1// Support for atomic operations -*- C++ -*- 
2 
3// Copyright (C) 2004-2019 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 
38namespace __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 static inline _Atomic_word  
48 __exchange_and_add(volatile _Atomic_word* __mem, int __val) 
49 { return __atomic_fetch_add(__mem, __val, __ATOMIC_ACQ_REL); } 
50 
51 static inline void 
52 __atomic_add(volatile _Atomic_word* __mem, int __val) 
53 { __atomic_fetch_add(__mem, __val, __ATOMIC_ACQ_REL); } 
54#else 
55 _Atomic_word 
56 __attribute__ ((__unused__)) 
57 __exchange_and_add(volatile _Atomic_word*, int) throw (); 
58 
59 void 
60 __attribute__ ((__unused__)) 
61 __atomic_add(volatile _Atomic_word*, int) throw (); 
62#endif 
63 
64 static inline _Atomic_word 
65 __exchange_and_add_single(_Atomic_word* __mem, int __val) 
66 { 
67 _Atomic_word __result = *__mem; 
68 *__mem += __val; 
69 return __result; 
70 } 
71 
72 static inline void 
73 __atomic_add_single(_Atomic_word* __mem, int __val) 
74 { *__mem += __val; } 
75 
76 static inline _Atomic_word 
77 __attribute__ ((__unused__)) 
78 __exchange_and_add_dispatch(_Atomic_word* __mem, int __val) 
79 { 
80#ifdef __GTHREADS 
81 if (__gthread_active_p()) 
82 return __exchange_and_add(__mem, __val); 
83 else 
84 return __exchange_and_add_single(__mem, __val); 
85#else 
86 return __exchange_and_add_single(__mem, __val); 
87#endif 
88 } 
89 
90 static inline void 
91 __attribute__ ((__unused__)) 
92 __atomic_add_dispatch(_Atomic_word* __mem, int __val) 
93 { 
94#ifdef __GTHREADS 
95 if (__gthread_active_p()) 
96 __atomic_add(__mem, __val); 
97 else 
98 __atomic_add_single(__mem, __val); 
99#else 
100 __atomic_add_single(__mem, __val); 
101#endif 
102 } 
103 
104_GLIBCXX_END_NAMESPACE_VERSION 
105} // namespace 
106 
107// Even if the CPU doesn't need a memory barrier, we need to ensure 
108// that the compiler doesn't reorder memory accesses across the 
109// barriers. 
110#ifndef _GLIBCXX_READ_MEM_BARRIER 
111#define _GLIBCXX_READ_MEM_BARRIER __atomic_thread_fence (__ATOMIC_ACQUIRE) 
112#endif 
113#ifndef _GLIBCXX_WRITE_MEM_BARRIER 
114#define _GLIBCXX_WRITE_MEM_BARRIER __atomic_thread_fence (__ATOMIC_RELEASE) 
115#endif 
116 
117#endif  
118