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 /*

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  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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  * 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

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 #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/g1AllocRegion.hpp"

 #include "gc_implementation/g1/g1HRPrinter.hpp"

 #include "gc_implementation/g1/g1RemSet.hpp"

 #include "gc_implementation/g1/g1MonitoringSupport.hpp"

 #include "gc_implementation/g1/heapRegionSeq.hpp"

 #include "gc_implementation/g1/heapRegionSets.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"

 // 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.

 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 GenerationCounters;

 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 */) { }

 };

 // 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

 // refence processing during STW evacuation pauses.

 class G1STWIsAliveClosure: public BoolObjectClosure {

   G1CollectedHeap* _g1;

 public:

   G1STWIsAliveClosure(G1CollectedHeap* g1) : _g1(g1) {}

   void do_object(oop p) { assert(false, "Do not call."); }

   bool do_object_b(oop p);

 };

 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 */) { }

 };

 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 <bool do_gen_barrier, 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.

   MasterFreeRegionList      _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.

   SecondaryFreeRegionList   _secondary_free_list;

   // It keeps track of the old regions.

   MasterOldRegionSet        _old_set;

   // It keeps track of the humongous regions.

   MasterHumongousRegionSet  _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();

   // It releases the GC alloc regions at the end of a GC.

   void release_gc_alloc_regions();

   // 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;

   // 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);

   // 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);

   // 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);

   // 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();

   // Enqueue any remaining discovered references

   // after processing.

   void enqueue_discovered_references();

 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. It does not assume that the reference

   // points into the heap; if it doesn't, it will return false.

   bool in_cset_fast_test(oop obj) {

     assert(_in_cset_fast_test != NULL, "sanity");

     if (_g1_committed.contains((HeapWord*) obj)) {

       // no need to subtract the bottom of the heap from obj,

       // _in_cset_fast_test is biased

       uintx index = (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;

     } else {

       return false;

     }

   }

   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;

   }

   G1HRPrinter* hr_printer() { return &_hr_printer; }

 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);

   // 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();

   // The g1 remembered set of the heap.

   G1RemSet* _g1_rem_set;

   // And it's mod ref barrier set, used to track updates for the above.

   ModRefBarrierSet* _mr_bs;

   // 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 Heap Region Rem Set Iterator.

   HeapRegionRemSetIterator** _rem_set_iterator;

   // 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);

   // 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,

                              OopClosure* non_root_closure);

   // 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,

                    size_t* pre_used,

                    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,

                              size_t* pre_used,

                              FreeRegionList* free_list,

                              HumongousRegionSet* humongous_proxy_set,

                              bool par);

   // 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;

   // Set the attribute indicating whether evacuation has failed in the

   // current collection.

   void set_evacuation_failed(bool b) { _evacuation_failed = b; }

   // Failed evacuations cause some logical from-space objects to have

   // forwarding pointers to themselves.  Reset them.

   void remove_self_forwarding_pointers();

   // When one is non-null, so is the other.  Together, they each pair is

   // an object with a preserved mark, and its mark value.

   GrowableArray<oop>*     _objs_with_preserved_marks;

   GrowableArray<markOop>* _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(OopsInHeapRegionClosure* cl, 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 ocurred.

   inline void reset_evacuation_should_fail();

 #endif // !PRODUCT

   // ("Weak") Reference processing support.

   //

   // G1 has 2 instances of the referece 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;

   // 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();

   // 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; }

   ModRefBarrierSet* mr_bs() const { return _mr_bs; }

   // The rem set iterator.

   HeapRegionRemSetIterator* rem_set_iterator(int i) {

     return _rem_set_iterator[i];

   }

   HeapRegionRemSetIterator* rem_set_iterator() {

     return _rem_set_iterator[0];

   }

   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 Concurent Marking reference processor...

   ReferenceProcessor* ref_processor_cm() const { return _ref_processor_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 definning 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;

   }

   bool is_in_humongous_set(HeapRegion* hr) {

     return hr->containing_set() == &_humongous_set;

   }

 #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 a evacuation has failed in the most-recent collection.

   bool evacuation_failed() { return _evacuation_failed; }

   // It will free a region if it has allocated objects in it that are

   // all dead. It calls either free_region() or

   // free_humongous_region() depending on the type of the region that

   // is passed to it.

   void free_region_if_empty(HeapRegion* hr,

                             size_t* pre_used,

                             FreeRegionList* free_list,

                             OldRegionSet* old_proxy_set,

                             HumongousRegionSet* humongous_proxy_set,

                             HRRSCleanupTask* hrrs_cleanup_task,

                             bool par);

   // It appends the free list to the master free list and updates the

   // master humongous list according to the contents of the proxy

   // list. It also adjusts the total used bytes according to pre_used

   // (if par is true, it will do so by taking the ParGCRareEvent_lock).

   void update_sets_after_freeing_regions(size_t pre_used,

                                        FreeRegionList* free_list,

                                        OldRegionSet* old_proxy_set,

                                        HumongousRegionSet* humongous_proxy_set,

                                        bool par);

   // 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;

   // 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 objects allocated since the last collection, calling

   // "cl.do_object" on each.  The heap must have been initialized properly

   // to support this function, or else this call will fail.

   virtual void object_iterate_since_last_GC(ObjectClosure* 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.

   virtual bool supports_tlab_allocation() const;

   virtual size_t tlab_capacity(Thread* thr) const;

   virtual size_t unsafe_max_tlab_alloc(Thread* thr) 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();

   // 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);

   virtual void print_on(outputStream* st) const;

   virtual void print_extended_on(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;

   // 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() { 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);

   }

   // The methods below are here for convenience and dispatch the

   // appropriate method depending on value of the given VerifyOption

   // parameter. The options for that parameter are:

   //

   // vo == UsePrevMarking -> use "prev" marking information,

   // vo == UseNextMarking -> use "next" marking information,

   // vo == UseMarkWord    -> use mark word from object header

   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

   }

   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);

   // 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;}

   ConcurrentMark* concurrent_mark() const { return _cm; }

   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();

 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;

   CardTableModRefBS* _ct_bs;

   G1RemSet* _g1_rem;

   G1ParGCAllocBuffer  _surviving_alloc_buffer;

   G1ParGCAllocBuffer  _tenured_alloc_buffer;

   G1ParGCAllocBuffer* _alloc_buffers[GCAllocPurposeCount];

   ageTable            _age_table;

   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;  }

   CardTableModRefBS* 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);

   ~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 */);

     }

   }

   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