1 // -*- C++ -*- 2 3 // Copyright (C) 2007, 2008, 2009 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 T Contained element type. */ 51 template<typename T> 52 class RestrictedBoundedConcurrentQueue 53 { 54 private: 55 /** @brief Array of elements, seen as cyclic buffer. */ 56 T* base; 57 58 /** @brief Maximal number of elements contained at the same time. */ 59 sequence_index_t max_size; 60 61 /** @brief Cyclic begin and end pointers contained in one 62 atomically changeable value. */ 63 _GLIBCXX_VOLATILE lcas_t 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. */ 68 RestrictedBoundedConcurrentQueue(sequence_index_t max_size) 69 { 70 this->max_size = max_size; 71 base = new T[max_size]; 72 borders = encode2(0, 0); 73 #pragma omp flush 74 } 75 76 /** @brief Destructor. Not to be called concurrent, of course. */ 77 ~RestrictedBoundedConcurrentQueue() 78 { delete[] 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 83 push_front(const T& t) 84 { 85 lcas_t former_borders = borders; 86 int former_front, former_back; 87 decode2(former_borders, former_front, former_back); 88 *(base + former_front % max_size) = t; 89 #if _GLIBCXX_ASSERTIONS 90 // Otherwise: front - back > max_size eventually. 91 _GLIBCXX_PARALLEL_ASSERT(((former_front + 1) - former_back) 92 <= max_size); 93 #endif 94 fetch_and_add(&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 100 pop_front(T& t) 101 { 102 int former_front, former_back; 103 #pragma omp flush 104 decode2(borders, former_front, former_back); 105 while (former_front > former_back) 106 { 107 // Chance. 108 lcas_t former_borders = encode2(former_front, former_back); 109 lcas_t new_borders = encode2(former_front - 1, former_back); 110 if (compare_and_swap(&borders, former_borders, new_borders)) 111 { 112 t = *(base + (former_front - 1) % max_size); 113 return true; 114 } 115 #pragma omp flush 116 decode2(borders, former_front, former_back); 117 } 118 return false; 119 } 120 121 /** @brief Pops one element from the queue at the front end. 122 * Must not be called concurrently with pop_front(). */ 123 bool 124 pop_back(T& t) //queue behavior 125 { 126 int former_front, former_back; 127 #pragma omp flush 128 decode2(borders, former_front, former_back); 129 while (former_front > former_back) 130 { 131 // Chance. 132 lcas_t former_borders = encode2(former_front, former_back); 133 lcas_t new_borders = encode2(former_front, former_back + 1); 134 if (compare_and_swap(&borders, former_borders, new_borders)) 135 { 136 t = *(base + former_back % max_size); 137 return true; 138 } 139 #pragma omp flush 140 decode2(borders, former_front, former_back); 141 } 142 return false; 143 } 144 }; 145 } //namespace __gnu_parallel 146 147 #undef _GLIBCXX_VOLATILE 148 149 #endif /* _GLIBCXX_PARALLEL_QUEUE_H */ 150
