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 /*

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

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  * published by the Free Software Foundation.

  *

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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>            CMTaskQueue;

 typedef GenericTaskQueueSet<CMTaskQueue> 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

   bool iterate(BitMapClosure* cl) { return _bm.iterate(cl); }

   bool iterate(BitMapClosure* cl, MemRegion mr);

   // 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);

   }

   void mostly_disjoint_range_union(BitMap*   from_bitmap,

                                    size_t    from_start_index,

                                    HeapWord* to_start_word,

                                    size_t    word_num);

   // 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.at_put(heapWordToOffset(addr), true);

   }

   void clear(HeapWord* addr) {

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

            "outside underlying space?");

     _bm.at_put(heapWordToOffset(addr), false);

   }

   bool parMark(HeapWord* addr) {

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

            "outside underlying space?");

     return _bm.par_at_put(heapWordToOffset(addr), true);

   }

   bool parClear(HeapWord* addr) {

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

            "outside underlying space?");

     return _bm.par_at_put(heapWordToOffset(addr), false);

   }

   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   _oops_do_bound;  // Number of elements to include in next iteration.

   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 size; a subsequent "oops_do" will iterate only over

   // indices valid at the time of this call.

   void set_oops_do_bound(jint bound = -1) {

     if (bound == -1) {

       _oops_do_bound = _index;

     } else {

       _oops_do_bound = bound;

     }

   }

   jint oops_do_bound() { return _oops_do_bound; }

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

   // the call above.

   void oops_do(OopClosure* f);

 };

 class CMRegionStack VALUE_OBJ_CLASS_SPEC {

   MemRegion* _base;

   jint _capacity;

   jint _index;

   jint _oops_do_bound;

   bool _overflow;

 public:

   CMRegionStack();

   ~CMRegionStack();

   void allocate(size_t size);

   // This is lock-free; assumes that it will only be called in parallel

   // with other "push" operations (no pops).

   void push_lock_free(MemRegion mr);

   // Lock-free; assumes that it will only be called in parallel

   // with other "pop" operations (no pushes).

   MemRegion pop_lock_free();

 #if 0

   // The routines that manipulate the region stack with a lock are

   // not currently used. They should be retained, however, as a

   // diagnostic aid.

   // These two are the implementations that use a lock. They can be

   // called concurrently with each other but they should not be called

   // concurrently with the lock-free versions (push() / pop()).

   void push_with_lock(MemRegion mr);

   MemRegion pop_with_lock();

 #endif

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

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

   bool overflow() { return _overflow; }

   void clear_overflow() { _overflow = false; }

   int  size() { return _index; }

   // It iterates over the entries in the region stack and it

   // invalidates (i.e. assigns MemRegion()) the ones that point to

   // regions in the collection set.

   bool invalidate_entries_into_cset();

   // This gives an upper bound up to which the iteration in

   // invalidate_entries_into_cset() will reach. This prevents

   // newly-added entries to be unnecessarily scanned.

   void set_oops_do_bound() {

     _oops_do_bound = _index;

   }

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

 };

 // 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 ConcurrentMarkThread;

 class ConcurrentMark: public CHeapObj {

   friend class ConcurrentMarkThread;

   friend class CMTask;

   friend class CMBitMapClosure;

   friend class CSMarkOopClosure;

   friend class CMGlobalObjectClosure;

   friend class CMRemarkTask;

   friend class CMConcurrentMarkingTask;

   friend class G1ParNoteEndTask;

   friend class CalcLiveObjectsClosure;

 protected:

   ConcurrentMarkThread* _cmThread;   // the thread doing the work

   G1CollectedHeap*      _g1h;        // the heap.

   size_t                _parallel_marking_threads; // the number of marking

                                                    // threads we'll 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;

   // CMS marking support structures

   CMBitMap                _markBitMap1;

   CMBitMap                _markBitMap2;

   CMBitMapRO*             _prevMarkBitMap; // completed mark bitmap

   CMBitMap*               _nextMarkBitMap; // under-construction mark bitmap

   bool                    _at_least_one_mark_complete;

   BitMap                  _region_bm;

   BitMap                  _card_bm;

   // Heap bounds

   HeapWord*               _heap_start;

   HeapWord*               _heap_end;

   // For gray objects

   CMMarkStack             _markStack; // Grey objects behind global finger.

   CMRegionStack           _regionStack; // Grey regions behind global finger.

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

                                     // always points to the end of the

                                     // last claimed region

   // marking tasks

   size_t                  _max_task_num; // maximum task number

   size_t                  _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;

   // These two fields are used to implement the optimisation that

   // avoids pushing objects on the global/region stack if there are

   // no collection set regions above the lowest finger.

   // This is the lowest finger (among the global and local fingers),

   // which is calculated before a new collection set is chosen.

   HeapWord* _min_finger;

   // If this flag is true, objects/regions that are marked below the

   // finger should be pushed on the stack(s). If this is flag is

   // false, it is safe not to push them on the stack(s).

   bool      _should_gray_objects;

   // 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

   WorkGang* _parallel_workers;

   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();

   // 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(size_t 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

   size_t parallel_marking_threads() { return _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; }

   size_t                  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 or region stack has overflown

   bool has_overflown()           { return _has_overflown; }

   void set_has_overflown()       { _has_overflown = true; }

   void clear_has_overflown()     { _has_overflown = false; }

   bool has_aborted()             { return _has_aborted; }

   bool restart_for_overflow()    { return _restart_for_overflow; }

   // Methods to enter the two overflow sync barriers

   void enter_first_sync_barrier(int task_num);

   void enter_second_sync_barrier(int task_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(); }

   // (Lock-free) Manipulation of the region stack

   bool region_stack_push_lock_free(MemRegion mr) {

     // Currently we only call the lock-free version during evacuation

     // pauses.

     assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");

     _regionStack.push_lock_free(mr);

     if (_regionStack.overflow()) {

       set_has_overflown();

       return false;

     }

     return true;

   }

   // Lock-free version of region-stack pop. Should only be

   // called in tandem with other lock-free pops.

   MemRegion region_stack_pop_lock_free() {

     return _regionStack.pop_lock_free();

   }

 #if 0

   // The routines that manipulate the region stack with a lock are

   // not currently used. They should be retained, however, as a

   // diagnostic aid.

   bool region_stack_push_with_lock(MemRegion mr) {

     // Currently we only call the lock-based version during either

     // concurrent marking or remark.

     assert(!SafepointSynchronize::is_at_safepoint() || !concurrent(),

            "if we are at a safepoint it should be the remark safepoint");

     _regionStack.push_with_lock(mr);

     if (_regionStack.overflow()) {

       set_has_overflown();

       return false;

     }

     return true;

   }

   MemRegion region_stack_pop_with_lock() {

     // Currently we only call the lock-based version during either

     // concurrent marking or remark.

     assert(!SafepointSynchronize::is_at_safepoint() || !concurrent(),

            "if we are at a safepoint it should be the remark safepoint");

     return _regionStack.pop_with_lock();

   }

 #endif

   int region_stack_size()               { return _regionStack.size(); }

   bool region_stack_overflow()          { return _regionStack.overflow(); }

   bool region_stack_empty()             { return _regionStack.isEmpty(); }

   // Iterate over any regions that were aborted while draining the

   // region stack (any such regions are saved in the corresponding

   // CMTask) and invalidate (i.e. assign to the empty MemRegion())

   // any regions that point into the collection set.

   bool invalidate_aborted_regions_in_cset();

   // Returns true if there are any aborted memory regions.

   bool has_aborted_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);

   }

   // It grays an object by first marking it. Then, if it's behind the

   // global finger, it also pushes it on the global stack.

   void deal_with_reference(oop obj);

   ConcurrentMark(ReservedSpace rs, int max_regions);

   ~ConcurrentMark();

   ConcurrentMarkThread* cmThread() { return _cmThread; }

   CMBitMapRO* prevMarkBitMap() const { return _prevMarkBitMap; }

   CMBitMap*   nextMarkBitMap() const { return _nextMarkBitMap; }

   // The following three are interaction between CM and

   // G1CollectedHeap

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

   // grayed and it's MT-safe. Currently, we just mark it. But, in the

   // future, we can experiment with pushing it on the stack and we can

   // do this without changing G1CollectedHeap.

   void grayRoot(oop p);

   // It's used during evacuation pauses to gray a region, if

   // necessary, and it's MT-safe. It assumes that the caller has

   // marked any objects on that region. If _should_gray_objects is

   // true and we're still doing concurrent marking, the region is

   // pushed on the region stack, if it is located below the global

   // finger, otherwise we do nothing.

   void grayRegionIfNecessary(MemRegion mr);

   // It's used during evacuation pauses to mark and, if necessary,

   // gray a single object and it's MT-safe. It assumes the caller did

   // not mark the object. If _should_gray_objects is true and we're

   // still doing concurrent marking, the objects is pushed on the

   // global stack, if it is located below the global finger, otherwise

   // we do nothing.

   void markAndGrayObjectIfNecessary(oop p);

   // 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. use_prev_marking decides

   // whether the prev (use_prev_marking == true) or next

   // (use_prev_marking == false) marking information 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 / abbreviations 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,

                        bool use_prev_marking, bool all) PRODUCT_RETURN;

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

   void clearNextBitmap();

   // main CMS steps and related support

   void checkpointRootsInitial();

   // 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();

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

   void markFromRoots();

   // Process all unprocessed SATB buffers. It is called at the

   // beginning of an evacuation pause.

   void drainAllSATBBuffers();

   void checkpointRootsFinal(bool clear_all_soft_refs);

   void checkpointRootsFinalWork();

   void calcDesiredRegions();

   void cleanup();

   void completeCleanup();

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

   // this carefully!

   void markPrev(oop p);

   void clear(oop p);

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

   // next bitmaps.  NB: the previous bitmap is usually read-only, so use

   // this carefully!

   void clearRangeBothMaps(MemRegion mr);

   // Record the current top of the mark and region stacks; a

   // subsequent oops_do() on the mark stack and

   // invalidate_entries_into_cset() on the region stack will iterate

   // only over indices valid at the time of this call.

   void set_oops_do_bound() {

     _markStack.set_oops_do_bound();

     _regionStack.set_oops_do_bound();

   }

   // Iterate over the oops in the mark stack and all local queues. It

   // also calls invalidate_entries_into_cset() on the region stack.

   void oops_do(OopClosure* f);

   // 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);

   void complete_marking_in_collection_set();

   // It indicates that a new collection set is being chosen.

   void newCSet();

   // It registers a collection set heap region with CM. This is used

   // to determine whether any heap regions are located above the finger.

   void registerCSetRegion(HeapRegion* hr);

   // Registers the maximum region-end associated with a set of

   // regions with CM. Again this is used to determine whether any

   // heap regions are located above the finger.

   void register_collection_set_finger(HeapWord* max_finger) {

     // max_finger is the highest heap region end of the regions currently

     // contained in the collection set. If this value is larger than

     // _min_finger then we need to gray objects.

     // This routine is like registerCSetRegion but for an entire

     // collection of regions.

     if (max_finger > _min_finger)

       _should_gray_objects = true;

   }

   // Returns "true" if at least one mark has been completed.

   bool at_least_one_mark_complete() { return _at_least_one_mark_complete; }

   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(int 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; }

 };

 // 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

   OopClosure*                 _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;

   // This is used only when we scan regions popped from the region

   // stack. It records what the last object on such a region we

   // scanned was. It is used to ensure that, if we abort region

   // iteration, we do not rescan the first part of the region. This

   // should be NULL when we're not scanning a region from the region

   // stack.

   HeapWord*                   _region_finger;

   // If we abort while scanning a region we record the remaining

   // unscanned portion and check this field when marking restarts.

   // This avoids having to push on the region stack while other

   // marking threads may still be popping regions.

   // If we were to push the unscanned portion directly to the

   // region stack then we would need to using locking versions

   // of the push and pop operations.

   MemRegion                   _aborted_region;

   // 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_aborted_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;

   // 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                         _region_stack_pops;

   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();

   // it resets the local fields after a task has finished scanning a

   // region

   void giveup_current_region();

   // 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);

   // 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();

   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 claimed() { return _claimed; }

   // Support routines for the partially scanned region that may be

   // recorded as a result of aborting while draining the CMRegionStack

   MemRegion aborted_region()    { return _aborted_region; }

   void set_aborted_region(MemRegion mr)

                                 { _aborted_region = mr; }

   // Clears any recorded partially scanned region

   void clear_aborted_region()   { set_aborted_region(MemRegion()); }

   void set_oop_closure(OopClosure* oop_closure) {

     _oop_closure = oop_closure;

   }

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

   // on the local queue

   void deal_with_reference(oop obj);

   // It scans an object and visits its children.

   void scan_object(oop obj) {

     assert(_nextMarkBitMap->isMarked((HeapWord*) obj), "invariant");

     if (_cm->verbose_high())

       gclog_or_tty->print_cr("[%d] we're scanning object "PTR_FORMAT,

                              _task_id, (void*) obj);

     size_t obj_size = obj->size();

     _words_scanned += obj_size;

     obj->oop_iterate(_oop_closure);

     statsOnly( ++_objs_scanned );

     check_limits();

   }

   // It pushes an object on the local queue.

   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();

   // It keeps popping regions from the region stack and processing

   // them until the region stack is empty.

   void drain_region_stack(BitMapClosure* closure);

   // 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;

   }

   // moves the region finger to a new location

   inline void move_region_finger_to(HeapWord* new_finger) {

     assert(new_finger < _cm->finger(), "invariant");

     _region_finger = new_finger;

   }

   CMTask(int task_num, ConcurrentMark *cm,

          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_

 };

 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_CONCURRENTMARK_HPP