libstdc++
atomicity.h
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1 // Support for atomic operations -*- C++ -*-
2 
3 // Copyright (C) 2004-2017 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
7 // terms of the GNU General Public License as published by the
8 // Free Software Foundation; either version 3, or (at your option)
9 // any later version.
10 
11 // This library is distributed in the hope that it will be useful,
12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 // GNU 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 ext/atomicity.h
26  * This file is a GNU extension to the Standard C++ Library.
27  */
28 
29 #ifndef _GLIBCXX_ATOMICITY_H
30 #define _GLIBCXX_ATOMICITY_H 1
31 
32 #pragma GCC system_header
33 
34 #include <bits/c++config.h>
35 #include <bits/gthr.h>
36 #include <bits/atomic_word.h>
37 
38 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
39 {
40 _GLIBCXX_BEGIN_NAMESPACE_VERSION
41 
42  // Functions for portable atomic access.
43  // To abstract locking primitives across all thread policies, use:
44  // __exchange_and_add_dispatch
45  // __atomic_add_dispatch
46 #ifdef _GLIBCXX_ATOMIC_BUILTINS
47  static inline _Atomic_word
48  __exchange_and_add(volatile _Atomic_word* __mem, int __val)
49  { return __atomic_fetch_add(__mem, __val, __ATOMIC_ACQ_REL); }
50 
51  static inline void
52  __atomic_add(volatile _Atomic_word* __mem, int __val)
53  { __atomic_fetch_add(__mem, __val, __ATOMIC_ACQ_REL); }
54 #else
55  _Atomic_word
56  __attribute__ ((__unused__))
57  __exchange_and_add(volatile _Atomic_word*, int) throw ();
58 
59  void
60  __attribute__ ((__unused__))
61  __atomic_add(volatile _Atomic_word*, int) throw ();
62 #endif
63 
64  static inline _Atomic_word
65  __exchange_and_add_single(_Atomic_word* __mem, int __val)
66  {
67  _Atomic_word __result = *__mem;
68  *__mem += __val;
69  return __result;
70  }
71 
72  static inline void
73  __atomic_add_single(_Atomic_word* __mem, int __val)
74  { *__mem += __val; }
75 
76  static inline _Atomic_word
77  __attribute__ ((__unused__))
78  __exchange_and_add_dispatch(_Atomic_word* __mem, int __val)
79  {
80 #ifdef __GTHREADS
81  if (__gthread_active_p())
82  return __exchange_and_add(__mem, __val);
83  else
84  return __exchange_and_add_single(__mem, __val);
85 #else
86  return __exchange_and_add_single(__mem, __val);
87 #endif
88  }
89 
90  static inline void
91  __attribute__ ((__unused__))
92  __atomic_add_dispatch(_Atomic_word* __mem, int __val)
93  {
94 #ifdef __GTHREADS
95  if (__gthread_active_p())
96  __atomic_add(__mem, __val);
97  else
98  __atomic_add_single(__mem, __val);
99 #else
100  __atomic_add_single(__mem, __val);
101 #endif
102  }
103 
104 _GLIBCXX_END_NAMESPACE_VERSION
105 } // namespace
106 
107 // Even if the CPU doesn't need a memory barrier, we need to ensure
108 // that the compiler doesn't reorder memory accesses across the
109 // barriers.
110 #ifndef _GLIBCXX_READ_MEM_BARRIER
111 #define _GLIBCXX_READ_MEM_BARRIER __atomic_thread_fence (__ATOMIC_ACQUIRE)
112 #endif
113 #ifndef _GLIBCXX_WRITE_MEM_BARRIER
114 #define _GLIBCXX_WRITE_MEM_BARRIER __atomic_thread_fence (__ATOMIC_RELEASE)
115 #endif
116 
117 #endif
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