libstdc++
atomicity.h
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00001 // Support for atomic operations -*- C++ -*-
00002 
00003 // Copyright (C) 2004-2015 Free Software Foundation, Inc.
00004 //
00005 // This file is part of the GNU ISO C++ Library.  This library is free
00006 // software; you can redistribute it and/or modify it under the
00007 // terms of the GNU General Public License as published by the
00008 // Free Software Foundation; either version 3, or (at your option)
00009 // any later version.
00010 
00011 // This library is distributed in the hope that it will be useful,
00012 // but WITHOUT ANY WARRANTY; without even the implied warranty of
00013 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00014 // GNU General Public License for more details.
00015 
00016 // Under Section 7 of GPL version 3, you are granted additional
00017 // permissions described in the GCC Runtime Library Exception, version
00018 // 3.1, as published by the Free Software Foundation.
00019 
00020 // You should have received a copy of the GNU General Public License and
00021 // a copy of the GCC Runtime Library Exception along with this program;
00022 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
00023 // <http://www.gnu.org/licenses/>.
00024 
00025 /** @file ext/atomicity.h
00026  *  This file is a GNU extension to the Standard C++ Library.
00027  */
00028 
00029 #ifndef _GLIBCXX_ATOMICITY_H
00030 #define _GLIBCXX_ATOMICITY_H    1
00031 
00032 #pragma GCC system_header
00033 
00034 #include <bits/c++config.h>
00035 #include <bits/gthr.h>
00036 #include <bits/atomic_word.h>
00037 
00038 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
00039 {
00040 _GLIBCXX_BEGIN_NAMESPACE_VERSION
00041 
00042   // Functions for portable atomic access.
00043   // To abstract locking primitives across all thread policies, use:
00044   // __exchange_and_add_dispatch
00045   // __atomic_add_dispatch
00046 #ifdef _GLIBCXX_ATOMIC_BUILTINS
00047   static inline _Atomic_word 
00048   __exchange_and_add(volatile _Atomic_word* __mem, int __val)
00049   { return __atomic_fetch_add(__mem, __val, __ATOMIC_ACQ_REL); }
00050 
00051   static inline void
00052   __atomic_add(volatile _Atomic_word* __mem, int __val)
00053   { __atomic_fetch_add(__mem, __val, __ATOMIC_ACQ_REL); }
00054 #else
00055   _Atomic_word
00056   __attribute__ ((__unused__))
00057   __exchange_and_add(volatile _Atomic_word*, int) throw ();
00058 
00059   void
00060   __attribute__ ((__unused__))
00061   __atomic_add(volatile _Atomic_word*, int) throw ();
00062 #endif
00063 
00064   static inline _Atomic_word
00065   __exchange_and_add_single(_Atomic_word* __mem, int __val)
00066   {
00067     _Atomic_word __result = *__mem;
00068     *__mem += __val;
00069     return __result;
00070   }
00071 
00072   static inline void
00073   __atomic_add_single(_Atomic_word* __mem, int __val)
00074   { *__mem += __val; }
00075 
00076   static inline _Atomic_word
00077   __attribute__ ((__unused__))
00078   __exchange_and_add_dispatch(_Atomic_word* __mem, int __val)
00079   {
00080 #ifdef __GTHREADS
00081     if (__gthread_active_p())
00082       return __exchange_and_add(__mem, __val);
00083     else
00084       return __exchange_and_add_single(__mem, __val);
00085 #else
00086     return __exchange_and_add_single(__mem, __val);
00087 #endif
00088   }
00089 
00090   static inline void
00091   __attribute__ ((__unused__))
00092   __atomic_add_dispatch(_Atomic_word* __mem, int __val)
00093   {
00094 #ifdef __GTHREADS
00095     if (__gthread_active_p())
00096       __atomic_add(__mem, __val);
00097     else
00098       __atomic_add_single(__mem, __val);
00099 #else
00100     __atomic_add_single(__mem, __val);
00101 #endif
00102   }
00103 
00104 _GLIBCXX_END_NAMESPACE_VERSION
00105 } // namespace
00106 
00107 // Even if the CPU doesn't need a memory barrier, we need to ensure
00108 // that the compiler doesn't reorder memory accesses across the
00109 // barriers.
00110 #ifndef _GLIBCXX_READ_MEM_BARRIER
00111 #define _GLIBCXX_READ_MEM_BARRIER __asm __volatile ("":::"memory")
00112 #endif
00113 #ifndef _GLIBCXX_WRITE_MEM_BARRIER
00114 #define _GLIBCXX_WRITE_MEM_BARRIER __asm __volatile ("":::"memory")
00115 #endif
00116 
00117 #endif