1 // Support for atomic operations -*- C++ -*-
2 
3 // Copyright (C) 2004-2018 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 
_GLIBCXX_VISIBILITY(default)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