1// Support for atomic operations -*- C++ -*-
2
3// Copyright (C) 2004-2024 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
41namespace __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