1  // Low-level functions for atomic operations: x86, x >= 3 version  -*- C++ -*-
       2  
       3  // Copyright (C) 2003-2023 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