Mercurial > jdk8-mips64-public > hotspot / file revision

 /*

  * Copyright 2001-2009 Sun Microsystems, Inc.  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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

  * CA 95054 USA or visit www.sun.com if you need additional information or

  * have any questions.

  *

  */

 // 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 HeapRegionSeq;

 class PermanentGenerationSpec;

 class GenerationSpec;

 class OopsInHeapRegionClosure;

 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 ConcurrentZFThread;

 // If want to accumulate detailed statistics on work queues

 // turn this on.

 #define G1_DETAILED_STATS 0

 #if G1_DETAILED_STATS

 #  define IF_G1_DETAILED_STATS(code) code

 #else

 #  define IF_G1_DETAILED_STATS(code)

 #endif

 typedef GenericTaskQueue<StarTask>    RefToScanQueue;

 typedef GenericTaskQueueSet<StarTask> RefToScanQueueSet;

 typedef int RegionIdx_t;   // needs to hold [ 0..max_regions() )

 typedef int CardIdx_t;     // needs to hold [ 0..CardsPerRegion )

 enum G1GCThreadGroups {

   G1CRGroup = 0,

   G1ZFGroup = 1,

   G1CMGroup = 2,

   G1CLGroup = 3

 };

 enum GCAllocPurpose {

   GCAllocForTenured,

   GCAllocForSurvived,

   GCAllocPurposeCount

 };

 class YoungList : public CHeapObj {

 private:

   G1CollectedHeap* _g1h;

   HeapRegion* _head;

   HeapRegion* _scan_only_head;

   HeapRegion* _scan_only_tail;

   size_t      _length;

   size_t      _scan_only_length;

   size_t      _last_sampled_rs_lengths;

   size_t      _sampled_rs_lengths;

   HeapRegion* _curr;

   HeapRegion* _curr_scan_only;

   HeapRegion* _survivor_head;

   HeapRegion* _survivor_tail;

   size_t      _survivor_length;

   void          empty_list(HeapRegion* list);

 public:

   YoungList(G1CollectedHeap* g1h);

   void          push_region(HeapRegion* hr);

   void          add_survivor_region(HeapRegion* hr);

   HeapRegion*   pop_region();

   void          empty_list();

   bool          is_empty() { return _length == 0; }

   size_t        length() { return _length; }

   size_t        scan_only_length() { return _scan_only_length; }

   size_t        survivor_length() { return _survivor_length; }

   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();

   HeapRegion* first_region() { return _head; }

   HeapRegion* first_scan_only_region() { return _scan_only_head; }

   HeapRegion* first_survivor_region() { return _survivor_head; }

   HeapRegion* last_survivor_region() { return _survivor_tail; }

   HeapRegion* par_get_next_scan_only_region() {

     MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);

     HeapRegion* ret = _curr_scan_only;

     if (ret != NULL)

       _curr_scan_only = ret->get_next_young_region();

     return ret;

   }

   // debugging

   bool          check_list_well_formed();

   bool          check_list_empty(bool ignore_scan_only_list,

                                  bool check_sample = true);

   void          print();

 };

 class RefineCardTableEntryClosure;

 class G1CollectedHeap : public SharedHeap {

   friend class VM_G1CollectForAllocation;

   friend class VM_GenCollectForPermanentAllocation;

   friend class VM_G1CollectFull;

   friend class VM_G1IncCollectionPause;

   friend class VMStructs;

   // Closures used in implementation.

   friend class G1ParCopyHelper;

   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 CountRCClosure;

   friend class EvacPopObjClosure;

   friend class G1ParCleanupCTTask;

   // Other related classes.

   friend class G1MarkSweep;

 private:

   enum SomePrivateConstants {

     VeryLargeInBytes = HeapRegion::GrainBytes/2,

     VeryLargeInWords = VeryLargeInBytes/HeapWordSize,

     MinHeapDeltaBytes = 10 * HeapRegion::GrainBytes,      // FIXME

     NumAPIs = HeapRegion::MaxAge

   };

   // The one and only G1CollectedHeap, so static functions can find it.

   static G1CollectedHeap* _g1h;

   // Storage for the G1 heap (excludes the permanent generation).

   VirtualSpace _g1_storage;

   MemRegion    _g1_reserved;

   // The part of _g1_storage that is currently committed.

   MemRegion _g1_committed;

   // The maximum part of _g1_storage that has ever been committed.

   MemRegion _g1_max_committed;

   // The number of regions that are completely free.

   size_t _free_regions;

   // The number of regions we could create by expansion.

   size_t _expansion_regions;

   // Return the number of free regions in the heap (by direct counting.)

   size_t count_free_regions();

   // Return the number of free regions on the free and unclean lists.

   size_t count_free_regions_list();

   // The block offset table for the G1 heap.

   G1BlockOffsetSharedArray* _bot_shared;

   // Move all of the regions off the free lists, then rebuild those free

   // lists, before and after full GC.

   void tear_down_region_lists();

   void rebuild_region_lists();

   // This sets all non-empty regions to need zero-fill (which they will if

   // they are empty after full collection.)

   void set_used_regions_to_need_zero_fill();

   // The sequence of all heap regions in the heap.

   HeapRegionSeq* _hrs;

   // The region from which normal-sized objects are currently being

   // allocated.  May be NULL.

   HeapRegion* _cur_alloc_region;

   // Postcondition: cur_alloc_region == NULL.

   void abandon_cur_alloc_region();

   void abandon_gc_alloc_regions();

   // The to-space memory regions into which objects are being copied during

   // a GC.

   HeapRegion* _gc_alloc_regions[GCAllocPurposeCount];

   size_t _gc_alloc_region_counts[GCAllocPurposeCount];

   // These are the regions, one per GCAllocPurpose, that are half-full

   // at the end of a collection and that we want to reuse during the

   // next collection.

   HeapRegion* _retained_gc_alloc_regions[GCAllocPurposeCount];

   // This specifies whether we will keep the last half-full region at

   // the end of a collection so that it can be reused during the next

   // collection (this is specified per GCAllocPurpose)

   bool _retain_gc_alloc_region[GCAllocPurposeCount];

   // A list of the regions that have been set to be alloc regions in the

   // current collection.

   HeapRegion* _gc_alloc_region_list;

   // When called by par thread, require par_alloc_during_gc_lock() to be held.

   void push_gc_alloc_region(HeapRegion* hr);

   // This should only be called single-threaded.  Undeclares all GC alloc

   // regions.

   void forget_alloc_region_list();

   // Should be used to set an alloc region, because there's other

   // associated bookkeeping.

   void set_gc_alloc_region(int purpose, HeapRegion* r);

   // Check well-formedness of alloc region list.

   bool check_gc_alloc_regions();

   // 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.

   size_t _in_cset_fast_test_length;

   volatile unsigned _gc_time_stamp;

   size_t* _surviving_young_words;

   void setup_surviving_young_words();

   void update_surviving_young_words(size_t* surv_young_words);

   void cleanup_surviving_young_words();

 protected:

   // Returns "true" iff none of the gc alloc regions have any allocations

   // since the last call to "save_marks".

   bool all_alloc_regions_no_allocs_since_save_marks();

   // Perform finalization stuff on all allocation regions.

   void retire_all_alloc_regions();

   // The number of regions allocated to hold humongous objects.

   int         _num_humongous_regions;

   YoungList*  _young_list;

   // The current policy object for the collector.

   G1CollectorPolicy* _g1_policy;

   // Parallel allocation lock to protect the current allocation region.

   Mutex  _par_alloc_during_gc_lock;

   Mutex* par_alloc_during_gc_lock() { return &_par_alloc_during_gc_lock; }

   // If possible/desirable, allocate a new HeapRegion for normal object

   // allocation sufficient for an allocation of the given "word_size".

   // If "do_expand" is true, will attempt to expand the heap if necessary

   // to to satisfy the request.  If "zero_filled" is true, requires a

   // zero-filled region.

   // (Returning NULL will trigger a GC.)

   virtual HeapRegion* newAllocRegion_work(size_t word_size,

                                           bool do_expand,

                                           bool zero_filled);

   virtual HeapRegion* newAllocRegion(size_t word_size,

                                      bool zero_filled = true) {

     return newAllocRegion_work(word_size, false, zero_filled);

   }

   virtual HeapRegion* newAllocRegionWithExpansion(int purpose,

                                                   size_t word_size,

                                                   bool zero_filled = true);

   // Attempt to allocate an object of the given (very large) "word_size".

   // Returns "NULL" on failure.

   virtual HeapWord* humongousObjAllocate(size_t word_size);

   // If possible, allocate a block of the given word_size, else return "NULL".

   // Returning NULL will trigger GC or heap expansion.

   // These two methods have rather awkward pre- and

   // post-conditions. If they are called outside a safepoint, then

   // they assume that the caller is holding the heap lock. Upon return

   // they release the heap lock, if they are returning a non-NULL

   // value. attempt_allocation_slow() also dirties the cards of a

   // newly-allocated young region after it releases the heap

   // lock. This change in interface was the neatest way to achieve

   // this card dirtying without affecting mem_allocate(), which is a

   // more frequently called method. We tried two or three different

   // approaches, but they were even more hacky.

   HeapWord* attempt_allocation(size_t word_size,

                                bool permit_collection_pause = true);

   HeapWord* attempt_allocation_slow(size_t word_size,

                                     bool permit_collection_pause = true);

   // 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* allocate_during_gc(GCAllocPurpose purpose, size_t word_size);

   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);

   // Retires an allocation region when it is full or at the end of a

   // GC pause.

   void  retire_alloc_region(HeapRegion* alloc_region, bool par);

   // Helper function for two callbacks below.

   // "full", if true, indicates that the GC is for a System.gc() request,

   // and should collect the entire heap.  If "clear_all_soft_refs" is true,

   // all soft references are cleared during the GC.  If "full" is false,

   // "word_size" describes the allocation that the GC should

   // attempt (at least) to satisfy.

   void do_collection(bool full, bool clear_all_soft_refs,

                      size_t word_size);

   // Callback from VM_G1CollectFull operation.

   // Perform a full collection.

   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);

   // 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".

   virtual HeapWord* expand_and_allocate(size_t word_size);

 public:

   // Expand the garbage-first heap by at least the given size (in bytes!).

   // (Rounds up to a HeapRegion boundary.)

   virtual void 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");

     int index = r->hrs_index();

     assert(0 <= (size_t) index && (size_t) 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

       size_t index = ((size_t) 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;

     }

   }

 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);

   // Do an incremental collection: identify a collection set, and evacuate

   // its live objects elsewhere.

   virtual void do_collection_pause();

   // The guts of the incremental collection pause, executed by the vm

   // thread.

   virtual void do_collection_pause_at_safepoint();

   // Actually do the work of evacuating the collection set.

   virtual void evacuate_collection_set();

   // If this is an appropriate right time, do a collection pause.

   // The "word_size" argument, if non-zero, indicates the size of an

   // allocation request that is prompting this query.

   void do_collection_pause_if_appropriate(size_t word_size);

   // 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();

   // After a collection pause, make the regions in the CS into free

   // regions.

   void free_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_perm"

   // (setting the generation to the perm generation.)  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 collecting_perm_gen,

                                SharedHeap::ScanningOption so,

                                OopClosure* scan_non_heap_roots,

                                OopsInHeapRegionClosure* scan_rs,

                                OopsInHeapRegionClosure* scan_so,

                                OopsInGenClosure* scan_perm,

                                int worker_i);

   void scan_scan_only_set(OopsInHeapRegionClosure* oc,

                           int worker_i);

   void scan_scan_only_region(HeapRegion* hr,

                              OopsInHeapRegionClosure* oc,

                              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);

   // Invoke "save_marks" on all heap regions.

   void save_marks();

   // Free a heap region.

   void free_region(HeapRegion* hr);

   // A component of "free_region", exposed for 'batching'.

   // All the params after "hr" are out params: the used bytes of the freed

   // region(s), the number of H regions cleared, the number of regions

   // freed, and pointers to the head and tail of a list of freed contig

   // regions, linked throught the "next_on_unclean_list" field.

   void free_region_work(HeapRegion* hr,

                         size_t& pre_used,

                         size_t& cleared_h,

                         size_t& freed_regions,

                         UncleanRegionList* list,

                         bool par = false);

   // The concurrent marker (and the thread it runs in.)

   ConcurrentMark* _cm;

   ConcurrentMarkThread* _cmThread;

   bool _mark_in_progress;

   // The concurrent refiner.

   ConcurrentG1Refine* _cg1r;

   // The concurrent zero-fill thread.

   ConcurrentZFThread* _czft;

   // 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.

   void handle_evacuation_failure(oop obj);

   oop handle_evacuation_failure_par(OopsInHeapRegionClosure* cl, oop obj);

   void handle_evacuation_failure_common(oop obj, markOop m);

   // Ensure that the relevant gc_alloc regions are set.

   void get_gc_alloc_regions();

   // We're done with GC alloc regions. We are going to tear down the

   // gc alloc list and remove the gc alloc tag from all the regions on

   // that list. However, we will also retain the last (i.e., the one

   // that is half-full) GC alloc region, per GCAllocPurpose, for

   // possible reuse during the next collection, provided

   // _retain_gc_alloc_region[] indicates that it should be the

   // case. Said regions are kept in the _retained_gc_alloc_regions[]

   // array. If the parameter totally is set, we will not retain any

   // regions, irrespective of what _retain_gc_alloc_region[]

   // indicates.

   void release_gc_alloc_regions(bool totally);

 #ifndef PRODUCT

   // Useful for debugging.

   void print_gc_alloc_regions();

 #endif // !PRODUCT

   // ("Weak") Reference processing support

   ReferenceProcessor* _ref_processor;

   enum G1H_process_strong_roots_tasks {

     G1H_PS_mark_stack_oops_do,

     G1H_PS_refProcessor_oops_do,

     // Leave this one last.

     G1H_PS_NumElements

   };

   SubTasksDone* _process_strong_tasks;

   // List of regions which require zero filling.

   UncleanRegionList _unclean_region_list;

   bool _unclean_regions_coming;

 public:

   void set_refine_cte_cl_concurrency(bool concurrent);

   RefToScanQueue *task_queue(int i);

   // A set of cards where updates happened during the GC

   DirtyCardQueueSet& dirty_card_queue_set() { return _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, permanent generation, and remembered and barrier sets

   // specified by the policy object.

   jint initialize();

   void ref_processing_init();

   void set_par_threads(int t) {

     SharedHeap::set_par_threads(t);

     _process_strong_tasks->set_par_threads(t);

   }

   virtual CollectedHeap::Name kind() const {

     return CollectedHeap::G1CollectedHeap;

   }

   // The current policy object for the collector.

   G1CollectorPolicy* g1_policy() const { return _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();

   }

   void increment_gc_time_stamp() {

     ++_gc_time_stamp;

     OrderAccess::fence();

   }

   void iterate_dirty_card_closure(bool concurrent, int worker_i);

   // The shared block offset table array.

   G1BlockOffsetSharedArray* bot_shared() const { return _bot_shared; }

   // Reference Processing accessor

   ReferenceProcessor* ref_processor() { return _ref_processor; }

   // Reserved (g1 only; super method includes perm), capacity and the used

   // portion in bytes.

   size_t g1_reserved_obj_bytes() { return _g1_reserved.byte_size(); }

   virtual size_t capacity() const;

   virtual size_t used() const;

   size_t recalculate_used() const;

 #ifndef PRODUCT

   size_t recalculate_used_regions() const;

 #endif // PRODUCT

   // These virtual functions do the actual allocation.

   virtual HeapWord* mem_allocate(size_t word_size,

                                  bool   is_noref,

                                  bool   is_tlab,

                                  bool* gc_overhead_limit_was_exceeded);

   // 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.

   size_t n_regions();

   // The number of regions that are completely free.

   size_t max_regions();

   // The number of regions that are completely free.

   size_t free_regions();

   // The number of regions that are not completely free.

   size_t used_regions() { return n_regions() - free_regions(); }

   // True iff the ZF thread should run.

   bool should_zf();

   // The number of regions available for "regular" expansion.

   size_t expansion_regions() { return _expansion_regions; }

 #ifndef PRODUCT

   bool regions_accounted_for();

   bool print_region_accounting_info();

   void print_region_counts();

 #endif

   HeapRegion* alloc_region_from_unclean_list(bool zero_filled);

   HeapRegion* alloc_region_from_unclean_list_locked(bool zero_filled);

   void put_region_on_unclean_list(HeapRegion* r);

   void put_region_on_unclean_list_locked(HeapRegion* r);

   void prepend_region_list_on_unclean_list(UncleanRegionList* list);

   void prepend_region_list_on_unclean_list_locked(UncleanRegionList* list);

   void set_unclean_regions_coming(bool b);

   void set_unclean_regions_coming_locked(bool b);

   // Wait for cleanup to be complete.

   void wait_for_cleanup_complete();

   // Like above, but assumes that the calling thread owns the Heap_lock.

   void wait_for_cleanup_complete_locked();

   // Return the head of the unclean list.

   HeapRegion* peek_unclean_region_list_locked();

   // Remove and return the head of the unclean list.

   HeapRegion* pop_unclean_region_list_locked();

   // List of regions which are zero filled and ready for allocation.

   HeapRegion* _free_region_list;

   // Number of elements on the free list.

   size_t _free_region_list_size;

   // If the head of the unclean list is ZeroFilled, move it to the free

   // list.

   bool move_cleaned_region_to_free_list_locked();

   bool move_cleaned_region_to_free_list();

   void put_free_region_on_list_locked(HeapRegion* r);

   void put_free_region_on_list(HeapRegion* r);

   // Remove and return the head element of the free list.

   HeapRegion* pop_free_region_list_locked();

   // If "zero_filled" is true, we first try the free list, then we try the

   // unclean list, zero-filling the result.  If "zero_filled" is false, we

   // first try the unclean list, then the zero-filled list.

   HeapRegion* alloc_free_region_from_lists(bool zero_filled);

   // Verify the integrity of the region lists.

   void remove_allocated_regions_from_lists();

   bool verify_region_lists();

   bool verify_region_lists_locked();

   size_t unclean_region_list_length();

   size_t free_region_list_length();

   // 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);

   // This interface assumes that it's being called by the

   // vm thread. It collects the heap assuming that the

   // heap lock is already held and that we are executing in

   // the context of the vm thread.

   virtual void collect_as_vm_thread(GCCause::Cause cause);

   // True iff a evacuation has failed in the most-recent collection.

   bool evacuation_failed() { return _evacuation_failed; }

   // Free a region if it is totally full of garbage.  Returns the number of

   // bytes freed (0 ==> didn't free it).

   size_t free_region_if_totally_empty(HeapRegion *hr);

   void free_region_if_totally_empty_work(HeapRegion *hr,

                                          size_t& pre_used,

                                          size_t& cleared_h_regions,

                                          size_t& freed_regions,

                                          UncleanRegionList* list,

                                          bool par = false);

   // If we've done free region work that yields the given changes, update

   // the relevant global variables.

   void finish_free_region_work(size_t pre_used,

                                size_t cleared_h_regions,

                                size_t freed_regions,

                                UncleanRegionList* list);

   // Returns "TRUE" iff "p" points into the allocated area 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 (excluding the permanent generation).

   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

   // committed in the heap

   MemRegion g1_committed() {

     return _g1_committed;

   }

   NOT_PRODUCT( bool is_in_closed_subset(const void* p) const; )

   // Dirty card table entries covering a list of young regions.

   void dirtyCardsForYoungRegions(CardTableModRefBS* ct_bs, HeapRegion* list);

   // 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(OopClosure* cl) {

     oop_iterate(cl, true);

   }

   void oop_iterate(OopClosure* cl, bool do_perm);

   // Same as above, restricted to a memory region.

   virtual void oop_iterate(MemRegion mr, OopClosure* cl) {

     oop_iterate(mr, cl, true);

   }

   void oop_iterate(MemRegion mr, OopClosure* cl, bool do_perm);

   // Iterate over all objects, calling "cl.do_object" on each.

   virtual void object_iterate(ObjectClosure* cl) {

     object_iterate(cl, true);

   }

   virtual void safe_object_iterate(ObjectClosure* cl) {

     object_iterate(cl, true);

   }

   void object_iterate(ObjectClosure* cl, bool do_perm);

   // 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);

   // Iterate over heap regions starting with r (or the first region if "r"

   // is NULL), in address order, terminating early if the "doHeapRegion"

   // method returns "true".

   void heap_region_iterate_from(HeapRegion* r, HeapRegionClosure* blk);

   // As above but starting from the region at index idx.

   void heap_region_iterate_from(int idx, HeapRegionClosure* blk);

   HeapRegion* region_at(size_t idx);

   // 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,

                                        int worker,

                                        jint claim_value);

   // It resets all the region claim values to the default.

   void reset_heap_region_claim_values();

 #ifdef ASSERT

   bool check_heap_region_claim_values(jint claim_value);

 #endif // ASSERT

   // 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.

   HeapRegion* heap_region_containing(const void* 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.

   HeapRegion* heap_region_containing_raw(const void* 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;

   virtual HeapWord* allocate_new_tlab(size_t size);

   // 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.

   virtual bool can_elide_tlab_store_barriers() const {

     // Since G1's TLAB's may, on occasion, come from non-young regions

     // as well. (Is there a flag controlling that? XXX)

     return false;

   }

   // Can a compiler elide a store barrier when it writes

   // a permanent oop into the heap?  Applies when the compiler

   // is storing x to the heap, where x->is_perm() is true.

   virtual bool can_elide_permanent_oop_store_barriers() const {

     // At least until perm gen collection is also G1-ified, at

     // which point this should return false.

     return true;

   }

   virtual bool allocs_are_zero_filled();

   // The boundary between a "large" and "small" array of primitives, in

   // words.

   virtual size_t large_typearray_limit();

   // Returns "true" iff the given word_size is "very large".

   static bool isHumongous(size_t word_size) {

     return word_size >= VeryLargeInWords;

   }

   // 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.

   // use_prev_marking == true  -> use "prev" marking information,

   // use_prev_marking == false -> use "next" marking information

   // NOTE: Only the "prev" marking information is guaranteed to be

   // consistent most of the time, so most calls to this should use

   // use_prev_marking == true. Currently, there is only one case where

   // this is called with use_prev_marking == false, which is to verify

   // the "next" marking information at the end of remark.

   void verify(bool allow_dirty, bool silent, bool use_prev_marking);

   // Override; it uses the "prev" marking information

   virtual void verify(bool allow_dirty, bool silent);

   // Default behavior by calling print(tty);

   virtual void print() const;

   // This calls print_on(st, PrintHeapAtGCExtended).

   virtual void print_on(outputStream* st) const;

   // If extended is true, it will print out information for all

   // regions in the heap by calling print_on_extended(st).

   virtual void print_on(outputStream* st, bool extended) const;

   virtual void print_on_extended(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;

   // If "addr" is a pointer into the (reserved?) heap, returns a positive

   // number indicating the "arena" within the heap in which "addr" falls.

   // Or else returns 0.

   virtual int addr_to_arena_id(void* addr) const;

   // Convenience function to be used in situations where the heap type can be

   // asserted to be this type.

   static G1CollectedHeap* heap();

   void empty_young_list();

   bool should_set_young_locked();

   void set_region_short_lived_locked(HeapRegion* hr);

   // add appropriate methods for any other surv rate groups

   void young_list_rs_length_sampling_init() {

     _young_list->rs_length_sampling_init();

   }

   bool young_list_rs_length_sampling_more() {

     return _young_list->rs_length_sampling_more();

   }

   void young_list_rs_length_sampling_next() {

     _young_list->rs_length_sampling_next();

   }

   size_t young_list_sampled_rs_lengths() {

     return _young_list->sampled_rs_lengths();

   }

   size_t young_list_length()   { return _young_list->length(); }

   size_t young_list_scan_only_length() {

                                       return _young_list->scan_only_length(); }

   HeapRegion* pop_region_from_young_list() {

     return _young_list->pop_region();

   }

   HeapRegion* young_list_first_region() {

     return _young_list->first_region();

   }

   // debugging

   bool check_young_list_well_formed() {

     return _young_list->check_list_well_formed();

   }

   bool check_young_list_empty(bool ignore_scan_only_list,

                               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();

   // This is called from the marksweep collector which then does

   // a concurrent mark and verifies that the results agree with

   // the stop the world marking.

   void checkConcurrentMark();

   void do_sync_mark();

   bool isMarkedPrev(oop obj) const;

   bool isMarkedNext(oop obj) const;

   // use_prev_marking == true  -> use "prev" marking information,

   // use_prev_marking == false -> use "next" marking information

   bool is_obj_dead_cond(const oop obj,

                         const HeapRegion* hr,

                         const bool use_prev_marking) const {

     if (use_prev_marking) {

       return is_obj_dead(obj, hr);

     } else {

       return is_obj_ill(obj, hr);

     }

   }

   // 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 is used when copying an object to survivor space.

   // If the object is marked live, then we mark the copy live.

   // If the object is allocated since the start of this mark

   // cycle, then we mark the copy live.

   // If the object has been around since the previous mark

   // phase, and hasn't been marked yet during this phase,

   // then we don't mark it, we just wait for the

   // current marking cycle to get to it.

   // 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 in permanent gen it isn't dead.

   // Added if it is NULL it isn't dead.

   // use_prev_marking == true  -> use "prev" marking information,

   // use_prev_marking == false -> use "next" marking information

   bool is_obj_dead_cond(const oop obj,

                         const bool use_prev_marking) {

     if (use_prev_marking) {

       return is_obj_dead(obj);

     } else {

       return is_obj_ill(obj);

     }

   }

   bool is_obj_dead(const oop obj) {

     const HeapRegion* hr = heap_region_containing(obj);

     if (hr == NULL) {

       if (Universe::heap()->is_in_permanent(obj))

         return false;

       else if (obj == NULL) return false;

       else return true;

     }

     else return is_obj_dead(obj, hr);

   }

   bool is_obj_ill(const oop obj) {

     const HeapRegion* hr = heap_region_containing(obj);

     if (hr == NULL) {

       if (Universe::heap()->is_in_permanent(obj))

         return false;

       else if (obj == NULL) return false;

       else return true;

     }

     else return is_obj_ill(obj, hr);

   }

   // 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();

   // <NEW PREDICTION>

   double predict_region_elapsed_time_ms(HeapRegion* hr, bool young);

   void check_if_region_is_too_expensive(double predicted_time_ms);

   size_t pending_card_num();

   size_t max_pending_card_num();

   size_t cards_scanned();

   // </NEW PREDICTION>

 protected:

   size_t _max_heap_capacity;

 //  debug_only(static void check_for_valid_allocation_state();)

 public:

   // Temporary: call to mark things unimplemented for the G1 heap (e.g.,

   // MemoryService).  In productization, we can make this assert false

   // to catch such places (as well as searching for calls to this...)

   static void g1_unimplemented();

 };

 #define use_local_bitmaps         1

 #define verify_local_bitmaps      0

 #define oop_buffer_length       256

 #ifndef PRODUCT

 class GCLabBitMap;

 class GCLabBitMapClosure: public BitMapClosure {

 private:

   ConcurrentMark* _cm;

   GCLabBitMap*    _bitmap;

 public:

   GCLabBitMapClosure(ConcurrentMark* cm,

                      GCLabBitMap* bitmap) {

     _cm     = cm;

     _bitmap = bitmap;

   }

   virtual bool do_bit(size_t offset);

 };

 #endif // !PRODUCT

 class GCLabBitMap: public BitMap {

 private:

   ConcurrentMark* _cm;

   int       _shifter;

   size_t    _bitmap_word_covers_words;

   // beginning of the heap

   HeapWord* _heap_start;

   // this is the actual start of the GCLab

   HeapWord* _real_start_word;

   // this is the actual end of the GCLab

   HeapWord* _real_end_word;

   // this is the first word, possibly located before the actual start

   // of the GCLab, that corresponds to the first bit of the bitmap

   HeapWord* _start_word;

   // size of a GCLab in words

   size_t _gclab_word_size;

   static int shifter() {

     return MinObjAlignment - 1;

   }

   // how many heap words does a single bitmap word corresponds to?

   static size_t bitmap_word_covers_words() {

     return BitsPerWord << shifter();

   }

   static size_t gclab_word_size() {

     return G1ParallelGCAllocBufferSize / HeapWordSize;

   }

   static size_t bitmap_size_in_bits() {

     size_t bits_in_bitmap = gclab_word_size() >> shifter();

     // We are going to ensure that the beginning of a word in this

     // bitmap also corresponds to the beginning of a word in the

     // global marking bitmap. To handle the case where a GCLab

     // starts from the middle of the bitmap, we need to add enough

     // space (i.e. up to a bitmap word) to ensure that we have

     // enough bits in the bitmap.

     return bits_in_bitmap + BitsPerWord - 1;

   }

 public:

   GCLabBitMap(HeapWord* heap_start)

     : BitMap(bitmap_size_in_bits()),

       _cm(G1CollectedHeap::heap()->concurrent_mark()),

       _shifter(shifter()),

       _bitmap_word_covers_words(bitmap_word_covers_words()),

       _heap_start(heap_start),

       _gclab_word_size(gclab_word_size()),

       _real_start_word(NULL),

       _real_end_word(NULL),

       _start_word(NULL)

   {

     guarantee( size_in_words() >= bitmap_size_in_words(),

                "just making sure");

   }

   inline unsigned heapWordToOffset(HeapWord* addr) {

     unsigned offset = (unsigned) pointer_delta(addr, _start_word) >> _shifter;

     assert(offset < size(), "offset should be within bounds");

     return offset;

   }

   inline HeapWord* offsetToHeapWord(size_t offset) {

     HeapWord* addr =  _start_word + (offset << _shifter);

     assert(_real_start_word <= addr && addr < _real_end_word, "invariant");

     return addr;

   }

   bool fields_well_formed() {

     bool ret1 = (_real_start_word == NULL) &&

                 (_real_end_word == NULL) &&

                 (_start_word == NULL);

     if (ret1)

       return true;

     bool ret2 = _real_start_word >= _start_word &&

       _start_word < _real_end_word &&

       (_real_start_word + _gclab_word_size) == _real_end_word &&

       (_start_word + _gclab_word_size + _bitmap_word_covers_words)

                                                               > _real_end_word;

     return ret2;

   }

   inline bool mark(HeapWord* addr) {

     guarantee(use_local_bitmaps, "invariant");

     assert(fields_well_formed(), "invariant");

     if (addr >= _real_start_word && addr < _real_end_word) {

       assert(!isMarked(addr), "should not have already been marked");

       // first mark it on the bitmap

       at_put(heapWordToOffset(addr), true);

       return true;

     } else {

       return false;

     }

   }

   inline bool isMarked(HeapWord* addr) {

     guarantee(use_local_bitmaps, "invariant");

     assert(fields_well_formed(), "invariant");

     return at(heapWordToOffset(addr));

   }

   void set_buffer(HeapWord* start) {

     guarantee(use_local_bitmaps, "invariant");

     clear();

     assert(start != NULL, "invariant");

     _real_start_word = start;

     _real_end_word   = start + _gclab_word_size;

     size_t diff =

       pointer_delta(start, _heap_start) % _bitmap_word_covers_words;

     _start_word = start - diff;

     assert(fields_well_formed(), "invariant");

   }

 #ifndef PRODUCT

   void verify() {

     // verify that the marks have been propagated

     GCLabBitMapClosure cl(_cm, this);

     iterate(&cl);

   }

 #endif // PRODUCT

   void retire() {

     guarantee(use_local_bitmaps, "invariant");

     assert(fields_well_formed(), "invariant");

     if (_start_word != NULL) {

       CMBitMap*       mark_bitmap = _cm->nextMarkBitMap();

       // this means that the bitmap was set up for the GCLab

       assert(_real_start_word != NULL && _real_end_word != NULL, "invariant");

       mark_bitmap->mostly_disjoint_range_union(this,

                                 0, // always start from the start of the bitmap

                                 _start_word,

                                 size_in_words());

       _cm->grayRegionIfNecessary(MemRegion(_real_start_word, _real_end_word));

 #ifndef PRODUCT

       if (use_local_bitmaps && verify_local_bitmaps)

         verify();

 #endif // PRODUCT

     } else {

       assert(_real_start_word == NULL && _real_end_word == NULL, "invariant");

     }

   }

   static size_t bitmap_size_in_words() {

     return (bitmap_size_in_bits() + BitsPerWord - 1) / BitsPerWord;

   }

 };

 class G1ParGCAllocBuffer: public ParGCAllocBuffer {

 private:

   bool        _retired;

   bool        _during_marking;

   GCLabBitMap _bitmap;

 public:

   G1ParGCAllocBuffer() :

     ParGCAllocBuffer(G1ParallelGCAllocBufferSize / HeapWordSize),

     _during_marking(G1CollectedHeap::heap()->mark_in_progress()),

     _bitmap(G1CollectedHeap::heap()->reserved_region().start()),

     _retired(false)

   { }

   inline bool mark(HeapWord* addr) {

     guarantee(use_local_bitmaps, "invariant");

     assert(_during_marking, "invariant");

     return _bitmap.mark(addr);

   }

   inline void set_buf(HeapWord* buf) {

     if (use_local_bitmaps && _during_marking)

       _bitmap.set_buffer(buf);

     ParGCAllocBuffer::set_buf(buf);

     _retired = false;

   }

   inline void retire(bool end_of_gc, bool retain) {

     if (_retired)

       return;

     if (use_local_bitmaps && _during_marking) {

       _bitmap.retire();

     }

     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;

   typedef GrowableArray<StarTask> OverflowQueue;

   OverflowQueue* _overflowed_refs;

   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;

   int _queue_num;

   int _term_attempts;

 #if G1_DETAILED_STATS

   int _pushes, _pops, _steals, _steal_attempts;

   int _overflow_pushes;

 #endif

   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 (64 / 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, int queue_num);

   ~G1ParScanThreadState() {

     FREE_C_HEAP_ARRAY(size_t, _surviving_young_words_base);

   }

   RefToScanQueue*   refs()            { return _refs;             }

   OverflowQueue*    overflowed_refs() { return _overflowed_refs;  }

   ageTable*         age_table()       { return &_age_table;       }

   G1ParGCAllocBuffer* alloc_buffer(GCAllocPurpose purpose) {

     return &_alloc_buffers[purpose];

   }

   size_t alloc_buffer_waste()                    { return _alloc_buffer_waste; }

   size_t undo_waste()                            { return _undo_waste; }

   template <class T> void push_on_queue(T* ref) {

     assert(ref != NULL, "invariant");

     assert(has_partial_array_mask(ref) ||

            _g1h->obj_in_cs(oopDesc::load_decode_heap_oop(ref)), "invariant");

 #ifdef ASSERT

     if (has_partial_array_mask(ref)) {

       oop p = clear_partial_array_mask(ref);

       // Verify that we point into the CS

       assert(_g1h->obj_in_cs(p), "Should be in CS");

     }

 #endif

     if (!refs()->push(ref)) {

       overflowed_refs()->push(ref);

       IF_G1_DETAILED_STATS(note_overflow_push());

     } else {

       IF_G1_DETAILED_STATS(note_push());

     }

   }

   void pop_from_queue(StarTask& ref) {

     if (refs()->pop_local(ref)) {

       assert((oop*)ref != NULL, "pop_local() returned true");

       assert(UseCompressedOops || !ref.is_narrow(), "Error");

       assert(has_partial_array_mask((oop*)ref) ||

              _g1h->obj_in_cs(ref.is_narrow() ? oopDesc::load_decode_heap_oop((narrowOop*)ref)

                                              : oopDesc::load_decode_heap_oop((oop*)ref)),

              "invariant");

       IF_G1_DETAILED_STATS(note_pop());

     } else {

       StarTask null_task;

       ref = null_task;

     }

   }

   void pop_from_overflow_queue(StarTask& ref) {

     StarTask new_ref = overflowed_refs()->pop();

     assert((oop*)new_ref != NULL, "pop() from a local non-empty stack");

     assert(UseCompressedOops || !new_ref.is_narrow(), "Error");

     assert(has_partial_array_mask((oop*)new_ref) ||

            _g1h->obj_in_cs(new_ref.is_narrow() ? oopDesc::load_decode_heap_oop((narrowOop*)new_ref)

                                                : oopDesc::load_decode_heap_oop((oop*)new_ref)),

              "invariant");

     ref = new_ref;

   }

   int refs_to_scan()                             { return refs()->size();                 }

   int overflowed_refs_to_scan()                  { return overflowed_refs()->length();    }

   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;

     if (word_sz * 100 <

         (size_t)(G1ParallelGCAllocBufferSize / HeapWordSize) *

                                                   ParallelGCBufferWastePct) {

       G1ParGCAllocBuffer* alloc_buf = alloc_buffer(purpose);

       add_to_alloc_buffer_waste(alloc_buf->words_remaining());

       alloc_buf->retire(false, false);

       HeapWord* buf =

         _g1h->par_allocate_during_gc(purpose, G1ParallelGCAllocBufferSize / HeapWordSize);

       if (buf == NULL) return NULL; // Let caller handle allocation failure.

       // Otherwise.

       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; }

   int  queue_num() { return _queue_num; }

   int term_attempts()   { return _term_attempts; }

   void note_term_attempt()  { _term_attempts++; }

 #if G1_DETAILED_STATS

   int pushes()          { return _pushes; }

   int pops()            { return _pops; }

   int steals()          { return _steals; }

   int steal_attempts()  { return _steal_attempts; }

   int overflow_pushes() { return _overflow_pushes; }

   void note_push()          { _pushes++; }

   void note_pop()           { _pops++; }

   void note_steal()         { _steals++; }

   void note_steal_attempt() { _steal_attempts++; }

   void note_overflow_push() { _overflow_pushes++; }

 #endif

   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() { 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() { return _term_time; }

   double elapsed() {

     return os::elapsedTime() - _start;

   }

   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].retire(true, false);

     }

   }

 private:

   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);

     }

   }

 public:

   void trim_queue() {

     // I've replicated the loop twice, first to drain the overflow

     // queue, second to drain the task queue. This is better than

     // having a single loop, which checks both conditions and, inside

     // it, either pops the overflow queue or the task queue, as each

     // loop is tighter. Also, the decision to drain the overflow queue

     // first is not arbitrary, as the overflow queue is not visible

     // to the other workers, whereas the task queue is. So, we want to

     // drain the "invisible" entries first, while allowing the other

     // workers to potentially steal the "visible" entries.

     while (refs_to_scan() > 0 || overflowed_refs_to_scan() > 0) {

       while (overflowed_refs_to_scan() > 0) {

         StarTask ref_to_scan;

         assert((oop*)ref_to_scan == NULL, "Constructed above");

         pop_from_overflow_queue(ref_to_scan);

         // We shouldn't have pushed it on the queue if it was not

         // pointing into the CSet.

         assert((oop*)ref_to_scan != NULL, "Follows from inner loop invariant");

         if (ref_to_scan.is_narrow()) {

           assert(UseCompressedOops, "Error");

           narrowOop* p = (narrowOop*)ref_to_scan;

           assert(!has_partial_array_mask(p) &&

                  _g1h->obj_in_cs(oopDesc::load_decode_heap_oop(p)), "sanity");

           deal_with_reference(p);

         } else {

           oop* p = (oop*)ref_to_scan;

           assert((has_partial_array_mask(p) && _g1h->obj_in_cs(clear_partial_array_mask(p))) ||

                  _g1h->obj_in_cs(oopDesc::load_decode_heap_oop(p)), "sanity");

           deal_with_reference(p);

         }

       }

       while (refs_to_scan() > 0) {

         StarTask ref_to_scan;

         assert((oop*)ref_to_scan == NULL, "Constructed above");

         pop_from_queue(ref_to_scan);

         if ((oop*)ref_to_scan != NULL) {

           if (ref_to_scan.is_narrow()) {

             assert(UseCompressedOops, "Error");

             narrowOop* p = (narrowOop*)ref_to_scan;

             assert(!has_partial_array_mask(p) &&

                    _g1h->obj_in_cs(oopDesc::load_decode_heap_oop(p)), "sanity");

             deal_with_reference(p);

           } else {

             oop* p = (oop*)ref_to_scan;

             assert((has_partial_array_mask(p) && _g1h->obj_in_cs(clear_partial_array_mask(p))) ||

                   _g1h->obj_in_cs(oopDesc::load_decode_heap_oop(p)), "sanity");

             deal_with_reference(p);

           }

         }

       }

     }

   }

 };