view src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.hpp @ 94:0834225a7916

6634032: CMS: Need CMSInitiatingPermOccupancyFraction for perm, divorcing from CMSInitiatingOccupancyFraction Summary: The option CMSInitiatingPermOccupancyFraction now controls perm triggering threshold. Even though the actual value of the threshold has not yet been changed, so there is no change in policy, we now have the infrastructure in place for dynamically deciding when to collect the perm gen, an issue that will be addressed in the near future. Reviewed-by: jmasa
author ysr
date Sun, 16 Mar 2008 21:57:25 -0700
parents a61af66fc99e
children ba764ed4b6f2
line wrap: on
line source
/*
 * 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?
  bool _should_unload_classes;
  unsigned int  _concurrent_cycles_since_last_unload;
  unsigned int concurrent_cycles_since_last_unload() const {
    return _concurrent_cycles_since_last_unload;
  }
  // Did we (allow) unload classes in the previous concurrent cycle?
  bool unloaded_classes_last_cycle() const {
    return concurrent_cycles_since_last_unload() == 0;
  }

  // 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;

  // 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;  }

  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 should_unload_classes() const {
    return _should_unload_classes;
  }
  bool update_should_unload_classes();

  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;
  }

  // accessors
  void set_expansion_cause(CMSExpansionCause::Cause v) { _expansion_cause = v;}
  CMSExpansionCause::Cause expansion_cause() const { return _expansion_cause; }

 private:
  // For parallel young-gen GC support.
  CMSParGCThreadState** _par_gc_thread_states;

  // Reason generation was expanded
  CMSExpansionCause::Cause _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;

  // Fraction of current occupancy at which to start a CMS collection which
  // will collect this generation (at least).
  double _initiating_occupancy;

 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;

  // getter and initializer for _initiating_occupancy field.
  double initiating_occupancy() const { return _initiating_occupancy; }
  void   init_initiating_occupancy(intx io, intx tr);

 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() const { 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);
  virtual bool should_concurrent_collect() const;
  virtual bool is_too_full() const;
  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);
};