1 // -*- C++ -*- 2 3 // Copyright (C) 2007-2018 Free Software Foundation, Inc. 4 // 5 // This file is part of the GNU ISO C++ Library. This library is free 6 // software; you can redistribute it and/or modify it under the terms 7 // of the GNU General Public License as published by the Free Software 8 // Foundation; either version 3, or (at your option) any later 9 // version. 10 11 // This library is distributed in the hope that it will be useful, but 12 // WITHOUT ANY WARRANTY; without even the implied warranty of 13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 14 // General Public License for more details. 15 16 // Under Section 7 of GPL version 3, you are granted additional 17 // permissions described in the GCC Runtime Library Exception, version 18 // 3.1, as published by the Free Software Foundation. 19 20 // You should have received a copy of the GNU General Public License and 21 // a copy of the GCC Runtime Library Exception along with this program; 22 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see 23 // <http://www.gnu.org/licenses/>. 24 25 /** @file parallel/queue.h 26 * @brief Lock-free double-ended queue. 27 * This file is a GNU parallel extension to the Standard C++ Library. 28 */ 29 30 // Written by Johannes Singler. 31 32 #ifndef _GLIBCXX_PARALLEL_QUEUE_H 33 #define _GLIBCXX_PARALLEL_QUEUE_H 1 34 35 #include <parallel/types.h> 36 #include <parallel/base.h> 37 #include <parallel/compatibility.h> 38 39 /** @brief Decide whether to declare certain variable volatile in this file. */ 40 #define _GLIBCXX_VOLATILE volatile 41 42 namespace __gnu_parallel 43 { 44 /**@brief Double-ended queue of bounded size, allowing lock-free 45 * atomic access. push_front() and pop_front() must not be called 46 * concurrently to each other, while pop_back() can be called 47 * concurrently at all times. 48 * @c empty(), @c size(), and @c top() are intentionally not provided. 49 * Calling them would not make sense in a concurrent setting. 50 * @param _Tp Contained element type. */ 51 template<typename _Tp> 52 class _RestrictedBoundedConcurrentQueue 53 { 54 private: 55 /** @brief Array of elements, seen as cyclic buffer. */ 56 _Tp* _M_base; 57 58 /** @brief Maximal number of elements contained at the same time. */ 59 _SequenceIndex _M_max_size; 60 61 /** @brief Cyclic __begin and __end pointers contained in one 62 atomically changeable value. */ 63 _GLIBCXX_VOLATILE _CASable _M_borders; 64 65 public: 66 /** @brief Constructor. Not to be called concurrent, of course. 67 * @param __max_size Maximal number of elements to be contained. */ _RestrictedBoundedConcurrentQueue(_SequenceIndex __max_size)68 _RestrictedBoundedConcurrentQueue(_SequenceIndex __max_size) 69 { 70 _M_max_size = __max_size; 71 _M_base = new _Tp[__max_size]; 72 _M_borders = __encode2(0, 0); 73 #pragma omp flush 74 } 75 76 /** @brief Destructor. Not to be called concurrent, of course. */ ~_RestrictedBoundedConcurrentQueue()77 ~_RestrictedBoundedConcurrentQueue() 78 { delete[] _M_base; } 79 80 /** @brief Pushes one element into the queue at the front end. 81 * Must not be called concurrently with pop_front(). */ 82 void push_front(const _Tp & __t)83 push_front(const _Tp& __t) 84 { 85 _CASable __former_borders = _M_borders; 86 int __former_front, __former_back; 87 __decode2(__former_borders, __former_front, __former_back); 88 *(_M_base + __former_front % _M_max_size) = __t; 89 #if _GLIBCXX_PARALLEL_ASSERTIONS 90 // Otherwise: front - back > _M_max_size eventually. 91 _GLIBCXX_PARALLEL_ASSERT(((__former_front + 1) - __former_back) 92 <= _M_max_size); 93 #endif 94 __fetch_and_add(&_M_borders, __encode2(1, 0)); 95 } 96 97 /** @brief Pops one element from the queue at the front end. 98 * Must not be called concurrently with pop_front(). */ 99 bool pop_front(_Tp & __t)100 pop_front(_Tp& __t) 101 { 102 int __former_front, __former_back; 103 #pragma omp flush 104 __decode2(_M_borders, __former_front, __former_back); 105 while (__former_front > __former_back) 106 { 107 // Chance. 108 _CASable __former_borders = __encode2(__former_front, 109 __former_back); 110 _CASable __new_borders = __encode2(__former_front - 1, 111 __former_back); 112 if (__compare_and_swap(&_M_borders, __former_borders, 113 __new_borders)) 114 { 115 __t = *(_M_base + (__former_front - 1) % _M_max_size); 116 return true; 117 } 118 #pragma omp flush 119 __decode2(_M_borders, __former_front, __former_back); 120 } 121 return false; 122 } 123 124 /** @brief Pops one element from the queue at the front end. 125 * Must not be called concurrently with pop_front(). */ 126 bool pop_back(_Tp & __t)127 pop_back(_Tp& __t) //queue behavior 128 { 129 int __former_front, __former_back; 130 #pragma omp flush 131 __decode2(_M_borders, __former_front, __former_back); 132 while (__former_front > __former_back) 133 { 134 // Chance. 135 _CASable __former_borders = __encode2(__former_front, 136 __former_back); 137 _CASable __new_borders = __encode2(__former_front, 138 __former_back + 1); 139 if (__compare_and_swap(&_M_borders, __former_borders, 140 __new_borders)) 141 { 142 __t = *(_M_base + __former_back % _M_max_size); 143 return true; 144 } 145 #pragma omp flush 146 __decode2(_M_borders, __former_front, __former_back); 147 } 148 return false; 149 } 150 }; 151 } //namespace __gnu_parallel 152 153 #undef _GLIBCXX_VOLATILE 154 155 #endif /* _GLIBCXX_PARALLEL_QUEUE_H */ 156