Rewrite of likely, unlikely, barrier and ACCESS_ONCE
[urcu.git] / compiler.h
CommitLineData
af02d47e
MD
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
2dc5fa0f
MD
28#define likely() __builtin_expect(!!(x), 1)
29#define unlikely() __builtin_expect(!!(x), 0)
30
31#define barrier() asm volatile("" : : : "memory");
32
af02d47e
MD
33/*
34 * Instruct the compiler to perform only a single access to a variable
35 * (prohibits merging and refetching). The compiler is also forbidden to reorder
36 * successive instances of ACCESS_ONCE(), but only when the compiler is aware of
37 * particular ordering. Compiler ordering can be ensured, for example, by
38 * putting two ACCESS_ONCE() in separate C statements.
39 *
40 * This macro does absolutely -nothing- to prevent the CPU from reordering,
41 * merging, or refetching absolutely anything at any time. Its main intended
42 * use is to mediate communication between process-level code and irq/NMI
43 * handlers, all running on the same CPU.
44 */
2dc5fa0f 45#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&x)
af02d47e
MD
46
47#endif /* _COMPILER_H */
This page took 0.030902 seconds and 4 git commands to generate.