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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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48 // initialization, as base's LINKER_INITIALIZED requires a constructor and on | 48 // initialization, as base's LINKER_INITIALIZED requires a constructor and on |
49 // some compilers (notably gcc 4.4) this still ends up needing runtime | 49 // some compilers (notably gcc 4.4) this still ends up needing runtime |
50 // initialization. | 50 // initialization. |
51 #define LAZY_INSTANCE_INITIALIZER {0} | 51 #define LAZY_INSTANCE_INITIALIZER {0} |
52 | 52 |
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 #ifndef NDEBUG | 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 << ": Bad boy, 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 the " |
66 "<Type> objects are word aligned."; | 66 "<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. |
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82 // base::LazyInstance<T>::Leaky my_leaky_lazy_instance; | 82 // base::LazyInstance<T>::Leaky my_leaky_lazy_instance; |
83 // instead of: | 83 // instead of: |
84 // base::LazyInstance<T, base::internal::LeakyLazyInstanceTraits<T> > | 84 // base::LazyInstance<T, base::internal::LeakyLazyInstanceTraits<T> > |
85 // my_leaky_lazy_instance; | 85 // my_leaky_lazy_instance; |
86 // (especially when T is MyLongTypeNameImplClientHolderFactory). | 86 // (especially when T is MyLongTypeNameImplClientHolderFactory). |
87 // Only use this internal::-qualified verbose form to extend this traits class | 87 // Only use this internal::-qualified verbose form to extend this traits class |
88 // (depending on its implementation details). | 88 // (depending on its implementation details). |
89 template <typename Type> | 89 template <typename Type> |
90 struct LeakyLazyInstanceTraits { | 90 struct LeakyLazyInstanceTraits { |
91 static const bool kRegisterOnExit = false; | 91 static const bool kRegisterOnExit = false; |
92 #ifndef NDEBUG | 92 #if DCHECK_IS_ON() |
93 static const bool kAllowedToAccessOnNonjoinableThread = true; | 93 static const bool kAllowedToAccessOnNonjoinableThread = true; |
94 #endif | 94 #endif |
95 | 95 |
96 static Type* New(void* instance) { | 96 static Type* New(void* instance) { |
97 ANNOTATE_SCOPED_MEMORY_LEAK; | 97 ANNOTATE_SCOPED_MEMORY_LEAK; |
98 return DefaultLazyInstanceTraits<Type>::New(instance); | 98 return DefaultLazyInstanceTraits<Type>::New(instance); |
99 } | 99 } |
100 static void Delete(Type* instance) { | 100 static void Delete(Type* instance) { |
101 } | 101 } |
102 }; | 102 }; |
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131 | 131 |
132 // Convenience typedef to avoid having to repeat Type for leaky lazy | 132 // Convenience typedef to avoid having to repeat Type for leaky lazy |
133 // instances. | 133 // instances. |
134 typedef LazyInstance<Type, internal::LeakyLazyInstanceTraits<Type> > Leaky; | 134 typedef LazyInstance<Type, internal::LeakyLazyInstanceTraits<Type> > Leaky; |
135 | 135 |
136 Type& Get() { | 136 Type& Get() { |
137 return *Pointer(); | 137 return *Pointer(); |
138 } | 138 } |
139 | 139 |
140 Type* Pointer() { | 140 Type* Pointer() { |
141 #ifndef NDEBUG | 141 #if DCHECK_IS_ON() |
142 // Avoid making TLS lookup on release builds. | 142 // Avoid making TLS lookup on release builds. |
143 if (!Traits::kAllowedToAccessOnNonjoinableThread) | 143 if (!Traits::kAllowedToAccessOnNonjoinableThread) |
144 ThreadRestrictions::AssertSingletonAllowed(); | 144 ThreadRestrictions::AssertSingletonAllowed(); |
145 #endif | 145 #endif |
146 // If any bit in the created mask is true, the instance has already been | 146 // If any bit in the created mask is true, the instance has already been |
147 // fully constructed. | 147 // fully constructed. |
148 static const subtle::AtomicWord kLazyInstanceCreatedMask = | 148 static const subtle::AtomicWord kLazyInstanceCreatedMask = |
149 ~internal::kLazyInstanceStateCreating; | 149 ~internal::kLazyInstanceStateCreating; |
150 | 150 |
151 // We will hopefully have fast access when the instance is already created. | 151 // We will hopefully have fast access when the instance is already created. |
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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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