1 // Support for atomic operations -*- C++ -*-
2
3 // Copyright (C) 2004-2020 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
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 inline _Atomic_word
48 __attribute__((__always_inline__))
49 __exchange_and_add(volatile _Atomic_word* __mem, int __val)
50 { return __atomic_fetch_add(__mem, __val, __ATOMIC_ACQ_REL); }
51
52 inline void
53 __attribute__((__always_inline__))
54 __atomic_add(volatile _Atomic_word* __mem, int __val)
55 { __atomic_fetch_add(__mem, __val, __ATOMIC_ACQ_REL); }
56 #else
57 _Atomic_word
58 __exchange_and_add(volatile _Atomic_word*, int) _GLIBCXX_NOTHROW;
59
60 void
61 __atomic_add(volatile _Atomic_word*, int) _GLIBCXX_NOTHROW;
62 #endif
63
64 inline _Atomic_word
65 __attribute__((__always_inline__))
66 __exchange_and_add_single(_Atomic_word* __mem, int __val)
67 {
68 _Atomic_word __result = *__mem;
69 *__mem += __val;
70 return __result;
71 }
72
73 inline void
74 __attribute__((__always_inline__))
75 __atomic_add_single(_Atomic_word* __mem, int __val)
76 { *__mem += __val; }
77
78 inline _Atomic_word
79 __attribute__ ((__always_inline__))
80 __exchange_and_add_dispatch(_Atomic_word* __mem, int __val)
81 {
82 #ifdef __GTHREADS
83 if (__gthread_active_p())
84 return __exchange_and_add(__mem, __val);
85 #endif
86 return __exchange_and_add_single(__mem, __val);
87 }
88
89 inline void
90 __attribute__ ((__always_inline__))
91 __atomic_add_dispatch(_Atomic_word* __mem, int __val)
92 {
93 #ifdef __GTHREADS
94 if (__gthread_active_p())
95 {
96 __atomic_add(__mem, __val);
97 return;
98 }
99 #endif
100 __atomic_add_single(__mem, __val);
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 __atomic_thread_fence (__ATOMIC_ACQUIRE)
111 #endif
112 #ifndef _GLIBCXX_WRITE_MEM_BARRIER
113 #define _GLIBCXX_WRITE_MEM_BARRIER __atomic_thread_fence (__ATOMIC_RELEASE)
114 #endif
115
116 #endif
117