1 // Support for atomic operations -*- C++ -*-
2
3 // Copyright (C) 2004-2018 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
_GLIBCXX_VISIBILITY(default)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
118