1 // Support for atomic operations -*- C++ -*-
2
3 // Copyright (C) 2004-2021 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 #if __has_include(<sys/single_threaded.h>)
38 # include <sys/single_threaded.h>
39 #endif
40
_GLIBCXX_VISIBILITY(default)41 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
42 {
43 _GLIBCXX_BEGIN_NAMESPACE_VERSION
44
45 __attribute__((__always_inline__))
46 inline bool
47 __is_single_threaded() _GLIBCXX_NOTHROW
48 {
49 #ifndef __GTHREADS
50 return true;
51 #elif __has_include(<sys/single_threaded.h>)
52 return ::__libc_single_threaded;
53 #else
54 return !__gthread_active_p();
55 #endif
56 }
57
58 // Functions for portable atomic access.
59 // To abstract locking primitives across all thread policies, use:
60 // __exchange_and_add_dispatch
61 // __atomic_add_dispatch
62 #ifdef _GLIBCXX_ATOMIC_BUILTINS
63 inline _Atomic_word
64 __attribute__((__always_inline__))
65 __exchange_and_add(volatile _Atomic_word* __mem, int __val)
66 { return __atomic_fetch_add(__mem, __val, __ATOMIC_ACQ_REL); }
67
68 inline void
69 __attribute__((__always_inline__))
70 __atomic_add(volatile _Atomic_word* __mem, int __val)
71 { __atomic_fetch_add(__mem, __val, __ATOMIC_ACQ_REL); }
72 #else
73 _Atomic_word
74 __exchange_and_add(volatile _Atomic_word*, int) _GLIBCXX_NOTHROW;
75
76 void
77 __atomic_add(volatile _Atomic_word*, int) _GLIBCXX_NOTHROW;
78 #endif
79
80 inline _Atomic_word
81 __attribute__((__always_inline__))
82 __exchange_and_add_single(_Atomic_word* __mem, int __val)
83 {
84 _Atomic_word __result = *__mem;
85 *__mem += __val;
86 return __result;
87 }
88
89 inline void
90 __attribute__((__always_inline__))
91 __atomic_add_single(_Atomic_word* __mem, int __val)
92 { *__mem += __val; }
93
94 inline _Atomic_word
95 __attribute__ ((__always_inline__))
96 __exchange_and_add_dispatch(_Atomic_word* __mem, int __val)
97 {
98 if (__is_single_threaded())
99 return __exchange_and_add_single(__mem, __val);
100 else
101 return __exchange_and_add(__mem, __val);
102 }
103
104 inline void
105 __attribute__ ((__always_inline__))
106 __atomic_add_dispatch(_Atomic_word* __mem, int __val)
107 {
108 if (__is_single_threaded())
109 __atomic_add_single(__mem, __val);
110 else
111 __atomic_add(__mem, __val);
112 }
113
114 _GLIBCXX_END_NAMESPACE_VERSION
115 } // namespace
116
117 // Even if the CPU doesn't need a memory barrier, we need to ensure
118 // that the compiler doesn't reorder memory accesses across the
119 // barriers.
120 #ifndef _GLIBCXX_READ_MEM_BARRIER
121 #define _GLIBCXX_READ_MEM_BARRIER __atomic_thread_fence (__ATOMIC_ACQUIRE)
122 #endif
123 #ifndef _GLIBCXX_WRITE_MEM_BARRIER
124 #define _GLIBCXX_WRITE_MEM_BARRIER __atomic_thread_fence (__ATOMIC_RELEASE)
125 #endif
126
127 #endif
128