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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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120 | 120 |
121 Type* Pointer() { | 121 Type* Pointer() { |
122 if (!Traits::kAllowedToAccessOnNonjoinableThread) | 122 if (!Traits::kAllowedToAccessOnNonjoinableThread) |
123 base::ThreadRestrictions::AssertSingletonAllowed(); | 123 base::ThreadRestrictions::AssertSingletonAllowed(); |
124 | 124 |
125 // We will hopefully have fast access when the instance is already created. | 125 // We will hopefully have fast access when the instance is already created. |
126 if ((base::subtle::NoBarrier_Load(&state_) != STATE_CREATED) && | 126 if ((base::subtle::NoBarrier_Load(&state_) != STATE_CREATED) && |
127 NeedsInstance()) { | 127 NeedsInstance()) { |
128 // Create the instance in the space provided by |buf_|. | 128 // Create the instance in the space provided by |buf_|. |
129 instance_ = Traits::New(buf_); | 129 instance_ = Traits::New(buf_); |
130 CompleteInstance(instance_, Traits::Delete); | 130 if (Traits::Delete != NULL) // Will be null for LeakyLazyInstannceTraits |
M-A Ruel
2010/12/13 17:30:51
LeakyLazyInstanceTraits
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131 CompleteInstance(this, OnExit); | |
131 } | 132 } |
132 | 133 |
133 // This annotation helps race detectors recognize correct lock-less | 134 // This annotation helps race detectors recognize correct lock-less |
134 // synchronization between different threads calling Pointer(). | 135 // synchronization between different threads calling Pointer(). |
135 // We suggest dynamic race detection tool that "Traits::New" above | 136 // We suggest dynamic race detection tool that "Traits::New" above |
136 // and CompleteInstance(...) happens before "return instance_" below. | 137 // and CompleteInstance(...) happens before "return instance_" below. |
137 // See the corresponding HAPPENS_BEFORE in CompleteInstance(...). | 138 // See the corresponding HAPPENS_BEFORE in CompleteInstance(...). |
138 ANNOTATE_HAPPENS_AFTER(&state_); | 139 ANNOTATE_HAPPENS_AFTER(&state_); |
139 return instance_; | 140 return instance_; |
140 } | 141 } |
141 | 142 |
142 private: | 143 private: |
144 // Adapter function for use with AtExit. This should be called single | |
145 // threaded, so don't use atomic operations. | |
146 // Calling OnExit while the instance is in use by other threads is a mistake. | |
147 static void OnExit(void* lazy_instance) { | |
148 LazyInstance<Type, Traits>* me = | |
149 reinterpret_cast<LazyInstance<Type, Traits>*>(lazy_instance); | |
150 Traits::Delete(me->instance_); | |
151 me->instance_ = NULL; | |
152 base::subtle::Release_Store(&me->state_, STATE_EMPTY); | |
153 } | |
154 | |
143 int8 buf_[sizeof(Type)]; // Preallocate the space for the Type instance. | 155 int8 buf_[sizeof(Type)]; // Preallocate the space for the Type instance. |
144 Type *instance_; | 156 Type *instance_; |
145 | 157 |
146 DISALLOW_COPY_AND_ASSIGN(LazyInstance); | 158 DISALLOW_COPY_AND_ASSIGN(LazyInstance); |
147 }; | 159 }; |
148 | 160 |
149 } // namespace base | 161 } // namespace base |
150 | 162 |
151 #endif // BASE_LAZY_INSTANCE_H_ | 163 #endif // BASE_LAZY_INSTANCE_H_ |
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