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 /*

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

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  * 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).

  *

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 #ifndef SHARE_VM_GC_IMPLEMENTATION_G1_CONCURRENTMARK_HPP

 #define SHARE_VM_GC_IMPLEMENTATION_G1_CONCURRENTMARK_HPP

 #include "gc_implementation/g1/heapRegionSets.hpp"

 #include "utilities/taskqueue.hpp"

 class G1CollectedHeap;

 class CMTask;

 typedef GenericTaskQueue<oop, mtGC>            CMTaskQueue;

 typedef GenericTaskQueueSet<CMTaskQueue, mtGC> CMTaskQueueSet;

 // Closure used by CM during concurrent reference discovery

 // and reference processing (during remarking) to determine

 // if a particular object is alive. It is primarily used

 // to determine if referents of discovered reference objects

 // are alive. An instance is also embedded into the

 // reference processor as the _is_alive_non_header field

 class G1CMIsAliveClosure: public BoolObjectClosure {

   G1CollectedHeap* _g1;

  public:

   G1CMIsAliveClosure(G1CollectedHeap* g1) : _g1(g1) { }

   void do_object(oop obj) {

     ShouldNotCallThis();

   }

   bool do_object_b(oop obj);

 };

 // A generic CM bit map.  This is essentially a wrapper around the BitMap

 // class, with one bit per (1<<_shifter) HeapWords.

 class CMBitMapRO VALUE_OBJ_CLASS_SPEC {

  protected:

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

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

   const int _shifter;          // map to char or bit

   VirtualSpace _virtual_space; // underlying the bit map

   BitMap    _bm;               // the bit map itself

  public:

   // constructor

   CMBitMapRO(ReservedSpace rs, int shifter);

   enum { do_yield = true };

   // inquiries

   HeapWord* startWord()   const { return _bmStartWord; }

   size_t    sizeInWords() const { return _bmWordSize;  }

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

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

   // read marks

   bool isMarked(HeapWord* addr) const {

     assert(_bmStartWord <= addr && addr < (_bmStartWord + _bmWordSize),

            "outside underlying space?");

     return _bm.at(heapWordToOffset(addr));

   }

   // iteration

   inline bool iterate(BitMapClosure* cl, MemRegion mr);

   inline bool iterate(BitMapClosure* cl);

   // Return the address corresponding to the next marked bit at or after

   // "addr", and before "limit", if "limit" is non-NULL.  If there is no

   // such bit, returns "limit" if that is non-NULL, or else "endWord()".

   HeapWord* getNextMarkedWordAddress(HeapWord* addr,

                                      HeapWord* limit = NULL) const;

   // Return the address corresponding to the next unmarked bit at or after

   // "addr", and before "limit", if "limit" is non-NULL.  If there is no

   // such bit, returns "limit" if that is non-NULL, or else "endWord()".

   HeapWord* getNextUnmarkedWordAddress(HeapWord* addr,

                                        HeapWord* limit = NULL) const;

   // conversion utilities

   // XXX Fix these so that offsets are size_t's...

   HeapWord* offsetToHeapWord(size_t offset) const {

     return _bmStartWord + (offset << _shifter);

   }

   size_t heapWordToOffset(HeapWord* addr) const {

     return pointer_delta(addr, _bmStartWord) >> _shifter;

   }

   int heapWordDiffToOffsetDiff(size_t diff) const;

   HeapWord* nextWord(HeapWord* addr) {

     return offsetToHeapWord(heapWordToOffset(addr) + 1);

   }

   // debugging

   NOT_PRODUCT(bool covers(ReservedSpace rs) const;)

 };

 class CMBitMap : public CMBitMapRO {

  public:

   // constructor

   CMBitMap(ReservedSpace rs, int shifter) :

     CMBitMapRO(rs, shifter) {}

   // write marks

   void mark(HeapWord* addr) {

     assert(_bmStartWord <= addr && addr < (_bmStartWord + _bmWordSize),

            "outside underlying space?");

     _bm.set_bit(heapWordToOffset(addr));

   }

   void clear(HeapWord* addr) {

     assert(_bmStartWord <= addr && addr < (_bmStartWord + _bmWordSize),

            "outside underlying space?");

     _bm.clear_bit(heapWordToOffset(addr));

   }

   bool parMark(HeapWord* addr) {

     assert(_bmStartWord <= addr && addr < (_bmStartWord + _bmWordSize),

            "outside underlying space?");

     return _bm.par_set_bit(heapWordToOffset(addr));

   }

   bool parClear(HeapWord* addr) {

     assert(_bmStartWord <= addr && addr < (_bmStartWord + _bmWordSize),

            "outside underlying space?");

     return _bm.par_clear_bit(heapWordToOffset(addr));

   }

   void markRange(MemRegion mr);

   void clearAll();

   void clearRange(MemRegion mr);

   // Starting at the bit corresponding to "addr" (inclusive), find the next

   // "1" bit, if any.  This bit starts some run of consecutive "1"'s; find

   // the end of this run (stopping at "end_addr").  Return the MemRegion

   // covering from the start of the region corresponding to the first bit

   // of the run to the end of the region corresponding to the last bit of

   // the run.  If there is no "1" bit at or after "addr", return an empty

   // MemRegion.

   MemRegion getAndClearMarkedRegion(HeapWord* addr, HeapWord* end_addr);

 };

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

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

 class CMMarkStack VALUE_OBJ_CLASS_SPEC {

   ConcurrentMark* _cm;

   oop*   _base;        // bottom of stack

   jint   _index;       // one more than last occupied index

   jint   _capacity;    // max #elements

   jint   _saved_index; // value of _index saved at start of GC

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

   bool   _overflow;

   DEBUG_ONLY(bool _drain_in_progress;)

   DEBUG_ONLY(bool _drain_in_progress_yields;)

  public:

   CMMarkStack(ConcurrentMark* cm);

   ~CMMarkStack();

   void allocate(size_t size);

   oop pop() {

     if (!isEmpty()) {

       return _base[--_index] ;

     }

     return NULL;

   }

   // If overflow happens, don't do the push, and record the overflow.

   // *Requires* that "ptr" is already marked.

   void push(oop ptr) {

     if (isFull()) {

       // Record overflow.

       _overflow = true;

       return;

     } else {

       _base[_index++] = ptr;

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

     }

   }

   // Non-block impl.  Note: concurrency is allowed only with other

   // "par_push" operations, not with "pop" or "drain".  We would need

   // parallel versions of them if such concurrency was desired.

   void par_push(oop ptr);

   // Pushes the first "n" elements of "ptr_arr" on the stack.

   // Non-block impl.  Note: concurrency is allowed only with other

   // "par_adjoin_arr" or "push" operations, not with "pop" or "drain".

   void par_adjoin_arr(oop* ptr_arr, int n);

   // Pushes the first "n" elements of "ptr_arr" on the stack.

   // Locking impl: concurrency is allowed only with

   // "par_push_arr" and/or "par_pop_arr" operations, which use the same

   // locking strategy.

   void par_push_arr(oop* ptr_arr, int n);

   // If returns false, the array was empty.  Otherwise, removes up to "max"

   // elements from the stack, and transfers them to "ptr_arr" in an

   // unspecified order.  The actual number transferred is given in "n" ("n

   // == 0" is deliberately redundant with the return value.)  Locking impl:

   // concurrency is allowed only with "par_push_arr" and/or "par_pop_arr"

   // operations, which use the same locking strategy.

   bool par_pop_arr(oop* ptr_arr, int max, int* n);

   // Drain the mark stack, applying the given closure to all fields of

   // objects on the stack.  (That is, continue until the stack is empty,

   // even if closure applications add entries to the stack.)  The "bm"

   // argument, if non-null, may be used to verify that only marked objects

   // are on the mark stack.  If "yield_after" is "true", then the

   // concurrent marker performing the drain offers to yield after

   // processing each object.  If a yield occurs, stops the drain operation

   // and returns false.  Otherwise, returns true.

   template<class OopClosureClass>

   bool drain(OopClosureClass* cl, CMBitMap* bm, bool yield_after = false);

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

   bool isFull()     { return _index == _capacity; }

   int maxElems()    { return _capacity; }

   bool overflow() { return _overflow; }

   void clear_overflow() { _overflow = false; }

   int  size() { return _index; }

   void setEmpty()   { _index = 0; clear_overflow(); }

   // Record the current index.

   void note_start_of_gc();

   // Make sure that we have not added any entries to the stack during GC.

   void note_end_of_gc();

   // iterate over the oops in the mark stack, up to the bound recorded via

   // the call above.

   void oops_do(OopClosure* f);

 };

 class ForceOverflowSettings VALUE_OBJ_CLASS_SPEC {

 private:

 #ifndef PRODUCT

   uintx _num_remaining;

   bool _force;

 #endif // !defined(PRODUCT)

 public:

   void init() PRODUCT_RETURN;

   void update() PRODUCT_RETURN;

   bool should_force() PRODUCT_RETURN_( return false; );

 };

 // this will enable a variety of different statistics per GC task

 #define _MARKING_STATS_       0

 // this will enable the higher verbose levels

 #define _MARKING_VERBOSE_     0

 #if _MARKING_STATS_

 #define statsOnly(statement)  \

 do {                          \

   statement ;                 \

 } while (0)

 #else // _MARKING_STATS_

 #define statsOnly(statement)  \

 do {                          \

 } while (0)

 #endif // _MARKING_STATS_

 typedef enum {

   no_verbose  = 0,   // verbose turned off

   stats_verbose,     // only prints stats at the end of marking

   low_verbose,       // low verbose, mostly per region and per major event

   medium_verbose,    // a bit more detailed than low

   high_verbose       // per object verbose

 } CMVerboseLevel;

 class YoungList;

 // Root Regions are regions that are not empty at the beginning of a

 // marking cycle and which we might collect during an evacuation pause

 // while the cycle is active. Given that, during evacuation pauses, we

 // do not copy objects that are explicitly marked, what we have to do

 // for the root regions is to scan them and mark all objects reachable

 // from them. According to the SATB assumptions, we only need to visit

 // each object once during marking. So, as long as we finish this scan

 // before the next evacuation pause, we can copy the objects from the

 // root regions without having to mark them or do anything else to them.

 //

 // Currently, we only support root region scanning once (at the start

 // of the marking cycle) and the root regions are all the survivor

 // regions populated during the initial-mark pause.

 class CMRootRegions VALUE_OBJ_CLASS_SPEC {

 private:

   YoungList*           _young_list;

   ConcurrentMark*      _cm;

   volatile bool        _scan_in_progress;

   volatile bool        _should_abort;

   HeapRegion* volatile _next_survivor;

 public:

   CMRootRegions();

   // We actually do most of the initialization in this method.

   void init(G1CollectedHeap* g1h, ConcurrentMark* cm);

   // Reset the claiming / scanning of the root regions.

   void prepare_for_scan();

   // Forces get_next() to return NULL so that the iteration aborts early.

   void abort() { _should_abort = true; }

   // Return true if the CM thread are actively scanning root regions,

   // false otherwise.

   bool scan_in_progress() { return _scan_in_progress; }

   // Claim the next root region to scan atomically, or return NULL if

   // all have been claimed.

   HeapRegion* claim_next();

   // Flag that we're done with root region scanning and notify anyone

   // who's waiting on it. If aborted is false, assume that all regions

   // have been claimed.

   void scan_finished();

   // If CM threads are still scanning root regions, wait until they

   // are done. Return true if we had to wait, false otherwise.

   bool wait_until_scan_finished();

 };

 class ConcurrentMarkThread;

 class ConcurrentMark: public CHeapObj<mtGC> {

   friend class ConcurrentMarkThread;

   friend class CMTask;

   friend class CMBitMapClosure;

   friend class CMGlobalObjectClosure;

   friend class CMRemarkTask;

   friend class CMConcurrentMarkingTask;

   friend class G1ParNoteEndTask;

   friend class CalcLiveObjectsClosure;

   friend class G1CMRefProcTaskProxy;

   friend class G1CMRefProcTaskExecutor;

   friend class G1CMParKeepAliveAndDrainClosure;

   friend class G1CMParDrainMarkingStackClosure;

 protected:

   ConcurrentMarkThread* _cmThread;   // the thread doing the work

   G1CollectedHeap*      _g1h;        // the heap.

   uint                  _parallel_marking_threads; // the number of marking

                                                    // threads we're use

   uint                  _max_parallel_marking_threads; // max number of marking

                                                    // threads we'll ever use

   double                _sleep_factor; // how much we have to sleep, with

                                        // respect to the work we just did, to

                                        // meet the marking overhead goal

   double                _marking_task_overhead; // marking target overhead for

                                                 // a single task

   // same as the two above, but for the cleanup task

   double                _cleanup_sleep_factor;

   double                _cleanup_task_overhead;

   FreeRegionList        _cleanup_list;

   // Concurrent marking support structures

   CMBitMap                _markBitMap1;

   CMBitMap                _markBitMap2;

   CMBitMapRO*             _prevMarkBitMap; // completed mark bitmap

   CMBitMap*               _nextMarkBitMap; // under-construction mark bitmap

   BitMap                  _region_bm;

   BitMap                  _card_bm;

   // Heap bounds

   HeapWord*               _heap_start;

   HeapWord*               _heap_end;

   // Root region tracking and claiming.

   CMRootRegions           _root_regions;

   // For gray objects

   CMMarkStack             _markStack; // Grey objects behind global finger.

   HeapWord* volatile      _finger;  // the global finger, region aligned,

                                     // always points to the end of the

                                     // last claimed region

   // marking tasks

   uint                    _max_task_num; // maximum task number

   uint                    _active_tasks; // task num currently active

   CMTask**                _tasks;        // task queue array (max_task_num len)

   CMTaskQueueSet*         _task_queues;  // task queue set

   ParallelTaskTerminator  _terminator;   // for termination

   // Two sync barriers that are used to synchronise tasks when an

   // overflow occurs. The algorithm is the following. All tasks enter

   // the first one to ensure that they have all stopped manipulating

   // the global data structures. After they exit it, they re-initialise

   // their data structures and task 0 re-initialises the global data

   // structures. Then, they enter the second sync barrier. This

   // ensure, that no task starts doing work before all data

   // structures (local and global) have been re-initialised. When they

   // exit it, they are free to start working again.

   WorkGangBarrierSync     _first_overflow_barrier_sync;

   WorkGangBarrierSync     _second_overflow_barrier_sync;

   // this is set by any task, when an overflow on the global data

   // structures is detected.

   volatile bool           _has_overflown;

   // true: marking is concurrent, false: we're in remark

   volatile bool           _concurrent;

   // set at the end of a Full GC so that marking aborts

   volatile bool           _has_aborted;

   // used when remark aborts due to an overflow to indicate that

   // another concurrent marking phase should start

   volatile bool           _restart_for_overflow;

   // This is true from the very start of concurrent marking until the

   // point when all the tasks complete their work. It is really used

   // to determine the points between the end of concurrent marking and

   // time of remark.

   volatile bool           _concurrent_marking_in_progress;

   // verbose level

   CMVerboseLevel          _verbose_level;

   // All of these times are in ms.

   NumberSeq _init_times;

   NumberSeq _remark_times;

   NumberSeq   _remark_mark_times;

   NumberSeq   _remark_weak_ref_times;

   NumberSeq _cleanup_times;

   double    _total_counting_time;

   double    _total_rs_scrub_time;

   double*   _accum_task_vtime;   // accumulated task vtime

   FlexibleWorkGang* _parallel_workers;

   ForceOverflowSettings _force_overflow_conc;

   ForceOverflowSettings _force_overflow_stw;

   void weakRefsWork(bool clear_all_soft_refs);

   void swapMarkBitMaps();

   // It resets the global marking data structures, as well as the

   // task local ones; should be called during initial mark.

   void reset();

   // It resets all the marking data structures.

   void clear_marking_state(bool clear_overflow = true);

   // It should be called to indicate which phase we're in (concurrent

   // mark or remark) and how many threads are currently active.

   void set_phase(uint active_tasks, bool concurrent);

   // We do this after we're done with marking so that the marking data

   // structures are initialised to a sensible and predictable state.

   void set_non_marking_state();

   // prints all gathered CM-related statistics

   void print_stats();

   bool cleanup_list_is_empty() {

     return _cleanup_list.is_empty();

   }

   // accessor methods

   uint parallel_marking_threads() { return _parallel_marking_threads; }

   uint max_parallel_marking_threads() { return _max_parallel_marking_threads;}

   double sleep_factor()             { return _sleep_factor; }

   double marking_task_overhead()    { return _marking_task_overhead;}

   double cleanup_sleep_factor()     { return _cleanup_sleep_factor; }

   double cleanup_task_overhead()    { return _cleanup_task_overhead;}

   HeapWord*               finger()        { return _finger;   }

   bool                    concurrent()    { return _concurrent; }

   uint                    active_tasks()  { return _active_tasks; }

   ParallelTaskTerminator* terminator()    { return &_terminator; }

   // It claims the next available region to be scanned by a marking

   // task. It might return NULL if the next region is empty or we have

   // run out of regions. In the latter case, out_of_regions()

   // determines whether we've really run out of regions or the task

   // should call claim_region() again.  This might seem a bit

   // awkward. Originally, the code was written so that claim_region()

   // either successfully returned with a non-empty region or there

   // were no more regions to be claimed. The problem with this was

   // that, in certain circumstances, it iterated over large chunks of

   // the heap finding only empty regions and, while it was working, it

   // was preventing the calling task to call its regular clock

   // method. So, this way, each task will spend very little time in

   // claim_region() and is allowed to call the regular clock method

   // frequently.

   HeapRegion* claim_region(int task);

   // It determines whether we've run out of regions to scan.

   bool        out_of_regions() { return _finger == _heap_end; }

   // Returns the task with the given id

   CMTask* task(int id) {

     assert(0 <= id && id < (int) _active_tasks,

            "task id not within active bounds");

     return _tasks[id];

   }

   // Returns the task queue with the given id

   CMTaskQueue* task_queue(int id) {

     assert(0 <= id && id < (int) _active_tasks,

            "task queue id not within active bounds");

     return (CMTaskQueue*) _task_queues->queue(id);

   }

   // Returns the task queue set

   CMTaskQueueSet* task_queues()  { return _task_queues; }

   // Access / manipulation of the overflow flag which is set to

   // indicate that the global stack has overflown

   bool has_overflown()           { return _has_overflown; }

   void set_has_overflown()       { _has_overflown = true; }

   void clear_has_overflown()     { _has_overflown = false; }

   bool restart_for_overflow()    { return _restart_for_overflow; }

   bool has_aborted()             { return _has_aborted; }

   // Methods to enter the two overflow sync barriers

   void enter_first_sync_barrier(int task_num);

   void enter_second_sync_barrier(int task_num);

   ForceOverflowSettings* force_overflow_conc() {

     return &_force_overflow_conc;

   }

   ForceOverflowSettings* force_overflow_stw() {

     return &_force_overflow_stw;

   }

   ForceOverflowSettings* force_overflow() {

     if (concurrent()) {

       return force_overflow_conc();

     } else {

       return force_overflow_stw();

     }

   }

   // Live Data Counting data structures...

   // These data structures are initialized at the start of

   // marking. They are written to while marking is active.

   // They are aggregated during remark; the aggregated values

   // are then used to populate the _region_bm, _card_bm, and

   // the total live bytes, which are then subsequently updated

   // during cleanup.

   // An array of bitmaps (one bit map per task). Each bitmap

   // is used to record the cards spanned by the live objects

   // marked by that task/worker.

   BitMap*  _count_card_bitmaps;

   // Used to record the number of marked live bytes

   // (for each region, by worker thread).

   size_t** _count_marked_bytes;

   // Card index of the bottom of the G1 heap. Used for biasing indices into

   // the card bitmaps.

   intptr_t _heap_bottom_card_num;

 public:

   // Manipulation of the global mark stack.

   // Notice that the first mark_stack_push is CAS-based, whereas the

   // two below are Mutex-based. This is OK since the first one is only

   // called during evacuation pauses and doesn't compete with the

   // other two (which are called by the marking tasks during

   // concurrent marking or remark).

   bool mark_stack_push(oop p) {

     _markStack.par_push(p);

     if (_markStack.overflow()) {

       set_has_overflown();

       return false;

     }

     return true;

   }

   bool mark_stack_push(oop* arr, int n) {

     _markStack.par_push_arr(arr, n);

     if (_markStack.overflow()) {

       set_has_overflown();

       return false;

     }

     return true;

   }

   void mark_stack_pop(oop* arr, int max, int* n) {

     _markStack.par_pop_arr(arr, max, n);

   }

   size_t mark_stack_size()                { return _markStack.size(); }

   size_t partial_mark_stack_size_target() { return _markStack.maxElems()/3; }

   bool mark_stack_overflow()              { return _markStack.overflow(); }

   bool mark_stack_empty()                 { return _markStack.isEmpty(); }

   CMRootRegions* root_regions() { return &_root_regions; }

   bool concurrent_marking_in_progress() {

     return _concurrent_marking_in_progress;

   }

   void set_concurrent_marking_in_progress() {

     _concurrent_marking_in_progress = true;

   }

   void clear_concurrent_marking_in_progress() {

     _concurrent_marking_in_progress = false;

   }

   void update_accum_task_vtime(int i, double vtime) {

     _accum_task_vtime[i] += vtime;

   }

   double all_task_accum_vtime() {

     double ret = 0.0;

     for (int i = 0; i < (int)_max_task_num; ++i)

       ret += _accum_task_vtime[i];

     return ret;

   }

   // Attempts to steal an object from the task queues of other tasks

   bool try_stealing(int task_num, int* hash_seed, oop& obj) {

     return _task_queues->steal(task_num, hash_seed, obj);

   }

   ConcurrentMark(ReservedSpace rs, uint max_regions);

   ~ConcurrentMark();

   ConcurrentMarkThread* cmThread() { return _cmThread; }

   CMBitMapRO* prevMarkBitMap() const { return _prevMarkBitMap; }

   CMBitMap*   nextMarkBitMap() const { return _nextMarkBitMap; }

   // Returns the number of GC threads to be used in a concurrent

   // phase based on the number of GC threads being used in a STW

   // phase.

   uint scale_parallel_threads(uint n_par_threads);

   // Calculates the number of GC threads to be used in a concurrent phase.

   uint calc_parallel_marking_threads();

   // The following three are interaction between CM and

   // G1CollectedHeap

   // This notifies CM that a root during initial-mark needs to be

   // grayed. It is MT-safe. word_size is the size of the object in

   // words. It is passed explicitly as sometimes we cannot calculate

   // it from the given object because it might be in an inconsistent

   // state (e.g., in to-space and being copied). So the caller is

   // responsible for dealing with this issue (e.g., get the size from

   // the from-space image when the to-space image might be

   // inconsistent) and always passing the size. hr is the region that

   // contains the object and it's passed optionally from callers who

   // might already have it (no point in recalculating it).

   inline void grayRoot(oop obj, size_t word_size,

                        uint worker_id, HeapRegion* hr = NULL);

   // It iterates over the heap and for each object it comes across it

   // will dump the contents of its reference fields, as well as

   // liveness information for the object and its referents. The dump

   // will be written to a file with the following name:

   // G1PrintReachableBaseFile + "." + str.

   // vo decides whether the prev (vo == UsePrevMarking), the next

   // (vo == UseNextMarking) marking information, or the mark word

   // (vo == UseMarkWord) will be used to determine the liveness of

   // each object / referent.

   // If all is true, all objects in the heap will be dumped, otherwise

   // only the live ones. In the dump the following symbols / breviations

   // are used:

   //   M : an explicitly live object (its bitmap bit is set)

   //   > : an implicitly live object (over tams)

   //   O : an object outside the G1 heap (typically: in the perm gen)

   //   NOT : a reference field whose referent is not live

   //   AND MARKED : indicates that an object is both explicitly and

   //   implicitly live (it should be one or the other, not both)

   void print_reachable(const char* str,

                        VerifyOption vo, bool all) PRODUCT_RETURN;

   // Clear the next marking bitmap (will be called concurrently).

   void clearNextBitmap();

   // These two do the work that needs to be done before and after the

   // initial root checkpoint. Since this checkpoint can be done at two

   // different points (i.e. an explicit pause or piggy-backed on a

   // young collection), then it's nice to be able to easily share the

   // pre/post code. It might be the case that we can put everything in

   // the post method. TP

   void checkpointRootsInitialPre();

   void checkpointRootsInitialPost();

   // Scan all the root regions and mark everything reachable from

   // them.

   void scanRootRegions();

   // Scan a single root region and mark everything reachable from it.

   void scanRootRegion(HeapRegion* hr, uint worker_id);

   // Do concurrent phase of marking, to a tentative transitive closure.

   void markFromRoots();

   void checkpointRootsFinal(bool clear_all_soft_refs);

   void checkpointRootsFinalWork();

   void cleanup();

   void completeCleanup();

   // Mark in the previous bitmap.  NB: this is usually read-only, so use

   // this carefully!

   inline void markPrev(oop p);

   // Clears marks for all objects in the given range, for the prev,

   // next, or both bitmaps.  NB: the previous bitmap is usually

   // read-only, so use this carefully!

   void clearRangePrevBitmap(MemRegion mr);

   void clearRangeNextBitmap(MemRegion mr);

   void clearRangeBothBitmaps(MemRegion mr);

   // Notify data structures that a GC has started.

   void note_start_of_gc() {

     _markStack.note_start_of_gc();

   }

   // Notify data structures that a GC is finished.

   void note_end_of_gc() {

     _markStack.note_end_of_gc();

   }

   // Verify that there are no CSet oops on the stacks (taskqueues /

   // global mark stack), enqueued SATB buffers, per-thread SATB

   // buffers, and fingers (global / per-task). The boolean parameters

   // decide which of the above data structures to verify. If marking

   // is not in progress, it's a no-op.

   void verify_no_cset_oops(bool verify_stacks,

                            bool verify_enqueued_buffers,

                            bool verify_thread_buffers,

                            bool verify_fingers) PRODUCT_RETURN;

   // It is called at the end of an evacuation pause during marking so

   // that CM is notified of where the new end of the heap is. It

   // doesn't do anything if concurrent_marking_in_progress() is false,

   // unless the force parameter is true.

   void update_g1_committed(bool force = false);

   bool isMarked(oop p) const {

     assert(p != NULL && p->is_oop(), "expected an oop");

     HeapWord* addr = (HeapWord*)p;

     assert(addr >= _nextMarkBitMap->startWord() ||

            addr < _nextMarkBitMap->endWord(), "in a region");

     return _nextMarkBitMap->isMarked(addr);

   }

   inline bool not_yet_marked(oop p) const;

   // XXX Debug code

   bool containing_card_is_marked(void* p);

   bool containing_cards_are_marked(void* start, void* last);

   bool isPrevMarked(oop p) const {

     assert(p != NULL && p->is_oop(), "expected an oop");

     HeapWord* addr = (HeapWord*)p;

     assert(addr >= _prevMarkBitMap->startWord() ||

            addr < _prevMarkBitMap->endWord(), "in a region");

     return _prevMarkBitMap->isMarked(addr);

   }

   inline bool do_yield_check(uint worker_i = 0);

   inline bool should_yield();

   // Called to abort the marking cycle after a Full GC takes palce.

   void abort();

   // This prints the global/local fingers. It is used for debugging.

   NOT_PRODUCT(void print_finger();)

   void print_summary_info();

   void print_worker_threads_on(outputStream* st) const;

   // The following indicate whether a given verbose level has been

   // set. Notice that anything above stats is conditional to

   // _MARKING_VERBOSE_ having been set to 1

   bool verbose_stats() {

     return _verbose_level >= stats_verbose;

   }

   bool verbose_low() {

     return _MARKING_VERBOSE_ && _verbose_level >= low_verbose;

   }

   bool verbose_medium() {

     return _MARKING_VERBOSE_ && _verbose_level >= medium_verbose;

   }

   bool verbose_high() {

     return _MARKING_VERBOSE_ && _verbose_level >= high_verbose;

   }

   // Counting data structure accessors

   // Returns the card number of the bottom of the G1 heap.

   // Used in biasing indices into accounting card bitmaps.

   intptr_t heap_bottom_card_num() const {

     return _heap_bottom_card_num;

   }

   // Returns the card bitmap for a given task or worker id.

   BitMap* count_card_bitmap_for(uint worker_id) {

     assert(0 <= worker_id && worker_id < _max_task_num, "oob");

     assert(_count_card_bitmaps != NULL, "uninitialized");

     BitMap* task_card_bm = &_count_card_bitmaps[worker_id];

     assert(task_card_bm->size() == _card_bm.size(), "size mismatch");

     return task_card_bm;

   }

   // Returns the array containing the marked bytes for each region,

   // for the given worker or task id.

   size_t* count_marked_bytes_array_for(uint worker_id) {

     assert(0 <= worker_id && worker_id < _max_task_num, "oob");

     assert(_count_marked_bytes != NULL, "uninitialized");

     size_t* marked_bytes_array = _count_marked_bytes[worker_id];

     assert(marked_bytes_array != NULL, "uninitialized");

     return marked_bytes_array;

   }

   // Returns the index in the liveness accounting card table bitmap

   // for the given address

   inline BitMap::idx_t card_bitmap_index_for(HeapWord* addr);

   // Counts the size of the given memory region in the the given

   // marked_bytes array slot for the given HeapRegion.

   // Sets the bits in the given card bitmap that are associated with the

   // cards that are spanned by the memory region.

   inline void count_region(MemRegion mr, HeapRegion* hr,

                            size_t* marked_bytes_array,

                            BitMap* task_card_bm);

   // Counts the given memory region in the task/worker counting

   // data structures for the given worker id.

   inline void count_region(MemRegion mr, HeapRegion* hr, uint worker_id);

   // Counts the given memory region in the task/worker counting

   // data structures for the given worker id.

   inline void count_region(MemRegion mr, uint worker_id);

   // Counts the given object in the given task/worker counting

   // data structures.

   inline void count_object(oop obj, HeapRegion* hr,

                            size_t* marked_bytes_array,

                            BitMap* task_card_bm);

   // Counts the given object in the task/worker counting data

   // structures for the given worker id.

   inline void count_object(oop obj, HeapRegion* hr, uint worker_id);

   // Attempts to mark the given object and, if successful, counts

   // the object in the given task/worker counting structures.

   inline bool par_mark_and_count(oop obj, HeapRegion* hr,

                                  size_t* marked_bytes_array,

                                  BitMap* task_card_bm);

   // Attempts to mark the given object and, if successful, counts

   // the object in the task/worker counting structures for the

   // given worker id.

   inline bool par_mark_and_count(oop obj, size_t word_size,

                                  HeapRegion* hr, uint worker_id);

   // Attempts to mark the given object and, if successful, counts

   // the object in the task/worker counting structures for the

   // given worker id.

   inline bool par_mark_and_count(oop obj, HeapRegion* hr, uint worker_id);

   // Similar to the above routine but we don't know the heap region that

   // contains the object to be marked/counted, which this routine looks up.

   inline bool par_mark_and_count(oop obj, uint worker_id);

   // Similar to the above routine but there are times when we cannot

   // safely calculate the size of obj due to races and we, therefore,

   // pass the size in as a parameter. It is the caller's reponsibility

   // to ensure that the size passed in for obj is valid.

   inline bool par_mark_and_count(oop obj, size_t word_size, uint worker_id);

   // Unconditionally mark the given object, and unconditinally count

   // the object in the counting structures for worker id 0.

   // Should *not* be called from parallel code.

   inline bool mark_and_count(oop obj, HeapRegion* hr);

   // Similar to the above routine but we don't know the heap region that

   // contains the object to be marked/counted, which this routine looks up.

   // Should *not* be called from parallel code.

   inline bool mark_and_count(oop obj);

 protected:

   // Clear all the per-task bitmaps and arrays used to store the

   // counting data.

   void clear_all_count_data();

   // Aggregates the counting data for each worker/task

   // that was constructed while marking. Also sets

   // the amount of marked bytes for each region and

   // the top at concurrent mark count.

   void aggregate_count_data();

   // Verification routine

   void verify_count_data();

 };

 // A class representing a marking task.

 class CMTask : public TerminatorTerminator {

 private:

   enum PrivateConstants {

     // the regular clock call is called once the scanned words reaches

     // this limit

     words_scanned_period          = 12*1024,

     // the regular clock call is called once the number of visited

     // references reaches this limit

     refs_reached_period           = 384,

     // initial value for the hash seed, used in the work stealing code

     init_hash_seed                = 17,

     // how many entries will be transferred between global stack and

     // local queues

     global_stack_transfer_size    = 16

   };

   int                         _task_id;

   G1CollectedHeap*            _g1h;

   ConcurrentMark*             _cm;

   CMBitMap*                   _nextMarkBitMap;

   // the task queue of this task

   CMTaskQueue*                _task_queue;

 private:

   // the task queue set---needed for stealing

   CMTaskQueueSet*             _task_queues;

   // indicates whether the task has been claimed---this is only  for

   // debugging purposes

   bool                        _claimed;

   // number of calls to this task

   int                         _calls;

   // when the virtual timer reaches this time, the marking step should

   // exit

   double                      _time_target_ms;

   // the start time of the current marking step

   double                      _start_time_ms;

   // the oop closure used for iterations over oops

   G1CMOopClosure*             _cm_oop_closure;

   // the region this task is scanning, NULL if we're not scanning any

   HeapRegion*                 _curr_region;

   // the local finger of this task, NULL if we're not scanning a region

   HeapWord*                   _finger;

   // limit of the region this task is scanning, NULL if we're not scanning one

   HeapWord*                   _region_limit;

   // the number of words this task has scanned

   size_t                      _words_scanned;

   // When _words_scanned reaches this limit, the regular clock is

   // called. Notice that this might be decreased under certain

   // circumstances (i.e. when we believe that we did an expensive

   // operation).

   size_t                      _words_scanned_limit;

   // the initial value of _words_scanned_limit (i.e. what it was

   // before it was decreased).

   size_t                      _real_words_scanned_limit;

   // the number of references this task has visited

   size_t                      _refs_reached;

   // When _refs_reached reaches this limit, the regular clock is

   // called. Notice this this might be decreased under certain

   // circumstances (i.e. when we believe that we did an expensive

   // operation).

   size_t                      _refs_reached_limit;

   // the initial value of _refs_reached_limit (i.e. what it was before

   // it was decreased).

   size_t                      _real_refs_reached_limit;

   // used by the work stealing stuff

   int                         _hash_seed;

   // if this is true, then the task has aborted for some reason

   bool                        _has_aborted;

   // set when the task aborts because it has met its time quota

   bool                        _has_timed_out;

   // true when we're draining SATB buffers; this avoids the task

   // aborting due to SATB buffers being available (as we're already

   // dealing with them)

   bool                        _draining_satb_buffers;

   // number sequence of past step times

   NumberSeq                   _step_times_ms;

   // elapsed time of this task

   double                      _elapsed_time_ms;

   // termination time of this task

   double                      _termination_time_ms;

   // when this task got into the termination protocol

   double                      _termination_start_time_ms;

   // true when the task is during a concurrent phase, false when it is

   // in the remark phase (so, in the latter case, we do not have to

   // check all the things that we have to check during the concurrent

   // phase, i.e. SATB buffer availability...)

   bool                        _concurrent;

   TruncatedSeq                _marking_step_diffs_ms;

   // Counting data structures. Embedding the task's marked_bytes_array

   // and card bitmap into the actual task saves having to go through

   // the ConcurrentMark object.

   size_t*                     _marked_bytes_array;

   BitMap*                     _card_bm;

   // LOTS of statistics related with this task

 #if _MARKING_STATS_

   NumberSeq                   _all_clock_intervals_ms;

   double                      _interval_start_time_ms;

   int                         _aborted;

   int                         _aborted_overflow;

   int                         _aborted_cm_aborted;

   int                         _aborted_yield;

   int                         _aborted_timed_out;

   int                         _aborted_satb;

   int                         _aborted_termination;

   int                         _steal_attempts;

   int                         _steals;

   int                         _clock_due_to_marking;

   int                         _clock_due_to_scanning;

   int                         _local_pushes;

   int                         _local_pops;

   int                         _local_max_size;

   int                         _objs_scanned;

   int                         _global_pushes;

   int                         _global_pops;

   int                         _global_max_size;

   int                         _global_transfers_to;

   int                         _global_transfers_from;

   int                         _regions_claimed;

   int                         _objs_found_on_bitmap;

   int                         _satb_buffers_processed;

 #endif // _MARKING_STATS_

   // it updates the local fields after this task has claimed

   // a new region to scan

   void setup_for_region(HeapRegion* hr);

   // it brings up-to-date the limit of the region

   void update_region_limit();

   // called when either the words scanned or the refs visited limit

   // has been reached

   void reached_limit();

   // recalculates the words scanned and refs visited limits

   void recalculate_limits();

   // decreases the words scanned and refs visited limits when we reach

   // an expensive operation

   void decrease_limits();

   // it checks whether the words scanned or refs visited reached their

   // respective limit and calls reached_limit() if they have

   void check_limits() {

     if (_words_scanned >= _words_scanned_limit ||

         _refs_reached >= _refs_reached_limit) {

       reached_limit();

     }

   }

   // this is supposed to be called regularly during a marking step as

   // it checks a bunch of conditions that might cause the marking step

   // to abort

   void regular_clock_call();

   bool concurrent() { return _concurrent; }

 public:

   // It resets the task; it should be called right at the beginning of

   // a marking phase.

   void reset(CMBitMap* _nextMarkBitMap);

   // it clears all the fields that correspond to a claimed region.

   void clear_region_fields();

   void set_concurrent(bool concurrent) { _concurrent = concurrent; }

   // The main method of this class which performs a marking step

   // trying not to exceed the given duration. However, it might exit

   // prematurely, according to some conditions (i.e. SATB buffers are

   // available for processing).

   void do_marking_step(double target_ms, bool do_stealing, bool do_termination);

   // These two calls start and stop the timer

   void record_start_time() {

     _elapsed_time_ms = os::elapsedTime() * 1000.0;

   }

   void record_end_time() {

     _elapsed_time_ms = os::elapsedTime() * 1000.0 - _elapsed_time_ms;

   }

   // returns the task ID

   int task_id() { return _task_id; }

   // From TerminatorTerminator. It determines whether this task should

   // exit the termination protocol after it's entered it.

   virtual bool should_exit_termination();

   // Resets the local region fields after a task has finished scanning a

   // region; or when they have become stale as a result of the region

   // being evacuated.

   void giveup_current_region();

   HeapWord* finger()            { return _finger; }

   bool has_aborted()            { return _has_aborted; }

   void set_has_aborted()        { _has_aborted = true; }

   void clear_has_aborted()      { _has_aborted = false; }

   bool has_timed_out()          { return _has_timed_out; }

   bool claimed()                { return _claimed; }

   void set_cm_oop_closure(G1CMOopClosure* cm_oop_closure);

   // It grays the object by marking it and, if necessary, pushing it

   // on the local queue

   inline void deal_with_reference(oop obj);

   // It scans an object and visits its children.

   void scan_object(oop obj);

   // It pushes an object on the local queue.

   inline void push(oop obj);

   // These two move entries to/from the global stack.

   void move_entries_to_global_stack();

   void get_entries_from_global_stack();

   // It pops and scans objects from the local queue. If partially is

   // true, then it stops when the queue size is of a given limit. If

   // partially is false, then it stops when the queue is empty.

   void drain_local_queue(bool partially);

   // It moves entries from the global stack to the local queue and

   // drains the local queue. If partially is true, then it stops when

   // both the global stack and the local queue reach a given size. If

   // partially if false, it tries to empty them totally.

   void drain_global_stack(bool partially);

   // It keeps picking SATB buffers and processing them until no SATB

   // buffers are available.

   void drain_satb_buffers();

   // moves the local finger to a new location

   inline void move_finger_to(HeapWord* new_finger) {

     assert(new_finger >= _finger && new_finger < _region_limit, "invariant");

     _finger = new_finger;

   }

   CMTask(int task_num, ConcurrentMark *cm,

          size_t* marked_bytes, BitMap* card_bm,

          CMTaskQueue* task_queue, CMTaskQueueSet* task_queues);

   // it prints statistics associated with this task

   void print_stats();

 #if _MARKING_STATS_

   void increase_objs_found_on_bitmap() { ++_objs_found_on_bitmap; }

 #endif // _MARKING_STATS_

 };

 // Class that's used to to print out per-region liveness

 // information. It's currently used at the end of marking and also

 // after we sort the old regions at the end of the cleanup operation.

 class G1PrintRegionLivenessInfoClosure: public HeapRegionClosure {

 private:

   outputStream* _out;

   // Accumulators for these values.

   size_t _total_used_bytes;

   size_t _total_capacity_bytes;

   size_t _total_prev_live_bytes;

   size_t _total_next_live_bytes;

   // These are set up when we come across a "stars humongous" region

   // (as this is where most of this information is stored, not in the

   // subsequent "continues humongous" regions). After that, for every

   // region in a given humongous region series we deduce the right

   // values for it by simply subtracting the appropriate amount from

   // these fields. All these values should reach 0 after we've visited

   // the last region in the series.

   size_t _hum_used_bytes;

   size_t _hum_capacity_bytes;

   size_t _hum_prev_live_bytes;

   size_t _hum_next_live_bytes;

   static double perc(size_t val, size_t total) {

     if (total == 0) {

       return 0.0;

     } else {

       return 100.0 * ((double) val / (double) total);

     }

   }

   static double bytes_to_mb(size_t val) {

     return (double) val / (double) M;

   }

   // See the .cpp file.

   size_t get_hum_bytes(size_t* hum_bytes);

   void get_hum_bytes(size_t* used_bytes, size_t* capacity_bytes,

                      size_t* prev_live_bytes, size_t* next_live_bytes);

 public:

   // The header and footer are printed in the constructor and

   // destructor respectively.

   G1PrintRegionLivenessInfoClosure(outputStream* out, const char* phase_name);

   virtual bool doHeapRegion(HeapRegion* r);

   ~G1PrintRegionLivenessInfoClosure();

 };

 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_CONCURRENTMARK_HPP