jdk8-mips64-public/hotspot: src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.hpp@2d127394260e (annotated)

src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.hpp@2d127394260e (annotated)

src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.hpp

Thu, 27 May 2010 18:01:56 -0700

author: kvn
date: Thu, 27 May 2010 18:01:56 -0700
changeset 1926: 2d127394260e
parent 1822: 0bfd3fb24150
child 1907: c18cbe5936b8
permissions: -rw-r--r--

6916623: Align object to 16 bytes to use Compressed Oops with java heap up to 64Gb
Summary: Added new product ObjectAlignmentInBytes flag to control object alignment.
Reviewed-by: twisti, ysr, iveresov

 /*
  * Copyright 2001-2010 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();
   // In support of adjusting of cms trigger ratios based on history
   // of concurrent mode failure.
   double cms_free_adjustment_factor(size_t free) const;
   void   adjust_cms_free_adjustment_factor(bool fail, size_t free);
  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 {
   const MemRegion  _span;
   const CMSBitMap* _bit_map;
   friend class CMSCollector;
  public:
   CMSIsAliveClosure(MemRegion span,
                     CMSBitMap* bit_map):
     _span(span),
     _bit_map(bit_map) {
     assert(!span.is_empty(), "Empty span could spell trouble");
   }
   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;
   }
   // Root scanning options for perm gen
   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;  }
   // 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; }
   // XXX Move these to CMSStats ??? FIX ME !!!
   elapsedTimer _inter_sweep_timer;   // time between sweeps
   elapsedTimer _intra_sweep_timer;   // time _in_ sweeps
   // padded decaying average estimates of the above
   AdaptivePaddedAverage _inter_sweep_estimate;
   AdaptivePaddedAverage _intra_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_preclean_ovflw;
   size_t        _ser_kac_ovflw;
   size_t        _par_kac_ovflw;
   NOT_PRODUCT(ssize_t _num_par_pushes;)
   // ("Weak") Reference processing support
   ReferenceProcessor*            _ref_processor;
   CMSIsAliveClosure              _is_alive_closure;
       // keep this textually after _markBitMap and _span; 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
  public:
   enum CollectorState {
     Resizing            = 0,
     Resetting           = 1,
     Idling              = 2,
     InitialMarking      = 3,
     Marking             = 4,
     Precleaning         = 5,
     AbortablePreclean   = 6,
     FinalMarking        = 7,
     Sweeping            = 8
   };
  protected:
   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;
   size_t _sweep_count;
   // 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
   // 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).
   static 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; }
   size_t sweep_count() const             { return _sweep_count; }
   void   increment_sweep_count()         { _sweep_count++; }
   // 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:
   // 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();
   // 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();
   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);
   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;
   // Inform this (non-young) generation that a promotion failure was
   // encountered during a collection of a younger generation that
   // promotes into this generation.
   virtual void promotion_failure_occurred();
   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);
   virtual bool expand(size_t bytes, size_t expand_bytes);
   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 safe_object_iterate(ObjectClosure* 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"); }
   void do_oop(narrowOop* 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);
   bool 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);
   bool 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;
  protected:
   void do_oop(oop p);
   template <class T> inline void do_oop_work(T *p) {
     oop obj = oopDesc::load_decode_heap_oop_not_null(p);
     do_oop(obj);
   }
  public:
   PushAndMarkVerifyClosure(CMSCollector* cms_collector,
                            MemRegion span,
                            CMSBitMap* verification_bm,
                            CMSBitMap* cms_bm,
                            CMSMarkStack*  mark_stack);
   void do_oop(oop* p);
   void do_oop(narrowOop* 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);
   bool 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:
   bool do_bit(size_t offset) {
     guarantee(false, "Should not have a 1 bit");
     return true;
   }
 };
 // 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.
 // This closure is currently used both during the final
 // remark stop-world phase, as well as during the concurrent
 // precleaning of the discovered reference lists.
 class CMSDrainMarkingStackClosure: public VoidClosure {
   CMSCollector*        _collector;
   MemRegion            _span;
   CMSMarkStack*        _mark_stack;
   CMSBitMap*           _bit_map;
   CMSKeepAliveClosure* _keep_alive;
   bool                 _concurrent_precleaning;
  public:
   CMSDrainMarkingStackClosure(CMSCollector* collector, MemRegion span,
                       CMSBitMap* bit_map, CMSMarkStack* mark_stack,
                       CMSKeepAliveClosure* keep_alive,
                       bool cpc):
     _collector(collector),
     _span(span),
     _bit_map(bit_map),
     _mark_stack(mark_stack),
     _keep_alive(keep_alive),
     _concurrent_precleaning(cpc) {
     assert(_concurrent_precleaning == _keep_alive->concurrent_precleaning(),
            "Mismatch");
   }
   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,
                                  CMSMarkStack* revisit_stack,
                                  OopTaskQueue* work_queue):
     _collector(collector),
     _span(span),
     _bit_map(bit_map),
     _work_queue(work_queue),
     _mark_and_push(collector, span, bit_map, revisit_stack, 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);
 };

Mercurial > jdk8-mips64-public > hotspot / annotate

src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.hpp@2d127394260e (annotated)

src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.hpp