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/usr/include/c++/8/parallel/queue.h

// -*- C++ -*-

// Copyright (C) 2007-2018 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_PARALLEL_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 */

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algo.h	78.15 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
algobase.h	16.75 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
algorithm	1.35 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
algorithmfwd.h	31.45 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
balanced_quicksort.h	16.55 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
base.h	12.08 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
basic_iterator.h	1.55 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
checkers.h	2.25 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
compatibility.h	3.70 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
compiletime_settings.h	2.80 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
equally_split.h	3.28 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
features.h	3.46 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
find.h	13.27 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
find_selectors.h	6.83 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
for_each.h	3.85 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
for_each_selectors.h	10.32 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
iterator.h	5.54 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
list_partition.h	6.39 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
losertree.h	27.92 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
merge.h	9.35 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
multiseq_selection.h	21.56 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
multiway_merge.h	68.88 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
multiway_mergesort.h	14.91 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
numeric	20.23 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
numericfwd.h	7.32 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
omp_loop.h	3.94 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
omp_loop_static.h	4.01 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
parallel.h	1.54 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
partial_sum.h	7.30 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
partition.h	14.61 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
par_loop.h	4.45 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
queue.h	5.41 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
quicksort.h	5.98 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
random_number.h	4.13 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
random_shuffle.h	18.24 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
search.h	5.26 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
settings.h	12.17 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
set_operations.h	14.25 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
sort.h	7.53 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
tags.h	5.84 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
types.h	3.63 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
unique_copy.h	6.02 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive
workstealing.h	9.39 KB	lrw-r--r--	2025-08-26 09:45:05	Edit Download recursive recursive