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1 | // -*- C++ -*- | |
2 | ||
3 | // Copyright (C) 2007-2020 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. */ | |
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. */ | |
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 | |
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 | |
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 | |
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 */ |