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Side by Side Diff: base/lazy_instance.h

Issue 9117038: Convert all remaining explicit LeakyLazyInstanceTraits users to ::Leaky (Closed) Base URL: svn://svn.chromium.org/chrome/trunk/src
Patch Set: rebase Created 8 years, 11 months ago
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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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66 // Use placement new to initialize our instance in our preallocated space. 66 // Use placement new to initialize our instance in our preallocated space.
67 // The parenthesis is very important here to force POD type initialization. 67 // The parenthesis is very important here to force POD type initialization.
68 return new (instance) Type(); 68 return new (instance) Type();
69 } 69 }
70 static void Delete(Type* instance) { 70 static void Delete(Type* instance) {
71 // Explicitly call the destructor. 71 // Explicitly call the destructor.
72 instance->~Type(); 72 instance->~Type();
73 } 73 }
74 }; 74 };
75 75
76 // We pull out some of the functionality into non-templated functions, so we
77 // can implement the more complicated pieces out of line in the .cc file.
78 namespace internal {
79
76 // Use LazyInstance<T>::Leaky for a less-verbose call-site typedef; e.g.: 80 // Use LazyInstance<T>::Leaky for a less-verbose call-site typedef; e.g.:
77 // base::LazyInstance<T>::Leaky my_leaky_lazy_instance; 81 // base::LazyInstance<T>::Leaky my_leaky_lazy_instance;
78 // instead of: 82 // instead of:
79 // base::LazyInstance<T, LeakyLazyInstanceTraits<T> > my_leaky_lazy_instance; 83 // base::LazyInstance<T, base::internal::LeakyLazyInstanceTraits<T> >
84 // my_leaky_lazy_instance;
80 // (especially when T is MyLongTypeNameImplClientHolderFactory). 85 // (especially when T is MyLongTypeNameImplClientHolderFactory).
86 // Only use this internal::-qualified verbose form to extend this traits class
87 // (depending on its implementation details).
81 template <typename Type> 88 template <typename Type>
82 struct LeakyLazyInstanceTraits { 89 struct LeakyLazyInstanceTraits {
83 static const bool kRegisterOnExit = false; 90 static const bool kRegisterOnExit = false;
84 static const bool kAllowedToAccessOnNonjoinableThread = true; 91 static const bool kAllowedToAccessOnNonjoinableThread = true;
85 92
86 static Type* New(void* instance) { 93 static Type* New(void* instance) {
87 return DefaultLazyInstanceTraits<Type>::New(instance); 94 return DefaultLazyInstanceTraits<Type>::New(instance);
88 } 95 }
89 static void Delete(Type* instance) { 96 static void Delete(Type* instance) {
90 } 97 }
91 }; 98 };
92 99
93 // We pull out some of the functionality into non-templated functions, so we
94 // can implement the more complicated pieces out of line in the .cc file.
95 namespace internal {
96
97 // Our AtomicWord doubles as a spinlock, where a value of 100 // Our AtomicWord doubles as a spinlock, where a value of
98 // kBeingCreatedMarker means the spinlock is being held for creation. 101 // kBeingCreatedMarker means the spinlock is being held for creation.
99 static const subtle::AtomicWord kLazyInstanceStateCreating = 1; 102 static const subtle::AtomicWord kLazyInstanceStateCreating = 1;
100 103
101 // Check if instance needs to be created. If so return true otherwise 104 // Check if instance needs to be created. If so return true otherwise
102 // if another thread has beat us, wait for instance to be created and 105 // if another thread has beat us, wait for instance to be created and
103 // return false. 106 // return false.
104 BASE_EXPORT bool NeedsLazyInstance(subtle::AtomicWord* state); 107 BASE_EXPORT bool NeedsLazyInstance(subtle::AtomicWord* state);
105 108
106 // After creating an instance, call this to register the dtor to be called 109 // After creating an instance, call this to register the dtor to be called
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117 public: 120 public:
118 // Do not define a destructor, as doing so makes LazyInstance a 121 // Do not define a destructor, as doing so makes LazyInstance a
119 // non-POD-struct. We don't want that because then a static initializer will 122 // non-POD-struct. We don't want that because then a static initializer will
120 // be created to register the (empty) destructor with atexit() under MSVC, for 123 // be created to register the (empty) destructor with atexit() under MSVC, for
121 // example. We handle destruction of the contained Type class explicitly via 124 // example. We handle destruction of the contained Type class explicitly via
122 // the OnExit member function, where needed. 125 // the OnExit member function, where needed.
123 // ~LazyInstance() {} 126 // ~LazyInstance() {}
124 127
125 // Convenience typedef to avoid having to repeat Type for leaky lazy 128 // Convenience typedef to avoid having to repeat Type for leaky lazy
126 // instances. 129 // instances.
127 typedef LazyInstance<Type, LeakyLazyInstanceTraits<Type> > Leaky; 130 typedef LazyInstance<Type, internal::LeakyLazyInstanceTraits<Type> > Leaky;
128 131
129 Type& Get() { 132 Type& Get() {
130 return *Pointer(); 133 return *Pointer();
131 } 134 }
132 135
133 Type* Pointer() { 136 Type* Pointer() {
134 #ifndef NDEBUG 137 #ifndef NDEBUG
135 // Avoid making TLS lookup on release builds. 138 // Avoid making TLS lookup on release builds.
136 if (!Traits::kAllowedToAccessOnNonjoinableThread) 139 if (!Traits::kAllowedToAccessOnNonjoinableThread)
137 ThreadRestrictions::AssertSingletonAllowed(); 140 ThreadRestrictions::AssertSingletonAllowed();
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198 LazyInstance<Type, Traits>* me = 201 LazyInstance<Type, Traits>* me =
199 reinterpret_cast<LazyInstance<Type, Traits>*>(lazy_instance); 202 reinterpret_cast<LazyInstance<Type, Traits>*>(lazy_instance);
200 Traits::Delete(me->instance()); 203 Traits::Delete(me->instance());
201 subtle::Release_Store(&me->private_instance_, 0); 204 subtle::Release_Store(&me->private_instance_, 0);
202 } 205 }
203 }; 206 };
204 207
205 } // namespace base 208 } // namespace base
206 209
207 #endif // BASE_LAZY_INSTANCE_H_ 210 #endif // BASE_LAZY_INSTANCE_H_
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