libstdc++-v3/config/cpu/i386/atomicity.h

   1 // Low-level functions for atomic operations: x86, x >= 3 version  -*- C++ -*-
   2
   3 // Copyright (C) 2003-2017 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 #include <ext/atomicity.h>
  26
  27 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
  28 {
  29 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  30
  31   template<int __inst>
  32     struct _Atomicity_lock
  33     {
  34       static volatile _Atomic_word _S_atomicity_lock;
  35     };
  36
  37   template<int __inst>
  38   volatile _Atomic_word _Atomicity_lock<__inst>::_S_atomicity_lock = 0;
  39
  40   template volatile _Atomic_word _Atomicity_lock<0>::_S_atomicity_lock;
  41
  42   _Atomic_word
  43   __attribute__ ((__unused__))
  44   __exchange_and_add(volatile _Atomic_word* __mem, int __val) throw ()
  45   {
  46     register _Atomic_word __result, __tmp = 1;
  47
  48     // Obtain the atomic exchange/add spin lock.
  49     do
  50       {
  51         __asm__ __volatile__ ("xchg{l} {%0,%1|%1,%0}"
  52                               : "=m" (_Atomicity_lock<0>::_S_atomicity_lock),
  53                               "+r" (__tmp)
  54                               : "m" (_Atomicity_lock<0>::_S_atomicity_lock));
  55       }
  56     while (__tmp);
  57
  58     __result = *__mem;
  59     *__mem += __val;
  60
  61     // Release spin lock.
  62     _Atomicity_lock<0>::_S_atomicity_lock = 0;
  63
  64     return __result;
  65   }
  66
  67   void
  68   __attribute__ ((__unused__))
  69   __atomic_add(volatile _Atomic_word* __mem, int __val) throw ()
  70   { __exchange_and_add(__mem, __val); }
  71
  72 _GLIBCXX_END_NAMESPACE_VERSION
  73 } // namespace