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 /*

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

  *

  * This code is free software; you can redistribute it and/or modify it

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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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  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

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 #ifndef SHARE_VM_GC_IMPLEMENTATION_PARALLELSCAVENGE_GCTASKMANAGER_HPP

 #define SHARE_VM_GC_IMPLEMENTATION_PARALLELSCAVENGE_GCTASKMANAGER_HPP

 #include "runtime/mutex.hpp"

 #include "utilities/growableArray.hpp"

 //

 // The GCTaskManager is a queue of GCTasks, and accessors

 // to allow the queue to be accessed from many threads.

 //

 // Forward declarations of types defined in this file.

 class GCTask;

 class GCTaskQueue;

 class SynchronizedGCTaskQueue;

 class GCTaskManager;

 class NotifyDoneClosure;

 // Some useful subclasses of GCTask.  You can also make up your own.

 class NoopGCTask;

 class BarrierGCTask;

 class ReleasingBarrierGCTask;

 class NotifyingBarrierGCTask;

 class WaitForBarrierGCTask;

 class IdleGCTask;

 // A free list of Monitor*'s.

 class MonitorSupply;

 // Forward declarations of classes referenced in this file via pointer.

 class GCTaskThread;

 class Mutex;

 class Monitor;

 class ThreadClosure;

 // The abstract base GCTask.

 class GCTask : public ResourceObj {

 public:

   // Known kinds of GCTasks, for predicates.

   class Kind : AllStatic {

   public:

     enum kind {

       unknown_task,

       ordinary_task,

       barrier_task,

       noop_task,

       idle_task

     };

     static const char* to_string(kind value);

   };

 private:

   // Instance state.

   const Kind::kind _kind;               // For runtime type checking.

   const uint       _affinity;           // Which worker should run task.

   GCTask*          _newer;              // Tasks are on doubly-linked ...

   GCTask*          _older;              // ... lists.

 public:

   virtual char* name() { return (char *)"task"; }

   // Abstract do_it method

   virtual void do_it(GCTaskManager* manager, uint which) = 0;

   // Accessors

   Kind::kind kind() const {

     return _kind;

   }

   uint affinity() const {

     return _affinity;

   }

   GCTask* newer() const {

     return _newer;

   }

   void set_newer(GCTask* n) {

     _newer = n;

   }

   GCTask* older() const {

     return _older;

   }

   void set_older(GCTask* p) {

     _older = p;

   }

   // Predicates.

   bool is_ordinary_task() const {

     return kind()==Kind::ordinary_task;

   }

   bool is_barrier_task() const {

     return kind()==Kind::barrier_task;

   }

   bool is_noop_task() const {

     return kind()==Kind::noop_task;

   }

   bool is_idle_task() const {

     return kind()==Kind::idle_task;

   }

   void print(const char* message) const PRODUCT_RETURN;

 protected:

   // Constructors: Only create subclasses.

   //     An ordinary GCTask.

   GCTask();

   //     A GCTask of a particular kind, usually barrier or noop.

   GCTask(Kind::kind kind);

   //     An ordinary GCTask with an affinity.

   GCTask(uint affinity);

   //     A GCTask of a particular kind, with and affinity.

   GCTask(Kind::kind kind, uint affinity);

   // We want a virtual destructor because virtual methods,

   // but since ResourceObj's don't have their destructors

   // called, we don't have one at all.  Instead we have

   // this method, which gets called by subclasses to clean up.

   virtual void destruct();

   // Methods.

   void initialize();

 };

 // A doubly-linked list of GCTasks.

 // The list is not synchronized, because sometimes we want to

 // build up a list and then make it available to other threads.

 // See also: SynchronizedGCTaskQueue.

 class GCTaskQueue : public ResourceObj {

 private:

   // Instance state.

   GCTask*    _insert_end;               // Tasks are enqueued at this end.

   GCTask*    _remove_end;               // Tasks are dequeued from this end.

   uint       _length;                   // The current length of the queue.

   const bool _is_c_heap_obj;            // Is this a CHeapObj?

 public:

   // Factory create and destroy methods.

   //     Create as ResourceObj.

   static GCTaskQueue* create();

   //     Create as CHeapObj.

   static GCTaskQueue* create_on_c_heap();

   //     Destroyer.

   static void destroy(GCTaskQueue* that);

   // Accessors.

   //     These just examine the state of the queue.

   bool is_empty() const {

     assert(((insert_end() == NULL && remove_end() == NULL) ||

             (insert_end() != NULL && remove_end() != NULL)),

            "insert_end and remove_end don't match");

     assert((insert_end() != NULL) || (_length == 0), "Not empty");

     return insert_end() == NULL;

   }

   uint length() const {

     return _length;

   }

   // Methods.

   //     Enqueue one task.

   void enqueue(GCTask* task);

   //     Enqueue a list of tasks.  Empties the argument list.

   void enqueue(GCTaskQueue* list);

   //     Dequeue one task.

   GCTask* dequeue();

   //     Dequeue one task, preferring one with affinity.

   GCTask* dequeue(uint affinity);

 protected:

   // Constructor. Clients use factory, but there might be subclasses.

   GCTaskQueue(bool on_c_heap);

   // Destructor-like method.

   // Because ResourceMark doesn't call destructors.

   // This method cleans up like one.

   virtual void destruct();

   // Accessors.

   GCTask* insert_end() const {

     return _insert_end;

   }

   void set_insert_end(GCTask* value) {

     _insert_end = value;

   }

   GCTask* remove_end() const {

     return _remove_end;

   }

   void set_remove_end(GCTask* value) {

     _remove_end = value;

   }

   void increment_length() {

     _length += 1;

   }

   void decrement_length() {

     _length -= 1;

   }

   void set_length(uint value) {

     _length = value;

   }

   bool is_c_heap_obj() const {

     return _is_c_heap_obj;

   }

   // Methods.

   void initialize();

   GCTask* remove();                     // Remove from remove end.

   GCTask* remove(GCTask* task);         // Remove from the middle.

   void print(const char* message) const PRODUCT_RETURN;

   // Debug support

   void verify_length() const PRODUCT_RETURN;

 };

 // A GCTaskQueue that can be synchronized.

 // This "has-a" GCTaskQueue and a mutex to do the exclusion.

 class SynchronizedGCTaskQueue : public CHeapObj<mtGC> {

 private:

   // Instance state.

   GCTaskQueue* _unsynchronized_queue;   // Has-a unsynchronized queue.

   Monitor *    _lock;                   // Lock to control access.

 public:

   // Factory create and destroy methods.

   static SynchronizedGCTaskQueue* create(GCTaskQueue* queue, Monitor * lock) {

     return new SynchronizedGCTaskQueue(queue, lock);

   }

   static void destroy(SynchronizedGCTaskQueue* that) {

     if (that != NULL) {

       delete that;

     }

   }

   // Accessors

   GCTaskQueue* unsynchronized_queue() const {

     return _unsynchronized_queue;

   }

   Monitor * lock() const {

     return _lock;

   }

   // GCTaskQueue wrapper methods.

   // These check that you hold the lock

   // and then call the method on the queue.

   bool is_empty() const {

     guarantee(own_lock(), "don't own the lock");

     return unsynchronized_queue()->is_empty();

   }

   void enqueue(GCTask* task) {

     guarantee(own_lock(), "don't own the lock");

     unsynchronized_queue()->enqueue(task);

   }

   void enqueue(GCTaskQueue* list) {

     guarantee(own_lock(), "don't own the lock");

     unsynchronized_queue()->enqueue(list);

   }

   GCTask* dequeue() {

     guarantee(own_lock(), "don't own the lock");

     return unsynchronized_queue()->dequeue();

   }

   GCTask* dequeue(uint affinity) {

     guarantee(own_lock(), "don't own the lock");

     return unsynchronized_queue()->dequeue(affinity);

   }

   uint length() const {

     guarantee(own_lock(), "don't own the lock");

     return unsynchronized_queue()->length();

   }

   // For guarantees.

   bool own_lock() const {

     return lock()->owned_by_self();

   }

 protected:

   // Constructor.  Clients use factory, but there might be subclasses.

   SynchronizedGCTaskQueue(GCTaskQueue* queue, Monitor * lock);

   // Destructor.  Not virtual because no virtuals.

   ~SynchronizedGCTaskQueue();

 };

 // This is an abstract base class for getting notifications

 // when a GCTaskManager is done.

 class NotifyDoneClosure : public CHeapObj<mtGC> {

 public:

   // The notification callback method.

   virtual void notify(GCTaskManager* manager) = 0;

 protected:

   // Constructor.

   NotifyDoneClosure() {

     // Nothing to do.

   }

   // Virtual destructor because virtual methods.

   virtual ~NotifyDoneClosure() {

     // Nothing to do.

   }

 };

 // Dynamic number of GC threads

 //

 //  GC threads wait in get_task() for work (i.e., a task) to perform.

 // When the number of GC threads was static, the number of tasks

 // created to do a job was equal to or greater than the maximum

 // number of GC threads (ParallelGCThreads).  The job might be divided

 // into a number of tasks greater than the number of GC threads for

 // load balancing (i.e., over partitioning).  The last task to be

 // executed by a GC thread in a job is a work stealing task.  A

 // GC  thread that gets a work stealing task continues to execute

 // that task until the job is done.  In the static number of GC theads

 // case, tasks are added to a queue (FIFO).  The work stealing tasks are

 // the last to be added.  Once the tasks are added, the GC threads grab

 // a task and go.  A single thread can do all the non-work stealing tasks

 // and then execute a work stealing and wait for all the other GC threads

 // to execute their work stealing task.

 //  In the dynamic number of GC threads implementation, idle-tasks are

 // created to occupy the non-participating or "inactive" threads.  An

 // idle-task makes the GC thread wait on a barrier that is part of the

 // GCTaskManager.  The GC threads that have been "idled" in a IdleGCTask

 // are released once all the active GC threads have finished their work

 // stealing tasks.  The GCTaskManager does not wait for all the "idled"

 // GC threads to resume execution. When those GC threads do resume

 // execution in the course of the thread scheduling, they call get_tasks()

 // as all the other GC threads do.  Because all the "idled" threads are

 // not required to execute in order to finish a job, it is possible for

 // a GC thread to still be "idled" when the next job is started.  Such

 // a thread stays "idled" for the next job.  This can result in a new

 // job not having all the expected active workers.  For example if on

 // job requests 4 active workers out of a total of 10 workers so the

 // remaining 6 are "idled", if the next job requests 6 active workers

 // but all 6 of the "idled" workers are still idle, then the next job

 // will only get 4 active workers.

 //  The implementation for the parallel old compaction phase has an

 // added complication.  In the static case parold partitions the chunks

 // ready to be filled into stacks, one for each GC thread.  A GC thread

 // executing a draining task (drains the stack of ready chunks)

 // claims a stack according to it's id (the unique ordinal value assigned

 // to each GC thread).  In the dynamic case not all GC threads will

 // actively participate so stacks with ready to fill chunks can only be

 // given to the active threads.  An initial implementation chose stacks

 // number 1-n to get the ready chunks and required that GC threads

 // 1-n be the active workers.  This was undesirable because it required

 // certain threads to participate.  In the final implementation a

 // list of stacks equal in number to the active workers are filled

 // with ready chunks.  GC threads that participate get a stack from

 // the task (DrainStacksCompactionTask), empty the stack, and then add it to a

 // recycling list at the end of the task.  If the same GC thread gets

 // a second task, it gets a second stack to drain and returns it.  The

 // stacks are added to a recycling list so that later stealing tasks

 // for this tasks can get a stack from the recycling list.  Stealing tasks

 // use the stacks in its work in a way similar to the draining tasks.

 // A thread is not guaranteed to get anything but a stealing task and

 // a thread that only gets a stealing task has to get a stack. A failed

 // implementation tried to have the GC threads keep the stack they used

 // during a draining task for later use in the stealing task but that didn't

 // work because as noted a thread is not guaranteed to get a draining task.

 //

 // For PSScavenge and ParCompactionManager the GC threads are

 // held in the GCTaskThread** _thread array in GCTaskManager.

 class GCTaskManager : public CHeapObj<mtGC> {

  friend class ParCompactionManager;

  friend class PSParallelCompact;

  friend class PSScavenge;

  friend class PSRefProcTaskExecutor;

  friend class RefProcTaskExecutor;

  friend class GCTaskThread;

  friend class IdleGCTask;

 private:

   // Instance state.

   NotifyDoneClosure*        _ndc;               // Notify on completion.

   const uint                _workers;           // Number of workers.

   Monitor*                  _monitor;           // Notification of changes.

   SynchronizedGCTaskQueue*  _queue;             // Queue of tasks.

   GCTaskThread**            _thread;            // Array of worker threads.

   uint                      _active_workers;    // Number of active workers.

   uint                      _busy_workers;      // Number of busy workers.

   uint                      _blocking_worker;   // The worker that's blocking.

   bool*                     _resource_flag;     // Array of flag per threads.

   uint                      _delivered_tasks;   // Count of delivered tasks.

   uint                      _completed_tasks;   // Count of completed tasks.

   uint                      _barriers;          // Count of barrier tasks.

   uint                      _emptied_queue;     // Times we emptied the queue.

   NoopGCTask*               _noop_task;         // The NoopGCTask instance.

   uint                      _noop_tasks;        // Count of noop tasks.

   WaitForBarrierGCTask*     _idle_inactive_task;// Task for inactive workers

   volatile uint             _idle_workers;      // Number of idled workers

 public:

   // Factory create and destroy methods.

   static GCTaskManager* create(uint workers) {

     return new GCTaskManager(workers);

   }

   static GCTaskManager* create(uint workers, NotifyDoneClosure* ndc) {

     return new GCTaskManager(workers, ndc);

   }

   static void destroy(GCTaskManager* that) {

     if (that != NULL) {

       delete that;

     }

   }

   // Accessors.

   uint busy_workers() const {

     return _busy_workers;

   }

   volatile uint idle_workers() const {

     return _idle_workers;

   }

   //     Pun between Monitor* and Mutex*

   Monitor* monitor() const {

     return _monitor;

   }

   Monitor * lock() const {

     return _monitor;

   }

   WaitForBarrierGCTask* idle_inactive_task() {

     return _idle_inactive_task;

   }

   // Methods.

   //     Add the argument task to be run.

   void add_task(GCTask* task);

   //     Add a list of tasks.  Removes task from the argument list.

   void add_list(GCTaskQueue* list);

   //     Claim a task for argument worker.

   GCTask* get_task(uint which);

   //     Note the completion of a task by the argument worker.

   void note_completion(uint which);

   //     Is the queue blocked from handing out new tasks?

   bool is_blocked() const {

     return (blocking_worker() != sentinel_worker());

   }

   //     Request that all workers release their resources.

   void release_all_resources();

   //     Ask if a particular worker should release its resources.

   bool should_release_resources(uint which); // Predicate.

   //     Note the release of resources by the argument worker.

   void note_release(uint which);

   //     Create IdleGCTasks for inactive workers and start workers

   void task_idle_workers();

   //     Release the workers in IdleGCTasks

   void release_idle_workers();

   // Constants.

   //     A sentinel worker identifier.

   static uint sentinel_worker() {

     return (uint) -1;                   // Why isn't there a max_uint?

   }

   //     Execute the task queue and wait for the completion.

   void execute_and_wait(GCTaskQueue* list);

   void print_task_time_stamps();

   void print_threads_on(outputStream* st);

   void threads_do(ThreadClosure* tc);

 protected:

   // Constructors.  Clients use factory, but there might be subclasses.

   //     Create a GCTaskManager with the appropriate number of workers.

   GCTaskManager(uint workers);

   //     Create a GCTaskManager that calls back when there's no more work.

   GCTaskManager(uint workers, NotifyDoneClosure* ndc);

   //     Make virtual if necessary.

   ~GCTaskManager();

   // Accessors.

   uint workers() const {

     return _workers;

   }

   void set_active_workers(uint v) {

     assert(v <= _workers, "Trying to set more workers active than there are");

     _active_workers = MIN2(v, _workers);

     assert(v != 0, "Trying to set active workers to 0");

     _active_workers = MAX2(1U, _active_workers);

   }

   // Sets the number of threads that will be used in a collection

   void set_active_gang();

   NotifyDoneClosure* notify_done_closure() const {

     return _ndc;

   }

   SynchronizedGCTaskQueue* queue() const {

     return _queue;

   }

   NoopGCTask* noop_task() const {

     return _noop_task;

   }

   //     Bounds-checking per-thread data accessors.

   GCTaskThread* thread(uint which);

   void set_thread(uint which, GCTaskThread* value);

   bool resource_flag(uint which);

   void set_resource_flag(uint which, bool value);

   // Modifier methods with some semantics.

   //     Is any worker blocking handing out new tasks?

   uint blocking_worker() const {

     return _blocking_worker;

   }

   void set_blocking_worker(uint value) {

     _blocking_worker = value;

   }

   void set_unblocked() {

     set_blocking_worker(sentinel_worker());

   }

   //     Count of busy workers.

   void reset_busy_workers() {

     _busy_workers = 0;

   }

   uint increment_busy_workers();

   uint decrement_busy_workers();

   //     Count of tasks delivered to workers.

   uint delivered_tasks() const {

     return _delivered_tasks;

   }

   void increment_delivered_tasks() {

     _delivered_tasks += 1;

   }

   void reset_delivered_tasks() {

     _delivered_tasks = 0;

   }

   //     Count of tasks completed by workers.

   uint completed_tasks() const {

     return _completed_tasks;

   }

   void increment_completed_tasks() {

     _completed_tasks += 1;

   }

   void reset_completed_tasks() {

     _completed_tasks = 0;

   }

   //     Count of barrier tasks completed.

   uint barriers() const {

     return _barriers;

   }

   void increment_barriers() {

     _barriers += 1;

   }

   void reset_barriers() {

     _barriers = 0;

   }

   //     Count of how many times the queue has emptied.

   uint emptied_queue() const {

     return _emptied_queue;

   }

   void increment_emptied_queue() {

     _emptied_queue += 1;

   }

   void reset_emptied_queue() {

     _emptied_queue = 0;

   }

   //     Count of the number of noop tasks we've handed out,

   //     e.g., to handle resource release requests.

   uint noop_tasks() const {

     return _noop_tasks;

   }

   void increment_noop_tasks() {

     _noop_tasks += 1;

   }

   void reset_noop_tasks() {

     _noop_tasks = 0;

   }

   void increment_idle_workers() {

     _idle_workers++;

   }

   void decrement_idle_workers() {

     _idle_workers--;

   }

   // Other methods.

   void initialize();

  public:

   // Return true if all workers are currently active.

   bool all_workers_active() { return workers() == active_workers(); }

   uint active_workers() const {

     return _active_workers;

   }

 };

 //

 // Some exemplary GCTasks.

 //

 // A noop task that does nothing,

 // except take us around the GCTaskThread loop.

 class NoopGCTask : public GCTask {

 private:

   const bool _is_c_heap_obj;            // Is this a CHeapObj?

 public:

   // Factory create and destroy methods.

   static NoopGCTask* create();

   static NoopGCTask* create_on_c_heap();

   static void destroy(NoopGCTask* that);

   virtual char* name() { return (char *)"noop task"; }

   // Methods from GCTask.

   void do_it(GCTaskManager* manager, uint which) {

     // Nothing to do.

   }

 protected:

   // Constructor.

   NoopGCTask(bool on_c_heap) :

     GCTask(GCTask::Kind::noop_task),

     _is_c_heap_obj(on_c_heap) {

     // Nothing to do.

   }

   // Destructor-like method.

   void destruct();

   // Accessors.

   bool is_c_heap_obj() const {

     return _is_c_heap_obj;

   }

 };

 // A BarrierGCTask blocks other tasks from starting,

 // and waits until it is the only task running.

 class BarrierGCTask : public GCTask {

 public:

   // Factory create and destroy methods.

   static BarrierGCTask* create() {

     return new BarrierGCTask();

   }

   static void destroy(BarrierGCTask* that) {

     if (that != NULL) {

       that->destruct();

       delete that;

     }

   }

   // Methods from GCTask.

   void do_it(GCTaskManager* manager, uint which);

 protected:

   // Constructor.  Clients use factory, but there might be subclasses.

   BarrierGCTask() :

     GCTask(GCTask::Kind::barrier_task) {

     // Nothing to do.

   }

   // Destructor-like method.

   void destruct();

   virtual char* name() { return (char *)"barrier task"; }

   // Methods.

   //     Wait for this to be the only task running.

   void do_it_internal(GCTaskManager* manager, uint which);

 };

 // A ReleasingBarrierGCTask is a BarrierGCTask

 // that tells all the tasks to release their resource areas.

 class ReleasingBarrierGCTask : public BarrierGCTask {

 public:

   // Factory create and destroy methods.

   static ReleasingBarrierGCTask* create() {

     return new ReleasingBarrierGCTask();

   }

   static void destroy(ReleasingBarrierGCTask* that) {

     if (that != NULL) {

       that->destruct();

       delete that;

     }

   }

   // Methods from GCTask.

   void do_it(GCTaskManager* manager, uint which);

 protected:

   // Constructor.  Clients use factory, but there might be subclasses.

   ReleasingBarrierGCTask() :

     BarrierGCTask() {

     // Nothing to do.

   }

   // Destructor-like method.

   void destruct();

 };

 // A NotifyingBarrierGCTask is a BarrierGCTask

 // that calls a notification method when it is the only task running.

 class NotifyingBarrierGCTask : public BarrierGCTask {

 private:

   // Instance state.

   NotifyDoneClosure* _ndc;              // The callback object.

 public:

   // Factory create and destroy methods.

   static NotifyingBarrierGCTask* create(NotifyDoneClosure* ndc) {

     return new NotifyingBarrierGCTask(ndc);

   }

   static void destroy(NotifyingBarrierGCTask* that) {

     if (that != NULL) {

       that->destruct();

       delete that;

     }

   }

   // Methods from GCTask.

   void do_it(GCTaskManager* manager, uint which);

 protected:

   // Constructor.  Clients use factory, but there might be subclasses.

   NotifyingBarrierGCTask(NotifyDoneClosure* ndc) :

     BarrierGCTask(),

     _ndc(ndc) {

     assert(notify_done_closure() != NULL, "can't notify on NULL");

   }

   // Destructor-like method.

   void destruct();

   // Accessor.

   NotifyDoneClosure* notify_done_closure() const { return _ndc; }

 };

 // A WaitForBarrierGCTask is a BarrierGCTask

 // with a method you can call to wait until

 // the BarrierGCTask is done.

 // This may cover many of the uses of NotifyingBarrierGCTasks.

 class WaitForBarrierGCTask : public BarrierGCTask {

   friend class GCTaskManager;

   friend class IdleGCTask;

 private:

   // Instance state.

   Monitor*      _monitor;                  // Guard and notify changes.

   volatile bool _should_wait;              // true=>wait, false=>proceed.

   const bool    _is_c_heap_obj;            // Was allocated on the heap.

 public:

   virtual char* name() { return (char *) "waitfor-barrier-task"; }

   // Factory create and destroy methods.

   static WaitForBarrierGCTask* create();

   static WaitForBarrierGCTask* create_on_c_heap();

   static void destroy(WaitForBarrierGCTask* that);

   // Methods.

   void     do_it(GCTaskManager* manager, uint which);

   void     wait_for(bool reset);

   void set_should_wait(bool value) {

     _should_wait = value;

   }

 protected:

   // Constructor.  Clients use factory, but there might be subclasses.

   WaitForBarrierGCTask(bool on_c_heap);

   // Destructor-like method.

   void destruct();

   // Accessors.

   Monitor* monitor() const {

     return _monitor;

   }

   bool should_wait() const {

     return _should_wait;

   }

   bool is_c_heap_obj() {

     return _is_c_heap_obj;

   }

 };

 // Task that is used to idle a GC task when fewer than

 // the maximum workers are wanted.

 class IdleGCTask : public GCTask {

   const bool    _is_c_heap_obj;            // Was allocated on the heap.

  public:

   bool is_c_heap_obj() {

     return _is_c_heap_obj;

   }

   // Factory create and destroy methods.

   static IdleGCTask* create();

   static IdleGCTask* create_on_c_heap();

   static void destroy(IdleGCTask* that);

   virtual char* name() { return (char *)"idle task"; }

   // Methods from GCTask.

   virtual void do_it(GCTaskManager* manager, uint which);

 protected:

   // Constructor.

   IdleGCTask(bool on_c_heap) :

     GCTask(GCTask::Kind::idle_task),

     _is_c_heap_obj(on_c_heap) {

     // Nothing to do.

   }

   // Destructor-like method.

   void destruct();

 };

 class MonitorSupply : public AllStatic {

 private:

   // State.

   //     Control multi-threaded access.

   static Mutex*                   _lock;

   //     The list of available Monitor*'s.

   static GrowableArray<Monitor*>* _freelist;

 public:

   // Reserve a Monitor*.

   static Monitor* reserve();

   // Release a Monitor*.

   static void release(Monitor* instance);

 private:

   // Accessors.

   static Mutex* lock() {

     return _lock;

   }

   static GrowableArray<Monitor*>* freelist() {

     return _freelist;

   }

 };

 #endif // SHARE_VM_GC_IMPLEMENTATION_PARALLELSCAVENGE_GCTASKMANAGER_HPP