atomicops.h revision 5821806d5e7f356e8fa4b058a389a808ea183019 
1// Copyright 2006-2008 The RE2 Authors.  All Rights Reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5#ifndef RE2_UTIL_ATOMICOPS_H__
6#define RE2_UTIL_ATOMICOPS_H__
7
8#if defined(__i386__)
9
10static inline void WriteMemoryBarrier() {
11  int x;
12  __asm__ __volatile__("xchgl (%0),%0"  // The lock prefix is implicit for xchg.
13                       :: "r" (&x));
14}
15
16#elif defined(__x86_64__)
17
18// 64-bit implementations of memory barrier can be simpler, because
19// "sfence" is guaranteed to exist.
20static inline void WriteMemoryBarrier() {
21  __asm__ __volatile__("sfence" : : : "memory");
22}
23
24#elif defined(__ppc__)
25
26static inline void WriteMemoryBarrier() {
27  __asm__ __volatile__("eieio" : : : "memory");
28}
29
30#elif defined(__alpha__)
31
32static inline void WriteMemoryBarrier() {
33  __asm__ __volatile__("wmb" : : : "memory");
34}
35
36#else
37
38#include "util/mutex.h"
39
40static inline void WriteMemoryBarrier() {
41  // Slight overkill, but good enough:
42  // any mutex implementation must have
43  // a read barrier after the lock operation and
44  // a write barrier before the unlock operation.
45  //
46  // It may be worthwhile to write architecture-specific
47  // barriers for the common platforms, as above, but
48  // this is a correct fallback.
49  re2::Mutex mu;
50  re2::MutexLock l(&mu);
51}
52
53/*
54#error Need WriteMemoryBarrier for architecture.
55
56// Windows
57inline void WriteMemoryBarrier() {
58  LONG x;
59  ::InterlockedExchange(&x, 0);
60}
61*/
62
63#endif
64
65// Alpha has very weak memory ordering. If relying on WriteBarriers, must one
66// use read barriers for the readers too.
67#if defined(__alpha__)
68
69static inline void MaybeReadMemoryBarrier() {
70  __asm__ __volatile__("mb" : : : "memory");
71}
72
73#else
74
75static inline void MaybeReadMemoryBarrier() {}
76
77#endif // __alpha__
78
79#endif  // RE2_UTIL_ATOMICOPS_H__
80