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 
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