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 | |
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 | |