atomicity.h source code [include/c++/7/ext/atomicity.h]

1	// Support for atomic operations -- C++ --
2
3	// Copyright (C) 2004-2017 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
38	namespace __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

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