1// Low-level functions for atomic operations: x86, x >= 3 version  -*- C++ -*-
2
3// Copyright (C) 2003, 2004, 2005, 2009 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_GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)
28
29  template<int __inst>
30    struct _Atomicity_lock
31    {
32      static volatile _Atomic_word _S_atomicity_lock;
33    };
34
35  template<int __inst>
36  volatile _Atomic_word _Atomicity_lock<__inst>::_S_atomicity_lock = 0;
37
38  template volatile _Atomic_word _Atomicity_lock<0>::_S_atomicity_lock;
39
40  _Atomic_word
41  __attribute__ ((__unused__))
42  __exchange_and_add(volatile _Atomic_word* __mem, int __val) throw ()
43  {
44    register _Atomic_word __result, __tmp = 1;
45
46    // Obtain the atomic exchange/add spin lock.
47    do
48      {
49	__asm__ __volatile__ ("xchg{l} {%0,%1|%1,%0}"
50			      : "=m" (_Atomicity_lock<0>::_S_atomicity_lock),
51			      "+r" (__tmp)
52			      : "m" (_Atomicity_lock<0>::_S_atomicity_lock));
53      }
54    while (__tmp);
55
56    __result = *__mem;
57    *__mem += __val;
58
59    // Release spin lock.
60    _Atomicity_lock<0>::_S_atomicity_lock = 0;
61
62    return __result;
63  }
64
65  void
66  __attribute__ ((__unused__))
67  __atomic_add(volatile _Atomic_word* __mem, int __val) throw ()
68  { __exchange_and_add(__mem, __val); }
69
70_GLIBCXX_END_NAMESPACE
71