1// Low-level functions for atomic operations: x86, x >= 3 version  -*- C++ -*-
2
3// Copyright (C) 2003, 2004, 2005 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 2, 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// You should have received a copy of the GNU General Public License along
17// with this library; see the file COPYING.  If not, write to the Free
18// Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
19// USA.
20
21// As a special exception, you may use this file as part of a free software
22// library without restriction.  Specifically, if other files instantiate
23// templates or use macros or inline functions from this file, or you compile
24// this file and link it with other files to produce an executable, this
25// file does not by itself cause the resulting executable to be covered by
26// the GNU General Public License.  This exception does not however
27// invalidate any other reasons why the executable file might be covered by
28// the GNU General Public License.
29
30#include <ext/atomicity.h>
31
32_GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)
33
34  template<int __inst>
35    struct _Atomicity_lock
36    {
37      static volatile _Atomic_word _S_atomicity_lock;
38    };
39
40  template<int __inst>
41  volatile _Atomic_word _Atomicity_lock<__inst>::_S_atomicity_lock = 0;
42
43  template volatile _Atomic_word _Atomicity_lock<0>::_S_atomicity_lock;
44
45  _Atomic_word
46  __attribute__ ((__unused__))
47  __exchange_and_add(volatile _Atomic_word* __mem, int __val)
48  {
49    register _Atomic_word __result, __tmp = 1;
50
51    // Obtain the atomic exchange/add spin lock.
52    do
53      {
54	__asm__ __volatile__ ("xchg{l} {%0,%1|%1,%0}"
55			      : "=m" (_Atomicity_lock<0>::_S_atomicity_lock),
56			      "+r" (__tmp)
57			      : "m" (_Atomicity_lock<0>::_S_atomicity_lock));
58      }
59    while (__tmp);
60
61    __result = *__mem;
62    *__mem += __val;
63
64    // Release spin lock.
65    _Atomicity_lock<0>::_S_atomicity_lock = 0;
66
67    return __result;
68  }
69
70  void
71  __attribute__ ((__unused__))
72  __atomic_add(volatile _Atomic_word* __mem, int __val)
73  { __exchange_and_add(__mem, __val); }
74
75_GLIBCXX_END_NAMESPACE
76