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 * 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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 * 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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// Forward declarations

class YieldingFlexibleWorkGang;

// Status of tasks

enum Status {

    INACTIVE,

    ACTIVE,

    YIELDING,

    YIELDED,

    ABORTING,

    ABORTED,

    COMPLETING,

    COMPLETED

};

// Class YieldingFlexibleGangWorker:

//   Several instances of this class run in parallel as workers for a gang.

class YieldingFlexibleGangWorker: public GangWorker {

public:

  // Ctor

  YieldingFlexibleGangWorker(AbstractWorkGang* gang, int id) :

    GangWorker(gang, id) { }

public:

  YieldingFlexibleWorkGang* yf_gang() const

    { return (YieldingFlexibleWorkGang*)gang(); }

protected: // Override from parent class

  virtual void loop();

};

// An abstract task to be worked on by a flexible work gang,

// and where the workers will periodically yield, usually

// in response to some condition that is signalled by means

// that are specific to the task at hand.

// You subclass this to supply your own work() method.

// A second feature of this kind of work gang is that

// it allows for the signalling of certain exceptional

// conditions that may be encountered during the performance

// of the task and that may require the task at hand to be

// `aborted' forthwith. Finally, these gangs are `flexible'

// in that they can operate at partial capacity with some

// gang workers waiting on the bench; in other words, the

// size of the active worker pool can flex (up to an apriori

// maximum) in response to task requests at certain points.

// The last part (the flexible part) has not yet been fully

// fleshed out and is a work in progress.

  Status _status;

  YieldingFlexibleWorkGang* _gang;

protected:

  // Constructor and desctructor: only construct subclasses.

    _status(INACTIVE),

  virtual ~YieldingFlexibleGangTask() { }

  friend class YieldingFlexibleWorkGang;

  friend class YieldingFlexibleGangWorker;

  NOT_PRODUCT(virtual bool is_YieldingFlexibleGang_task() const {

    return true;

  })

  void set_status(Status s) {

    _status = s;

  }

  YieldingFlexibleWorkGang* gang() {

    return _gang;

  }

  void set_gang(YieldingFlexibleWorkGang* gang) {

    assert(_gang == NULL || gang == NULL, "Clobber without intermediate reset?");

    _gang = gang;

  }

public:

  // The abstract work method.

  // The argument tells you which member of the gang you are.

  virtual void work(int i) = 0;

  // Subclasses should call the parent's yield() method

  // after having done any work specific to the subclass.

  virtual void yield();

  // An abstract method supplied by

  // a concrete sub-class which is used by the coordinator

  // to do any "central yielding" work.

  virtual void coordinator_yield() = 0;

  // Subclasses should call the parent's abort() method

  // after having done any work specific to the sunbclass.

  virtual void abort();

  Status status()  const { return _status; }

  bool yielded()   const { return _status == YIELDED; }

  bool completed() const { return _status == COMPLETED; }

  bool aborted()   const { return _status == ABORTED; }

  bool active()    const { return _status == ACTIVE; }

};

// Class YieldingWorkGang: A subclass of WorkGang.

// In particular, a YieldingWorkGang is made up of

// YieldingGangWorkers, and provides infrastructure

// supporting yielding to the "GangOverseer",

// being the thread that orchestrates the WorkGang via run_task().

  // Here's the public interface to this class.

public:

  // Constructor and destructor.

  YieldingFlexibleWorkGang(const char* name, int workers,

                           bool are_GC_task_threads);

  YieldingFlexibleGangTask* yielding_task() const {

    assert(task() == NULL || task()->is_YieldingFlexibleGang_task(),

           "Incorrect cast");

    return (YieldingFlexibleGangTask*)task();

  }

  // Run a task; returns when the task is done, or the workers yield,

  // or the task is aborted, or the work gang is terminated via stop().

  // A task that has been yielded can be continued via this same interface

  // by using the same task repeatedly as the argument to the call.

  // It is expected that the YieldingFlexibleGangTask carries the appropriate

  // continuation information used by workers to continue the task

  // from its last yield point. Thus, a completed task will return

  // immediately with no actual work having been done by the workers.

  void run_task(AbstractGangTask* task) {

    guarantee(false, "Use start_task instead");

  }

  void start_task(YieldingFlexibleGangTask* new_task);

  void continue_task(YieldingFlexibleGangTask* gang_task);

  // Abort a currently running task, if any; returns when all the workers

  // have stopped working on the current task and have returned to their

  // waiting stations.

  void abort_task();

  // Yield: workers wait at their current working stations

  // until signalled to proceed by the overseer.

  void yield();

  // Abort: workers are expected to return to their waiting

  // stations, whence they are ready for the next task dispatched

  // by the overseer.

  void abort();

private:

  int _active_workers;

  int _yielded_workers;

  void wait_for_gang();

public:

  // Accessors for fields

  int active_workers() const {

    return _active_workers;

  }

  int yielded_workers() const {

    return _yielded_workers;

  }

private:

  friend class YieldingFlexibleGangWorker;

  void reset(); // NYI

};