libstdc++
queue.h
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1 // -*- C++ -*-
2 
3 // Copyright (C) 2007-2019 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
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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
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18 // 3.1, as published by the Free Software Foundation.
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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>
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. */
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. */
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 */
_Tp __fetch_and_add(volatile _Tp *__ptr, _Tp __addend)
Add a value to a variable, atomically.
Double-ended queue of bounded size, allowing lock-free atomic access. push_front() and pop_front() mu...
Definition: queue.h:52
#define _GLIBCXX_VOLATILE
Decide whether to declare certain variable volatile in this file.
Definition: queue.h:40
Sequential helper functions. This file is a GNU parallel extension to the Standard C++ Library...
uint64_t _SequenceIndex
Unsigned integer to index __elements. The total number of elements for each algorithm must fit into t...
Definition: types.h:117
GNU parallel code for public use.
_RestrictedBoundedConcurrentQueue(_SequenceIndex __max_size)
Constructor. Not to be called concurrent, of course.
Definition: queue.h:68
_CASable __encode2(int __a, int __b)
Encode two integers into one gnu_parallel::_CASable.
int64_t _CASable
Longest compare-and-swappable integer type on this platform.
Definition: types.h:127
bool pop_front(_Tp &__t)
Pops one element from the queue at the front end. Must not be called concurrently with pop_front()...
Definition: queue.h:100
void push_front(const _Tp &__t)
Pushes one element into the queue at the front end. Must not be called concurrently with pop_front()...
Definition: queue.h:83
bool pop_back(_Tp &__t)
Pops one element from the queue at the front end. Must not be called concurrently with pop_front()...
Definition: queue.h:127
~_RestrictedBoundedConcurrentQueue()
Destructor. Not to be called concurrent, of course.
Definition: queue.h:77
void __decode2(_CASable __x, int &__a, int &__b)
Decode two integers from one gnu_parallel::_CASable.
Basic types and typedefs. This file is a GNU parallel extension to the Standard C++ Library...
bool __compare_and_swap(volatile _Tp *__ptr, _Tp __comparand, _Tp __replacement)
Compare-and-swap.
Compatibility layer, mostly concerned with atomic operations.