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1 // Copyright (c) 2009 The Chromium Authors. All rights reserved. | 1 // Copyright (c) 2011 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 // Weak pointers help in cases where you have many objects referring back to a | 5 // Weak pointers help in cases where you have many objects referring back to a |
6 // shared object and you wish for the lifetime of the shared object to not be | 6 // shared object and you wish for the lifetime of the shared object to not be |
7 // bound to the lifetime of the referrers. In other words, this is useful when | 7 // bound to the lifetime of the referrers. In other words, this is useful when |
8 // reference counting is not a good fit. | 8 // reference counting is not a good fit. |
9 // | 9 // |
10 // A common alternative to weak pointers is to have the shared object hold a | 10 // A common alternative to weak pointers is to have the shared object hold a |
11 // list of all referrers, and then when the shared object is destroyed, it | 11 // list of all referrers, and then when the shared object is destroyed, it |
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45 // dereferencing the Controller back pointer after the Controller has been | 45 // dereferencing the Controller back pointer after the Controller has been |
46 // destroyed. | 46 // destroyed. |
47 // | 47 // |
48 // WARNING: weak pointers are not threadsafe!!! You must only use a WeakPtr | 48 // WARNING: weak pointers are not threadsafe!!! You must only use a WeakPtr |
49 // instance on thread where it was created. | 49 // instance on thread where it was created. |
50 | 50 |
51 #ifndef BASE_WEAK_PTR_H_ | 51 #ifndef BASE_WEAK_PTR_H_ |
52 #define BASE_WEAK_PTR_H_ | 52 #define BASE_WEAK_PTR_H_ |
53 #pragma once | 53 #pragma once |
54 | 54 |
| 55 #include "base/base_api.h" |
55 #include "base/logging.h" | 56 #include "base/logging.h" |
56 #include "base/ref_counted.h" | 57 #include "base/ref_counted.h" |
57 #include "base/threading/non_thread_safe.h" | 58 #include "base/threading/non_thread_safe.h" |
58 | 59 |
59 namespace base { | 60 namespace base { |
60 | 61 |
61 namespace internal { | 62 namespace internal { |
62 // These classes are part of the WeakPtr implementation. | 63 // These classes are part of the WeakPtr implementation. |
63 // DO NOT USE THESE CLASSES DIRECTLY YOURSELF. | 64 // DO NOT USE THESE CLASSES DIRECTLY YOURSELF. |
64 | 65 |
65 class WeakReference { | 66 class BASE_API WeakReference { |
66 public: | 67 public: |
67 class Flag : public RefCounted<Flag>, public base::NonThreadSafe { | 68 class Flag : public RefCounted<Flag>, public base::NonThreadSafe { |
68 public: | 69 public: |
69 Flag(Flag** handle); | 70 Flag(Flag** handle); |
70 ~Flag(); | 71 ~Flag(); |
71 | 72 |
72 void AddRef() const; | 73 void AddRef() const; |
73 void Release() const; | 74 void Release() const; |
74 void Invalidate(); | 75 void Invalidate(); |
75 bool IsValid() const; | 76 bool IsValid() const; |
76 | 77 |
77 void DetachFromThread() { base::NonThreadSafe::DetachFromThread(); } | 78 void DetachFromThread() { base::NonThreadSafe::DetachFromThread(); } |
78 | 79 |
79 private: | 80 private: |
80 Flag** handle_; | 81 Flag** handle_; |
81 }; | 82 }; |
82 | 83 |
83 WeakReference(); | 84 WeakReference(); |
84 WeakReference(Flag* flag); | 85 WeakReference(Flag* flag); |
85 ~WeakReference(); | 86 ~WeakReference(); |
86 | 87 |
87 bool is_valid() const; | 88 bool is_valid() const; |
88 | 89 |
89 private: | 90 private: |
90 scoped_refptr<Flag> flag_; | 91 scoped_refptr<Flag> flag_; |
91 }; | 92 }; |
92 | 93 |
93 class WeakReferenceOwner { | 94 class BASE_API WeakReferenceOwner { |
94 public: | 95 public: |
95 WeakReferenceOwner(); | 96 WeakReferenceOwner(); |
96 ~WeakReferenceOwner(); | 97 ~WeakReferenceOwner(); |
97 | 98 |
98 WeakReference GetRef() const; | 99 WeakReference GetRef() const; |
99 | 100 |
100 bool HasRefs() const { | 101 bool HasRefs() const { |
101 return flag_ != NULL; | 102 return flag_ != NULL; |
102 } | 103 } |
103 | 104 |
104 void Invalidate(); | 105 void Invalidate(); |
105 | 106 |
106 // Indicates that this object will be used on another thread from now on. | 107 // Indicates that this object will be used on another thread from now on. |
107 void DetachFromThread() { | 108 void DetachFromThread() { |
108 if (flag_) flag_->DetachFromThread(); | 109 if (flag_) flag_->DetachFromThread(); |
109 } | 110 } |
110 | 111 |
111 private: | 112 private: |
112 mutable WeakReference::Flag* flag_; | 113 mutable WeakReference::Flag* flag_; |
113 }; | 114 }; |
114 | 115 |
115 // This class simplifies the implementation of WeakPtr's type conversion | 116 // This class simplifies the implementation of WeakPtr's type conversion |
116 // constructor by avoiding the need for a public accessor for ref_. A | 117 // constructor by avoiding the need for a public accessor for ref_. A |
117 // WeakPtr<T> cannot access the private members of WeakPtr<U>, so this | 118 // WeakPtr<T> cannot access the private members of WeakPtr<U>, so this |
118 // base class gives us a way to access ref_ in a protected fashion. | 119 // base class gives us a way to access ref_ in a protected fashion. |
119 class WeakPtrBase { | 120 class BASE_API WeakPtrBase { |
120 public: | 121 public: |
121 WeakPtrBase(); | 122 WeakPtrBase(); |
122 ~WeakPtrBase(); | 123 ~WeakPtrBase(); |
123 | 124 |
124 protected: | 125 protected: |
125 WeakPtrBase(const WeakReference& ref); | 126 WeakPtrBase(const WeakReference& ref); |
126 | 127 |
127 WeakReference ref_; | 128 WeakReference ref_; |
128 }; | 129 }; |
129 | 130 |
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236 | 237 |
237 private: | 238 private: |
238 internal::WeakReferenceOwner weak_reference_owner_; | 239 internal::WeakReferenceOwner weak_reference_owner_; |
239 T* ptr_; | 240 T* ptr_; |
240 DISALLOW_IMPLICIT_CONSTRUCTORS(WeakPtrFactory); | 241 DISALLOW_IMPLICIT_CONSTRUCTORS(WeakPtrFactory); |
241 }; | 242 }; |
242 | 243 |
243 } // namespace base | 244 } // namespace base |
244 | 245 |
245 #endif // BASE_WEAK_PTR_H_ | 246 #endif // BASE_WEAK_PTR_H_ |
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