jdk8-mips64-public/hotspot: src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp@58fc1b1523dc (annotated)

src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp@58fc1b1523dc (annotated)

src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp

Fri, 14 Mar 2014 10:15:46 +0100

author: brutisso
date: Fri, 14 Mar 2014 10:15:46 +0100
changeset 6385: 58fc1b1523dc
parent 6376: cfd4aac53239
child 6402: 191174b49bec
permissions: -rw-r--r--

8034079: G1: Refactor the HeapRegionSet hierarchy
Reviewed-by: tschatzl, pliden

 /*
  * Copyright (c) 2001, 2013, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 only, as
  * published by the Free Software Foundation.
  *
  * This code is distributed in the hope that it will be useful, but WITHOUT
  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  * version 2 for more details (a copy is included in the LICENSE file that
  * accompanied this code).
  *
  * You should have received a copy of the GNU General Public License version
  * 2 along with this work; if not, write to the Free Software Foundation,
  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  *
  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  * or visit www.oracle.com if you need additional information or have any
  * questions.
  *
  */
 #ifndef SHARE_VM_GC_IMPLEMENTATION_G1_G1COLLECTEDHEAP_HPP
 #define SHARE_VM_GC_IMPLEMENTATION_G1_G1COLLECTEDHEAP_HPP
 #include "gc_implementation/g1/concurrentMark.hpp"
 #include "gc_implementation/g1/evacuationInfo.hpp"
 #include "gc_implementation/g1/g1AllocRegion.hpp"
 #include "gc_implementation/g1/g1HRPrinter.hpp"
 #include "gc_implementation/g1/g1MonitoringSupport.hpp"
 #include "gc_implementation/g1/g1RemSet.hpp"
 #include "gc_implementation/g1/g1SATBCardTableModRefBS.hpp"
 #include "gc_implementation/g1/g1YCTypes.hpp"
 #include "gc_implementation/g1/heapRegionSeq.hpp"
 #include "gc_implementation/g1/heapRegionSet.hpp"
 #include "gc_implementation/shared/hSpaceCounters.hpp"
 #include "gc_implementation/shared/parGCAllocBuffer.hpp"
 #include "memory/barrierSet.hpp"
 #include "memory/memRegion.hpp"
 #include "memory/sharedHeap.hpp"
 #include "utilities/stack.hpp"
 // A "G1CollectedHeap" is an implementation of a java heap for HotSpot.
 // It uses the "Garbage First" heap organization and algorithm, which
 // may combine concurrent marking with parallel, incremental compaction of
 // heap subsets that will yield large amounts of garbage.
 // Forward declarations
 class HeapRegion;
 class HRRSCleanupTask;
 class GenerationSpec;
 class OopsInHeapRegionClosure;
 class G1KlassScanClosure;
 class G1ScanHeapEvacClosure;
 class ObjectClosure;
 class SpaceClosure;
 class CompactibleSpaceClosure;
 class Space;
 class G1CollectorPolicy;
 class GenRemSet;
 class G1RemSet;
 class HeapRegionRemSetIterator;
 class ConcurrentMark;
 class ConcurrentMarkThread;
 class ConcurrentG1Refine;
 class ConcurrentGCTimer;
 class GenerationCounters;
 class STWGCTimer;
 class G1NewTracer;
 class G1OldTracer;
 class EvacuationFailedInfo;
 class nmethod;
 class Ticks;
 typedef OverflowTaskQueue<StarTask, mtGC>         RefToScanQueue;
 typedef GenericTaskQueueSet<RefToScanQueue, mtGC> RefToScanQueueSet;
 typedef int RegionIdx_t;   // needs to hold [ 0..max_regions() )
 typedef int CardIdx_t;     // needs to hold [ 0..CardsPerRegion )
 enum GCAllocPurpose {
   GCAllocForTenured,
   GCAllocForSurvived,
   GCAllocPurposeCount
 };
 class YoungList : public CHeapObj<mtGC> {
 private:
   G1CollectedHeap* _g1h;
   HeapRegion* _head;
   HeapRegion* _survivor_head;
   HeapRegion* _survivor_tail;
   HeapRegion* _curr;
   uint        _length;
   uint        _survivor_length;
   size_t      _last_sampled_rs_lengths;
   size_t      _sampled_rs_lengths;
   void         empty_list(HeapRegion* list);
 public:
   YoungList(G1CollectedHeap* g1h);
   void         push_region(HeapRegion* hr);
   void         add_survivor_region(HeapRegion* hr);
   void         empty_list();
   bool         is_empty() { return _length == 0; }
   uint         length() { return _length; }
   uint         survivor_length() { return _survivor_length; }
   // Currently we do not keep track of the used byte sum for the
   // young list and the survivors and it'd be quite a lot of work to
   // do so. When we'll eventually replace the young list with
   // instances of HeapRegionLinkedList we'll get that for free. So,
   // we'll report the more accurate information then.
   size_t       eden_used_bytes() {
     assert(length() >= survivor_length(), "invariant");
     return (size_t) (length() - survivor_length()) * HeapRegion::GrainBytes;
   }
   size_t       survivor_used_bytes() {
     return (size_t) survivor_length() * HeapRegion::GrainBytes;
   }
   void rs_length_sampling_init();
   bool rs_length_sampling_more();
   void rs_length_sampling_next();
   void reset_sampled_info() {
     _last_sampled_rs_lengths =   0;
   }
   size_t sampled_rs_lengths() { return _last_sampled_rs_lengths; }
   // for development purposes
   void reset_auxilary_lists();
   void clear() { _head = NULL; _length = 0; }
   void clear_survivors() {
     _survivor_head    = NULL;
     _survivor_tail    = NULL;
     _survivor_length  = 0;
   }
   HeapRegion* first_region() { return _head; }
   HeapRegion* first_survivor_region() { return _survivor_head; }
   HeapRegion* last_survivor_region() { return _survivor_tail; }
   // debugging
   bool          check_list_well_formed();
   bool          check_list_empty(bool check_sample = true);
   void          print();
 };
 class MutatorAllocRegion : public G1AllocRegion {
 protected:
   virtual HeapRegion* allocate_new_region(size_t word_size, bool force);
   virtual void retire_region(HeapRegion* alloc_region, size_t allocated_bytes);
 public:
   MutatorAllocRegion()
     : G1AllocRegion("Mutator Alloc Region", false /* bot_updates */) { }
 };
 class SurvivorGCAllocRegion : public G1AllocRegion {
 protected:
   virtual HeapRegion* allocate_new_region(size_t word_size, bool force);
   virtual void retire_region(HeapRegion* alloc_region, size_t allocated_bytes);
 public:
   SurvivorGCAllocRegion()
   : G1AllocRegion("Survivor GC Alloc Region", false /* bot_updates */) { }
 };
 class OldGCAllocRegion : public G1AllocRegion {
 protected:
   virtual HeapRegion* allocate_new_region(size_t word_size, bool force);
   virtual void retire_region(HeapRegion* alloc_region, size_t allocated_bytes);
 public:
   OldGCAllocRegion()
   : G1AllocRegion("Old GC Alloc Region", true /* bot_updates */) { }
 };
 // The G1 STW is alive closure.
 // An instance is embedded into the G1CH and used as the
 // (optional) _is_alive_non_header closure in the STW
 // reference processor. It is also extensively used during
 // reference processing during STW evacuation pauses.
 class G1STWIsAliveClosure: public BoolObjectClosure {
   G1CollectedHeap* _g1;
 public:
   G1STWIsAliveClosure(G1CollectedHeap* g1) : _g1(g1) {}
   bool do_object_b(oop p);
 };
 class RefineCardTableEntryClosure;
 class G1CollectedHeap : public SharedHeap {
   friend class VM_G1CollectForAllocation;
   friend class VM_G1CollectFull;
   friend class VM_G1IncCollectionPause;
   friend class VMStructs;
   friend class MutatorAllocRegion;
   friend class SurvivorGCAllocRegion;
   friend class OldGCAllocRegion;
   // Closures used in implementation.
   template <G1Barrier barrier, bool do_mark_object>
   friend class G1ParCopyClosure;
   friend class G1IsAliveClosure;
   friend class G1EvacuateFollowersClosure;
   friend class G1ParScanThreadState;
   friend class G1ParScanClosureSuper;
   friend class G1ParEvacuateFollowersClosure;
   friend class G1ParTask;
   friend class G1FreeGarbageRegionClosure;
   friend class RefineCardTableEntryClosure;
   friend class G1PrepareCompactClosure;
   friend class RegionSorter;
   friend class RegionResetter;
   friend class CountRCClosure;
   friend class EvacPopObjClosure;
   friend class G1ParCleanupCTTask;
   // Other related classes.
   friend class G1MarkSweep;
 private:
   // The one and only G1CollectedHeap, so static functions can find it.
   static G1CollectedHeap* _g1h;
   static size_t _humongous_object_threshold_in_words;
   // Storage for the G1 heap.
   VirtualSpace _g1_storage;
   MemRegion    _g1_reserved;
   // The part of _g1_storage that is currently committed.
   MemRegion _g1_committed;
   // The master free list. It will satisfy all new region allocations.
   FreeRegionList _free_list;
   // The secondary free list which contains regions that have been
   // freed up during the cleanup process. This will be appended to the
   // master free list when appropriate.
   FreeRegionList _secondary_free_list;
   // It keeps track of the old regions.
   HeapRegionSet _old_set;
   // It keeps track of the humongous regions.
   HeapRegionSet _humongous_set;
   // The number of regions we could create by expansion.
   uint _expansion_regions;
   // The block offset table for the G1 heap.
   G1BlockOffsetSharedArray* _bot_shared;
   // Tears down the region sets / lists so that they are empty and the
   // regions on the heap do not belong to a region set / list. The
   // only exception is the humongous set which we leave unaltered. If
   // free_list_only is true, it will only tear down the master free
   // list. It is called before a Full GC (free_list_only == false) or
   // before heap shrinking (free_list_only == true).
   void tear_down_region_sets(bool free_list_only);
   // Rebuilds the region sets / lists so that they are repopulated to
   // reflect the contents of the heap. The only exception is the
   // humongous set which was not torn down in the first place. If
   // free_list_only is true, it will only rebuild the master free
   // list. It is called after a Full GC (free_list_only == false) or
   // after heap shrinking (free_list_only == true).
   void rebuild_region_sets(bool free_list_only);
   // The sequence of all heap regions in the heap.
   HeapRegionSeq _hrs;
   // Alloc region used to satisfy mutator allocation requests.
   MutatorAllocRegion _mutator_alloc_region;
   // Alloc region used to satisfy allocation requests by the GC for
   // survivor objects.
   SurvivorGCAllocRegion _survivor_gc_alloc_region;
   // PLAB sizing policy for survivors.
   PLABStats _survivor_plab_stats;
   // Alloc region used to satisfy allocation requests by the GC for
   // old objects.
   OldGCAllocRegion _old_gc_alloc_region;
   // PLAB sizing policy for tenured objects.
   PLABStats _old_plab_stats;
   PLABStats* stats_for_purpose(GCAllocPurpose purpose) {
     PLABStats* stats = NULL;
     switch (purpose) {
     case GCAllocForSurvived:
       stats = &_survivor_plab_stats;
       break;
     case GCAllocForTenured:
       stats = &_old_plab_stats;
       break;
     default:
       assert(false, "unrecognized GCAllocPurpose");
     }
     return stats;
   }
   // The last old region we allocated to during the last GC.
   // Typically, it is not full so we should re-use it during the next GC.
   HeapRegion* _retained_old_gc_alloc_region;
   // It specifies whether we should attempt to expand the heap after a
   // region allocation failure. If heap expansion fails we set this to
   // false so that we don't re-attempt the heap expansion (it's likely
   // that subsequent expansion attempts will also fail if one fails).
   // Currently, it is only consulted during GC and it's reset at the
   // start of each GC.
   bool _expand_heap_after_alloc_failure;
   // It resets the mutator alloc region before new allocations can take place.
   void init_mutator_alloc_region();
   // It releases the mutator alloc region.
   void release_mutator_alloc_region();
   // It initializes the GC alloc regions at the start of a GC.
   void init_gc_alloc_regions(EvacuationInfo& evacuation_info);
   // It releases the GC alloc regions at the end of a GC.
   void release_gc_alloc_regions(uint no_of_gc_workers, EvacuationInfo& evacuation_info);
   // It does any cleanup that needs to be done on the GC alloc regions
   // before a Full GC.
   void abandon_gc_alloc_regions();
   // Helper for monitoring and management support.
   G1MonitoringSupport* _g1mm;
   // Determines PLAB size for a particular allocation purpose.
   size_t desired_plab_sz(GCAllocPurpose purpose);
   // Outside of GC pauses, the number of bytes used in all regions other
   // than the current allocation region.
   size_t _summary_bytes_used;
   // This is used for a quick test on whether a reference points into
   // the collection set or not. Basically, we have an array, with one
   // byte per region, and that byte denotes whether the corresponding
   // region is in the collection set or not. The entry corresponding
   // the bottom of the heap, i.e., region 0, is pointed to by
   // _in_cset_fast_test_base.  The _in_cset_fast_test field has been
   // biased so that it actually points to address 0 of the address
   // space, to make the test as fast as possible (we can simply shift
   // the address to address into it, instead of having to subtract the
   // bottom of the heap from the address before shifting it; basically
   // it works in the same way the card table works).
   bool* _in_cset_fast_test;
   // The allocated array used for the fast test on whether a reference
   // points into the collection set or not. This field is also used to
   // free the array.
   bool* _in_cset_fast_test_base;
   // The length of the _in_cset_fast_test_base array.
   uint _in_cset_fast_test_length;
   volatile unsigned _gc_time_stamp;
   size_t* _surviving_young_words;
   G1HRPrinter _hr_printer;
   void setup_surviving_young_words();
   void update_surviving_young_words(size_t* surv_young_words);
   void cleanup_surviving_young_words();
   // It decides whether an explicit GC should start a concurrent cycle
   // instead of doing a STW GC. Currently, a concurrent cycle is
   // explicitly started if:
   // (a) cause == _gc_locker and +GCLockerInvokesConcurrent, or
   // (b) cause == _java_lang_system_gc and +ExplicitGCInvokesConcurrent.
   // (c) cause == _g1_humongous_allocation
   bool should_do_concurrent_full_gc(GCCause::Cause cause);
   // Keeps track of how many "old marking cycles" (i.e., Full GCs or
   // concurrent cycles) we have started.
   volatile unsigned int _old_marking_cycles_started;
   // Keeps track of how many "old marking cycles" (i.e., Full GCs or
   // concurrent cycles) we have completed.
   volatile unsigned int _old_marking_cycles_completed;
   bool _concurrent_cycle_started;
   // This is a non-product method that is helpful for testing. It is
   // called at the end of a GC and artificially expands the heap by
   // allocating a number of dead regions. This way we can induce very
   // frequent marking cycles and stress the cleanup / concurrent
   // cleanup code more (as all the regions that will be allocated by
   // this method will be found dead by the marking cycle).
   void allocate_dummy_regions() PRODUCT_RETURN;
   // Clear RSets after a compaction. It also resets the GC time stamps.
   void clear_rsets_post_compaction();
   // If the HR printer is active, dump the state of the regions in the
   // heap after a compaction.
   void print_hrs_post_compaction();
   double verify(bool guard, const char* msg);
   void verify_before_gc();
   void verify_after_gc();
   void log_gc_header();
   void log_gc_footer(double pause_time_sec);
   // These are macros so that, if the assert fires, we get the correct
   // line number, file, etc.
 #define heap_locking_asserts_err_msg(_extra_message_)                         \
   err_msg("%s : Heap_lock locked: %s, at safepoint: %s, is VM thread: %s",    \
           (_extra_message_),                                                  \
           BOOL_TO_STR(Heap_lock->owned_by_self()),                            \
           BOOL_TO_STR(SafepointSynchronize::is_at_safepoint()),               \
           BOOL_TO_STR(Thread::current()->is_VM_thread()))
 #define assert_heap_locked()                                                  \
   do {                                                                        \
     assert(Heap_lock->owned_by_self(),                                        \
            heap_locking_asserts_err_msg("should be holding the Heap_lock"));  \
   } while (0)
 #define assert_heap_locked_or_at_safepoint(_should_be_vm_thread_)             \
   do {                                                                        \
     assert(Heap_lock->owned_by_self() ||                                      \
            (SafepointSynchronize::is_at_safepoint() &&                        \
              ((_should_be_vm_thread_) == Thread::current()->is_VM_thread())), \
            heap_locking_asserts_err_msg("should be holding the Heap_lock or " \
                                         "should be at a safepoint"));         \
   } while (0)
 #define assert_heap_locked_and_not_at_safepoint()                             \
   do {                                                                        \
     assert(Heap_lock->owned_by_self() &&                                      \
                                     !SafepointSynchronize::is_at_safepoint(), \
           heap_locking_asserts_err_msg("should be holding the Heap_lock and " \
                                        "should not be at a safepoint"));      \
   } while (0)
 #define assert_heap_not_locked()                                              \
   do {                                                                        \
     assert(!Heap_lock->owned_by_self(),                                       \
         heap_locking_asserts_err_msg("should not be holding the Heap_lock")); \
   } while (0)
 #define assert_heap_not_locked_and_not_at_safepoint()                         \
   do {                                                                        \
     assert(!Heap_lock->owned_by_self() &&                                     \
                                     !SafepointSynchronize::is_at_safepoint(), \
       heap_locking_asserts_err_msg("should not be holding the Heap_lock and " \
                                    "should not be at a safepoint"));          \
   } while (0)
 #define assert_at_safepoint(_should_be_vm_thread_)                            \
   do {                                                                        \
     assert(SafepointSynchronize::is_at_safepoint() &&                         \
               ((_should_be_vm_thread_) == Thread::current()->is_VM_thread()), \
            heap_locking_asserts_err_msg("should be at a safepoint"));         \
   } while (0)
 #define assert_not_at_safepoint()                                             \
   do {                                                                        \
     assert(!SafepointSynchronize::is_at_safepoint(),                          \
            heap_locking_asserts_err_msg("should not be at a safepoint"));     \
   } while (0)
 protected:
   // The young region list.
   YoungList*  _young_list;
   // The current policy object for the collector.
   G1CollectorPolicy* _g1_policy;
   // This is the second level of trying to allocate a new region. If
   // new_region() didn't find a region on the free_list, this call will
   // check whether there's anything available on the
   // secondary_free_list and/or wait for more regions to appear on
   // that list, if _free_regions_coming is set.
   HeapRegion* new_region_try_secondary_free_list();
   // Try to allocate a single non-humongous HeapRegion sufficient for
   // an allocation of the given word_size. If do_expand is true,
   // attempt to expand the heap if necessary to satisfy the allocation
   // request.
   HeapRegion* new_region(size_t word_size, bool do_expand);
   // Attempt to satisfy a humongous allocation request of the given
   // size by finding a contiguous set of free regions of num_regions
   // length and remove them from the master free list. Return the
   // index of the first region or G1_NULL_HRS_INDEX if the search
   // was unsuccessful.
   uint humongous_obj_allocate_find_first(uint num_regions,
                                          size_t word_size);
   // Initialize a contiguous set of free regions of length num_regions
   // and starting at index first so that they appear as a single
   // humongous region.
   HeapWord* humongous_obj_allocate_initialize_regions(uint first,
                                                       uint num_regions,
                                                       size_t word_size);
   // Attempt to allocate a humongous object of the given size. Return
   // NULL if unsuccessful.
   HeapWord* humongous_obj_allocate(size_t word_size);
   // The following two methods, allocate_new_tlab() and
   // mem_allocate(), are the two main entry points from the runtime
   // into the G1's allocation routines. They have the following
   // assumptions:
   //
   // * They should both be called outside safepoints.
   //
   // * They should both be called without holding the Heap_lock.
   //
   // * All allocation requests for new TLABs should go to
   //   allocate_new_tlab().
   //
   // * All non-TLAB allocation requests should go to mem_allocate().
   //
   // * If either call cannot satisfy the allocation request using the
   //   current allocating region, they will try to get a new one. If
   //   this fails, they will attempt to do an evacuation pause and
   //   retry the allocation.
   //
   // * If all allocation attempts fail, even after trying to schedule
   //   an evacuation pause, allocate_new_tlab() will return NULL,
   //   whereas mem_allocate() will attempt a heap expansion and/or
   //   schedule a Full GC.
   //
   // * We do not allow humongous-sized TLABs. So, allocate_new_tlab
   //   should never be called with word_size being humongous. All
   //   humongous allocation requests should go to mem_allocate() which
   //   will satisfy them with a special path.
   virtual HeapWord* allocate_new_tlab(size_t word_size);
   virtual HeapWord* mem_allocate(size_t word_size,
                                  bool*  gc_overhead_limit_was_exceeded);
   // The following three methods take a gc_count_before_ret
   // parameter which is used to return the GC count if the method
   // returns NULL. Given that we are required to read the GC count
   // while holding the Heap_lock, and these paths will take the
   // Heap_lock at some point, it's easier to get them to read the GC
   // count while holding the Heap_lock before they return NULL instead
   // of the caller (namely: mem_allocate()) having to also take the
   // Heap_lock just to read the GC count.
   // First-level mutator allocation attempt: try to allocate out of
   // the mutator alloc region without taking the Heap_lock. This
   // should only be used for non-humongous allocations.
   inline HeapWord* attempt_allocation(size_t word_size,
                                       unsigned int* gc_count_before_ret,
                                       int* gclocker_retry_count_ret);
   // Second-level mutator allocation attempt: take the Heap_lock and
   // retry the allocation attempt, potentially scheduling a GC
   // pause. This should only be used for non-humongous allocations.
   HeapWord* attempt_allocation_slow(size_t word_size,
                                     unsigned int* gc_count_before_ret,
                                     int* gclocker_retry_count_ret);
   // Takes the Heap_lock and attempts a humongous allocation. It can
   // potentially schedule a GC pause.
   HeapWord* attempt_allocation_humongous(size_t word_size,
                                          unsigned int* gc_count_before_ret,
                                          int* gclocker_retry_count_ret);
   // Allocation attempt that should be called during safepoints (e.g.,
   // at the end of a successful GC). expect_null_mutator_alloc_region
   // specifies whether the mutator alloc region is expected to be NULL
   // or not.
   HeapWord* attempt_allocation_at_safepoint(size_t word_size,
                                        bool expect_null_mutator_alloc_region);
   // It dirties the cards that cover the block so that so that the post
   // write barrier never queues anything when updating objects on this
   // block. It is assumed (and in fact we assert) that the block
   // belongs to a young region.
   inline void dirty_young_block(HeapWord* start, size_t word_size);
   // Allocate blocks during garbage collection. Will ensure an
   // allocation region, either by picking one or expanding the
   // heap, and then allocate a block of the given size. The block
   // may not be a humongous - it must fit into a single heap region.
   HeapWord* par_allocate_during_gc(GCAllocPurpose purpose, size_t word_size);
   HeapWord* allocate_during_gc_slow(GCAllocPurpose purpose,
                                     HeapRegion*    alloc_region,
                                     bool           par,
                                     size_t         word_size);
   // Ensure that no further allocations can happen in "r", bearing in mind
   // that parallel threads might be attempting allocations.
   void par_allocate_remaining_space(HeapRegion* r);
   // Allocation attempt during GC for a survivor object / PLAB.
   inline HeapWord* survivor_attempt_allocation(size_t word_size);
   // Allocation attempt during GC for an old object / PLAB.
   inline HeapWord* old_attempt_allocation(size_t word_size);
   // These methods are the "callbacks" from the G1AllocRegion class.
   // For mutator alloc regions.
   HeapRegion* new_mutator_alloc_region(size_t word_size, bool force);
   void retire_mutator_alloc_region(HeapRegion* alloc_region,
                                    size_t allocated_bytes);
   // For GC alloc regions.
   HeapRegion* new_gc_alloc_region(size_t word_size, uint count,
                                   GCAllocPurpose ap);
   void retire_gc_alloc_region(HeapRegion* alloc_region,
                               size_t allocated_bytes, GCAllocPurpose ap);
   // - if explicit_gc is true, the GC is for a System.gc() or a heap
   //   inspection request and should collect the entire heap
   // - if clear_all_soft_refs is true, all soft references should be
   //   cleared during the GC
   // - if explicit_gc is false, word_size describes the allocation that
   //   the GC should attempt (at least) to satisfy
   // - it returns false if it is unable to do the collection due to the
   //   GC locker being active, true otherwise
   bool do_collection(bool explicit_gc,
                      bool clear_all_soft_refs,
                      size_t word_size);
   // Callback from VM_G1CollectFull operation.
   // Perform a full collection.
   virtual void do_full_collection(bool clear_all_soft_refs);
   // Resize the heap if necessary after a full collection.  If this is
   // after a collect-for allocation, "word_size" is the allocation size,
   // and will be considered part of the used portion of the heap.
   void resize_if_necessary_after_full_collection(size_t word_size);
   // Callback from VM_G1CollectForAllocation operation.
   // This function does everything necessary/possible to satisfy a
   // failed allocation request (including collection, expansion, etc.)
   HeapWord* satisfy_failed_allocation(size_t word_size, bool* succeeded);
   // Attempting to expand the heap sufficiently
   // to support an allocation of the given "word_size".  If
   // successful, perform the allocation and return the address of the
   // allocated block, or else "NULL".
   HeapWord* expand_and_allocate(size_t word_size);
   // Process any reference objects discovered during
   // an incremental evacuation pause.
   void process_discovered_references(uint no_of_gc_workers);
   // Enqueue any remaining discovered references
   // after processing.
   void enqueue_discovered_references(uint no_of_gc_workers);
 public:
   G1MonitoringSupport* g1mm() {
     assert(_g1mm != NULL, "should have been initialized");
     return _g1mm;
   }
   // Expand the garbage-first heap by at least the given size (in bytes!).
   // Returns true if the heap was expanded by the requested amount;
   // false otherwise.
   // (Rounds up to a HeapRegion boundary.)
   bool expand(size_t expand_bytes);
   // Do anything common to GC's.
   virtual void gc_prologue(bool full);
   virtual void gc_epilogue(bool full);
   // We register a region with the fast "in collection set" test. We
   // simply set to true the array slot corresponding to this region.
   void register_region_with_in_cset_fast_test(HeapRegion* r) {
     assert(_in_cset_fast_test_base != NULL, "sanity");
     assert(r->in_collection_set(), "invariant");
     uint index = r->hrs_index();
     assert(index < _in_cset_fast_test_length, "invariant");
     assert(!_in_cset_fast_test_base[index], "invariant");
     _in_cset_fast_test_base[index] = true;
   }
   // This is a fast test on whether a reference points into the
   // collection set or not. Assume that the reference
   // points into the heap.
   bool in_cset_fast_test(oop obj) {
     assert(_in_cset_fast_test != NULL, "sanity");
     assert(_g1_committed.contains((HeapWord*) obj), err_msg("Given reference outside of heap, is "PTR_FORMAT, (HeapWord*)obj));
     // no need to subtract the bottom of the heap from obj,
     // _in_cset_fast_test is biased
     uintx index = cast_from_oop<uintx>(obj) >> HeapRegion::LogOfHRGrainBytes;
     bool ret = _in_cset_fast_test[index];
     // let's make sure the result is consistent with what the slower
     // test returns
     assert( ret || !obj_in_cs(obj), "sanity");
     assert(!ret ||  obj_in_cs(obj), "sanity");
     return ret;
   }
   void clear_cset_fast_test() {
     assert(_in_cset_fast_test_base != NULL, "sanity");
     memset(_in_cset_fast_test_base, false,
            (size_t) _in_cset_fast_test_length * sizeof(bool));
   }
   // This is called at the start of either a concurrent cycle or a Full
   // GC to update the number of old marking cycles started.
   void increment_old_marking_cycles_started();
   // This is called at the end of either a concurrent cycle or a Full
   // GC to update the number of old marking cycles completed. Those two
   // can happen in a nested fashion, i.e., we start a concurrent
   // cycle, a Full GC happens half-way through it which ends first,
   // and then the cycle notices that a Full GC happened and ends
   // too. The concurrent parameter is a boolean to help us do a bit
   // tighter consistency checking in the method. If concurrent is
   // false, the caller is the inner caller in the nesting (i.e., the
   // Full GC). If concurrent is true, the caller is the outer caller
   // in this nesting (i.e., the concurrent cycle). Further nesting is
   // not currently supported. The end of this call also notifies
   // the FullGCCount_lock in case a Java thread is waiting for a full
   // GC to happen (e.g., it called System.gc() with
   // +ExplicitGCInvokesConcurrent).
   void increment_old_marking_cycles_completed(bool concurrent);
   unsigned int old_marking_cycles_completed() {
     return _old_marking_cycles_completed;
   }
   void register_concurrent_cycle_start(const Ticks& start_time);
   void register_concurrent_cycle_end();
   void trace_heap_after_concurrent_cycle();
   G1YCType yc_type();
   G1HRPrinter* hr_printer() { return &_hr_printer; }
   // Frees a non-humongous region by initializing its contents and
   // adding it to the free list that's passed as a parameter (this is
   // usually a local list which will be appended to the master free
   // list later). The used bytes of freed regions are accumulated in
   // pre_used. If par is true, the region's RSet will not be freed
   // up. The assumption is that this will be done later.
   void free_region(HeapRegion* hr,
                    FreeRegionList* free_list,
                    bool par);
   // Frees a humongous region by collapsing it into individual regions
   // and calling free_region() for each of them. The freed regions
   // will be added to the free list that's passed as a parameter (this
   // is usually a local list which will be appended to the master free
   // list later). The used bytes of freed regions are accumulated in
   // pre_used. If par is true, the region's RSet will not be freed
   // up. The assumption is that this will be done later.
   void free_humongous_region(HeapRegion* hr,
                              FreeRegionList* free_list,
                              bool par);
 protected:
   // Shrink the garbage-first heap by at most the given size (in bytes!).
   // (Rounds down to a HeapRegion boundary.)
   virtual void shrink(size_t expand_bytes);
   void shrink_helper(size_t expand_bytes);
   #if TASKQUEUE_STATS
   static void print_taskqueue_stats_hdr(outputStream* const st = gclog_or_tty);
   void print_taskqueue_stats(outputStream* const st = gclog_or_tty) const;
   void reset_taskqueue_stats();
   #endif // TASKQUEUE_STATS
   // Schedule the VM operation that will do an evacuation pause to
   // satisfy an allocation request of word_size. *succeeded will
   // return whether the VM operation was successful (it did do an
   // evacuation pause) or not (another thread beat us to it or the GC
   // locker was active). Given that we should not be holding the
   // Heap_lock when we enter this method, we will pass the
   // gc_count_before (i.e., total_collections()) as a parameter since
   // it has to be read while holding the Heap_lock. Currently, both
   // methods that call do_collection_pause() release the Heap_lock
   // before the call, so it's easy to read gc_count_before just before.
   HeapWord* do_collection_pause(size_t         word_size,
                                 unsigned int   gc_count_before,
                                 bool*          succeeded,
                                 GCCause::Cause gc_cause);
   // The guts of the incremental collection pause, executed by the vm
   // thread. It returns false if it is unable to do the collection due
   // to the GC locker being active, true otherwise
   bool do_collection_pause_at_safepoint(double target_pause_time_ms);
   // Actually do the work of evacuating the collection set.
   void evacuate_collection_set(EvacuationInfo& evacuation_info);
   // The g1 remembered set of the heap.
   G1RemSet* _g1_rem_set;
   // A set of cards that cover the objects for which the Rsets should be updated
   // concurrently after the collection.
   DirtyCardQueueSet _dirty_card_queue_set;
   // The closure used to refine a single card.
   RefineCardTableEntryClosure* _refine_cte_cl;
   // A function to check the consistency of dirty card logs.
   void check_ct_logs_at_safepoint();
   // A DirtyCardQueueSet that is used to hold cards that contain
   // references into the current collection set. This is used to
   // update the remembered sets of the regions in the collection
   // set in the event of an evacuation failure.
   DirtyCardQueueSet _into_cset_dirty_card_queue_set;
   // After a collection pause, make the regions in the CS into free
   // regions.
   void free_collection_set(HeapRegion* cs_head, EvacuationInfo& evacuation_info);
   // Abandon the current collection set without recording policy
   // statistics or updating free lists.
   void abandon_collection_set(HeapRegion* cs_head);
   // Applies "scan_non_heap_roots" to roots outside the heap,
   // "scan_rs" to roots inside the heap (having done "set_region" to
   // indicate the region in which the root resides),
   // and does "scan_metadata" If "scan_rs" is
   // NULL, then this step is skipped.  The "worker_i"
   // param is for use with parallel roots processing, and should be
   // the "i" of the calling parallel worker thread's work(i) function.
   // In the sequential case this param will be ignored.
   void g1_process_strong_roots(bool is_scavenging,
                                ScanningOption so,
                                OopClosure* scan_non_heap_roots,
                                OopsInHeapRegionClosure* scan_rs,
                                G1KlassScanClosure* scan_klasses,
                                int worker_i);
   // Apply "blk" to all the weak roots of the system.  These include
   // JNI weak roots, the code cache, system dictionary, symbol table,
   // string table, and referents of reachable weak refs.
   void g1_process_weak_roots(OopClosure* root_closure);
   // Notifies all the necessary spaces that the committed space has
   // been updated (either expanded or shrunk). It should be called
   // after _g1_storage is updated.
   void update_committed_space(HeapWord* old_end, HeapWord* new_end);
   // The concurrent marker (and the thread it runs in.)
   ConcurrentMark* _cm;
   ConcurrentMarkThread* _cmThread;
   bool _mark_in_progress;
   // The concurrent refiner.
   ConcurrentG1Refine* _cg1r;
   // The parallel task queues
   RefToScanQueueSet *_task_queues;
   // True iff a evacuation has failed in the current collection.
   bool _evacuation_failed;
   EvacuationFailedInfo* _evacuation_failed_info_array;
   // Failed evacuations cause some logical from-space objects to have
   // forwarding pointers to themselves.  Reset them.
   void remove_self_forwarding_pointers();
   // Together, these store an object with a preserved mark, and its mark value.
   Stack<oop, mtGC>     _objs_with_preserved_marks;
   Stack<markOop, mtGC> _preserved_marks_of_objs;
   // Preserve the mark of "obj", if necessary, in preparation for its mark
   // word being overwritten with a self-forwarding-pointer.
   void preserve_mark_if_necessary(oop obj, markOop m);
   // The stack of evac-failure objects left to be scanned.
   GrowableArray<oop>*    _evac_failure_scan_stack;
   // The closure to apply to evac-failure objects.
   OopsInHeapRegionClosure* _evac_failure_closure;
   // Set the field above.
   void
   set_evac_failure_closure(OopsInHeapRegionClosure* evac_failure_closure) {
     _evac_failure_closure = evac_failure_closure;
   }
   // Push "obj" on the scan stack.
   void push_on_evac_failure_scan_stack(oop obj);
   // Process scan stack entries until the stack is empty.
   void drain_evac_failure_scan_stack();
   // True iff an invocation of "drain_scan_stack" is in progress; to
   // prevent unnecessary recursion.
   bool _drain_in_progress;
   // Do any necessary initialization for evacuation-failure handling.
   // "cl" is the closure that will be used to process evac-failure
   // objects.
   void init_for_evac_failure(OopsInHeapRegionClosure* cl);
   // Do any necessary cleanup for evacuation-failure handling data
   // structures.
   void finalize_for_evac_failure();
   // An attempt to evacuate "obj" has failed; take necessary steps.
   oop handle_evacuation_failure_par(G1ParScanThreadState* _par_scan_state, oop obj);
   void handle_evacuation_failure_common(oop obj, markOop m);
 #ifndef PRODUCT
   // Support for forcing evacuation failures. Analogous to
   // PromotionFailureALot for the other collectors.
   // Records whether G1EvacuationFailureALot should be in effect
   // for the current GC
   bool _evacuation_failure_alot_for_current_gc;
   // Used to record the GC number for interval checking when
   // determining whether G1EvaucationFailureALot is in effect
   // for the current GC.
   size_t _evacuation_failure_alot_gc_number;
   // Count of the number of evacuations between failures.
   volatile size_t _evacuation_failure_alot_count;
   // Set whether G1EvacuationFailureALot should be in effect
   // for the current GC (based upon the type of GC and which
   // command line flags are set);
   inline bool evacuation_failure_alot_for_gc_type(bool gcs_are_young,
                                                   bool during_initial_mark,
                                                   bool during_marking);
   inline void set_evacuation_failure_alot_for_current_gc();
   // Return true if it's time to cause an evacuation failure.
   inline bool evacuation_should_fail();
   // Reset the G1EvacuationFailureALot counters.  Should be called at
   // the end of an evacuation pause in which an evacuation failure occurred.
   inline void reset_evacuation_should_fail();
 #endif // !PRODUCT
   // ("Weak") Reference processing support.
   //
   // G1 has 2 instances of the reference processor class. One
   // (_ref_processor_cm) handles reference object discovery
   // and subsequent processing during concurrent marking cycles.
   //
   // The other (_ref_processor_stw) handles reference object
   // discovery and processing during full GCs and incremental
   // evacuation pauses.
   //
   // During an incremental pause, reference discovery will be
   // temporarily disabled for _ref_processor_cm and will be
   // enabled for _ref_processor_stw. At the end of the evacuation
   // pause references discovered by _ref_processor_stw will be
   // processed and discovery will be disabled. The previous
   // setting for reference object discovery for _ref_processor_cm
   // will be re-instated.
   //
   // At the start of marking:
   //  * Discovery by the CM ref processor is verified to be inactive
   //    and it's discovered lists are empty.
   //  * Discovery by the CM ref processor is then enabled.
   //
   // At the end of marking:
   //  * Any references on the CM ref processor's discovered
   //    lists are processed (possibly MT).
   //
   // At the start of full GC we:
   //  * Disable discovery by the CM ref processor and
   //    empty CM ref processor's discovered lists
   //    (without processing any entries).
   //  * Verify that the STW ref processor is inactive and it's
   //    discovered lists are empty.
   //  * Temporarily set STW ref processor discovery as single threaded.
   //  * Temporarily clear the STW ref processor's _is_alive_non_header
   //    field.
   //  * Finally enable discovery by the STW ref processor.
   //
   // The STW ref processor is used to record any discovered
   // references during the full GC.
   //
   // At the end of a full GC we:
   //  * Enqueue any reference objects discovered by the STW ref processor
   //    that have non-live referents. This has the side-effect of
   //    making the STW ref processor inactive by disabling discovery.
   //  * Verify that the CM ref processor is still inactive
   //    and no references have been placed on it's discovered
   //    lists (also checked as a precondition during initial marking).
   // The (stw) reference processor...
   ReferenceProcessor* _ref_processor_stw;
   STWGCTimer* _gc_timer_stw;
   ConcurrentGCTimer* _gc_timer_cm;
   G1OldTracer* _gc_tracer_cm;
   G1NewTracer* _gc_tracer_stw;
   // During reference object discovery, the _is_alive_non_header
   // closure (if non-null) is applied to the referent object to
   // determine whether the referent is live. If so then the
   // reference object does not need to be 'discovered' and can
   // be treated as a regular oop. This has the benefit of reducing
   // the number of 'discovered' reference objects that need to
   // be processed.
   //
   // Instance of the is_alive closure for embedding into the
   // STW reference processor as the _is_alive_non_header field.
   // Supplying a value for the _is_alive_non_header field is
   // optional but doing so prevents unnecessary additions to
   // the discovered lists during reference discovery.
   G1STWIsAliveClosure _is_alive_closure_stw;
   // The (concurrent marking) reference processor...
   ReferenceProcessor* _ref_processor_cm;
   // Instance of the concurrent mark is_alive closure for embedding
   // into the Concurrent Marking reference processor as the
   // _is_alive_non_header field. Supplying a value for the
   // _is_alive_non_header field is optional but doing so prevents
   // unnecessary additions to the discovered lists during reference
   // discovery.
   G1CMIsAliveClosure _is_alive_closure_cm;
   // Cache used by G1CollectedHeap::start_cset_region_for_worker().
   HeapRegion** _worker_cset_start_region;
   // Time stamp to validate the regions recorded in the cache
   // used by G1CollectedHeap::start_cset_region_for_worker().
   // The heap region entry for a given worker is valid iff
   // the associated time stamp value matches the current value
   // of G1CollectedHeap::_gc_time_stamp.
   unsigned int* _worker_cset_start_region_time_stamp;
   enum G1H_process_strong_roots_tasks {
     G1H_PS_filter_satb_buffers,
     G1H_PS_refProcessor_oops_do,
     // Leave this one last.
     G1H_PS_NumElements
   };
   SubTasksDone* _process_strong_tasks;
   volatile bool _free_regions_coming;
 public:
   SubTasksDone* process_strong_tasks() { return _process_strong_tasks; }
   void set_refine_cte_cl_concurrency(bool concurrent);
   RefToScanQueue *task_queue(int i) const;
   // A set of cards where updates happened during the GC
   DirtyCardQueueSet& dirty_card_queue_set() { return _dirty_card_queue_set; }
   // A DirtyCardQueueSet that is used to hold cards that contain
   // references into the current collection set. This is used to
   // update the remembered sets of the regions in the collection
   // set in the event of an evacuation failure.
   DirtyCardQueueSet& into_cset_dirty_card_queue_set()
         { return _into_cset_dirty_card_queue_set; }
   // Create a G1CollectedHeap with the specified policy.
   // Must call the initialize method afterwards.
   // May not return if something goes wrong.
   G1CollectedHeap(G1CollectorPolicy* policy);
   // Initialize the G1CollectedHeap to have the initial and
   // maximum sizes and remembered and barrier sets
   // specified by the policy object.
   jint initialize();
   // Return the (conservative) maximum heap alignment for any G1 heap
   static size_t conservative_max_heap_alignment();
   // Initialize weak reference processing.
   virtual void ref_processing_init();
   void set_par_threads(uint t) {
     SharedHeap::set_par_threads(t);
     // Done in SharedHeap but oddly there are
     // two _process_strong_tasks's in a G1CollectedHeap
     // so do it here too.
     _process_strong_tasks->set_n_threads(t);
   }
   // Set _n_par_threads according to a policy TBD.
   void set_par_threads();
   void set_n_termination(int t) {
     _process_strong_tasks->set_n_threads(t);
   }
   virtual CollectedHeap::Name kind() const {
     return CollectedHeap::G1CollectedHeap;
   }
   // The current policy object for the collector.
   G1CollectorPolicy* g1_policy() const { return _g1_policy; }
   virtual CollectorPolicy* collector_policy() const { return (CollectorPolicy*) g1_policy(); }
   // Adaptive size policy.  No such thing for g1.
   virtual AdaptiveSizePolicy* size_policy() { return NULL; }
   // The rem set and barrier set.
   G1RemSet* g1_rem_set() const { return _g1_rem_set; }
   unsigned get_gc_time_stamp() {
     return _gc_time_stamp;
   }
   void reset_gc_time_stamp() {
     _gc_time_stamp = 0;
     OrderAccess::fence();
     // Clear the cached CSet starting regions and time stamps.
     // Their validity is dependent on the GC timestamp.
     clear_cset_start_regions();
   }
   void check_gc_time_stamps() PRODUCT_RETURN;
   void increment_gc_time_stamp() {
     ++_gc_time_stamp;
     OrderAccess::fence();
   }
   // Reset the given region's GC timestamp. If it's starts humongous,
   // also reset the GC timestamp of its corresponding
   // continues humongous regions too.
   void reset_gc_time_stamps(HeapRegion* hr);
   void iterate_dirty_card_closure(CardTableEntryClosure* cl,
                                   DirtyCardQueue* into_cset_dcq,
                                   bool concurrent, int worker_i);
   // The shared block offset table array.
   G1BlockOffsetSharedArray* bot_shared() const { return _bot_shared; }
   // Reference Processing accessors
   // The STW reference processor....
   ReferenceProcessor* ref_processor_stw() const { return _ref_processor_stw; }
   // The Concurrent Marking reference processor...
   ReferenceProcessor* ref_processor_cm() const { return _ref_processor_cm; }
   ConcurrentGCTimer* gc_timer_cm() const { return _gc_timer_cm; }
   G1OldTracer* gc_tracer_cm() const { return _gc_tracer_cm; }
   virtual size_t capacity() const;
   virtual size_t used() const;
   // This should be called when we're not holding the heap lock. The
   // result might be a bit inaccurate.
   size_t used_unlocked() const;
   size_t recalculate_used() const;
   // These virtual functions do the actual allocation.
   // Some heaps may offer a contiguous region for shared non-blocking
   // allocation, via inlined code (by exporting the address of the top and
   // end fields defining the extent of the contiguous allocation region.)
   // But G1CollectedHeap doesn't yet support this.
   // Return an estimate of the maximum allocation that could be performed
   // without triggering any collection or expansion activity.  In a
   // generational collector, for example, this is probably the largest
   // allocation that could be supported (without expansion) in the youngest
   // generation.  It is "unsafe" because no locks are taken; the result
   // should be treated as an approximation, not a guarantee, for use in
   // heuristic resizing decisions.
   virtual size_t unsafe_max_alloc();
   virtual bool is_maximal_no_gc() const {
     return _g1_storage.uncommitted_size() == 0;
   }
   // The total number of regions in the heap.
   uint n_regions() { return _hrs.length(); }
   // The max number of regions in the heap.
   uint max_regions() { return _hrs.max_length(); }
   // The number of regions that are completely free.
   uint free_regions() { return _free_list.length(); }
   // The number of regions that are not completely free.
   uint used_regions() { return n_regions() - free_regions(); }
   // The number of regions available for "regular" expansion.
   uint expansion_regions() { return _expansion_regions; }
   // Factory method for HeapRegion instances. It will return NULL if
   // the allocation fails.
   HeapRegion* new_heap_region(uint hrs_index, HeapWord* bottom);
   void verify_not_dirty_region(HeapRegion* hr) PRODUCT_RETURN;
   void verify_dirty_region(HeapRegion* hr) PRODUCT_RETURN;
   void verify_dirty_young_list(HeapRegion* head) PRODUCT_RETURN;
   void verify_dirty_young_regions() PRODUCT_RETURN;
   // verify_region_sets() performs verification over the region
   // lists. It will be compiled in the product code to be used when
   // necessary (i.e., during heap verification).
   void verify_region_sets();
   // verify_region_sets_optional() is planted in the code for
   // list verification in non-product builds (and it can be enabled in
   // product builds by defining HEAP_REGION_SET_FORCE_VERIFY to be 1).
 #if HEAP_REGION_SET_FORCE_VERIFY
   void verify_region_sets_optional() {
     verify_region_sets();
   }
 #else // HEAP_REGION_SET_FORCE_VERIFY
   void verify_region_sets_optional() { }
 #endif // HEAP_REGION_SET_FORCE_VERIFY
 #ifdef ASSERT
   bool is_on_master_free_list(HeapRegion* hr) {
     return hr->containing_set() == &_free_list;
   }
 #endif // ASSERT
   // Wrapper for the region list operations that can be called from
   // methods outside this class.
   void secondary_free_list_add_as_tail(FreeRegionList* list) {
     _secondary_free_list.add_as_tail(list);
   }
   void append_secondary_free_list() {
     _free_list.add_as_head(&_secondary_free_list);
   }
   void append_secondary_free_list_if_not_empty_with_lock() {
     // If the secondary free list looks empty there's no reason to
     // take the lock and then try to append it.
     if (!_secondary_free_list.is_empty()) {
       MutexLockerEx x(SecondaryFreeList_lock, Mutex::_no_safepoint_check_flag);
       append_secondary_free_list();
     }
   }
   void old_set_remove(HeapRegion* hr) {
     _old_set.remove(hr);
   }
   size_t non_young_capacity_bytes() {
     return _old_set.total_capacity_bytes() + _humongous_set.total_capacity_bytes();
   }
   void set_free_regions_coming();
   void reset_free_regions_coming();
   bool free_regions_coming() { return _free_regions_coming; }
   void wait_while_free_regions_coming();
   // Determine whether the given region is one that we are using as an
   // old GC alloc region.
   bool is_old_gc_alloc_region(HeapRegion* hr) {
     return hr == _retained_old_gc_alloc_region;
   }
   // Perform a collection of the heap; intended for use in implementing
   // "System.gc".  This probably implies as full a collection as the
   // "CollectedHeap" supports.
   virtual void collect(GCCause::Cause cause);
   // The same as above but assume that the caller holds the Heap_lock.
   void collect_locked(GCCause::Cause cause);
   // True iff an evacuation has failed in the most-recent collection.
   bool evacuation_failed() { return _evacuation_failed; }
   void remove_from_old_sets(const HeapRegionSetCount& old_regions_removed, const HeapRegionSetCount& humongous_regions_removed);
   void prepend_to_freelist(FreeRegionList* list);
   void decrement_summary_bytes(size_t bytes);
   // Returns "TRUE" iff "p" points into the committed areas of the heap.
   virtual bool is_in(const void* p) const;
   // Return "TRUE" iff the given object address is within the collection
   // set.
   inline bool obj_in_cs(oop obj);
   // Return "TRUE" iff the given object address is in the reserved
   // region of g1.
   bool is_in_g1_reserved(const void* p) const {
     return _g1_reserved.contains(p);
   }
   // Returns a MemRegion that corresponds to the space that has been
   // reserved for the heap
   MemRegion g1_reserved() {
     return _g1_reserved;
   }
   // Returns a MemRegion that corresponds to the space that has been
   // committed in the heap
   MemRegion g1_committed() {
     return _g1_committed;
   }
   virtual bool is_in_closed_subset(const void* p) const;
   G1SATBCardTableModRefBS* g1_barrier_set() {
     return (G1SATBCardTableModRefBS*) barrier_set();
   }
   // This resets the card table to all zeros.  It is used after
   // a collection pause which used the card table to claim cards.
   void cleanUpCardTable();
   // Iteration functions.
   // Iterate over all the ref-containing fields of all objects, calling
   // "cl.do_oop" on each.
   virtual void oop_iterate(ExtendedOopClosure* cl);
   // Same as above, restricted to a memory region.
   void oop_iterate(MemRegion mr, ExtendedOopClosure* cl);
   // Iterate over all objects, calling "cl.do_object" on each.
   virtual void object_iterate(ObjectClosure* cl);
   virtual void safe_object_iterate(ObjectClosure* cl) {
     object_iterate(cl);
   }
   // Iterate over all spaces in use in the heap, in ascending address order.
   virtual void space_iterate(SpaceClosure* cl);
   // Iterate over heap regions, in address order, terminating the
   // iteration early if the "doHeapRegion" method returns "true".
   void heap_region_iterate(HeapRegionClosure* blk) const;
   // Return the region with the given index. It assumes the index is valid.
   HeapRegion* region_at(uint index) const { return _hrs.at(index); }
   // Divide the heap region sequence into "chunks" of some size (the number
   // of regions divided by the number of parallel threads times some
   // overpartition factor, currently 4).  Assumes that this will be called
   // in parallel by ParallelGCThreads worker threads with discinct worker
   // ids in the range [0..max(ParallelGCThreads-1, 1)], that all parallel
   // calls will use the same "claim_value", and that that claim value is
   // different from the claim_value of any heap region before the start of
   // the iteration.  Applies "blk->doHeapRegion" to each of the regions, by
   // attempting to claim the first region in each chunk, and, if
   // successful, applying the closure to each region in the chunk (and
   // setting the claim value of the second and subsequent regions of the
   // chunk.)  For now requires that "doHeapRegion" always returns "false",
   // i.e., that a closure never attempt to abort a traversal.
   void heap_region_par_iterate_chunked(HeapRegionClosure* blk,
                                        uint worker,
                                        uint no_of_par_workers,
                                        jint claim_value);
   // It resets all the region claim values to the default.
   void reset_heap_region_claim_values();
   // Resets the claim values of regions in the current
   // collection set to the default.
   void reset_cset_heap_region_claim_values();
 #ifdef ASSERT
   bool check_heap_region_claim_values(jint claim_value);
   // Same as the routine above but only checks regions in the
   // current collection set.
   bool check_cset_heap_region_claim_values(jint claim_value);
 #endif // ASSERT
   // Clear the cached cset start regions and (more importantly)
   // the time stamps. Called when we reset the GC time stamp.
   void clear_cset_start_regions();
   // Given the id of a worker, obtain or calculate a suitable
   // starting region for iterating over the current collection set.
   HeapRegion* start_cset_region_for_worker(int worker_i);
   // This is a convenience method that is used by the
   // HeapRegionIterator classes to calculate the starting region for
   // each worker so that they do not all start from the same region.
   HeapRegion* start_region_for_worker(uint worker_i, uint no_of_par_workers);
   // Iterate over the regions (if any) in the current collection set.
   void collection_set_iterate(HeapRegionClosure* blk);
   // As above but starting from region r
   void collection_set_iterate_from(HeapRegion* r, HeapRegionClosure *blk);
   // Returns the first (lowest address) compactible space in the heap.
   virtual CompactibleSpace* first_compactible_space();
   // A CollectedHeap will contain some number of spaces.  This finds the
   // space containing a given address, or else returns NULL.
   virtual Space* space_containing(const void* addr) const;
   // A G1CollectedHeap will contain some number of heap regions.  This
   // finds the region containing a given address, or else returns NULL.
   template <class T>
   inline HeapRegion* heap_region_containing(const T addr) const;
   // Like the above, but requires "addr" to be in the heap (to avoid a
   // null-check), and unlike the above, may return an continuing humongous
   // region.
   template <class T>
   inline HeapRegion* heap_region_containing_raw(const T addr) const;
   // A CollectedHeap is divided into a dense sequence of "blocks"; that is,
   // each address in the (reserved) heap is a member of exactly
   // one block.  The defining characteristic of a block is that it is
   // possible to find its size, and thus to progress forward to the next
   // block.  (Blocks may be of different sizes.)  Thus, blocks may
   // represent Java objects, or they might be free blocks in a
   // free-list-based heap (or subheap), as long as the two kinds are
   // distinguishable and the size of each is determinable.
   // Returns the address of the start of the "block" that contains the
   // address "addr".  We say "blocks" instead of "object" since some heaps
   // may not pack objects densely; a chunk may either be an object or a
   // non-object.
   virtual HeapWord* block_start(const void* addr) const;
   // Requires "addr" to be the start of a chunk, and returns its size.
   // "addr + size" is required to be the start of a new chunk, or the end
   // of the active area of the heap.
   virtual size_t block_size(const HeapWord* addr) const;
   // Requires "addr" to be the start of a block, and returns "TRUE" iff
   // the block is an object.
   virtual bool block_is_obj(const HeapWord* addr) const;
   // Does this heap support heap inspection? (+PrintClassHistogram)
   virtual bool supports_heap_inspection() const { return true; }
   // Section on thread-local allocation buffers (TLABs)
   // See CollectedHeap for semantics.
   bool supports_tlab_allocation() const;
   size_t tlab_capacity(Thread* ignored) const;
   size_t tlab_used(Thread* ignored) const;
   size_t max_tlab_size() const;
   size_t unsafe_max_tlab_alloc(Thread* ignored) const;
   // Can a compiler initialize a new object without store barriers?
   // This permission only extends from the creation of a new object
   // via a TLAB up to the first subsequent safepoint. If such permission
   // is granted for this heap type, the compiler promises to call
   // defer_store_barrier() below on any slow path allocation of
   // a new object for which such initializing store barriers will
   // have been elided. G1, like CMS, allows this, but should be
   // ready to provide a compensating write barrier as necessary
   // if that storage came out of a non-young region. The efficiency
   // of this implementation depends crucially on being able to
   // answer very efficiently in constant time whether a piece of
   // storage in the heap comes from a young region or not.
   // See ReduceInitialCardMarks.
   virtual bool can_elide_tlab_store_barriers() const {
     return true;
   }
   virtual bool card_mark_must_follow_store() const {
     return true;
   }
   bool is_in_young(const oop obj) {
     HeapRegion* hr = heap_region_containing(obj);
     return hr != NULL && hr->is_young();
   }
 #ifdef ASSERT
   virtual bool is_in_partial_collection(const void* p);
 #endif
   virtual bool is_scavengable(const void* addr);
   // We don't need barriers for initializing stores to objects
   // in the young gen: for the SATB pre-barrier, there is no
   // pre-value that needs to be remembered; for the remembered-set
   // update logging post-barrier, we don't maintain remembered set
   // information for young gen objects.
   virtual bool can_elide_initializing_store_barrier(oop new_obj) {
     return is_in_young(new_obj);
   }
   // Returns "true" iff the given word_size is "very large".
   static bool isHumongous(size_t word_size) {
     // Note this has to be strictly greater-than as the TLABs
     // are capped at the humongous thresold and we want to
     // ensure that we don't try to allocate a TLAB as
     // humongous and that we don't allocate a humongous
     // object in a TLAB.
     return word_size > _humongous_object_threshold_in_words;
   }
   // Update mod union table with the set of dirty cards.
   void updateModUnion();
   // Set the mod union bits corresponding to the given memRegion.  Note
   // that this is always a safe operation, since it doesn't clear any
   // bits.
   void markModUnionRange(MemRegion mr);
   // Records the fact that a marking phase is no longer in progress.
   void set_marking_complete() {
     _mark_in_progress = false;
   }
   void set_marking_started() {
     _mark_in_progress = true;
   }
   bool mark_in_progress() {
     return _mark_in_progress;
   }
   // Print the maximum heap capacity.
   virtual size_t max_capacity() const;
   virtual jlong millis_since_last_gc();
   // Convenience function to be used in situations where the heap type can be
   // asserted to be this type.
   static G1CollectedHeap* heap();
   void set_region_short_lived_locked(HeapRegion* hr);
   // add appropriate methods for any other surv rate groups
   YoungList* young_list() const { return _young_list; }
   // debugging
   bool check_young_list_well_formed() {
     return _young_list->check_list_well_formed();
   }
   bool check_young_list_empty(bool check_heap,
                               bool check_sample = true);
   // *** Stuff related to concurrent marking.  It's not clear to me that so
   // many of these need to be public.
   // The functions below are helper functions that a subclass of
   // "CollectedHeap" can use in the implementation of its virtual
   // functions.
   // This performs a concurrent marking of the live objects in a
   // bitmap off to the side.
   void doConcurrentMark();
   bool isMarkedPrev(oop obj) const;
   bool isMarkedNext(oop obj) const;
   // Determine if an object is dead, given the object and also
   // the region to which the object belongs. An object is dead
   // iff a) it was not allocated since the last mark and b) it
   // is not marked.
   bool is_obj_dead(const oop obj, const HeapRegion* hr) const {
     return
       !hr->obj_allocated_since_prev_marking(obj) &&
       !isMarkedPrev(obj);
   }
   // This function returns true when an object has been
   // around since the previous marking and hasn't yet
   // been marked during this marking.
   bool is_obj_ill(const oop obj, const HeapRegion* hr) const {
     return
       !hr->obj_allocated_since_next_marking(obj) &&
       !isMarkedNext(obj);
   }
   // Determine if an object is dead, given only the object itself.
   // This will find the region to which the object belongs and
   // then call the region version of the same function.
   // Added if it is NULL it isn't dead.
   bool is_obj_dead(const oop obj) const {
     const HeapRegion* hr = heap_region_containing(obj);
     if (hr == NULL) {
       if (obj == NULL) return false;
       else return true;
     }
     else return is_obj_dead(obj, hr);
   }
   bool is_obj_ill(const oop obj) const {
     const HeapRegion* hr = heap_region_containing(obj);
     if (hr == NULL) {
       if (obj == NULL) return false;
       else return true;
     }
     else return is_obj_ill(obj, hr);
   }
   bool allocated_since_marking(oop obj, HeapRegion* hr, VerifyOption vo);
   HeapWord* top_at_mark_start(HeapRegion* hr, VerifyOption vo);
   bool is_marked(oop obj, VerifyOption vo);
   const char* top_at_mark_start_str(VerifyOption vo);
   ConcurrentMark* concurrent_mark() const { return _cm; }
   // Refinement
   ConcurrentG1Refine* concurrent_g1_refine() const { return _cg1r; }
   // The dirty cards region list is used to record a subset of regions
   // whose cards need clearing. The list if populated during the
   // remembered set scanning and drained during the card table
   // cleanup. Although the methods are reentrant, population/draining
   // phases must not overlap. For synchronization purposes the last
   // element on the list points to itself.
   HeapRegion* _dirty_cards_region_list;
   void push_dirty_cards_region(HeapRegion* hr);
   HeapRegion* pop_dirty_cards_region();
   // Optimized nmethod scanning support routines
   // Register the given nmethod with the G1 heap
   virtual void register_nmethod(nmethod* nm);
   // Unregister the given nmethod from the G1 heap
   virtual void unregister_nmethod(nmethod* nm);
   // Migrate the nmethods in the code root lists of the regions
   // in the collection set to regions in to-space. In the event
   // of an evacuation failure, nmethods that reference objects
   // that were not successfullly evacuated are not migrated.
   void migrate_strong_code_roots();
   // During an initial mark pause, mark all the code roots that
   // point into regions *not* in the collection set.
   void mark_strong_code_roots(uint worker_id);
   // Rebuild the stong code root lists for each region
   // after a full GC
   void rebuild_strong_code_roots();
   // Delete entries for dead interned string and clean up unreferenced symbols
   // in symbol table, possibly in parallel.
   void unlink_string_and_symbol_table(BoolObjectClosure* is_alive, bool unlink_strings = true, bool unlink_symbols = true);
   // Verification
   // The following is just to alert the verification code
   // that a full collection has occurred and that the
   // remembered sets are no longer up to date.
   bool _full_collection;
   void set_full_collection() { _full_collection = true;}
   void clear_full_collection() {_full_collection = false;}
   bool full_collection() {return _full_collection;}
   // Perform any cleanup actions necessary before allowing a verification.
   virtual void prepare_for_verify();
   // Perform verification.
   // vo == UsePrevMarking  -> use "prev" marking information,
   // vo == UseNextMarking -> use "next" marking information
   // vo == UseMarkWord    -> use the mark word in the object header
   //
   // NOTE: Only the "prev" marking information is guaranteed to be
   // consistent most of the time, so most calls to this should use
   // vo == UsePrevMarking.
   // Currently, there is only one case where this is called with
   // vo == UseNextMarking, which is to verify the "next" marking
   // information at the end of remark.
   // Currently there is only one place where this is called with
   // vo == UseMarkWord, which is to verify the marking during a
   // full GC.
   void verify(bool silent, VerifyOption vo);
   // Override; it uses the "prev" marking information
   virtual void verify(bool silent);
   // The methods below are here for convenience and dispatch the
   // appropriate method depending on value of the given VerifyOption
   // parameter. The values for that parameter, and their meanings,
   // are the same as those above.
   bool is_obj_dead_cond(const oop obj,
                         const HeapRegion* hr,
                         const VerifyOption vo) const {
     switch (vo) {
     case VerifyOption_G1UsePrevMarking: return is_obj_dead(obj, hr);
     case VerifyOption_G1UseNextMarking: return is_obj_ill(obj, hr);
     case VerifyOption_G1UseMarkWord:    return !obj->is_gc_marked();
     default:                            ShouldNotReachHere();
     }
     return false; // keep some compilers happy
   }
   bool is_obj_dead_cond(const oop obj,
                         const VerifyOption vo) const {
     switch (vo) {
     case VerifyOption_G1UsePrevMarking: return is_obj_dead(obj);
     case VerifyOption_G1UseNextMarking: return is_obj_ill(obj);
     case VerifyOption_G1UseMarkWord:    return !obj->is_gc_marked();
     default:                            ShouldNotReachHere();
     }
     return false; // keep some compilers happy
   }
   // Printing
   virtual void print_on(outputStream* st) const;
   virtual void print_extended_on(outputStream* st) const;
   virtual void print_on_error(outputStream* st) const;
   virtual void print_gc_threads_on(outputStream* st) const;
   virtual void gc_threads_do(ThreadClosure* tc) const;
   // Override
   void print_tracing_info() const;
   // The following two methods are helpful for debugging RSet issues.
   void print_cset_rsets() PRODUCT_RETURN;
   void print_all_rsets() PRODUCT_RETURN;
 public:
   void stop_conc_gc_threads();
   size_t pending_card_num();
   size_t cards_scanned();
 protected:
   size_t _max_heap_capacity;
 };
 class G1ParGCAllocBuffer: public ParGCAllocBuffer {
 private:
   bool        _retired;
 public:
   G1ParGCAllocBuffer(size_t gclab_word_size);
   void set_buf(HeapWord* buf) {
     ParGCAllocBuffer::set_buf(buf);
     _retired = false;
   }
   void retire(bool end_of_gc, bool retain) {
     if (_retired)
       return;
     ParGCAllocBuffer::retire(end_of_gc, retain);
     _retired = true;
   }
 };
 class G1ParScanThreadState : public StackObj {
 protected:
   G1CollectedHeap* _g1h;
   RefToScanQueue*  _refs;
   DirtyCardQueue   _dcq;
   G1SATBCardTableModRefBS* _ct_bs;
   G1RemSet* _g1_rem;
   G1ParGCAllocBuffer  _surviving_alloc_buffer;
   G1ParGCAllocBuffer  _tenured_alloc_buffer;
   G1ParGCAllocBuffer* _alloc_buffers[GCAllocPurposeCount];
   ageTable            _age_table;
   G1ParScanClosure    _scanner;
   size_t           _alloc_buffer_waste;
   size_t           _undo_waste;
   OopsInHeapRegionClosure*      _evac_failure_cl;
   G1ParScanHeapEvacClosure*     _evac_cl;
   G1ParScanPartialArrayClosure* _partial_scan_cl;
   int  _hash_seed;
   uint _queue_num;
   size_t _term_attempts;
   double _start;
   double _start_strong_roots;
   double _strong_roots_time;
   double _start_term;
   double _term_time;
   // Map from young-age-index (0 == not young, 1 is youngest) to
   // surviving words. base is what we get back from the malloc call
   size_t* _surviving_young_words_base;
   // this points into the array, as we use the first few entries for padding
   size_t* _surviving_young_words;
 #define PADDING_ELEM_NUM (DEFAULT_CACHE_LINE_SIZE / sizeof(size_t))
   void   add_to_alloc_buffer_waste(size_t waste) { _alloc_buffer_waste += waste; }
   void   add_to_undo_waste(size_t waste)         { _undo_waste += waste; }
   DirtyCardQueue& dirty_card_queue()             { return _dcq;  }
   G1SATBCardTableModRefBS* ctbs()                { return _ct_bs; }
   template <class T> void immediate_rs_update(HeapRegion* from, T* p, int tid) {
     if (!from->is_survivor()) {
       _g1_rem->par_write_ref(from, p, tid);
     }
   }
   template <class T> void deferred_rs_update(HeapRegion* from, T* p, int tid) {
     // If the new value of the field points to the same region or
     // is the to-space, we don't need to include it in the Rset updates.
     if (!from->is_in_reserved(oopDesc::load_decode_heap_oop(p)) && !from->is_survivor()) {
       size_t card_index = ctbs()->index_for(p);
       // If the card hasn't been added to the buffer, do it.
       if (ctbs()->mark_card_deferred(card_index)) {
         dirty_card_queue().enqueue((jbyte*)ctbs()->byte_for_index(card_index));
       }
     }
   }
 public:
   G1ParScanThreadState(G1CollectedHeap* g1h, uint queue_num, ReferenceProcessor* rp);
   ~G1ParScanThreadState() {
     FREE_C_HEAP_ARRAY(size_t, _surviving_young_words_base, mtGC);
   }
   RefToScanQueue*   refs()            { return _refs;             }
   ageTable*         age_table()       { return &_age_table;       }
   G1ParGCAllocBuffer* alloc_buffer(GCAllocPurpose purpose) {
     return _alloc_buffers[purpose];
   }
   size_t alloc_buffer_waste() const              { return _alloc_buffer_waste; }
   size_t undo_waste() const                      { return _undo_waste; }
 #ifdef ASSERT
   bool verify_ref(narrowOop* ref) const;
   bool verify_ref(oop* ref) const;
   bool verify_task(StarTask ref) const;
 #endif // ASSERT
   template <class T> void push_on_queue(T* ref) {
     assert(verify_ref(ref), "sanity");
     refs()->push(ref);
   }
   template <class T> void update_rs(HeapRegion* from, T* p, int tid) {
     if (G1DeferredRSUpdate) {
       deferred_rs_update(from, p, tid);
     } else {
       immediate_rs_update(from, p, tid);
     }
   }
   HeapWord* allocate_slow(GCAllocPurpose purpose, size_t word_sz) {
     HeapWord* obj = NULL;
     size_t gclab_word_size = _g1h->desired_plab_sz(purpose);
     if (word_sz * 100 < gclab_word_size * ParallelGCBufferWastePct) {
       G1ParGCAllocBuffer* alloc_buf = alloc_buffer(purpose);
       add_to_alloc_buffer_waste(alloc_buf->words_remaining());
       alloc_buf->retire(false /* end_of_gc */, false /* retain */);
       HeapWord* buf = _g1h->par_allocate_during_gc(purpose, gclab_word_size);
       if (buf == NULL) return NULL; // Let caller handle allocation failure.
       // Otherwise.
       alloc_buf->set_word_size(gclab_word_size);
       alloc_buf->set_buf(buf);
       obj = alloc_buf->allocate(word_sz);
       assert(obj != NULL, "buffer was definitely big enough...");
     } else {
       obj = _g1h->par_allocate_during_gc(purpose, word_sz);
     }
     return obj;
   }
   HeapWord* allocate(GCAllocPurpose purpose, size_t word_sz) {
     HeapWord* obj = alloc_buffer(purpose)->allocate(word_sz);
     if (obj != NULL) return obj;
     return allocate_slow(purpose, word_sz);
   }
   void undo_allocation(GCAllocPurpose purpose, HeapWord* obj, size_t word_sz) {
     if (alloc_buffer(purpose)->contains(obj)) {
       assert(alloc_buffer(purpose)->contains(obj + word_sz - 1),
              "should contain whole object");
       alloc_buffer(purpose)->undo_allocation(obj, word_sz);
     } else {
       CollectedHeap::fill_with_object(obj, word_sz);
       add_to_undo_waste(word_sz);
     }
   }
   void set_evac_failure_closure(OopsInHeapRegionClosure* evac_failure_cl) {
     _evac_failure_cl = evac_failure_cl;
   }
   OopsInHeapRegionClosure* evac_failure_closure() {
     return _evac_failure_cl;
   }
   void set_evac_closure(G1ParScanHeapEvacClosure* evac_cl) {
     _evac_cl = evac_cl;
   }
   void set_partial_scan_closure(G1ParScanPartialArrayClosure* partial_scan_cl) {
     _partial_scan_cl = partial_scan_cl;
   }
   int* hash_seed() { return &_hash_seed; }
   uint queue_num() { return _queue_num; }
   size_t term_attempts() const  { return _term_attempts; }
   void note_term_attempt() { _term_attempts++; }
   void start_strong_roots() {
     _start_strong_roots = os::elapsedTime();
   }
   void end_strong_roots() {
     _strong_roots_time += (os::elapsedTime() - _start_strong_roots);
   }
   double strong_roots_time() const { return _strong_roots_time; }
   void start_term_time() {
     note_term_attempt();
     _start_term = os::elapsedTime();
   }
   void end_term_time() {
     _term_time += (os::elapsedTime() - _start_term);
   }
   double term_time() const { return _term_time; }
   double elapsed_time() const {
     return os::elapsedTime() - _start;
   }
   static void
     print_termination_stats_hdr(outputStream* const st = gclog_or_tty);
   void
     print_termination_stats(int i, outputStream* const st = gclog_or_tty) const;
   size_t* surviving_young_words() {
     // We add on to hide entry 0 which accumulates surviving words for
     // age -1 regions (i.e. non-young ones)
     return _surviving_young_words;
   }
   void retire_alloc_buffers() {
     for (int ap = 0; ap < GCAllocPurposeCount; ++ap) {
       size_t waste = _alloc_buffers[ap]->words_remaining();
       add_to_alloc_buffer_waste(waste);
       _alloc_buffers[ap]->flush_stats_and_retire(_g1h->stats_for_purpose((GCAllocPurpose)ap),
                                                  true /* end_of_gc */,
                                                  false /* retain */);
     }
   }
   oop copy_to_survivor_space(oop const obj);
   template <class T> void deal_with_reference(T* ref_to_scan) {
     if (has_partial_array_mask(ref_to_scan)) {
       _partial_scan_cl->do_oop_nv(ref_to_scan);
     } else {
       // Note: we can use "raw" versions of "region_containing" because
       // "obj_to_scan" is definitely in the heap, and is not in a
       // humongous region.
       HeapRegion* r = _g1h->heap_region_containing_raw(ref_to_scan);
       _evac_cl->set_region(r);
       _evac_cl->do_oop_nv(ref_to_scan);
     }
   }
   void deal_with_reference(StarTask ref) {
     assert(verify_task(ref), "sanity");
     if (ref.is_narrow()) {
       deal_with_reference((narrowOop*)ref);
     } else {
       deal_with_reference((oop*)ref);
     }
   }
 public:
   void trim_queue();
 };
 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1COLLECTEDHEAP_HPP

Mercurial > jdk8-mips64-public > hotspot / annotate

src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp@58fc1b1523dc (annotated)

src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp