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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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