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1 /* | 1 /* |
2 * Copyright 2014 Google Inc. | 2 * Copyright 2014 Google Inc. |
3 * | 3 * |
4 * Use of this source code is governed by a BSD-style license that can be | 4 * Use of this source code is governed by a BSD-style license that can be |
5 * found in the LICENSE file. | 5 * found in the LICENSE file. |
6 */ | 6 */ |
7 | 7 |
8 #ifndef SkLazyPtr_DEFINED | 8 #ifndef SkLazyPtr_DEFINED |
9 #define SkLazyPtr_DEFINED | 9 #define SkLazyPtr_DEFINED |
10 | 10 |
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96 // _through_ our atomically set pointer, there is a data dependency between our | 96 // _through_ our atomically set pointer, there is a data dependency between our |
97 // atomic and the guarded data, and so we only need writer-releases / | 97 // atomic and the guarded data, and so we only need writer-releases / |
98 // reader-consumes memory pairing rather than the more general write-releases / | 98 // reader-consumes memory pairing rather than the more general write-releases / |
99 // reader-acquires convention. | 99 // reader-acquires convention. |
100 // | 100 // |
101 // This is nice, because a consume load is free on all our platforms: x86, | 101 // This is nice, because a consume load is free on all our platforms: x86, |
102 // ARM, MIPS. In contrast, an acquire load issues a memory barrier on non-x86. | 102 // ARM, MIPS. In contrast, an acquire load issues a memory barrier on non-x86. |
103 | 103 |
104 template <typename T> | 104 template <typename T> |
105 T consume_load(T* ptr) { | 105 T consume_load(T* ptr) { |
106 #if DYNAMIC_ANNOTATIONS_ENABLED | 106 #if defined(THREAD_SANITIZER) |
107 // TSAN gets anxious if we don't tell it what we're actually doing, a consum
e load. | 107 // TSAN gets anxious if we don't tell it what we're actually doing, a consum
e load. |
108 return sk_atomic_load(ptr, sk_memory_order_consume); | 108 return sk_atomic_load(ptr, sk_memory_order_consume); |
109 #else | 109 #else |
110 // All current compilers blindly upgrade consume memory order to acquire mem
ory order. | 110 // All current compilers blindly upgrade consume memory order to acquire mem
ory order. |
111 // For our purposes, though, no memory barrier is required, so we lie and us
e relaxed. | 111 // For our purposes, though, no memory barrier is required, so we lie and us
e relaxed. |
112 return sk_atomic_load(ptr, sk_memory_order_relaxed); | 112 return sk_atomic_load(ptr, sk_memory_order_relaxed); |
113 #endif | 113 #endif |
114 } | 114 } |
115 | 115 |
116 // This has no constructor and must be zero-initalized (the macro above does thi
s). | 116 // This has no constructor and must be zero-initalized (the macro above does thi
s). |
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170 T* ptr = Private::consume_load(&fPtr); | 170 T* ptr = Private::consume_load(&fPtr); |
171 return ptr ? ptr : Private::try_cas<T*, Destroy>(&fPtr, create()); | 171 return ptr ? ptr : Private::try_cas<T*, Destroy>(&fPtr, create()); |
172 } | 172 } |
173 | 173 |
174 private: | 174 private: |
175 mutable T* fPtr; | 175 mutable T* fPtr; |
176 }; | 176 }; |
177 | 177 |
178 | 178 |
179 #endif//SkLazyPtr_DEFINED | 179 #endif//SkLazyPtr_DEFINED |
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