapRegion* r = heap->get_region(c - 1);
 948     if (r->is_humongous_start()) {
 949       oop old_obj = cast_to_oop(r->bottom());
 950       if (!old_obj->is_forwarded()) {
 951         // No need to move the object, it stays at the same slot
 952         continue;
 953       }
 954       size_t words_size = old_obj->size();
 955       size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
 956 
 957       size_t old_start = r->index();
 958       size_t old_end   = old_start + num_regions - 1;
 959       size_t new_start = heap->heap_region_index_containing(forwarding->forwardee(old_obj));
 960       size_t new_end   = new_start + num_regions - 1;
 961       assert(old_start != new_start, "must be real move");
 962       assert(r->is_stw_move_allowed(), "Region " SIZE_FORMAT " should be movable", r->index());
 963 
 964       Copy::aligned_conjoint_words(heap->get_region(old_start)->bottom(),
 965                                    heap->get_region(new_start)->bottom(),
 966                                    words_size);
 967 
 968       oop new_obj = cast_to_oop(heap->get_region(new_start)->bottom());
 969       new_obj->init_mark();
 970 
 971       {
 972         for (size_t c = old_start; c <= old_end; c++) {
 973           ShenandoahHeapRegion* r = heap->get_region(c);
 974           r->make_regular_bypass();
 975           r->set_top(r->bottom());
 976         }
 977 
 978         for (size_t c = new_start; c <= new_end; c++) {
 979           ShenandoahHeapRegion* r = heap->get_region(c);
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