--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/share/vm/gc_implementation/g1/concurrentMark.hpp	Thu Jun 05 15:57:56 2008 -0700
@@ -0,0 +1,1049 @@
+/*
+ * Copyright 2001-2007 Sun Microsystems, Inc.  All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ *
+ */
+
+class G1CollectedHeap;
+class CMTask;
+typedef GenericTaskQueue<oop> CMTaskQueue;
+typedef GenericTaskQueueSet<oop> CMTaskQueueSet;
+
+// A generic CM bit map.  This is essentially a wrapper around the BitMap
+// class, with one bit per (1<<_shifter) HeapWords.
+
+class CMBitMapRO {
+ 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 {
+  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 {
+  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(MemRegion mr);
+
+  // Lock-free; assumes that it will only be called in parallel
+  // with other "pop" operations (no pushes).
+  MemRegion pop();
+
+  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_
+
+// Some extra guarantees that I like to also enable in optimised mode
+// when debugging. If you want to enable them, comment out the assert
+// macro and uncomment out the guaratee macro
+// #define tmp_guarantee_CM(expr, str) guarantee(expr, str)
+#define tmp_guarantee_CM(expr, str) assert(expr, str)
+
+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 {
+  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;
+
+  // Stuff related to age cohort processing.
+  struct ParCleanupThreadState {
+    char _pre[64];
+    UncleanRegionList list;
+    char _post[64];
+  };
+  ParCleanupThreadState** _par_cleanup_thread_state;
+
+  // 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;
+
+  COTracker               _cleanup_co_tracker;
+
+  // 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();
+
+  // 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) {
+    guarantee( 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) {
+    guarantee( 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(); }
+
+  // Manipulation of the region stack
+  bool region_stack_push(MemRegion mr) {
+    _regionStack.push(mr);
+    if (_regionStack.overflow()) {
+      set_has_overflown();
+      return false;
+    }
+    return true;
+  }
+  MemRegion region_stack_pop()          { return _regionStack.pop(); }
+  int region_stack_size()               { return _regionStack.size(); }
+  bool region_stack_overflow()          { return _regionStack.overflow(); }
+  bool region_stack_empty()             { return _regionStack.isEmpty(); }
+
+  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);
+
+  // This iterates over the bitmap of the previous marking and prints
+  // out all objects that are marked on the bitmap and indicates
+  // whether what they point to is also marked or not.
+  void print_prev_bitmap_reachable();
+
+  // 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);
+
+  // 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();
+
+  void disable_co_trackers();
+
+  // This prints the global/local fingers. It is used for debugging.
+  NOT_PRODUCT(void print_finger();)
+
+  void print_summary_info();
+
+  // 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;
+  // 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;
+
+  // concurrent overhead over a single CPU for this task
+  COTracker                   _co_tracker;
+
+  // 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;
+
+  // 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; }
+
+  void enable_co_tracker() {
+    guarantee( !_co_tracker.enabled(), "invariant" );
+    _co_tracker.enable();
+  }
+  void disable_co_tracker() {
+    guarantee( _co_tracker.enabled(), "invariant" );
+    _co_tracker.disable();
+  }
+  bool co_tracker_enabled() {
+    return _co_tracker.enabled();
+  }
+  void reset_co_tracker(double starting_conc_overhead = 0.0) {
+    _co_tracker.reset(starting_conc_overhead);
+  }
+  void start_co_tracker() {
+    _co_tracker.start();
+  }
+  void update_co_tracker(bool force_end = false) {
+    _co_tracker.update(force_end);
+  }
+
+  // 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; }
+
+  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) {
+    tmp_guarantee_CM( _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) {
+    tmp_guarantee_CM( 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) {
+    tmp_guarantee_CM( 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_
+};