atomicity.h

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00001 // Support for atomic operations -*- C++ -*-
00002 
00003 // Copyright (C) 2004, 2005, 2006, 2008, 2009 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 atomicity.h
00026  *  This is an internal header file, included by other library headers.
00027  *  You should not attempt to use it directly.
00028  */
00029 
00030 #ifndef _GLIBCXX_ATOMICITY_H
00031 #define _GLIBCXX_ATOMICITY_H    1
00032 
00033 #include <bits/c++config.h>
00034 #include <bits/gthr.h>
00035 #include <bits/atomic_word.h>
00036 
00037 _GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)
00038 
00039   // Functions for portable atomic access.
00040   // To abstract locking primitives across all thread policies, use:
00041   // __exchange_and_add_dispatch
00042   // __atomic_add_dispatch
00043 #ifdef _GLIBCXX_ATOMIC_BUILTINS_4
00044   static inline _Atomic_word 
00045   __exchange_and_add(volatile _Atomic_word* __mem, int __val)
00046   { return __sync_fetch_and_add(__mem, __val); }
00047 
00048   static inline void
00049   __atomic_add(volatile _Atomic_word* __mem, int __val)
00050   { __sync_fetch_and_add(__mem, __val); }
00051 #else
00052   _Atomic_word
00053   __attribute__ ((__unused__))
00054   __exchange_and_add(volatile _Atomic_word*, int);
00055 
00056   void
00057   __attribute__ ((__unused__))
00058   __atomic_add(volatile _Atomic_word*, int);
00059 #endif
00060 
00061   static inline _Atomic_word
00062   __exchange_and_add_single(_Atomic_word* __mem, int __val)
00063   {
00064     _Atomic_word __result = *__mem;
00065     *__mem += __val;
00066     return __result;
00067   }
00068 
00069   static inline void
00070   __atomic_add_single(_Atomic_word* __mem, int __val)
00071   { *__mem += __val; }
00072 
00073   static inline _Atomic_word
00074   __attribute__ ((__unused__))
00075   __exchange_and_add_dispatch(_Atomic_word* __mem, int __val)
00076   {
00077 #ifdef __GTHREADS
00078     if (__gthread_active_p())
00079       return __exchange_and_add(__mem, __val);
00080     else
00081       return __exchange_and_add_single(__mem, __val);
00082 #else
00083     return __exchange_and_add_single(__mem, __val);
00084 #endif
00085   }
00086 
00087   static inline void
00088   __attribute__ ((__unused__))
00089   __atomic_add_dispatch(_Atomic_word* __mem, int __val)
00090   {
00091 #ifdef __GTHREADS
00092     if (__gthread_active_p())
00093       __atomic_add(__mem, __val);
00094     else
00095       __atomic_add_single(__mem, __val);
00096 #else
00097     __atomic_add_single(__mem, __val);
00098 #endif
00099   }
00100 
00101 _GLIBCXX_END_NAMESPACE
00102 
00103 // Even if the CPU doesn't need a memory barrier, we need to ensure
00104 // that the compiler doesn't reorder memory accesses across the
00105 // barriers.
00106 #ifndef _GLIBCXX_READ_MEM_BARRIER
00107 #define _GLIBCXX_READ_MEM_BARRIER __asm __volatile ("":::"memory")
00108 #endif
00109 #ifndef _GLIBCXX_WRITE_MEM_BARRIER
00110 #define _GLIBCXX_WRITE_MEM_BARRIER __asm __volatile ("":::"memory")
00111 #endif
00112 
00113 #endif 

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