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

 /*

  * Copyright 2001-2007 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.

  *

  */

 // ConcurrentMarkSweepGeneration is in support of a concurrent

 // mark-sweep old generation in the Detlefs-Printezis--Boehm-Demers-Schenker

 // style. We assume, for now, that this generation is always the

 // seniormost generation (modulo the PermGeneration), and for simplicity

 // in the first implementation, that this generation is a single compactible

 // space. Neither of these restrictions appears essential, and will be

 // relaxed in the future when more time is available to implement the

 // greater generality (and there's a need for it).

 //

 // Concurrent mode failures are currently handled by

 // means of a sliding mark-compact.

 class CMSAdaptiveSizePolicy;

 class CMSConcMarkingTask;

 class CMSGCAdaptivePolicyCounters;

 class ConcurrentMarkSweepGeneration;

 class ConcurrentMarkSweepPolicy;

 class ConcurrentMarkSweepThread;

 class CompactibleFreeListSpace;

 class FreeChunk;

 class PromotionInfo;

 class ScanMarkedObjectsAgainCarefullyClosure;

 // A generic CMS bit map. It's the basis for both the CMS marking bit map

 // as well as for the mod union table (in each case only a subset of the

 // methods are used). This is essentially a wrapper around the BitMap class,

 // with one bit per (1<<_shifter) HeapWords. (i.e. for the marking bit map,

 // we have _shifter == 0. and for the mod union table we have

 // shifter == CardTableModRefBS::card_shift - LogHeapWordSize.)

 // XXX 64-bit issues in BitMap?

 class CMSBitMap VALUE_OBJ_CLASS_SPEC {

   friend class VMStructs;

   HeapWord* _bmStartWord;   // base address of range covered by map

   size_t    _bmWordSize;    // map size (in #HeapWords covered)

   const int _shifter;       // shifts to convert HeapWord to bit position

   VirtualSpace _virtual_space; // underlying the bit map

   BitMap    _bm;            // the bit map itself

  public:

   Mutex* const _lock;       // mutex protecting _bm;

  public:

   // constructor

   CMSBitMap(int shifter, int mutex_rank, const char* mutex_name);

   // allocates the actual storage for the map

   bool allocate(MemRegion mr);

   // field getter

   Mutex* lock() const { return _lock; }

   // locking verifier convenience function

   void assert_locked() const PRODUCT_RETURN;

   // inquiries

   HeapWord* startWord()   const { return _bmStartWord; }

   size_t    sizeInWords() const { return _bmWordSize;  }

   size_t    sizeInBits()  const { return _bm.size();   }

   // the following is one past the last word in space

   HeapWord* endWord()     const { return _bmStartWord + _bmWordSize; }

   // reading marks

   bool isMarked(HeapWord* addr) const;

   bool par_isMarked(HeapWord* addr) const; // do not lock checks

   bool isUnmarked(HeapWord* addr) const;

   bool isAllClear() const;

   // writing marks

   void mark(HeapWord* addr);

   // For marking by parallel GC threads;

   // returns true if we did, false if another thread did

   bool par_mark(HeapWord* addr);

   void mark_range(MemRegion mr);

   void par_mark_range(MemRegion mr);

   void mark_large_range(MemRegion mr);

   void par_mark_large_range(MemRegion mr);

   void par_clear(HeapWord* addr); // For unmarking by parallel GC threads.

   void clear_range(MemRegion mr);

   void par_clear_range(MemRegion mr);

   void clear_large_range(MemRegion mr);

   void par_clear_large_range(MemRegion mr);

   void clear_all();

   void clear_all_incrementally();  // Not yet implemented!!

   NOT_PRODUCT(

     // checks the memory region for validity

     void region_invariant(MemRegion mr);

   )

   // iteration

   void iterate(BitMapClosure* cl) {

     _bm.iterate(cl);

   }

   void iterate(BitMapClosure* cl, HeapWord* left, HeapWord* right);

   void dirty_range_iterate_clear(MemRegionClosure* cl);

   void dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl);

   // auxiliary support for iteration

   HeapWord* getNextMarkedWordAddress(HeapWord* addr) const;

   HeapWord* getNextMarkedWordAddress(HeapWord* start_addr,

                                             HeapWord* end_addr) const;

   HeapWord* getNextUnmarkedWordAddress(HeapWord* addr) const;

   HeapWord* getNextUnmarkedWordAddress(HeapWord* start_addr,

                                               HeapWord* end_addr) const;

   MemRegion getAndClearMarkedRegion(HeapWord* addr);

   MemRegion getAndClearMarkedRegion(HeapWord* start_addr,

                                            HeapWord* end_addr);

   // conversion utilities

   HeapWord* offsetToHeapWord(size_t offset) const;

   size_t    heapWordToOffset(HeapWord* addr) const;

   size_t    heapWordDiffToOffsetDiff(size_t diff) const;

   // debugging

   // is this address range covered by the bit-map?

   NOT_PRODUCT(

     bool covers(MemRegion mr) const;

     bool covers(HeapWord* start, size_t size = 0) const;

   )

   void verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) PRODUCT_RETURN;

 };

 // Represents a marking stack used by the CMS collector.

 // Ideally this should be GrowableArray<> just like MSC's marking stack(s).

 class CMSMarkStack: public CHeapObj  {

   //

   friend class CMSCollector;   // to get at expasion stats further below

   //

   VirtualSpace _virtual_space;  // space for the stack

   oop*   _base;      // bottom of stack

   size_t _index;     // one more than last occupied index

   size_t _capacity;  // max #elements

   Mutex  _par_lock;  // an advisory lock used in case of parallel access

   NOT_PRODUCT(size_t _max_depth;)  // max depth plumbed during run

  protected:

   size_t _hit_limit;      // we hit max stack size limit

   size_t _failed_double;  // we failed expansion before hitting limit

  public:

   CMSMarkStack():

     _par_lock(Mutex::event, "CMSMarkStack._par_lock", true),

     _hit_limit(0),

     _failed_double(0) {}

   bool allocate(size_t size);

   size_t capacity() const { return _capacity; }

   oop pop() {

     if (!isEmpty()) {

       return _base[--_index] ;

     }

     return NULL;

   }

   bool push(oop ptr) {

     if (isFull()) {

       return false;

     } else {

       _base[_index++] = ptr;

       NOT_PRODUCT(_max_depth = MAX2(_max_depth, _index));

       return true;

     }

   }

   bool isEmpty() const { return _index == 0; }

   bool isFull()  const {

     assert(_index <= _capacity, "buffer overflow");

     return _index == _capacity;

   }

   size_t length() { return _index; }

   // "Parallel versions" of some of the above

   oop par_pop() {

     // lock and pop

     MutexLockerEx x(&_par_lock, Mutex::_no_safepoint_check_flag);

     return pop();

   }

   bool par_push(oop ptr) {

     // lock and push

     MutexLockerEx x(&_par_lock, Mutex::_no_safepoint_check_flag);

     return push(ptr);

   }

   // Forcibly reset the stack, losing all of its contents.

   void reset() {

     _index = 0;

   }

   // Expand the stack, typically in response to an overflow condition

   void expand();

   // Compute the least valued stack element.

   oop least_value(HeapWord* low) {

      oop least = (oop)low;

      for (size_t i = 0; i < _index; i++) {

        least = MIN2(least, _base[i]);

      }

      return least;

   }

   // Exposed here to allow stack expansion in || case

   Mutex* par_lock() { return &_par_lock; }

 };

 class CardTableRS;

 class CMSParGCThreadState;

 class ModUnionClosure: public MemRegionClosure {

  protected:

   CMSBitMap* _t;

  public:

   ModUnionClosure(CMSBitMap* t): _t(t) { }

   void do_MemRegion(MemRegion mr);

 };

 class ModUnionClosurePar: public ModUnionClosure {

  public:

   ModUnionClosurePar(CMSBitMap* t): ModUnionClosure(t) { }

   void do_MemRegion(MemRegion mr);

 };

 // Survivor Chunk Array in support of parallelization of

 // Survivor Space rescan.

 class ChunkArray: public CHeapObj {

   size_t _index;

   size_t _capacity;

   HeapWord** _array;   // storage for array

  public:

   ChunkArray() : _index(0), _capacity(0), _array(NULL) {}

   ChunkArray(HeapWord** a, size_t c):

     _index(0), _capacity(c), _array(a) {}

   HeapWord** array() { return _array; }

   void set_array(HeapWord** a) { _array = a; }

   size_t capacity() { return _capacity; }

   void set_capacity(size_t c) { _capacity = c; }

   size_t end() {

     assert(_index < capacity(), "_index out of bounds");

     return _index;

   }  // exclusive

   HeapWord* nth(size_t n) {

     assert(n < end(), "Out of bounds access");

     return _array[n];

   }

   void reset() {

     _index = 0;

   }

   void record_sample(HeapWord* p, size_t sz) {

     // For now we do not do anything with the size

     if (_index < _capacity) {

       _array[_index++] = p;

     }

   }

 };

 //

 // Timing, allocation and promotion statistics for gc scheduling and incremental

 // mode pacing.  Most statistics are exponential averages.

 //

 class CMSStats VALUE_OBJ_CLASS_SPEC {

  private:

   ConcurrentMarkSweepGeneration* const _cms_gen;   // The cms (old) gen.

   // The following are exponential averages with factor alpha:

   //   avg = (100 - alpha) * avg + alpha * cur_sample

   //

   //   The durations measure:  end_time[n] - start_time[n]

   //   The periods measure:    start_time[n] - start_time[n-1]

   //

   // The cms period and duration include only concurrent collections; time spent

   // in foreground cms collections due to System.gc() or because of a failure to

   // keep up are not included.

   //

   // There are 3 alphas to "bootstrap" the statistics.  The _saved_alpha is the

   // real value, but is used only after the first period.  A value of 100 is

   // used for the first sample so it gets the entire weight.

   unsigned int _saved_alpha; // 0-100

   unsigned int _gc0_alpha;

   unsigned int _cms_alpha;

   double _gc0_duration;

   double _gc0_period;

   size_t _gc0_promoted;         // bytes promoted per gc0

   double _cms_duration;

   double _cms_duration_pre_sweep; // time from initiation to start of sweep

   double _cms_duration_per_mb;

   double _cms_period;

   size_t _cms_allocated;        // bytes of direct allocation per gc0 period

   // Timers.

   elapsedTimer _cms_timer;

   TimeStamp    _gc0_begin_time;

   TimeStamp    _cms_begin_time;

   TimeStamp    _cms_end_time;

   // Snapshots of the amount used in the CMS generation.

   size_t _cms_used_at_gc0_begin;

   size_t _cms_used_at_gc0_end;

   size_t _cms_used_at_cms_begin;

   // Used to prevent the duty cycle from being reduced in the middle of a cms

   // cycle.

   bool _allow_duty_cycle_reduction;

   enum {

     _GC0_VALID = 0x1,

     _CMS_VALID = 0x2,

     _ALL_VALID = _GC0_VALID | _CMS_VALID

   };

   unsigned int _valid_bits;

   unsigned int _icms_duty_cycle;        // icms duty cycle (0-100).

  protected:

   // Return a duty cycle that avoids wild oscillations, by limiting the amount

   // of change between old_duty_cycle and new_duty_cycle (the latter is treated

   // as a recommended value).

   static unsigned int icms_damped_duty_cycle(unsigned int old_duty_cycle,

                                              unsigned int new_duty_cycle);

   unsigned int icms_update_duty_cycle_impl();

  public:

   CMSStats(ConcurrentMarkSweepGeneration* cms_gen,

            unsigned int alpha = CMSExpAvgFactor);

   // Whether or not the statistics contain valid data; higher level statistics

   // cannot be called until this returns true (they require at least one young

   // gen and one cms cycle to have completed).

   bool valid() const;

   // Record statistics.

   void record_gc0_begin();

   void record_gc0_end(size_t cms_gen_bytes_used);

   void record_cms_begin();

   void record_cms_end();

   // Allow management of the cms timer, which must be stopped/started around

   // yield points.

   elapsedTimer& cms_timer()     { return _cms_timer; }

   void start_cms_timer()        { _cms_timer.start(); }

   void stop_cms_timer()         { _cms_timer.stop(); }

   // Basic statistics; units are seconds or bytes.

   double gc0_period() const     { return _gc0_period; }

   double gc0_duration() const   { return _gc0_duration; }

   size_t gc0_promoted() const   { return _gc0_promoted; }

   double cms_period() const          { return _cms_period; }

   double cms_duration() const        { return _cms_duration; }

   double cms_duration_per_mb() const { return _cms_duration_per_mb; }

   size_t cms_allocated() const       { return _cms_allocated; }

   size_t cms_used_at_gc0_end() const { return _cms_used_at_gc0_end;}

   // Seconds since the last background cms cycle began or ended.

   double cms_time_since_begin() const;

   double cms_time_since_end() const;

   // Higher level statistics--caller must check that valid() returns true before

   // calling.

   // Returns bytes promoted per second of wall clock time.

   double promotion_rate() const;

   // Returns bytes directly allocated per second of wall clock time.

   double cms_allocation_rate() const;

   // Rate at which space in the cms generation is being consumed (sum of the

   // above two).

   double cms_consumption_rate() const;

   // Returns an estimate of the number of seconds until the cms generation will

   // fill up, assuming no collection work is done.

   double time_until_cms_gen_full() const;

   // Returns an estimate of the number of seconds remaining until

   // the cms generation collection should start.

   double time_until_cms_start() const;

   // End of higher level statistics.

   // Returns the cms incremental mode duty cycle, as a percentage (0-100).

   unsigned int icms_duty_cycle() const { return _icms_duty_cycle; }

   // Update the duty cycle and return the new value.

   unsigned int icms_update_duty_cycle();

   // Debugging.

   void print_on(outputStream* st) const PRODUCT_RETURN;

   void print() const { print_on(gclog_or_tty); }

 };

 // A closure related to weak references processing which

 // we embed in the CMSCollector, since we need to pass

 // it to the reference processor for secondary filtering

 // of references based on reachability of referent;

 // see role of _is_alive_non_header closure in the

 // ReferenceProcessor class.

 // For objects in the CMS generation, this closure checks

 // if the object is "live" (reachable). Used in weak

 // reference processing.

 class CMSIsAliveClosure: public BoolObjectClosure {

   MemRegion  _span;

   const CMSBitMap* _bit_map;

   friend class CMSCollector;

  protected:

   void set_span(MemRegion span) { _span = span; }

  public:

   CMSIsAliveClosure(CMSBitMap* bit_map):

     _bit_map(bit_map) { }

   CMSIsAliveClosure(MemRegion span,

                     CMSBitMap* bit_map):

     _span(span),

     _bit_map(bit_map) { }

   void do_object(oop obj) {

     assert(false, "not to be invoked");

   }

   bool do_object_b(oop obj);

 };

 // Implements AbstractRefProcTaskExecutor for CMS.

 class CMSRefProcTaskExecutor: public AbstractRefProcTaskExecutor {

 public:

   CMSRefProcTaskExecutor(CMSCollector& collector)

     : _collector(collector)

   { }

   // Executes a task using worker threads.

   virtual void execute(ProcessTask& task);

   virtual void execute(EnqueueTask& task);

 private:

   CMSCollector& _collector;

 };

 class CMSCollector: public CHeapObj {

   friend class VMStructs;

   friend class ConcurrentMarkSweepThread;

   friend class ConcurrentMarkSweepGeneration;

   friend class CompactibleFreeListSpace;

   friend class CMSParRemarkTask;

   friend class CMSConcMarkingTask;

   friend class CMSRefProcTaskProxy;

   friend class CMSRefProcTaskExecutor;

   friend class ScanMarkedObjectsAgainCarefullyClosure;  // for sampling eden

   friend class SurvivorSpacePrecleanClosure;            // --- ditto -------

   friend class PushOrMarkClosure;             // to access _restart_addr

   friend class Par_PushOrMarkClosure;             // to access _restart_addr

   friend class MarkFromRootsClosure;          //  -- ditto --

                                               // ... and for clearing cards

   friend class Par_MarkFromRootsClosure;      //  to access _restart_addr

                                               // ... and for clearing cards

   friend class Par_ConcMarkingClosure;        //  to access _restart_addr etc.

   friend class MarkFromRootsVerifyClosure;    // to access _restart_addr

   friend class PushAndMarkVerifyClosure;      //  -- ditto --

   friend class MarkRefsIntoAndScanClosure;    // to access _overflow_list

   friend class PushAndMarkClosure;            //  -- ditto --

   friend class Par_PushAndMarkClosure;        //  -- ditto --

   friend class CMSKeepAliveClosure;           //  -- ditto --

   friend class CMSDrainMarkingStackClosure;   //  -- ditto --

   friend class CMSInnerParMarkAndPushClosure; //  -- ditto --

   NOT_PRODUCT(friend class ScanMarkedObjectsAgainClosure;) //  assertion on _overflow_list

   friend class ReleaseForegroundGC;  // to access _foregroundGCShouldWait

   friend class VM_CMS_Operation;

   friend class VM_CMS_Initial_Mark;

   friend class VM_CMS_Final_Remark;

  private:

   jlong _time_of_last_gc;

   void update_time_of_last_gc(jlong now) {

     _time_of_last_gc = now;

   }

   OopTaskQueueSet* _task_queues;

   // Overflow list of grey objects, threaded through mark-word

   // Manipulated with CAS in the parallel/multi-threaded case.

   oop _overflow_list;

   // The following array-pair keeps track of mark words

   // displaced for accomodating overflow list above.

   // This code will likely be revisited under RFE#4922830.

   GrowableArray<oop>*     _preserved_oop_stack;

   GrowableArray<markOop>* _preserved_mark_stack;

   int*             _hash_seed;

   // In support of multi-threaded concurrent phases

   YieldingFlexibleWorkGang* _conc_workers;

   // Performance Counters

   CollectorCounters* _gc_counters;

   // Initialization Errors

   bool _completed_initialization;

   // In support of ExplicitGCInvokesConcurrent

   static   bool _full_gc_requested;

   unsigned int  _collection_count_start;

   // Should we unload classes this concurrent cycle?

   // Set in response to a concurrent full gc request.

   bool _unload_classes;

   bool _unloaded_classes_last_cycle;

   // Did we (allow) unload classes in the previous concurrent cycle?

   bool cms_unloaded_classes_last_cycle() const {

     return _unloaded_classes_last_cycle || CMSClassUnloadingEnabled;

   }

   // Verification support

   CMSBitMap     _verification_mark_bm;

   void verify_after_remark_work_1();

   void verify_after_remark_work_2();

   // true if any verification flag is on.

   bool _verifying;

   bool verifying() const { return _verifying; }

   void set_verifying(bool v) { _verifying = v; }

   // Collector policy

   ConcurrentMarkSweepPolicy* _collector_policy;

   ConcurrentMarkSweepPolicy* collector_policy() { return _collector_policy; }

   // Check whether the gc time limit has been

   // exceeded and set the size policy flag

   // appropriately.

   void check_gc_time_limit();

   // XXX Move these to CMSStats ??? FIX ME !!!

   elapsedTimer _sweep_timer;

   AdaptivePaddedAverage _sweep_estimate;

  protected:

   ConcurrentMarkSweepGeneration* _cmsGen;  // old gen (CMS)

   ConcurrentMarkSweepGeneration* _permGen; // perm gen

   MemRegion                      _span;    // span covering above two

   CardTableRS*                   _ct;      // card table

   // CMS marking support structures

   CMSBitMap     _markBitMap;

   CMSBitMap     _modUnionTable;

   CMSMarkStack  _markStack;

   CMSMarkStack  _revisitStack;            // used to keep track of klassKlass objects

                                           // to revisit

   CMSBitMap     _perm_gen_verify_bit_map; // Mark bit map for perm gen verification support.

   HeapWord*     _restart_addr; // in support of marking stack overflow

   void          lower_restart_addr(HeapWord* low);

   // Counters in support of marking stack / work queue overflow handling:

   // a non-zero value indicates certain types of overflow events during

   // the current CMS cycle and could lead to stack resizing efforts at

   // an opportune future time.

   size_t        _ser_pmc_preclean_ovflw;

   size_t        _ser_pmc_remark_ovflw;

   size_t        _par_pmc_remark_ovflw;

   size_t        _ser_kac_ovflw;

   size_t        _par_kac_ovflw;

   NOT_PRODUCT(size_t _num_par_pushes;)

   // ("Weak") Reference processing support

   ReferenceProcessor*            _ref_processor;

   CMSIsAliveClosure              _is_alive_closure;

       // keep this textually after _markBitMap; c'tor dependency

   ConcurrentMarkSweepThread*     _cmsThread;   // the thread doing the work

   ModUnionClosure    _modUnionClosure;

   ModUnionClosurePar _modUnionClosurePar;

   // CMS abstract state machine

   // initial_state: Idling

   // next_state(Idling)            = {Marking}

   // next_state(Marking)           = {Precleaning, Sweeping}

   // next_state(Precleaning)       = {AbortablePreclean, FinalMarking}

   // next_state(AbortablePreclean) = {FinalMarking}

   // next_state(FinalMarking)      = {Sweeping}

   // next_state(Sweeping)          = {Resizing}

   // next_state(Resizing)          = {Resetting}

   // next_state(Resetting)         = {Idling}

   // The numeric values below are chosen so that:

   // . _collectorState <= Idling ==  post-sweep && pre-mark

   // . _collectorState in (Idling, Sweeping) == {initial,final}marking ||

   //                                            precleaning || abortablePrecleanb

   enum CollectorState {

     Resizing            = 0,

     Resetting           = 1,

     Idling              = 2,

     InitialMarking      = 3,

     Marking             = 4,

     Precleaning         = 5,

     AbortablePreclean   = 6,

     FinalMarking        = 7,

     Sweeping            = 8

   };

   static CollectorState _collectorState;

   // State related to prologue/epilogue invocation for my generations

   bool _between_prologue_and_epilogue;

   // Signalling/State related to coordination between fore- and backgroud GC

   // Note: When the baton has been passed from background GC to foreground GC,

   // _foregroundGCIsActive is true and _foregroundGCShouldWait is false.

   static bool _foregroundGCIsActive;    // true iff foreground collector is active or

                                  // wants to go active

   static bool _foregroundGCShouldWait;  // true iff background GC is active and has not

                                  // yet passed the baton to the foreground GC

   // Support for CMSScheduleRemark (abortable preclean)

   bool _abort_preclean;

   bool _start_sampling;

   int    _numYields;

   size_t _numDirtyCards;

   uint   _sweepCount;

   // number of full gc's since the last concurrent gc.

   uint   _full_gcs_since_conc_gc;

   // if occupancy exceeds this, start a new gc cycle

   double _initiatingOccupancy;

   // occupancy used for bootstrapping stats

   double _bootstrap_occupancy;

   // timer

   elapsedTimer _timer;

   // Timing, allocation and promotion statistics, used for scheduling.

   CMSStats      _stats;

   // Allocation limits installed in the young gen, used only in

   // CMSIncrementalMode.  When an allocation in the young gen would cross one of

   // these limits, the cms generation is notified and the cms thread is started

   // or stopped, respectively.

   HeapWord*     _icms_start_limit;

   HeapWord*     _icms_stop_limit;

   enum CMS_op_type {

     CMS_op_checkpointRootsInitial,

     CMS_op_checkpointRootsFinal

   };

   void do_CMS_operation(CMS_op_type op);

   bool stop_world_and_do(CMS_op_type op);

   OopTaskQueueSet* task_queues() { return _task_queues; }

   int*             hash_seed(int i) { return &_hash_seed[i]; }

   YieldingFlexibleWorkGang* conc_workers() { return _conc_workers; }

   // Support for parallelizing Eden rescan in CMS remark phase

   void sample_eden(); // ... sample Eden space top

  private:

   // Support for parallelizing young gen rescan in CMS remark phase

   Generation* _young_gen;  // the younger gen

   HeapWord** _top_addr;    // ... Top of Eden

   HeapWord** _end_addr;    // ... End of Eden

   HeapWord** _eden_chunk_array; // ... Eden partitioning array

   size_t     _eden_chunk_index; // ... top (exclusive) of array

   size_t     _eden_chunk_capacity;  // ... max entries in array

   // Support for parallelizing survivor space rescan

   HeapWord** _survivor_chunk_array;

   size_t     _survivor_chunk_index;

   size_t     _survivor_chunk_capacity;

   size_t*    _cursor;

   ChunkArray* _survivor_plab_array;

   // Support for marking stack overflow handling

   bool take_from_overflow_list(size_t num, CMSMarkStack* to_stack);

   bool par_take_from_overflow_list(size_t num, OopTaskQueue* to_work_q);

   void push_on_overflow_list(oop p);

   void par_push_on_overflow_list(oop p);

   // the following is, obviously, not, in general, "MT-stable"

   bool overflow_list_is_empty() const;

   void preserve_mark_if_necessary(oop p);

   void par_preserve_mark_if_necessary(oop p);

   void preserve_mark_work(oop p, markOop m);

   void restore_preserved_marks_if_any();

   NOT_PRODUCT(bool no_preserved_marks() const;)

   // in support of testing overflow code

   NOT_PRODUCT(int _overflow_counter;)

   NOT_PRODUCT(bool simulate_overflow();)       // sequential

   NOT_PRODUCT(bool par_simulate_overflow();)   // MT version

   int _roots_scanning_options;

   int roots_scanning_options() const      { return _roots_scanning_options; }

   void add_root_scanning_option(int o)    { _roots_scanning_options |= o;   }

   void remove_root_scanning_option(int o) { _roots_scanning_options &= ~o;  }

   // CMS work methods

   void checkpointRootsInitialWork(bool asynch); // initial checkpoint work

   // a return value of false indicates failure due to stack overflow

   bool markFromRootsWork(bool asynch);  // concurrent marking work

  public:   // FIX ME!!! only for testing

   bool do_marking_st(bool asynch);      // single-threaded marking

   bool do_marking_mt(bool asynch);      // multi-threaded  marking

  private:

   // concurrent precleaning work

   size_t preclean_mod_union_table(ConcurrentMarkSweepGeneration* gen,

                                   ScanMarkedObjectsAgainCarefullyClosure* cl);

   size_t preclean_card_table(ConcurrentMarkSweepGeneration* gen,

                              ScanMarkedObjectsAgainCarefullyClosure* cl);

   // Does precleaning work, returning a quantity indicative of

   // the amount of "useful work" done.

   size_t preclean_work(bool clean_refs, bool clean_survivors);

   void abortable_preclean(); // Preclean while looking for possible abort

   void initialize_sequential_subtasks_for_young_gen_rescan(int i);

   // Helper function for above; merge-sorts the per-thread plab samples

   void merge_survivor_plab_arrays(ContiguousSpace* surv);

   // Resets (i.e. clears) the per-thread plab sample vectors

   void reset_survivor_plab_arrays();

   // final (second) checkpoint work

   void checkpointRootsFinalWork(bool asynch, bool clear_all_soft_refs,

                                 bool init_mark_was_synchronous);

   // work routine for parallel version of remark

   void do_remark_parallel();

   // work routine for non-parallel version of remark

   void do_remark_non_parallel();

   // reference processing work routine (during second checkpoint)

   void refProcessingWork(bool asynch, bool clear_all_soft_refs);

   // concurrent sweeping work

   void sweepWork(ConcurrentMarkSweepGeneration* gen, bool asynch);

   // (concurrent) resetting of support data structures

   void reset(bool asynch);

   // Clear _expansion_cause fields of constituent generations

   void clear_expansion_cause();

   // An auxilliary method used to record the ends of

   // used regions of each generation to limit the extent of sweep

   void save_sweep_limits();

   // Resize the generations included in the collector.

   void compute_new_size();

   // A work method used by foreground collection to determine

   // what type of collection (compacting or not, continuing or fresh)

   // it should do.

   void decide_foreground_collection_type(bool clear_all_soft_refs,

     bool* should_compact, bool* should_start_over);

   // A work method used by the foreground collector to do

   // a mark-sweep-compact.

   void do_compaction_work(bool clear_all_soft_refs);

   // A work method used by the foreground collector to do

   // a mark-sweep, after taking over from a possibly on-going

   // concurrent mark-sweep collection.

   void do_mark_sweep_work(bool clear_all_soft_refs,

     CollectorState first_state, bool should_start_over);

   // If the backgrould GC is active, acquire control from the background

   // GC and do the collection.

   void acquire_control_and_collect(bool   full, bool clear_all_soft_refs);

   // For synchronizing passing of control from background to foreground

   // GC.  waitForForegroundGC() is called by the background

   // collector.  It if had to wait for a foreground collection,

   // it returns true and the background collection should assume

   // that the collection was finished by the foreground

   // collector.

   bool waitForForegroundGC();

   // Incremental mode triggering:  recompute the icms duty cycle and set the

   // allocation limits in the young gen.

   void icms_update_allocation_limits();

   size_t block_size_using_printezis_bits(HeapWord* addr) const;

   size_t block_size_if_printezis_bits(HeapWord* addr) const;

   HeapWord* next_card_start_after_block(HeapWord* addr) const;

   void setup_cms_unloading_and_verification_state();

  public:

   CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,

                ConcurrentMarkSweepGeneration* permGen,

                CardTableRS*                   ct,

                ConcurrentMarkSweepPolicy*     cp);

   ConcurrentMarkSweepThread* cmsThread() { return _cmsThread; }

   ReferenceProcessor* ref_processor() { return _ref_processor; }

   void ref_processor_init();

   Mutex* bitMapLock()        const { return _markBitMap.lock();    }

   static CollectorState abstract_state() { return _collectorState;  }

   double initiatingOccupancy() const { return _initiatingOccupancy; }

   bool should_abort_preclean() const; // Whether preclean should be aborted.

   size_t get_eden_used() const;

   size_t get_eden_capacity() const;

   ConcurrentMarkSweepGeneration* cmsGen() { return _cmsGen; }

   // locking checks

   NOT_PRODUCT(static bool have_cms_token();)

   // XXXPERM bool should_collect(bool full, size_t size, bool tlab);

   bool shouldConcurrentCollect();

   void collect(bool   full,

                bool   clear_all_soft_refs,

                size_t size,

                bool   tlab);

   void collect_in_background(bool clear_all_soft_refs);

   void collect_in_foreground(bool clear_all_soft_refs);

   // In support of ExplicitGCInvokesConcurrent

   static void request_full_gc(unsigned int full_gc_count);

   // Should we unload classes in a particular concurrent cycle?

   bool cms_should_unload_classes() const {

     assert(!_unload_classes ||  ExplicitGCInvokesConcurrentAndUnloadsClasses,

            "Inconsistency; see CR 6541037");

     return _unload_classes || CMSClassUnloadingEnabled;

   }

   void direct_allocated(HeapWord* start, size_t size);

   // Object is dead if not marked and current phase is sweeping.

   bool is_dead_obj(oop obj) const;

   // After a promotion (of "start"), do any necessary marking.

   // If "par", then it's being done by a parallel GC thread.

   // The last two args indicate if we need precise marking

   // and if so the size of the object so it can be dirtied

   // in its entirety.

   void promoted(bool par, HeapWord* start,

                 bool is_obj_array, size_t obj_size);

   HeapWord* allocation_limit_reached(Space* space, HeapWord* top,

                                      size_t word_size);

   void getFreelistLocks() const;

   void releaseFreelistLocks() const;

   bool haveFreelistLocks() const;

   // GC prologue and epilogue

   void gc_prologue(bool full);

   void gc_epilogue(bool full);

   jlong time_of_last_gc(jlong now) {

     if (_collectorState <= Idling) {

       // gc not in progress

       return _time_of_last_gc;

     } else {

       // collection in progress

       return now;

     }

   }

   // Support for parallel remark of survivor space

   void* get_data_recorder(int thr_num);

   CMSBitMap* markBitMap()  { return &_markBitMap; }

   void directAllocated(HeapWord* start, size_t size);

   // main CMS steps and related support

   void checkpointRootsInitial(bool asynch);

   bool markFromRoots(bool asynch);  // a return value of false indicates failure

                                     // due to stack overflow

   void preclean();

   void checkpointRootsFinal(bool asynch, bool clear_all_soft_refs,

                             bool init_mark_was_synchronous);

   void sweep(bool asynch);

   // Check that the currently executing thread is the expected

   // one (foreground collector or background collector).

   void check_correct_thread_executing()        PRODUCT_RETURN;

   // XXXPERM void print_statistics()           PRODUCT_RETURN;

   bool is_cms_reachable(HeapWord* addr);

   // Performance Counter Support

   CollectorCounters* counters()    { return _gc_counters; }

   // timer stuff

   void    startTimer() { assert(!_timer.is_active(), "Error"); _timer.start();   }

   void    stopTimer()  { assert( _timer.is_active(), "Error"); _timer.stop();    }

   void    resetTimer() { assert(!_timer.is_active(), "Error"); _timer.reset();   }

   double  timerValue() { assert(!_timer.is_active(), "Error"); return _timer.seconds(); }

   int  yields()          { return _numYields; }

   void resetYields()     { _numYields = 0;    }

   void incrementYields() { _numYields++;      }

   void resetNumDirtyCards()               { _numDirtyCards = 0; }

   void incrementNumDirtyCards(size_t num) { _numDirtyCards += num; }

   size_t  numDirtyCards()                 { return _numDirtyCards; }

   static bool foregroundGCShouldWait() { return _foregroundGCShouldWait; }

   static void set_foregroundGCShouldWait(bool v) { _foregroundGCShouldWait = v; }

   static bool foregroundGCIsActive() { return _foregroundGCIsActive; }

   static void set_foregroundGCIsActive(bool v) { _foregroundGCIsActive = v; }

   uint  sweepCount() const             { return _sweepCount; }

   void incrementSweepCount()           { _sweepCount++; }

   // Timers/stats for gc scheduling and incremental mode pacing.

   CMSStats& stats() { return _stats; }

   // Convenience methods that check whether CMSIncrementalMode is enabled and

   // forward to the corresponding methods in ConcurrentMarkSweepThread.

   static void start_icms();

   static void stop_icms();    // Called at the end of the cms cycle.

   static void disable_icms(); // Called before a foreground collection.

   static void enable_icms();  // Called after a foreground collection.

   void icms_wait();          // Called at yield points.

   // Adaptive size policy

   CMSAdaptiveSizePolicy* size_policy();

   CMSGCAdaptivePolicyCounters* gc_adaptive_policy_counters();

   // debugging

   void verify(bool);

   bool verify_after_remark();

   void verify_ok_to_terminate() const PRODUCT_RETURN;

   void verify_work_stacks_empty() const PRODUCT_RETURN;

   void verify_overflow_empty() const PRODUCT_RETURN;

   // convenience methods in support of debugging

   static const size_t skip_header_HeapWords() PRODUCT_RETURN0;

   HeapWord* block_start(const void* p) const PRODUCT_RETURN0;

   // accessors

   CMSMarkStack* verification_mark_stack() { return &_markStack; }

   CMSBitMap*    verification_mark_bm()    { return &_verification_mark_bm; }

   // Get the bit map with a perm gen "deadness" information.

   CMSBitMap* perm_gen_verify_bit_map()       { return &_perm_gen_verify_bit_map; }

   // Initialization errors

   bool completed_initialization() { return _completed_initialization; }

 };

 class CMSExpansionCause : public AllStatic  {

  public:

   enum Cause {

     _no_expansion,

     _satisfy_free_ratio,

     _satisfy_promotion,

     _satisfy_allocation,

     _allocate_par_lab,

     _allocate_par_spooling_space,

     _adaptive_size_policy

   };

   // Return a string describing the cause of the expansion.

   static const char* to_string(CMSExpansionCause::Cause cause);

 };

 class ConcurrentMarkSweepGeneration: public CardGeneration {

   friend class VMStructs;

   friend class ConcurrentMarkSweepThread;

   friend class ConcurrentMarkSweep;

   friend class CMSCollector;

  protected:

   static CMSCollector*       _collector; // the collector that collects us

   CompactibleFreeListSpace*  _cmsSpace;  // underlying space (only one for now)

   // Performance Counters

   GenerationCounters*      _gen_counters;

   GSpaceCounters*          _space_counters;

   // Words directly allocated, used by CMSStats.

   size_t _direct_allocated_words;

   // Non-product stat counters

   NOT_PRODUCT(

     int _numObjectsPromoted;

     int _numWordsPromoted;

     int _numObjectsAllocated;

     int _numWordsAllocated;

   )

   // Used for sizing decisions

   bool _incremental_collection_failed;

   bool incremental_collection_failed() {

     return _incremental_collection_failed;

   }

   void set_incremental_collection_failed() {

     _incremental_collection_failed = true;

   }

   void clear_incremental_collection_failed() {

     _incremental_collection_failed = false;

   }

  private:

   // For parallel young-gen GC support.

   CMSParGCThreadState** _par_gc_thread_states;

   // Reason generation was expanded

   CMSExpansionCause::Cause _expansion_cause;

   // accessors

   void set_expansion_cause(CMSExpansionCause::Cause v) { _expansion_cause = v;}

   CMSExpansionCause::Cause expansion_cause() { return _expansion_cause; }

   // In support of MinChunkSize being larger than min object size

   const double _dilatation_factor;

   enum CollectionTypes {

     Concurrent_collection_type          = 0,

     MS_foreground_collection_type       = 1,

     MSC_foreground_collection_type      = 2,

     Unknown_collection_type             = 3

   };

   CollectionTypes _debug_collection_type;

  protected:

   // Grow generation by specified size (returns false if unable to grow)

   bool grow_by(size_t bytes);

   // Grow generation to reserved size.

   bool grow_to_reserved();

   // Shrink generation by specified size (returns false if unable to shrink)

   virtual void shrink_by(size_t bytes);

   // Update statistics for GC

   virtual void update_gc_stats(int level, bool full);

   // Maximum available space in the generation (including uncommitted)

   // space.

   size_t max_available() const;

  public:

   ConcurrentMarkSweepGeneration(ReservedSpace rs, size_t initial_byte_size,

                                 int level, CardTableRS* ct,

                                 bool use_adaptive_freelists,

                                 FreeBlockDictionary::DictionaryChoice);

   // Accessors

   CMSCollector* collector() const { return _collector; }

   static void set_collector(CMSCollector* collector) {

     assert(_collector == NULL, "already set");

     _collector = collector;

   }

   CompactibleFreeListSpace*  cmsSpace() const { return _cmsSpace;  }

   Mutex* freelistLock() const;

   virtual Generation::Name kind() { return Generation::ConcurrentMarkSweep; }

   // Adaptive size policy

   CMSAdaptiveSizePolicy* size_policy();

   bool refs_discovery_is_atomic() const { return false; }

   bool refs_discovery_is_mt()     const {

     // Note: CMS does MT-discovery during the parallel-remark

     // phases. Use ReferenceProcessorMTMutator to make refs

     // discovery MT-safe during such phases or other parallel

     // discovery phases in the future. This may all go away

     // if/when we decide that refs discovery is sufficiently

     // rare that the cost of the CAS's involved is in the

     // noise. That's a measurement that should be done, and

     // the code simplified if that turns out to be the case.

     return false;

   }

   // Override

   virtual void ref_processor_init();

   void clear_expansion_cause() { _expansion_cause = CMSExpansionCause::_no_expansion; }

   // Space enquiries

   size_t capacity() const;

   size_t used() const;

   size_t free() const;

   double occupancy()      { return ((double)used())/((double)capacity()); }

   size_t contiguous_available() const;

   size_t unsafe_max_alloc_nogc() const;

   // over-rides

   MemRegion used_region() const;

   MemRegion used_region_at_save_marks() const;

   // Does a "full" (forced) collection invoked on this generation collect

   // all younger generations as well? Note that the second conjunct is a

   // hack to allow the collection of the younger gen first if the flag is

   // set. This is better than using th policy's should_collect_gen0_first()

   // since that causes us to do an extra unnecessary pair of restart-&-stop-world.

   virtual bool full_collects_younger_generations() const {

     return UseCMSCompactAtFullCollection && !CollectGen0First;

   }

   void space_iterate(SpaceClosure* blk, bool usedOnly = false);

   // Support for compaction

   CompactibleSpace* first_compaction_space() const;

   // Adjust quantites in the generation affected by

   // the compaction.

   void reset_after_compaction();

   // Allocation support

   HeapWord* allocate(size_t size, bool tlab);

   HeapWord* have_lock_and_allocate(size_t size, bool tlab);

   oop       promote(oop obj, size_t obj_size, oop* ref);

   HeapWord* par_allocate(size_t size, bool tlab) {

     return allocate(size, tlab);

   }

   // Incremental mode triggering.

   HeapWord* allocation_limit_reached(Space* space, HeapWord* top,

                                      size_t word_size);

   // Used by CMSStats to track direct allocation.  The value is sampled and

   // reset after each young gen collection.

   size_t direct_allocated_words() const { return _direct_allocated_words; }

   void reset_direct_allocated_words()   { _direct_allocated_words = 0; }

   // Overrides for parallel promotion.

   virtual oop par_promote(int thread_num,

                           oop obj, markOop m, size_t word_sz);

   // This one should not be called for CMS.

   virtual void par_promote_alloc_undo(int thread_num,

                                       HeapWord* obj, size_t word_sz);

   virtual void par_promote_alloc_done(int thread_num);

   virtual void par_oop_since_save_marks_iterate_done(int thread_num);

   virtual bool promotion_attempt_is_safe(size_t promotion_in_bytes,

     bool younger_handles_promotion_failure) const;

   bool should_collect(bool full, size_t size, bool tlab);

     // XXXPERM

   bool shouldConcurrentCollect(double initiatingOccupancy); // XXXPERM

   void collect(bool   full,

                bool   clear_all_soft_refs,

                size_t size,

                bool   tlab);

   HeapWord* expand_and_allocate(size_t word_size,

                                 bool tlab,

                                 bool parallel = false);

   // GC prologue and epilogue

   void gc_prologue(bool full);

   void gc_prologue_work(bool full, bool registerClosure,

                         ModUnionClosure* modUnionClosure);

   void gc_epilogue(bool full);

   void gc_epilogue_work(bool full);

   // Time since last GC of this generation

   jlong time_of_last_gc(jlong now) {

     return collector()->time_of_last_gc(now);

   }

   void update_time_of_last_gc(jlong now) {

     collector()-> update_time_of_last_gc(now);

   }

   // Allocation failure

   void expand(size_t bytes, size_t expand_bytes,

     CMSExpansionCause::Cause cause);

   void shrink(size_t bytes);

   HeapWord* expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz);

   bool expand_and_ensure_spooling_space(PromotionInfo* promo);

   // Iteration support and related enquiries

   void save_marks();

   bool no_allocs_since_save_marks();

   void object_iterate_since_last_GC(ObjectClosure* cl);

   void younger_refs_iterate(OopsInGenClosure* cl);

   // Iteration support specific to CMS generations

   void save_sweep_limit();

   // More iteration support

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

   virtual void oop_iterate(OopClosure* cl);

   virtual void object_iterate(ObjectClosure* cl);

   // Need to declare the full complement of closures, whether we'll

   // override them or not, or get message from the compiler:

   //   oop_since_save_marks_iterate_nv hides virtual function...

   #define CMS_SINCE_SAVE_MARKS_DECL(OopClosureType, nv_suffix) \

     void oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl);

   ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DECL)

   // Smart allocation  XXX -- move to CFLSpace?

   void setNearLargestChunk();

   bool isNearLargestChunk(HeapWord* addr);

   // Get the chunk at the end of the space.  Delagates to

   // the space.

   FreeChunk* find_chunk_at_end();

   // Overriding of unused functionality (sharing not yet supported with CMS)

   void pre_adjust_pointers();

   void post_compact();

   // Debugging

   void prepare_for_verify();

   void verify(bool allow_dirty);

   void print_statistics()               PRODUCT_RETURN;

   // Performance Counters support

   virtual void update_counters();

   virtual void update_counters(size_t used);

   void initialize_performance_counters();

   CollectorCounters* counters()  { return collector()->counters(); }

   // Support for parallel remark of survivor space

   void* get_data_recorder(int thr_num) {

     //Delegate to collector

     return collector()->get_data_recorder(thr_num);

   }

   // Printing

   const char* name() const;

   virtual const char* short_name() const { return "CMS"; }

   void        print() const;

   void printOccupancy(const char* s);

   bool must_be_youngest() const { return false; }

   bool must_be_oldest()   const { return true; }

   void compute_new_size();

   CollectionTypes debug_collection_type() { return _debug_collection_type; }

   void rotate_debug_collection_type();

 };

 class ASConcurrentMarkSweepGeneration : public ConcurrentMarkSweepGeneration {

   // Return the size policy from the heap's collector

   // policy casted to CMSAdaptiveSizePolicy*.

   CMSAdaptiveSizePolicy* cms_size_policy() const;

   // Resize the generation based on the adaptive size

   // policy.

   void resize(size_t cur_promo, size_t desired_promo);

   // Return the GC counters from the collector policy

   CMSGCAdaptivePolicyCounters* gc_adaptive_policy_counters();

   virtual void shrink_by(size_t bytes);

  public:

   virtual void compute_new_size();

   ASConcurrentMarkSweepGeneration(ReservedSpace rs, size_t initial_byte_size,

                                   int level, CardTableRS* ct,

                                   bool use_adaptive_freelists,

                                   FreeBlockDictionary::DictionaryChoice

                                     dictionaryChoice) :

     ConcurrentMarkSweepGeneration(rs, initial_byte_size, level, ct,

       use_adaptive_freelists, dictionaryChoice) {}

   virtual const char* short_name() const { return "ASCMS"; }

   virtual Generation::Name kind() { return Generation::ASConcurrentMarkSweep; }

   virtual void update_counters();

   virtual void update_counters(size_t used);

 };

 //

 // Closures of various sorts used by CMS to accomplish its work

 //

 // This closure is used to check that a certain set of oops is empty.

 class FalseClosure: public OopClosure {

  public:

   void do_oop(oop* p) {

     guarantee(false, "Should be an empty set");

   }

 };

 // This closure is used to do concurrent marking from the roots

 // following the first checkpoint.

 class MarkFromRootsClosure: public BitMapClosure {

   CMSCollector*  _collector;

   MemRegion      _span;

   CMSBitMap*     _bitMap;

   CMSBitMap*     _mut;

   CMSMarkStack*  _markStack;

   CMSMarkStack*  _revisitStack;

   bool           _yield;

   int            _skipBits;

   HeapWord*      _finger;

   HeapWord*      _threshold;

   DEBUG_ONLY(bool _verifying;)

  public:

   MarkFromRootsClosure(CMSCollector* collector, MemRegion span,

                        CMSBitMap* bitMap,

                        CMSMarkStack*  markStack,

                        CMSMarkStack*  revisitStack,

                        bool should_yield, bool verifying = false);

   void do_bit(size_t offset);

   void reset(HeapWord* addr);

   inline void do_yield_check();

  private:

   void scanOopsInOop(HeapWord* ptr);

   void do_yield_work();

 };

 // This closure is used to do concurrent multi-threaded

 // marking from the roots following the first checkpoint.

 // XXX This should really be a subclass of The serial version

 // above, but i have not had the time to refactor things cleanly.

 // That willbe done for Dolphin.

 class Par_MarkFromRootsClosure: public BitMapClosure {

   CMSCollector*  _collector;

   MemRegion      _whole_span;

   MemRegion      _span;

   CMSBitMap*     _bit_map;

   CMSBitMap*     _mut;

   OopTaskQueue*  _work_queue;

   CMSMarkStack*  _overflow_stack;

   CMSMarkStack*  _revisit_stack;

   bool           _yield;

   int            _skip_bits;

   HeapWord*      _finger;

   HeapWord*      _threshold;

   CMSConcMarkingTask* _task;

  public:

   Par_MarkFromRootsClosure(CMSConcMarkingTask* task, CMSCollector* collector,

                        MemRegion span,

                        CMSBitMap* bit_map,

                        OopTaskQueue* work_queue,

                        CMSMarkStack*  overflow_stack,

                        CMSMarkStack*  revisit_stack,

                        bool should_yield);

   void do_bit(size_t offset);

   inline void do_yield_check();

  private:

   void scan_oops_in_oop(HeapWord* ptr);

   void do_yield_work();

   bool get_work_from_overflow_stack();

 };

 // The following closures are used to do certain kinds of verification of

 // CMS marking.

 class PushAndMarkVerifyClosure: public OopClosure {

   CMSCollector*    _collector;

   MemRegion        _span;

   CMSBitMap*       _verification_bm;

   CMSBitMap*       _cms_bm;

   CMSMarkStack*    _mark_stack;

  public:

   PushAndMarkVerifyClosure(CMSCollector* cms_collector,

                            MemRegion span,

                            CMSBitMap* verification_bm,

                            CMSBitMap* cms_bm,

                            CMSMarkStack*  mark_stack);

   void do_oop(oop* p);

   // Deal with a stack overflow condition

   void handle_stack_overflow(HeapWord* lost);

 };

 class MarkFromRootsVerifyClosure: public BitMapClosure {

   CMSCollector*  _collector;

   MemRegion      _span;

   CMSBitMap*     _verification_bm;

   CMSBitMap*     _cms_bm;

   CMSMarkStack*  _mark_stack;

   HeapWord*      _finger;

   PushAndMarkVerifyClosure _pam_verify_closure;

  public:

   MarkFromRootsVerifyClosure(CMSCollector* collector, MemRegion span,

                              CMSBitMap* verification_bm,

                              CMSBitMap* cms_bm,

                              CMSMarkStack*  mark_stack);

   void do_bit(size_t offset);

   void reset(HeapWord* addr);

 };

 // This closure is used to check that a certain set of bits is

 // "empty" (i.e. the bit vector doesn't have any 1-bits).

 class FalseBitMapClosure: public BitMapClosure {

  public:

   void do_bit(size_t offset) {

     guarantee(false, "Should not have a 1 bit");

   }

 };

 // This closure is used during the second checkpointing phase

 // to rescan the marked objects on the dirty cards in the mod

 // union table and the card table proper. It's invoked via

 // MarkFromDirtyCardsClosure below. It uses either

 // [Par_]MarkRefsIntoAndScanClosure (Par_ in the parallel case)

 // declared in genOopClosures.hpp to accomplish some of its work.

 // In the parallel case the bitMap is shared, so access to

 // it needs to be suitably synchronized for updates by embedded

 // closures that update it; however, this closure itself only

 // reads the bit_map and because it is idempotent, is immune to

 // reading stale values.

 class ScanMarkedObjectsAgainClosure: public UpwardsObjectClosure {

   #ifdef ASSERT

     CMSCollector*          _collector;

     MemRegion              _span;

     union {

       CMSMarkStack*        _mark_stack;

       OopTaskQueue*        _work_queue;

     };

   #endif // ASSERT

   bool                       _parallel;

   CMSBitMap*                 _bit_map;

   union {

     MarkRefsIntoAndScanClosure*     _scan_closure;

     Par_MarkRefsIntoAndScanClosure* _par_scan_closure;

   };

  public:

   ScanMarkedObjectsAgainClosure(CMSCollector* collector,

                                 MemRegion span,

                                 ReferenceProcessor* rp,

                                 CMSBitMap* bit_map,

                                 CMSMarkStack*  mark_stack,

                                 CMSMarkStack*  revisit_stack,

                                 MarkRefsIntoAndScanClosure* cl):

     #ifdef ASSERT

       _collector(collector),

       _span(span),

       _mark_stack(mark_stack),

     #endif // ASSERT

     _parallel(false),

     _bit_map(bit_map),

     _scan_closure(cl) { }

   ScanMarkedObjectsAgainClosure(CMSCollector* collector,

                                 MemRegion span,

                                 ReferenceProcessor* rp,

                                 CMSBitMap* bit_map,

                                 OopTaskQueue* work_queue,

                                 CMSMarkStack* revisit_stack,

                                 Par_MarkRefsIntoAndScanClosure* cl):

     #ifdef ASSERT

       _collector(collector),

       _span(span),

       _work_queue(work_queue),

     #endif // ASSERT

     _parallel(true),

     _bit_map(bit_map),

     _par_scan_closure(cl) { }

   void do_object(oop obj) {

     guarantee(false, "Call do_object_b(oop, MemRegion) instead");

   }

   bool do_object_b(oop obj) {

     guarantee(false, "Call do_object_b(oop, MemRegion) form instead");

     return false;

   }

   bool do_object_bm(oop p, MemRegion mr);

 };

 // This closure is used during the second checkpointing phase

 // to rescan the marked objects on the dirty cards in the mod

 // union table and the card table proper. It invokes

 // ScanMarkedObjectsAgainClosure above to accomplish much of its work.

 // In the parallel case, the bit map is shared and requires

 // synchronized access.

 class MarkFromDirtyCardsClosure: public MemRegionClosure {

   CompactibleFreeListSpace*      _space;

   ScanMarkedObjectsAgainClosure  _scan_cl;

   size_t                         _num_dirty_cards;

  public:

   MarkFromDirtyCardsClosure(CMSCollector* collector,

                             MemRegion span,

                             CompactibleFreeListSpace* space,

                             CMSBitMap* bit_map,

                             CMSMarkStack* mark_stack,

                             CMSMarkStack* revisit_stack,

                             MarkRefsIntoAndScanClosure* cl):

     _space(space),

     _num_dirty_cards(0),

     _scan_cl(collector, span, collector->ref_processor(), bit_map,

                  mark_stack, revisit_stack, cl) { }

   MarkFromDirtyCardsClosure(CMSCollector* collector,

                             MemRegion span,

                             CompactibleFreeListSpace* space,

                             CMSBitMap* bit_map,

                             OopTaskQueue* work_queue,

                             CMSMarkStack* revisit_stack,

                             Par_MarkRefsIntoAndScanClosure* cl):

     _space(space),

     _num_dirty_cards(0),

     _scan_cl(collector, span, collector->ref_processor(), bit_map,

              work_queue, revisit_stack, cl) { }

   void do_MemRegion(MemRegion mr);

   void set_space(CompactibleFreeListSpace* space) { _space = space; }

   size_t num_dirty_cards() { return _num_dirty_cards; }

 };

 // This closure is used in the non-product build to check

 // that there are no MemRegions with a certain property.

 class FalseMemRegionClosure: public MemRegionClosure {

   void do_MemRegion(MemRegion mr) {

     guarantee(!mr.is_empty(), "Shouldn't be empty");

     guarantee(false, "Should never be here");

   }

 };

 // This closure is used during the precleaning phase

 // to "carefully" rescan marked objects on dirty cards.

 // It uses MarkRefsIntoAndScanClosure declared in genOopClosures.hpp

 // to accomplish some of its work.

 class ScanMarkedObjectsAgainCarefullyClosure: public ObjectClosureCareful {

   CMSCollector*                  _collector;

   MemRegion                      _span;

   bool                           _yield;

   Mutex*                         _freelistLock;

   CMSBitMap*                     _bitMap;

   CMSMarkStack*                  _markStack;

   MarkRefsIntoAndScanClosure*    _scanningClosure;

  public:

   ScanMarkedObjectsAgainCarefullyClosure(CMSCollector* collector,

                                          MemRegion     span,

                                          CMSBitMap* bitMap,

                                          CMSMarkStack*  markStack,

                                          CMSMarkStack*  revisitStack,

                                          MarkRefsIntoAndScanClosure* cl,

                                          bool should_yield):

     _collector(collector),

     _span(span),

     _yield(should_yield),

     _bitMap(bitMap),

     _markStack(markStack),

     _scanningClosure(cl) {

   }

   void do_object(oop p) {

     guarantee(false, "call do_object_careful instead");

   }

   size_t      do_object_careful(oop p) {

     guarantee(false, "Unexpected caller");

     return 0;

   }

   size_t      do_object_careful_m(oop p, MemRegion mr);

   void setFreelistLock(Mutex* m) {

     _freelistLock = m;

     _scanningClosure->set_freelistLock(m);

   }

  private:

   inline bool do_yield_check();

   void do_yield_work();

 };

 class SurvivorSpacePrecleanClosure: public ObjectClosureCareful {

   CMSCollector*                  _collector;

   MemRegion                      _span;

   bool                           _yield;

   CMSBitMap*                     _bit_map;

   CMSMarkStack*                  _mark_stack;

   PushAndMarkClosure*            _scanning_closure;

   unsigned int                   _before_count;

  public:

   SurvivorSpacePrecleanClosure(CMSCollector* collector,

                                MemRegion     span,

                                CMSBitMap*    bit_map,

                                CMSMarkStack* mark_stack,

                                PushAndMarkClosure* cl,

                                unsigned int  before_count,

                                bool          should_yield):

     _collector(collector),

     _span(span),

     _yield(should_yield),

     _bit_map(bit_map),

     _mark_stack(mark_stack),

     _scanning_closure(cl),

     _before_count(before_count)

   { }

   void do_object(oop p) {

     guarantee(false, "call do_object_careful instead");

   }

   size_t      do_object_careful(oop p);

   size_t      do_object_careful_m(oop p, MemRegion mr) {

     guarantee(false, "Unexpected caller");

     return 0;

   }

  private:

   inline void do_yield_check();

   void do_yield_work();

 };

 // This closure is used to accomplish the sweeping work

 // after the second checkpoint but before the concurrent reset

 // phase.

 //

 // Terminology

 //   left hand chunk (LHC) - block of one or more chunks currently being

 //     coalesced.  The LHC is available for coalescing with a new chunk.

 //   right hand chunk (RHC) - block that is currently being swept that is

 //     free or garbage that can be coalesced with the LHC.

 // _inFreeRange is true if there is currently a LHC

 // _lastFreeRangeCoalesced is true if the LHC consists of more than one chunk.

 // _freeRangeInFreeLists is true if the LHC is in the free lists.

 // _freeFinger is the address of the current LHC

 class SweepClosure: public BlkClosureCareful {

   CMSCollector*                  _collector;  // collector doing the work

   ConcurrentMarkSweepGeneration* _g;    // Generation being swept

   CompactibleFreeListSpace*      _sp;   // Space being swept

   HeapWord*                      _limit;

   Mutex*                         _freelistLock; // Free list lock (in space)

   CMSBitMap*                     _bitMap;       // Marking bit map (in

                                                 // generation)

   bool                           _inFreeRange;  // Indicates if we are in the

                                                 // midst of a free run

   bool                           _freeRangeInFreeLists;

                                         // Often, we have just found

                                         // a free chunk and started

                                         // a new free range; we do not

                                         // eagerly remove this chunk from

                                         // the free lists unless there is

                                         // a possibility of coalescing.

                                         // When true, this flag indicates

                                         // that the _freeFinger below

                                         // points to a potentially free chunk

                                         // that may still be in the free lists

   bool                           _lastFreeRangeCoalesced;

                                         // free range contains chunks

                                         // coalesced

   bool                           _yield;

                                         // Whether sweeping should be

                                         // done with yields. For instance

                                         // when done by the foreground

                                         // collector we shouldn't yield.

   HeapWord*                      _freeFinger;   // When _inFreeRange is set, the

                                                 // pointer to the "left hand

                                                 // chunk"

   size_t                         _freeRangeSize;

                                         // When _inFreeRange is set, this

                                         // indicates the accumulated size

                                         // of the "left hand chunk"

   NOT_PRODUCT(

     size_t                       _numObjectsFreed;

     size_t                       _numWordsFreed;

     size_t                       _numObjectsLive;

     size_t                       _numWordsLive;

     size_t                       _numObjectsAlreadyFree;

     size_t                       _numWordsAlreadyFree;

     FreeChunk*                   _last_fc;

   )

  private:

   // Code that is common to a free chunk or garbage when

   // encountered during sweeping.

   void doPostIsFreeOrGarbageChunk(FreeChunk *fc,

                                   size_t chunkSize);

   // Process a free chunk during sweeping.

   void doAlreadyFreeChunk(FreeChunk *fc);

   // Process a garbage chunk during sweeping.

   size_t doGarbageChunk(FreeChunk *fc);

   // Process a live chunk during sweeping.

   size_t doLiveChunk(FreeChunk* fc);

   // Accessors.

   HeapWord* freeFinger() const          { return _freeFinger; }

   void set_freeFinger(HeapWord* v)      { _freeFinger = v; }

   size_t freeRangeSize() const          { return _freeRangeSize; }

   void set_freeRangeSize(size_t v)      { _freeRangeSize = v; }

   bool inFreeRange()    const           { return _inFreeRange; }

   void set_inFreeRange(bool v)          { _inFreeRange = v; }

   bool lastFreeRangeCoalesced() const    { return _lastFreeRangeCoalesced; }

   void set_lastFreeRangeCoalesced(bool v) { _lastFreeRangeCoalesced = v; }

   bool freeRangeInFreeLists() const     { return _freeRangeInFreeLists; }

   void set_freeRangeInFreeLists(bool v) { _freeRangeInFreeLists = v; }

   // Initialize a free range.

   void initialize_free_range(HeapWord* freeFinger, bool freeRangeInFreeLists);

   // Return this chunk to the free lists.

   void flushCurFreeChunk(HeapWord* chunk, size_t size);

   // Check if we should yield and do so when necessary.

   inline void do_yield_check(HeapWord* addr);

   // Yield

   void do_yield_work(HeapWord* addr);

   // Debugging/Printing

   void record_free_block_coalesced(FreeChunk* fc) const PRODUCT_RETURN;

  public:

   SweepClosure(CMSCollector* collector, ConcurrentMarkSweepGeneration* g,

                CMSBitMap* bitMap, bool should_yield);

   ~SweepClosure();

   size_t       do_blk_careful(HeapWord* addr);

 };

 // Closures related to weak references processing

 // During CMS' weak reference processing, this is a

 // work-routine/closure used to complete transitive

 // marking of objects as live after a certain point

 // in which an initial set has been completely accumulated.

 class CMSDrainMarkingStackClosure: public VoidClosure {

   CMSCollector*        _collector;

   MemRegion            _span;

   CMSMarkStack*        _mark_stack;

   CMSBitMap*           _bit_map;

   CMSKeepAliveClosure* _keep_alive;

  public:

   CMSDrainMarkingStackClosure(CMSCollector* collector, MemRegion span,

                       CMSBitMap* bit_map, CMSMarkStack* mark_stack,

                       CMSKeepAliveClosure* keep_alive):

     _collector(collector),

     _span(span),

     _bit_map(bit_map),

     _mark_stack(mark_stack),

     _keep_alive(keep_alive) { }

   void do_void();

 };

 // A parallel version of CMSDrainMarkingStackClosure above.

 class CMSParDrainMarkingStackClosure: public VoidClosure {

   CMSCollector*           _collector;

   MemRegion               _span;

   OopTaskQueue*           _work_queue;

   CMSBitMap*              _bit_map;

   CMSInnerParMarkAndPushClosure _mark_and_push;

  public:

   CMSParDrainMarkingStackClosure(CMSCollector* collector,

                                  MemRegion span, CMSBitMap* bit_map,

                                  OopTaskQueue* work_queue):

     _collector(collector),

     _span(span),

     _bit_map(bit_map),

     _work_queue(work_queue),

     _mark_and_push(collector, span, bit_map, work_queue) { }

  public:

   void trim_queue(uint max);

   void do_void();

 };

 // Allow yielding or short-circuiting of reference list

 // prelceaning work.

 class CMSPrecleanRefsYieldClosure: public YieldClosure {

   CMSCollector* _collector;

   void do_yield_work();

  public:

   CMSPrecleanRefsYieldClosure(CMSCollector* collector):

     _collector(collector) {}

   virtual bool should_return();

 };

 // Convenience class that locks free list locks for given CMS collector

 class FreelistLocker: public StackObj {

  private:

   CMSCollector* _collector;

  public:

   FreelistLocker(CMSCollector* collector):

     _collector(collector) {

     _collector->getFreelistLocks();

   }

   ~FreelistLocker() {

     _collector->releaseFreelistLocks();

   }

 };

 // Mark all dead objects in a given space.

 class MarkDeadObjectsClosure: public BlkClosure {

   const CMSCollector*             _collector;

   const CompactibleFreeListSpace* _sp;

   CMSBitMap*                      _live_bit_map;

   CMSBitMap*                      _dead_bit_map;

 public:

   MarkDeadObjectsClosure(const CMSCollector* collector,

                          const CompactibleFreeListSpace* sp,

                          CMSBitMap *live_bit_map,

                          CMSBitMap *dead_bit_map) :

     _collector(collector),

     _sp(sp),

     _live_bit_map(live_bit_map),

     _dead_bit_map(dead_bit_map) {}

   size_t do_blk(HeapWord* addr);

 };