1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
|
// Copyright (c) 2011 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// For atomic operations on reference counts, see atomic_refcount.h.
// For atomic operations on sequence numbers, see atomic_sequence_num.h.
// The routines exported by this module are subtle. If you use them, even if
// you get the code right, it will depend on careful reasoning about atomicity
// and memory ordering; it will be less readable, and harder to maintain. If
// you plan to use these routines, you should have a good reason, such as solid
// evidence that performance would otherwise suffer, or there being no
// alternative. You should assume only properties explicitly guaranteed by the
// specifications in this file. You are almost certainly _not_ writing code
// just for the x86; if you assume x86 semantics, x86 hardware bugs and
// implementations on other archtectures will cause your code to break. If you
// do not know what you are doing, avoid these routines, and use a Mutex.
//
// It is incorrect to make direct assignments to/from an atomic variable.
// You should use one of the Load or Store routines. The NoBarrier
// versions are provided when no barriers are needed:
// NoBarrier_Store()
// NoBarrier_Load()
// Although there are currently no compiler enforcement, you are encouraged
// to use these.
//
#ifndef BASE_ATOMICOPS_H_
#define BASE_ATOMICOPS_H_
#pragma once
#include "base/basictypes.h"
#include "build/build_config.h"
namespace base {
namespace subtle {
typedef int32 Atomic32;
#ifdef ARCH_CPU_64_BITS
// We need to be able to go between Atomic64 and AtomicWord implicitly. This
// means Atomic64 and AtomicWord should be the same type on 64-bit.
#if defined(OS_NACL)
// NaCl's intptr_t is not actually 64-bits on 64-bit!
// http://code.google.com/p/nativeclient/issues/detail?id=1162
typedef int64_t Atomic64;
#else
typedef intptr_t Atomic64;
#endif
#endif
// Use AtomicWord for a machine-sized pointer. It will use the Atomic32 or
// Atomic64 routines below, depending on your architecture.
typedef intptr_t AtomicWord;
// Atomically execute:
// result = *ptr;
// if (*ptr == old_value)
// *ptr = new_value;
// return result;
//
// I.e., replace "*ptr" with "new_value" if "*ptr" used to be "old_value".
// Always return the old value of "*ptr"
//
// This routine implies no memory barriers.
Atomic32 NoBarrier_CompareAndSwap(volatile Atomic32* ptr,
Atomic32 old_value,
Atomic32 new_value);
// Atomically store new_value into *ptr, returning the previous value held in
// *ptr. This routine implies no memory barriers.
Atomic32 NoBarrier_AtomicExchange(volatile Atomic32* ptr, Atomic32 new_value);
// Atomically increment *ptr by "increment". Returns the new value of
// *ptr with the increment applied. This routine implies no memory barriers.
Atomic32 NoBarrier_AtomicIncrement(volatile Atomic32* ptr, Atomic32 increment);
Atomic32 Barrier_AtomicIncrement(volatile Atomic32* ptr,
Atomic32 increment);
// These following lower-level operations are typically useful only to people
// implementing higher-level synchronization operations like spinlocks,
// mutexes, and condition-variables. They combine CompareAndSwap(), a load, or
// a store with appropriate memory-ordering instructions. "Acquire" operations
// ensure that no later memory access can be reordered ahead of the operation.
// "Release" operations ensure that no previous memory access can be reordered
// after the operation. "Barrier" operations have both "Acquire" and "Release"
// semantics. A MemoryBarrier() has "Barrier" semantics, but does no memory
// access.
Atomic32 Acquire_CompareAndSwap(volatile Atomic32* ptr,
Atomic32 old_value,
Atomic32 new_value);
Atomic32 Release_CompareAndSwap(volatile Atomic32* ptr,
Atomic32 old_value,
Atomic32 new_value);
void MemoryBarrier();
void NoBarrier_Store(volatile Atomic32* ptr, Atomic32 value);
void Acquire_Store(volatile Atomic32* ptr, Atomic32 value);
void Release_Store(volatile Atomic32* ptr, Atomic32 value);
Atomic32 NoBarrier_Load(volatile const Atomic32* ptr);
Atomic32 Acquire_Load(volatile const Atomic32* ptr);
Atomic32 Release_Load(volatile const Atomic32* ptr);
// 64-bit atomic operations (only available on 64-bit processors).
#ifdef ARCH_CPU_64_BITS
Atomic64 NoBarrier_CompareAndSwap(volatile Atomic64* ptr,
Atomic64 old_value,
Atomic64 new_value);
Atomic64 NoBarrier_AtomicExchange(volatile Atomic64* ptr, Atomic64 new_value);
Atomic64 NoBarrier_AtomicIncrement(volatile Atomic64* ptr, Atomic64 increment);
Atomic64 Barrier_AtomicIncrement(volatile Atomic64* ptr, Atomic64 increment);
Atomic64 Acquire_CompareAndSwap(volatile Atomic64* ptr,
Atomic64 old_value,
Atomic64 new_value);
Atomic64 Release_CompareAndSwap(volatile Atomic64* ptr,
Atomic64 old_value,
Atomic64 new_value);
void NoBarrier_Store(volatile Atomic64* ptr, Atomic64 value);
void Acquire_Store(volatile Atomic64* ptr, Atomic64 value);
void Release_Store(volatile Atomic64* ptr, Atomic64 value);
Atomic64 NoBarrier_Load(volatile const Atomic64* ptr);
Atomic64 Acquire_Load(volatile const Atomic64* ptr);
Atomic64 Release_Load(volatile const Atomic64* ptr);
#endif // ARCH_CPU_64_BITS
} // namespace base::subtle
} // namespace base
// Include our platform specific implementation.
#if defined(OS_WIN) && defined(COMPILER_MSVC) && defined(ARCH_CPU_X86_FAMILY)
#include "base/atomicops_internals_x86_msvc.h"
#elif defined(OS_MACOSX) && defined(ARCH_CPU_X86_FAMILY)
#include "base/atomicops_internals_x86_macosx.h"
#elif defined(COMPILER_GCC) && defined(ARCH_CPU_X86_FAMILY)
#include "base/atomicops_internals_x86_gcc.h"
#elif defined(COMPILER_GCC) && defined(ARCH_CPU_ARM_FAMILY)
#include "base/atomicops_internals_arm_gcc.h"
#else
#error "Atomic operations are not supported on your platform"
#endif
// On some platforms we need additional declarations to make
// AtomicWord compatible with our other Atomic* types.
#if defined(OS_MACOSX) || defined(OS_OPENBSD)
#include "base/atomicops_internals_atomicword_compat.h"
#endif
#endif // BASE_ATOMICOPS_H_
|
