libstdc++
atomicity.h
Go to the documentation of this file.
1 // Support for atomic operations -*- C++ -*-
2 
3 // Copyright (C) 2004, 2005, 2006, 2008, 2009, 2010
4 // Free Software Foundation, Inc.
5 //
6 // This file is part of the GNU ISO C++ Library. This library is free
7 // software; you can redistribute it and/or modify it under the
8 // terms of the GNU General Public License as published by the
9 // Free Software Foundation; either version 3, or (at your option)
10 // any later version.
11 
12 // This library is distributed in the hope that it will be useful,
13 // but WITHOUT ANY WARRANTY; without even the implied warranty of
14 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 // GNU General Public License for more details.
16 
17 // Under Section 7 of GPL version 3, you are granted additional
18 // permissions described in the GCC Runtime Library Exception, version
19 // 3.1, as published by the Free Software Foundation.
20 
21 // You should have received a copy of the GNU General Public License and
22 // a copy of the GCC Runtime Library Exception along with this program;
23 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
24 // <http://www.gnu.org/licenses/>.
25 
26 /** @file ext/atomicity.h
27  * This file is a GNU extension to the Standard C++ Library.
28  */
29 
30 #ifndef _GLIBCXX_ATOMICITY_H
31 #define _GLIBCXX_ATOMICITY_H 1
32 
33 #include <bits/c++config.h>
34 #include <bits/gthr.h>
35 #include <bits/atomic_word.h>
36 
37 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
38 {
39 _GLIBCXX_BEGIN_NAMESPACE_VERSION
40 
41  // Functions for portable atomic access.
42  // To abstract locking primitives across all thread policies, use:
43  // __exchange_and_add_dispatch
44  // __atomic_add_dispatch
45 #ifdef _GLIBCXX_ATOMIC_BUILTINS_4
46  static inline _Atomic_word
47  __exchange_and_add(volatile _Atomic_word* __mem, int __val)
48  { return __sync_fetch_and_add(__mem, __val); }
49 
50  static inline void
51  __atomic_add(volatile _Atomic_word* __mem, int __val)
52  { __sync_fetch_and_add(__mem, __val); }
53 #else
54  _Atomic_word
55  __attribute__ ((__unused__))
56  __exchange_and_add(volatile _Atomic_word*, int) throw ();
57 
58  void
59  __attribute__ ((__unused__))
60  __atomic_add(volatile _Atomic_word*, int) throw ();
61 #endif
62 
63  static inline _Atomic_word
64  __exchange_and_add_single(_Atomic_word* __mem, int __val)
65  {
66  _Atomic_word __result = *__mem;
67  *__mem += __val;
68  return __result;
69  }
70 
71  static inline void
72  __atomic_add_single(_Atomic_word* __mem, int __val)
73  { *__mem += __val; }
74 
75  static inline _Atomic_word
76  __attribute__ ((__unused__))
77  __exchange_and_add_dispatch(_Atomic_word* __mem, int __val)
78  {
79 #ifdef __GTHREADS
80  if (__gthread_active_p())
81  return __exchange_and_add(__mem, __val);
82  else
83  return __exchange_and_add_single(__mem, __val);
84 #else
85  return __exchange_and_add_single(__mem, __val);
86 #endif
87  }
88 
89  static inline void
90  __attribute__ ((__unused__))
91  __atomic_add_dispatch(_Atomic_word* __mem, int __val)
92  {
93 #ifdef __GTHREADS
94  if (__gthread_active_p())
95  __atomic_add(__mem, __val);
96  else
97  __atomic_add_single(__mem, __val);
98 #else
99  __atomic_add_single(__mem, __val);
100 #endif
101  }
102 
103 _GLIBCXX_END_NAMESPACE_VERSION
104 } // namespace
105 
106 // Even if the CPU doesn't need a memory barrier, we need to ensure
107 // that the compiler doesn't reorder memory accesses across the
108 // barriers.
109 #ifndef _GLIBCXX_READ_MEM_BARRIER
110 #define _GLIBCXX_READ_MEM_BARRIER __asm __volatile ("":::"memory")
111 #endif
112 #ifndef _GLIBCXX_WRITE_MEM_BARRIER
113 #define _GLIBCXX_WRITE_MEM_BARRIER __asm __volatile ("":::"memory")
114 #endif
115 
116 #endif