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Side by Side Diff: base/lazy_instance.h

Issue 187903007: Make kAllowedToAccessOnNonjoinableThread debug-only. (Closed) Base URL: svn://svn.chromium.org/chrome/trunk/src
Patch Set: more Created 6 years, 9 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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50 // initialization, as base's LINKER_INITIALIZED requires a constructor and on 50 // initialization, as base's LINKER_INITIALIZED requires a constructor and on
51 // some compilers (notably gcc 4.4) this still ends up needing runtime 51 // some compilers (notably gcc 4.4) this still ends up needing runtime
52 // initialization. 52 // initialization.
53 #define LAZY_INSTANCE_INITIALIZER {0} 53 #define LAZY_INSTANCE_INITIALIZER {0}
54 54
55 namespace base { 55 namespace base {
56 56
57 template <typename Type> 57 template <typename Type>
58 struct DefaultLazyInstanceTraits { 58 struct DefaultLazyInstanceTraits {
59 static const bool kRegisterOnExit = true; 59 static const bool kRegisterOnExit = true;
60 #ifndef NDEBUG
60 static const bool kAllowedToAccessOnNonjoinableThread = false; 61 static const bool kAllowedToAccessOnNonjoinableThread = false;
62 #endif
61 63
62 static Type* New(void* instance) { 64 static Type* New(void* instance) {
63 DCHECK_EQ(reinterpret_cast<uintptr_t>(instance) & (ALIGNOF(Type) - 1), 0u) 65 DCHECK_EQ(reinterpret_cast<uintptr_t>(instance) & (ALIGNOF(Type) - 1), 0u)
64 << ": Bad boy, the buffer passed to placement new is not aligned!\n" 66 << ": Bad boy, the buffer passed to placement new is not aligned!\n"
65 "This may break some stuff like SSE-based optimizations assuming the " 67 "This may break some stuff like SSE-based optimizations assuming the "
66 "<Type> objects are word aligned."; 68 "<Type> objects are word aligned.";
67 // Use placement new to initialize our instance in our preallocated space. 69 // Use placement new to initialize our instance in our preallocated space.
68 // The parenthesis is very important here to force POD type initialization. 70 // The parenthesis is very important here to force POD type initialization.
69 return new (instance) Type(); 71 return new (instance) Type();
70 } 72 }
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82 // base::LazyInstance<T>::Leaky my_leaky_lazy_instance; 84 // base::LazyInstance<T>::Leaky my_leaky_lazy_instance;
83 // instead of: 85 // instead of:
84 // base::LazyInstance<T, base::internal::LeakyLazyInstanceTraits<T> > 86 // base::LazyInstance<T, base::internal::LeakyLazyInstanceTraits<T> >
85 // my_leaky_lazy_instance; 87 // my_leaky_lazy_instance;
86 // (especially when T is MyLongTypeNameImplClientHolderFactory). 88 // (especially when T is MyLongTypeNameImplClientHolderFactory).
87 // Only use this internal::-qualified verbose form to extend this traits class 89 // Only use this internal::-qualified verbose form to extend this traits class
88 // (depending on its implementation details). 90 // (depending on its implementation details).
89 template <typename Type> 91 template <typename Type>
90 struct LeakyLazyInstanceTraits { 92 struct LeakyLazyInstanceTraits {
91 static const bool kRegisterOnExit = false; 93 static const bool kRegisterOnExit = false;
94 #ifndef NDEBUG
92 static const bool kAllowedToAccessOnNonjoinableThread = true; 95 static const bool kAllowedToAccessOnNonjoinableThread = true;
96 #endif
93 97
94 static Type* New(void* instance) { 98 static Type* New(void* instance) {
95 ANNOTATE_SCOPED_MEMORY_LEAK; 99 ANNOTATE_SCOPED_MEMORY_LEAK;
96 return DefaultLazyInstanceTraits<Type>::New(instance); 100 return DefaultLazyInstanceTraits<Type>::New(instance);
97 } 101 }
98 static void Delete(Type* instance) { 102 static void Delete(Type* instance) {
99 } 103 }
100 }; 104 };
101 105
102 // Our AtomicWord doubles as a spinlock, where a value of 106 // Our AtomicWord doubles as a spinlock, where a value of
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203 LazyInstance<Type, Traits>* me = 207 LazyInstance<Type, Traits>* me =
204 reinterpret_cast<LazyInstance<Type, Traits>*>(lazy_instance); 208 reinterpret_cast<LazyInstance<Type, Traits>*>(lazy_instance);
205 Traits::Delete(me->instance()); 209 Traits::Delete(me->instance());
206 subtle::NoBarrier_Store(&me->private_instance_, 0); 210 subtle::NoBarrier_Store(&me->private_instance_, 0);
207 } 211 }
208 }; 212 };
209 213
210 } // namespace base 214 } // namespace base
211 215
212 #endif // BASE_LAZY_INSTANCE_H_ 216 #endif // BASE_LAZY_INSTANCE_H_
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