| // -*- C++ -*- |
| |
| // Copyright (C) 2007-2021 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 */ |