1// Copyright (c) 2009 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5// This file is an internal atomic implementation, include base/atomicops.h
6// instead. This file is for platforms that use GCC intrinsics rather than
7// platform-specific assembly code for atomic operations.
8
9#ifndef BASE_ATOMICOPS_INTERNALS_GCC_H_
10#define BASE_ATOMICOPS_INTERNALS_GCC_H_
11
12namespace base {
13namespace subtle {
14
15inline Atomic32 NoBarrier_CompareAndSwap(volatile Atomic32* ptr,
16                                         Atomic32 old_value,
17                                         Atomic32 new_value) {
18  Atomic32 prev_value;
19  do {
20    if (__sync_bool_compare_and_swap(ptr, old_value, new_value))
21      return old_value;
22    prev_value = *ptr;
23  } while (prev_value == old_value);
24  return prev_value;
25}
26
27inline Atomic32 NoBarrier_AtomicExchange(volatile Atomic32* ptr,
28                                         Atomic32 new_value) {
29  Atomic32 old_value;
30  do {
31    old_value = *ptr;
32  } while (!__sync_bool_compare_and_swap(ptr, old_value, new_value));
33  return old_value;
34}
35
36inline Atomic32 NoBarrier_AtomicIncrement(volatile Atomic32* ptr,
37                                          Atomic32 increment) {
38  return Barrier_AtomicIncrement(ptr, increment);
39}
40
41inline Atomic32 Barrier_AtomicIncrement(volatile Atomic32* ptr,
42                                        Atomic32 increment) {
43  for (;;) {
44    // Atomic exchange the old value with an incremented one.
45    Atomic32 old_value = *ptr;
46    Atomic32 new_value = old_value + increment;
47    if (__sync_bool_compare_and_swap(ptr, old_value, new_value)) {
48      // The exchange took place as expected.
49      return new_value;
50    }
51    // Otherwise, *ptr changed mid-loop and we need to retry.
52  }
53}
54
55inline Atomic32 Acquire_CompareAndSwap(volatile Atomic32* ptr,
56                                       Atomic32 old_value,
57                                       Atomic32 new_value) {
58  // Since NoBarrier_CompareAndSwap uses __sync_bool_compare_and_swap, which
59  // is a full memory barrier, none is needed here or below in Release.
60  return NoBarrier_CompareAndSwap(ptr, old_value, new_value);
61}
62
63inline Atomic32 Release_CompareAndSwap(volatile Atomic32* ptr,
64                                       Atomic32 old_value,
65                                       Atomic32 new_value) {
66  return NoBarrier_CompareAndSwap(ptr, old_value, new_value);
67}
68
69inline void NoBarrier_Store(volatile Atomic32* ptr, Atomic32 value) {
70  *ptr = value;
71}
72
73inline void MemoryBarrier() {
74  __sync_synchronize();
75}
76
77inline void Acquire_Store(volatile Atomic32* ptr, Atomic32 value) {
78  *ptr = value;
79  MemoryBarrier();
80}
81
82inline void Release_Store(volatile Atomic32* ptr, Atomic32 value) {
83  MemoryBarrier();
84  *ptr = value;
85}
86
87inline Atomic32 NoBarrier_Load(volatile const Atomic32* ptr) {
88  return *ptr;
89}
90
91inline Atomic32 Acquire_Load(volatile const Atomic32* ptr) {
92  Atomic32 value = *ptr;
93  MemoryBarrier();
94  return value;
95}
96
97inline Atomic32 Release_Load(volatile const Atomic32* ptr) {
98  MemoryBarrier();
99  return *ptr;
100}
101
102}  // namespace base::subtle
103}  // namespace base
104
105#endif  // BASE_ATOMICOPS_INTERNALS_GCC_H_
106
107