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// -*- C++ -*-

// Copyright (C) 2007, 2008, 2009, 2010 Free Software Foundation, Inc.

//

// This file is part of the GNU ISO C++ Library.  This library is free

// software; you can redistribute it and/or modify it under the terms

// of the GNU General Public License as published by the Free Software

// Foundation; either version 3, or (at your option) any later

// version.

// This library 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 for more details.

// Under Section 7 of GPL version 3, you are granted additional

// permissions described in the GCC Runtime Library Exception, version

// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and

// a copy of the GCC Runtime Library Exception along with this program;

// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see

// <http://www.gnu.org/licenses/>.

/** @file parallel/queue.h

 *  @brief Lock-free double-ended queue.

 *  This file is a GNU parallel extension to the Standard C++ Library.

 */

// Written by Johannes Singler.

#ifndef _GLIBCXX_PARALLEL_QUEUE_H

#define _GLIBCXX_PARALLEL_QUEUE_H 1

#include <parallel/types.h>

#include <parallel/base.h>

#include <parallel/compatibility.h>

/** @brief Decide whether to declare certain variable volatile in this file. */

#define _GLIBCXX_VOLATILE volatile

namespace __gnu_parallel

{

  /**@brief Double-ended queue of bounded size, allowing lock-free

   *  atomic access.  push_front() and pop_front() must not be called

   *  concurrently to each other, while pop_back() can be called

   *  concurrently at all times.

   *  @c empty(), @c size(), and @c top() are intentionally not provided.

   *  Calling them would not make sense in a concurrent setting.

   *  @param _Tp Contained element type. */

  template<typename _Tp>

    class _RestrictedBoundedConcurrentQueue

    {

    private:

      /** @brief Array of elements, seen as cyclic buffer. */

      _Tp* _M_base;

      /** @brief Maximal number of elements contained at the same time. */

      _SequenceIndex _M_max_size;

      /** @brief Cyclic __begin and __end pointers contained in one

          atomically changeable value. */

      _GLIBCXX_VOLATILE _CASable _M_borders;

    public:

      /** @brief Constructor. Not to be called concurrent, of course.

       *  @param __max_size Maximal number of elements to be contained. */

      _RestrictedBoundedConcurrentQueue(_SequenceIndex __max_size)

      {

        _M_max_size = __max_size;

        _M_base = new _Tp[__max_size];

        _M_borders = __encode2(0, 0);

#pragma omp flush

      }

      /** @brief Destructor. Not to be called concurrent, of course. */

      ~_RestrictedBoundedConcurrentQueue()

      { delete[] _M_base; }

      /** @brief Pushes one element into the queue at the front end.

       *  Must not be called concurrently with pop_front(). */

      void

      push_front(const _Tp& __t)

      {

        _CASable __former_borders = _M_borders;

        int __former_front, __former_back;

        __decode2(__former_borders, __former_front, __former_back);

        *(_M_base + __former_front % _M_max_size) = __t;

#if _GLIBCXX_ASSERTIONS

        // Otherwise: front - back > _M_max_size eventually.

        _GLIBCXX_PARALLEL_ASSERT(((__former_front + 1) - __former_back)

                                 <= _M_max_size);

#endif

        __fetch_and_add(&_M_borders, __encode2(1, 0));

      }

      /** @brief Pops one element from the queue at the front end.

       *  Must not be called concurrently with pop_front(). */

      bool

      pop_front(_Tp& __t)

      {

        int __former_front, __former_back;

#pragma omp flush

        __decode2(_M_borders, __former_front, __former_back);

        while (__former_front > __former_back)

          {

            // Chance.

            _CASable __former_borders = __encode2(__former_front,

                                                  __former_back);

            _CASable __new_borders = __encode2(__former_front - 1,

                                               __former_back);

            if (__compare_and_swap(&_M_borders, __former_borders,

                                   __new_borders))

              {

                __t = *(_M_base + (__former_front - 1) % _M_max_size);

                return true;

              }

#pragma omp flush

            __decode2(_M_borders, __former_front, __former_back);

          }

        return false;

      }

      /** @brief Pops one element from the queue at the front end.

       *  Must not be called concurrently with pop_front(). */

      bool

      pop_back(_Tp& __t)        //queue behavior

      {

        int __former_front, __former_back;

#pragma omp flush

        __decode2(_M_borders, __former_front, __former_back);

        while (__former_front > __former_back)

          {

            // Chance.

            _CASable __former_borders = __encode2(__former_front,

                                                  __former_back);

            _CASable __new_borders = __encode2(__former_front,

                                               __former_back + 1);

            if (__compare_and_swap(&_M_borders, __former_borders,

                                   __new_borders))

              {

                __t = *(_M_base + __former_back % _M_max_size);

                return true;

              }

#pragma omp flush

            __decode2(_M_borders, __former_front, __former_back);

          }

        return false;

      }

  };

}       //namespace __gnu_parallel

#undef _GLIBCXX_VOLATILE

#endif /* _GLIBCXX_PARALLEL_QUEUE_H */