fb09ca2b9b238ceec418ba5c21c660b4cebcb7fd
[urcu.git] / compiler.h
1 #ifndef _COMPILER_H
2 #define _COMPILER_H
3
4 /*
5 * compiler.h
6 *
7 * Compiler definitions.
8 *
9 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
10 *
11 * This library is free software; you can redistribute it and/or
12 * modify it under the terms of the GNU Lesser General Public
13 * License as published by the Free Software Foundation; either
14 * version 2.1 of the License, or (at your option) any later version.
15 *
16 * This library is distributed in the hope that it will be useful,
17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
19 * Lesser General Public License for more details.
20 *
21 * You should have received a copy of the GNU Lesser General Public
22 * License along with this library; if not, write to the Free Software
23 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
24 *
25 * IBM's contributions to this file may be relicensed under LGPLv2 or later.
26 */
27
28 /*
29 * Instruct the compiler to perform only a single access to a variable
30 * (prohibits merging and refetching). The compiler is also forbidden to reorder
31 * successive instances of ACCESS_ONCE(), but only when the compiler is aware of
32 * particular ordering. Compiler ordering can be ensured, for example, by
33 * putting two ACCESS_ONCE() in separate C statements.
34 *
35 * This macro does absolutely -nothing- to prevent the CPU from reordering,
36 * merging, or refetching absolutely anything at any time. Its main intended
37 * use is to mediate communication between process-level code and irq/NMI
38 * handlers, all running on the same CPU.
39 */
40
41 #endif /* _COMPILER_H */
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