/*

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

 * or visit www.oracle.com if you need additional information or have any

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 *

 */

#include "memory/allocation.hpp"

// A SuspendibleThreadSet is a set of threads that can be suspended.

// A thread can join and later leave the set, and periodically yield.

// If some thread (not in the set) requests, via synchronize(), that

// the threads be suspended, then the requesting thread is blocked

// until all the threads in the set have yielded or left the set. Threads

// may not enter the set when an attempted suspension is in progress. The

// suspending thread later calls desynchronize(), allowing the suspended

// threads to continue.

class SuspendibleThreadSet : public AllStatic {

  friend class SuspendibleThreadSetJoiner;

  friend class SuspendibleThreadSetLeaver;

private:

  static uint   _nthreads;

  static uint   _nthreads_stopped;

  static bool   _suspend_all;

  static double _suspend_all_start;

  static bool is_synchronized();

  // Add the current thread to the set. May block if a suspension is in progress.

  static void join();

  // Removes the current thread from the set.

  static void leave();

public:

  // Returns true if an suspension is in progress.

  static bool should_yield() { return _suspend_all; }

  // Suspends the current thread if a suspension is in progress.

  static void yield();

  // Returns when all threads in the set are suspended.

  static void synchronize();

  // Resumes all suspended threads in the set.

  static void desynchronize();

};

class SuspendibleThreadSetJoiner : public StackObj {

private:

  bool _active;

public:

  SuspendibleThreadSetJoiner(bool active = true) : _active(active) {

    if (_active) {

      SuspendibleThreadSet::join();

    }

  }

  ~SuspendibleThreadSetJoiner() {

    if (_active) {

      SuspendibleThreadSet::leave();

    }

  }

  bool should_yield() {

    if (_active) {

      return SuspendibleThreadSet::should_yield();

    } else {

      return false;

    }

  }

  void yield() {

    assert(_active, "Thread has not joined the suspendible thread set");

    SuspendibleThreadSet::yield();

  }

};

class SuspendibleThreadSetLeaver : public StackObj {

private:

  bool _active;

public:

  SuspendibleThreadSetLeaver(bool active = true) : _active(active) {

    if (_active) {

      SuspendibleThreadSet::leave();

    }

  }

  ~SuspendibleThreadSetLeaver() {

    if (_active) {

      SuspendibleThreadSet::join();

    }

  }

};