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Side by Side Diff: base/lazy_instance.h

Issue 1812: Just by implementing a destructor (even if it's not doing anything), MSVC wil... (Closed) Base URL: svn://chrome-svn/chrome/trunk/src/
Patch Set: Created 12 years, 3 months ago
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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.
(...skipping 46 matching lines...) Expand 10 before | Expand all | Expand 10 after
57 // can implement the more complicated pieces out of line in the .cc file. 57 // can implement the more complicated pieces out of line in the .cc file.
58 class LazyInstanceHelper { 58 class LazyInstanceHelper {
59 protected: 59 protected:
60 enum { 60 enum {
61 STATE_EMPTY = 0, 61 STATE_EMPTY = 0,
62 STATE_CREATING = 1, 62 STATE_CREATING = 1,
63 STATE_CREATED = 2 63 STATE_CREATED = 2
64 }; 64 };
65 65
66 explicit LazyInstanceHelper(LinkerInitialized x) { /* state_ is 0 */ } 66 explicit LazyInstanceHelper(LinkerInitialized x) { /* state_ is 0 */ }
67 ~LazyInstanceHelper() { } 67 // Declaring a destructor (even if it's empty) will cause MSVC to register a
68 // static initializer to register the empty destructor with at_exit().
68 69
69 // Make sure that instance is created, creating or waiting for it to be 70 // Make sure that instance is created, creating or waiting for it to be
70 // created if neccessary. Constructs with |ctor| in the space provided by 71 // created if neccessary. Constructs with |ctor| in the space provided by
71 // |instance| and registers dtor for destruction at program exit. 72 // |instance| and registers dtor for destruction at program exit.
72 void EnsureInstance(void* instance, void (*ctor)(void*), void (*dtor)(void*)); 73 void EnsureInstance(void* instance, void (*ctor)(void*), void (*dtor)(void*));
73 74
74 base::subtle::Atomic32 state_; 75 base::subtle::Atomic32 state_;
75 76
76 private: 77 private:
77 DISALLOW_COPY_AND_ASSIGN(LazyInstanceHelper); 78 DISALLOW_COPY_AND_ASSIGN(LazyInstanceHelper);
78 }; 79 };
79 80
80 template <typename Type, typename Traits = DefaultLazyInstanceTraits<Type> > 81 template <typename Type, typename Traits = DefaultLazyInstanceTraits<Type> >
81 class LazyInstance : public LazyInstanceHelper { 82 class LazyInstance : public LazyInstanceHelper {
82 public: 83 public:
83 explicit LazyInstance(LinkerInitialized x) : LazyInstanceHelper(x) { } 84 explicit LazyInstance(LinkerInitialized x) : LazyInstanceHelper(x) { }
84 ~LazyInstance() { } 85 // Declaring a destructor (even if it's empty) will cause MSVC to register a
86 // static initializer to register the empty destructor with at_exit().
85 87
86 Type& Get() { 88 Type& Get() {
87 return *Pointer(); 89 return *Pointer();
88 } 90 }
89 91
90 Type* Pointer() { 92 Type* Pointer() {
91 Type* instance = reinterpret_cast<Type*>(&buf_); 93 Type* instance = reinterpret_cast<Type*>(&buf_);
92 94
93 // We will hopefully have fast access when the instance is already created. 95 // We will hopefully have fast access when the instance is already created.
94 if (base::subtle::NoBarrier_Load(&state_) != STATE_CREATED) 96 if (base::subtle::NoBarrier_Load(&state_) != STATE_CREATED)
95 EnsureInstance(instance, Traits::New, Traits::Delete); 97 EnsureInstance(instance, Traits::New, Traits::Delete);
96 98
97 return instance; 99 return instance;
98 } 100 }
99 101
100 private: 102 private:
101 int8 buf_[sizeof(Type)]; // Preallocate the space for the Type instance. 103 int8 buf_[sizeof(Type)]; // Preallocate the space for the Type instance.
102 104
103 DISALLOW_COPY_AND_ASSIGN(LazyInstance); 105 DISALLOW_COPY_AND_ASSIGN(LazyInstance);
104 }; 106 };
105 107
106 } // namespace base 108 } // namespace base
107 109
108 #endif // BASE_LAZY_INSTANCE_H_ 110 #endif // BASE_LAZY_INSTANCE_H_
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