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1 // Copyright (c) 2014 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, use atomicops.h instead. | |
6 // | |
7 // This implementation uses C++11 atomics' member functions. The code base is | |
8 // currently written assuming atomicity revolves around accesses instead of | |
9 // C++11's memory locations. The burden is on the programmer to ensure that all | |
10 // memory locations accessed atomically are never accessed non-atomically (tsan | |
11 // should help with this). | |
12 // | |
13 // TODO(jfb) Modify the atomicops.h API and user code to declare atomic | |
14 // locations as truly atomic. See the static_assert below. | |
15 // | |
16 // Of note in this implementation: | |
17 // * All NoBarrier variants are implemented as relaxed. | |
18 // * All Barrier variants are implemented as sequentially-consistent. | |
19 // * Compare exchange's failure ordering is always the same as the success one | |
20 // (except for release, which fails as relaxed): using a weaker ordering is | |
21 // only valid under certain uses of compare exchange. | |
22 // * Acquire store doesn't exist in the C11 memory model, it is instead | |
23 // implemented as a relaxed store followed by a sequentially consistent | |
24 // fence. | |
25 // * Release load doesn't exist in the C11 memory model, it is instead | |
26 // implemented as sequentially consistent fence followed by a relaxed load. | |
27 // * Atomic increment is expected to return the post-incremented value, whereas | |
28 // C11 fetch add returns the previous value. The implementation therefore | |
29 // needs to increment twice (which the compiler should be able to detect and | |
30 // optimize). | |
31 | |
32 #ifndef BASE_ATOMICOPS_INTERNALS_PORTABLE_H_ | |
33 #define BASE_ATOMICOPS_INTERNALS_PORTABLE_H_ | |
34 | |
35 #include <atomic> | |
36 | |
37 namespace base { | |
38 namespace subtle { | |
39 | |
40 // This implementation is transitional and maintains the original API for | |
41 // atomicops.h. This requires casting memory locations to the atomic types, and | |
42 // assumes that the API and the C++11 implementation are layout-compatible, | |
43 // which isn't true for all implementations or hardware platforms. The static | |
44 // assertion should detect this issue, were it to fire then this header | |
45 // shouldn't be used. | |
46 // | |
47 // TODO(jfb) If this header manages to stay committed then the API should be | |
48 // modified, and all call sites updated. | |
49 typedef volatile std::atomic<Atomic32>* AtomicLocation32; | |
50 static_assert(sizeof(*(AtomicLocation32) nullptr) == sizeof(Atomic32), | |
51 "incompatible 32-bit atomic layout"); | |
52 | |
53 inline void MemoryBarrier() { | |
54 #if defined(__GLIBCXX__) | |
55 // Work around libstdc++ bug 51038 where atomic_thread_fence was declared but | |
56 // not defined, leading to the linker complaining about undefined references. | |
57 __atomic_thread_fence(std::memory_order_seq_cst); | |
58 #else | |
59 std::atomic_thread_fence(std::memory_order_seq_cst); | |
60 #endif | |
61 } | |
62 | |
63 inline Atomic32 NoBarrier_CompareAndSwap(volatile Atomic32* ptr, | |
64 Atomic32 old_value, | |
65 Atomic32 new_value) { | |
66 ((AtomicLocation32)ptr) | |
67 ->compare_exchange_strong(old_value, | |
68 new_value, | |
69 std::memory_order_relaxed, | |
70 std::memory_order_relaxed); | |
71 return old_value; | |
72 } | |
73 | |
74 inline Atomic32 NoBarrier_AtomicExchange(volatile Atomic32* ptr, | |
75 Atomic32 new_value) { | |
76 return ((AtomicLocation32)ptr) | |
77 ->exchange(new_value, std::memory_order_relaxed); | |
78 } | |
79 | |
80 inline Atomic32 NoBarrier_AtomicIncrement(volatile Atomic32* ptr, | |
81 Atomic32 increment) { | |
82 return increment + | |
83 ((AtomicLocation32)ptr) | |
84 ->fetch_add(increment, std::memory_order_relaxed); | |
85 } | |
86 | |
87 inline Atomic32 Barrier_AtomicIncrement(volatile Atomic32* ptr, | |
88 Atomic32 increment) { | |
89 return increment + ((AtomicLocation32)ptr)->fetch_add(increment); | |
90 } | |
91 | |
92 inline Atomic32 Acquire_CompareAndSwap(volatile Atomic32* ptr, | |
93 Atomic32 old_value, | |
94 Atomic32 new_value) { | |
95 ((AtomicLocation32)ptr) | |
96 ->compare_exchange_strong(old_value, | |
97 new_value, | |
98 std::memory_order_acquire, | |
99 std::memory_order_acquire); | |
100 return old_value; | |
101 } | |
102 | |
103 inline Atomic32 Release_CompareAndSwap(volatile Atomic32* ptr, | |
104 Atomic32 old_value, | |
105 Atomic32 new_value) { | |
106 ((AtomicLocation32)ptr) | |
107 ->compare_exchange_strong(old_value, | |
108 new_value, | |
109 std::memory_order_release, | |
110 std::memory_order_relaxed); | |
111 return old_value; | |
112 } | |
113 | |
114 inline void NoBarrier_Store(volatile Atomic32* ptr, Atomic32 value) { | |
115 ((AtomicLocation32)ptr)->store(value, std::memory_order_relaxed); | |
116 } | |
117 | |
118 inline void Acquire_Store(volatile Atomic32* ptr, Atomic32 value) { | |
119 ((AtomicLocation32)ptr)->store(value, std::memory_order_relaxed); | |
120 MemoryBarrier(); | |
121 } | |
122 | |
123 inline void Release_Store(volatile Atomic32* ptr, Atomic32 value) { | |
124 ((AtomicLocation32)ptr)->store(value, std::memory_order_release); | |
125 } | |
126 | |
127 inline Atomic32 NoBarrier_Load(volatile const Atomic32* ptr) { | |
128 return ((AtomicLocation32)ptr)->load(std::memory_order_relaxed); | |
129 } | |
130 | |
131 inline Atomic32 Acquire_Load(volatile const Atomic32* ptr) { | |
132 return ((AtomicLocation32)ptr)->load(std::memory_order_acquire); | |
133 } | |
134 | |
135 inline Atomic32 Release_Load(volatile const Atomic32* ptr) { | |
136 MemoryBarrier(); | |
137 return ((AtomicLocation32)ptr)->load(std::memory_order_relaxed); | |
138 } | |
139 | |
140 #ifdef ARCH_CPU_64_BITS | |
willchan no longer on Chromium
2014/10/13 17:42:22
Any reason not to use defined() instead?
JF
2014/10/13 17:51:59
Done, I was following what the other files did.
| |
141 | |
142 typedef volatile std::atomic<Atomic64>* AtomicLocation64; | |
143 static_assert(sizeof(*(AtomicLocation64) nullptr) == sizeof(Atomic64), | |
144 "incompatible 64-bit atomic layout"); | |
145 | |
146 inline Atomic64 NoBarrier_CompareAndSwap(volatile Atomic64* ptr, | |
147 Atomic64 old_value, | |
148 Atomic64 new_value) { | |
149 ((AtomicLocation64)ptr) | |
150 ->compare_exchange_strong(old_value, | |
151 new_value, | |
152 std::memory_order_relaxed, | |
153 std::memory_order_relaxed); | |
154 return old_value; | |
155 } | |
156 | |
157 inline Atomic64 NoBarrier_AtomicExchange(volatile Atomic64* ptr, | |
158 Atomic64 new_value) { | |
159 return ((AtomicLocation64)ptr) | |
160 ->exchange(new_value, std::memory_order_relaxed); | |
161 } | |
162 | |
163 inline Atomic64 NoBarrier_AtomicIncrement(volatile Atomic64* ptr, | |
164 Atomic64 increment) { | |
165 return increment + | |
166 ((AtomicLocation64)ptr) | |
167 ->fetch_add(increment, std::memory_order_relaxed); | |
168 } | |
169 | |
170 inline Atomic64 Barrier_AtomicIncrement(volatile Atomic64* ptr, | |
171 Atomic64 increment) { | |
172 return increment + ((AtomicLocation64)ptr)->fetch_add(increment); | |
173 } | |
174 | |
175 inline Atomic64 Acquire_CompareAndSwap(volatile Atomic64* ptr, | |
176 Atomic64 old_value, | |
177 Atomic64 new_value) { | |
178 ((AtomicLocation64)ptr) | |
179 ->compare_exchange_strong(old_value, | |
180 new_value, | |
181 std::memory_order_acquire, | |
182 std::memory_order_acquire); | |
183 return old_value; | |
184 } | |
185 | |
186 inline Atomic64 Release_CompareAndSwap(volatile Atomic64* ptr, | |
187 Atomic64 old_value, | |
188 Atomic64 new_value) { | |
189 ((AtomicLocation64)ptr) | |
190 ->compare_exchange_strong(old_value, | |
191 new_value, | |
192 std::memory_order_release, | |
193 std::memory_order_relaxed); | |
194 return old_value; | |
195 } | |
196 | |
197 inline void NoBarrier_Store(volatile Atomic64* ptr, Atomic64 value) { | |
198 ((AtomicLocation64)ptr)->store(value, std::memory_order_relaxed); | |
199 } | |
200 | |
201 inline void Acquire_Store(volatile Atomic64* ptr, Atomic64 value) { | |
202 ((AtomicLocation64)ptr)->store(value, std::memory_order_relaxed); | |
203 MemoryBarrier(); | |
204 } | |
205 | |
206 inline void Release_Store(volatile Atomic64* ptr, Atomic64 value) { | |
207 ((AtomicLocation64)ptr)->store(value, std::memory_order_release); | |
208 } | |
209 | |
210 inline Atomic64 NoBarrier_Load(volatile const Atomic64* ptr) { | |
211 return ((AtomicLocation64)ptr)->load(std::memory_order_relaxed); | |
212 } | |
213 | |
214 inline Atomic64 Acquire_Load(volatile const Atomic64* ptr) { | |
215 return ((AtomicLocation64)ptr)->load(std::memory_order_acquire); | |
216 } | |
217 | |
218 inline Atomic64 Release_Load(volatile const Atomic64* ptr) { | |
219 MemoryBarrier(); | |
220 return ((AtomicLocation64)ptr)->load(std::memory_order_relaxed); | |
221 } | |
222 | |
223 #endif // ARCH_CPU_64_BITS | |
224 } | |
225 } // namespace base::subtle | |
226 | |
227 #endif // BASE_ATOMICOPS_INTERNALS_PORTABLE_H_ | |
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