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1 /* | 1 /* |
2 * Copyright 2012 Google Inc. | 2 * Copyright 2012 Google Inc. |
3 * | 3 * |
4 * Use of this source code is governed by a BSD-style license that can be | 4 * Use of this source code is governed by a BSD-style license that can be |
5 * found in the LICENSE file. | 5 * found in the LICENSE file. |
6 */ | 6 */ |
7 | 7 |
8 #ifndef SkWeakRefCnt_DEFINED | 8 #ifndef SkWeakRefCnt_DEFINED |
9 #define SkWeakRefCnt_DEFINED | 9 #define SkWeakRefCnt_DEFINED |
10 | 10 |
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80 | 80 |
81 /** Creates a strong reference from a weak reference, if possible. The | 81 /** Creates a strong reference from a weak reference, if possible. The |
82 caller must already be an owner. If try_ref() returns true the owner | 82 caller must already be an owner. If try_ref() returns true the owner |
83 is in posession of an additional strong reference. Both the original | 83 is in posession of an additional strong reference. Both the original |
84 reference and new reference must be properly unreferenced. If try_ref() | 84 reference and new reference must be properly unreferenced. If try_ref() |
85 returns false, no strong reference could be created and the owner's | 85 returns false, no strong reference could be created and the owner's |
86 reference is in the same state as before the call. | 86 reference is in the same state as before the call. |
87 */ | 87 */ |
88 bool SK_WARN_UNUSED_RESULT try_ref() const { | 88 bool SK_WARN_UNUSED_RESULT try_ref() const { |
89 if (sk_atomic_conditional_inc(&fRefCnt) != 0) { | 89 if (sk_atomic_conditional_inc(&fRefCnt) != 0) { |
90 // Aquire barrier (L/SL), if not provided above. | 90 // Acquire barrier (L/SL), if not provided above. |
91 // Prevents subsequent code from happening before the increment. | 91 // Prevents subsequent code from happening before the increment. |
92 sk_membar_aquire__after_atomic_conditional_inc(); | 92 sk_membar_acquire__after_atomic_conditional_inc(); |
93 return true; | 93 return true; |
94 } | 94 } |
95 return false; | 95 return false; |
96 } | 96 } |
97 | 97 |
98 /** Increment the weak reference count. Must be balanced by a call to | 98 /** Increment the weak reference count. Must be balanced by a call to |
99 weak_unref(). | 99 weak_unref(). |
100 */ | 100 */ |
101 void weak_ref() const { | 101 void weak_ref() const { |
102 SkASSERT(fRefCnt > 0); | 102 SkASSERT(fRefCnt > 0); |
103 SkASSERT(fWeakCnt > 0); | 103 SkASSERT(fWeakCnt > 0); |
104 sk_atomic_inc(&fWeakCnt); // No barrier required. | 104 sk_atomic_inc(&fWeakCnt); // No barrier required. |
105 } | 105 } |
106 | 106 |
107 /** Decrement the weak reference count. If the weak reference count is 1 | 107 /** Decrement the weak reference count. If the weak reference count is 1 |
108 before the decrement, then call delete on the object. Note that if this | 108 before the decrement, then call delete on the object. Note that if this |
109 is the case, then the object needs to have been allocated via new, and | 109 is the case, then the object needs to have been allocated via new, and |
110 not on the stack. | 110 not on the stack. |
111 */ | 111 */ |
112 void weak_unref() const { | 112 void weak_unref() const { |
113 SkASSERT(fWeakCnt > 0); | 113 SkASSERT(fWeakCnt > 0); |
114 // Release barrier (SL/S), if not provided below. | 114 // Release barrier (SL/S), if not provided below. |
115 if (sk_atomic_dec(&fWeakCnt) == 1) { | 115 if (sk_atomic_dec(&fWeakCnt) == 1) { |
116 // Aquire barrier (L/SL), if not provided above. | 116 // Acquire barrier (L/SL), if not provided above. |
117 // Prevents code in destructor from happening before the decrement. | 117 // Prevents code in destructor from happening before the decrement. |
118 sk_membar_aquire__after_atomic_dec(); | 118 sk_membar_acquire__after_atomic_dec(); |
119 #ifdef SK_DEBUG | 119 #ifdef SK_DEBUG |
120 // so our destructor won't complain | 120 // so our destructor won't complain |
121 fWeakCnt = 1; | 121 fWeakCnt = 1; |
122 #endif | 122 #endif |
123 SkRefCnt::internal_dispose(); | 123 SkRefCnt::internal_dispose(); |
124 } | 124 } |
125 } | 125 } |
126 | 126 |
127 /** Returns true if there are no strong references to the object. When this | 127 /** Returns true if there are no strong references to the object. When this |
128 is the case all future calls to try_ref() will return false. | 128 is the case all future calls to try_ref() will return false. |
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150 weak_unref(); | 150 weak_unref(); |
151 } | 151 } |
152 | 152 |
153 /* Invariant: fWeakCnt = #weak + (fRefCnt > 0 ? 1 : 0) */ | 153 /* Invariant: fWeakCnt = #weak + (fRefCnt > 0 ? 1 : 0) */ |
154 mutable int32_t fWeakCnt; | 154 mutable int32_t fWeakCnt; |
155 | 155 |
156 typedef SkRefCnt INHERITED; | 156 typedef SkRefCnt INHERITED; |
157 }; | 157 }; |
158 | 158 |
159 #endif | 159 #endif |
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