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| 1 // Copyright (c) 2008 The Chromium Authors. All rights reserved. | 1 // Copyright (c) 2008 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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| 30 // | 30 // |
| 31 // MyClass* ptr = my_instance.Pointer(); | 31 // MyClass* ptr = my_instance.Pointer(); |
| 32 // ptr->DoDoDo(); // MyClass::DoDoDo | 32 // ptr->DoDoDo(); // MyClass::DoDoDo |
| 33 // } | 33 // } |
| 34 | 34 |
| 35 #ifndef BASE_LAZY_INSTANCE_H_ | 35 #ifndef BASE_LAZY_INSTANCE_H_ |
| 36 #define BASE_LAZY_INSTANCE_H_ | 36 #define BASE_LAZY_INSTANCE_H_ |
| 37 | 37 |
| 38 #include "base/atomicops.h" | 38 #include "base/atomicops.h" |
| 39 #include "base/basictypes.h" | 39 #include "base/basictypes.h" |
| 40 #include "base/dynamic_annotations.h" | 40 #include "base/third_party/dynamic_annotations/dynamic_annotations.h" |
| 41 | 41 |
| 42 namespace base { | 42 namespace base { |
| 43 | 43 |
| 44 template <typename Type> | 44 template <typename Type> |
| 45 struct DefaultLazyInstanceTraits { | 45 struct DefaultLazyInstanceTraits { |
| 46 static Type* New(void* instance) { | 46 static Type* New(void* instance) { |
| 47 // Use placement new to initialize our instance in our preallocated space. | 47 // Use placement new to initialize our instance in our preallocated space. |
| 48 // The parenthesis is very important here to force POD type initialization. | 48 // The parenthesis is very important here to force POD type initialization. |
| 49 return new (instance) Type(); | 49 return new (instance) Type(); |
| 50 } | 50 } |
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| 120 private: | 120 private: |
| 121 int8 buf_[sizeof(Type)]; // Preallocate the space for the Type instance. | 121 int8 buf_[sizeof(Type)]; // Preallocate the space for the Type instance. |
| 122 Type *instance_; | 122 Type *instance_; |
| 123 | 123 |
| 124 DISALLOW_COPY_AND_ASSIGN(LazyInstance); | 124 DISALLOW_COPY_AND_ASSIGN(LazyInstance); |
| 125 }; | 125 }; |
| 126 | 126 |
| 127 } // namespace base | 127 } // namespace base |
| 128 | 128 |
| 129 #endif // BASE_LAZY_INSTANCE_H_ | 129 #endif // BASE_LAZY_INSTANCE_H_ |
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