]>
Commit | Line | Data |
---|---|---|
c2ba9709 JS |
1 | // -*- C++ -*- |
2 | ||
5817ff8e | 3 | // Copyright (C) 2007, 2008 Free Software Foundation, Inc. |
c2ba9709 JS |
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 2, 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 | // You should have received a copy of the GNU General Public License | |
17 | // along with this library; see the file COPYING. If not, write to | |
18 | // the Free Software Foundation, 59 Temple Place - Suite 330, Boston, | |
19 | // MA 02111-1307, USA. | |
20 | ||
21 | // As a special exception, you may use this file as part of a free | |
22 | // software library without restriction. Specifically, if other files | |
23 | // instantiate templates or use macros or inline functions from this | |
24 | // file, or you compile this file and link it with other files to | |
25 | // produce an executable, this file does not by itself cause the | |
26 | // resulting executable to be covered by the GNU General Public | |
27 | // License. This exception does not however invalidate any other | |
28 | // reasons why the executable file might be covered by the GNU General | |
29 | // Public License. | |
30 | ||
31 | /** @file parallel/queue.h | |
32 | * @brief Lock-free double-ended queue. | |
33 | * This file is a GNU parallel extension to the Standard C++ Library. | |
34 | */ | |
35 | ||
36 | // Written by Johannes Singler. | |
37 | ||
38 | #ifndef _GLIBCXX_PARALLEL_QUEUE_H | |
39 | #define _GLIBCXX_PARALLEL_QUEUE_H 1 | |
40 | ||
41 | #include <parallel/types.h> | |
42 | #include <parallel/base.h> | |
43 | #include <parallel/compatibility.h> | |
44 | ||
45 | /** @brief Decide whether to declare certain variable volatile in this file. */ | |
46 | #define _GLIBCXX_VOLATILE volatile | |
47 | ||
48 | namespace __gnu_parallel | |
49 | { | |
50 | /**@brief Double-ended queue of bounded size, allowing lock-free | |
51 | * atomic access. push_front() and pop_front() must not be called | |
52 | * concurrently to each other, while pop_back() can be called | |
53 | * concurrently at all times. | |
54 | * @c empty(), @c size(), and @c top() are intentionally not provided. | |
55 | * Calling them would not make sense in a concurrent setting. | |
56 | * @param T Contained element type. */ | |
57 | template<typename T> | |
5817ff8e | 58 | class RestrictedBoundedConcurrentQueue |
c2ba9709 | 59 | { |
5817ff8e PC |
60 | private: |
61 | /** @brief Array of elements, seen as cyclic buffer. */ | |
62 | T* base; | |
63 | ||
64 | /** @brief Maximal number of elements contained at the same time. */ | |
65 | sequence_index_t max_size; | |
66 | ||
67 | /** @brief Cyclic begin and end pointers contained in one | |
68 | atomically changeable value. */ | |
69 | _GLIBCXX_VOLATILE lcas_t borders; | |
70 | ||
71 | public: | |
72 | /** @brief Constructor. Not to be called concurrent, of course. | |
73 | * @param max_size Maximal number of elements to be contained. */ | |
74 | RestrictedBoundedConcurrentQueue(sequence_index_t max_size) | |
75 | { | |
76 | this->max_size = max_size; | |
77 | base = new T[max_size]; | |
78 | borders = encode2(0, 0); | |
c2ba9709 | 79 | #pragma omp flush |
5817ff8e PC |
80 | } |
81 | ||
82 | /** @brief Destructor. Not to be called concurrent, of course. */ | |
83 | ~RestrictedBoundedConcurrentQueue() | |
84 | { delete[] base; } | |
85 | ||
86 | /** @brief Pushes one element into the queue at the front end. | |
87 | * Must not be called concurrently with pop_front(). */ | |
88 | void | |
89 | push_front(const T& t) | |
90 | { | |
91 | lcas_t former_borders = borders; | |
92 | int former_front, former_back; | |
93 | decode2(former_borders, former_front, former_back); | |
94 | *(base + former_front % max_size) = t; | |
c2ba9709 | 95 | #if _GLIBCXX_ASSERTIONS |
5817ff8e PC |
96 | // Otherwise: front - back > max_size eventually. |
97 | _GLIBCXX_PARALLEL_ASSERT(((former_front + 1) - former_back) | |
98 | <= max_size); | |
c2ba9709 | 99 | #endif |
5817ff8e PC |
100 | fetch_and_add(&borders, encode2(1, 0)); |
101 | } | |
102 | ||
103 | /** @brief Pops one element from the queue at the front end. | |
104 | * Must not be called concurrently with pop_front(). */ | |
105 | bool | |
106 | pop_front(T& t) | |
107 | { | |
108 | int former_front, former_back; | |
c2ba9709 | 109 | #pragma omp flush |
5817ff8e PC |
110 | decode2(borders, former_front, former_back); |
111 | while (former_front > former_back) | |
112 | { | |
113 | // Chance. | |
114 | lcas_t former_borders = encode2(former_front, former_back); | |
115 | lcas_t new_borders = encode2(former_front - 1, former_back); | |
116 | if (compare_and_swap(&borders, former_borders, new_borders)) | |
117 | { | |
118 | t = *(base + (former_front - 1) % max_size); | |
119 | return true; | |
120 | } | |
c2ba9709 | 121 | #pragma omp flush |
5817ff8e PC |
122 | decode2(borders, former_front, former_back); |
123 | } | |
124 | return false; | |
125 | } | |
126 | ||
127 | /** @brief Pops one element from the queue at the front end. | |
128 | * Must not be called concurrently with pop_front(). */ | |
129 | bool | |
130 | pop_back(T& t) //queue behavior | |
131 | { | |
132 | int former_front, former_back; | |
c2ba9709 | 133 | #pragma omp flush |
5817ff8e PC |
134 | decode2(borders, former_front, former_back); |
135 | while (former_front > former_back) | |
136 | { | |
137 | // Chance. | |
138 | lcas_t former_borders = encode2(former_front, former_back); | |
139 | lcas_t new_borders = encode2(former_front, former_back + 1); | |
140 | if (compare_and_swap(&borders, former_borders, new_borders)) | |
141 | { | |
142 | t = *(base + former_back % max_size); | |
143 | return true; | |
144 | } | |
c2ba9709 | 145 | #pragma omp flush |
5817ff8e PC |
146 | decode2(borders, former_front, former_back); |
147 | } | |
148 | return false; | |
149 | } | |
c2ba9709 JS |
150 | }; |
151 | } //namespace __gnu_parallel | |
152 | ||
153 | #undef _GLIBCXX_VOLATILE | |
154 | ||
155 | #endif |