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Editing: 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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