libstdc++-v3/include/ext/atomicity.h

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