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1 // Copyright (c) 2012 The Chromium Authors. All rights reserved. | 1 // Copyright (c) 2012 The Chromium Authors. All rights reserved. |
2 // Use of this source code is governed by a BSD-style license that can be | 2 // Use of this source code is governed by a BSD-style license that can be |
3 // found in the LICENSE file. | 3 // found in the LICENSE file. |
4 | 4 |
5 // The LazyInstance<Type, Traits> class manages a single instance of Type, | 5 // The LazyInstance<Type, Traits> class manages a single instance of Type, |
6 // which will be lazily created on the first time it's accessed. This class is | 6 // which will be lazily created on the first time it's accessed. This class is |
7 // useful for places you would normally use a function-level static, but you | 7 // useful for places you would normally use a function-level static, but you |
8 // need to have guaranteed thread-safety. The Type constructor will only ever | 8 // need to have guaranteed thread-safety. The Type constructor will only ever |
9 // be called once, even if two threads are racing to create the object. Get() | 9 // be called once, even if two threads are racing to create the object. Get() |
10 // and Pointer() will always return the same, completely initialized instance. | 10 // and Pointer() will always return the same, completely initialized instance. |
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53 namespace base { | 53 namespace base { |
54 | 54 |
55 template <typename Type> | 55 template <typename Type> |
56 struct DefaultLazyInstanceTraits { | 56 struct DefaultLazyInstanceTraits { |
57 static const bool kRegisterOnExit = true; | 57 static const bool kRegisterOnExit = true; |
58 #if DCHECK_IS_ON() | 58 #if DCHECK_IS_ON() |
59 static const bool kAllowedToAccessOnNonjoinableThread = false; | 59 static const bool kAllowedToAccessOnNonjoinableThread = false; |
60 #endif | 60 #endif |
61 | 61 |
62 static Type* New(void* instance) { | 62 static Type* New(void* instance) { |
63 DCHECK_EQ(reinterpret_cast<uintptr_t>(instance) & (ALIGNOF(Type) - 1), 0u) | 63 DCHECK_EQ(reinterpret_cast<uintptr_t>(instance) & (alignof(Type) - 1), 0u) |
64 << ": Bad boy, the buffer passed to placement new is not aligned!\n" | 64 << "The buffer passed to placement new is not aligned!\n" |
65 "This may break some stuff like SSE-based optimizations assuming the " | 65 "This may break some stuff like SSE-based optimizations assuming " |
66 "<Type> objects are word aligned."; | 66 "the <Type> objects are word aligned."; |
67 // Use placement new to initialize our instance in our preallocated space. | 67 // Use placement new to initialize our instance in our preallocated space. |
68 // The parenthesis is very important here to force POD type initialization. | 68 // The parenthesis is very important here to force POD type initialization. |
69 return new (instance) Type(); | 69 return new (instance) Type(); |
70 } | 70 } |
71 static void Delete(Type* instance) { | 71 static void Delete(Type* instance) { |
72 // Explicitly call the destructor. | 72 // Explicitly call the destructor. |
73 instance->~Type(); | 73 instance->~Type(); |
74 } | 74 } |
75 }; | 75 }; |
76 | 76 |
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177 return p == instance(); | 177 return p == instance(); |
178 } | 178 } |
179 } | 179 } |
180 | 180 |
181 // Effectively private: member data is only public to allow the linker to | 181 // Effectively private: member data is only public to allow the linker to |
182 // statically initialize it and to maintain a POD class. DO NOT USE FROM | 182 // statically initialize it and to maintain a POD class. DO NOT USE FROM |
183 // OUTSIDE THIS CLASS. | 183 // OUTSIDE THIS CLASS. |
184 | 184 |
185 subtle::AtomicWord private_instance_; | 185 subtle::AtomicWord private_instance_; |
186 // Preallocated space for the Type instance. | 186 // Preallocated space for the Type instance. |
187 base::AlignedMemory<sizeof(Type), ALIGNOF(Type)> private_buf_; | 187 base::AlignedMemory<sizeof(Type), alignof(Type)> private_buf_; |
188 | 188 |
189 private: | 189 private: |
190 Type* instance() { | 190 Type* instance() { |
191 return reinterpret_cast<Type*>(subtle::NoBarrier_Load(&private_instance_)); | 191 return reinterpret_cast<Type*>(subtle::NoBarrier_Load(&private_instance_)); |
192 } | 192 } |
193 | 193 |
194 // Adapter function for use with AtExit. This should be called single | 194 // Adapter function for use with AtExit. This should be called single |
195 // threaded, so don't synchronize across threads. | 195 // threaded, so don't synchronize across threads. |
196 // Calling OnExit while the instance is in use by other threads is a mistake. | 196 // Calling OnExit while the instance is in use by other threads is a mistake. |
197 static void OnExit(void* lazy_instance) { | 197 static void OnExit(void* lazy_instance) { |
198 LazyInstance<Type, Traits>* me = | 198 LazyInstance<Type, Traits>* me = |
199 reinterpret_cast<LazyInstance<Type, Traits>*>(lazy_instance); | 199 reinterpret_cast<LazyInstance<Type, Traits>*>(lazy_instance); |
200 Traits::Delete(me->instance()); | 200 Traits::Delete(me->instance()); |
201 subtle::NoBarrier_Store(&me->private_instance_, 0); | 201 subtle::NoBarrier_Store(&me->private_instance_, 0); |
202 } | 202 } |
203 }; | 203 }; |
204 | 204 |
205 } // namespace base | 205 } // namespace base |
206 | 206 |
207 #endif // BASE_LAZY_INSTANCE_H_ | 207 #endif // BASE_LAZY_INSTANCE_H_ |
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