1 /*
2 * Copyright (C) 2006 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #ifndef SkRefCnt_DEFINED
18 #define SkRefCnt_DEFINED
19
20 #include "SkThread.h"
21
22 /** \class SkRefCnt
23
24 SkRefCnt is the base class for objects that may be shared by multiple
25 objects. When a new owner wants a reference, it calls ref(). When an owner
26 wants to release its reference, it calls unref(). When the shared object's
27 reference count goes to zero as the result of an unref() call, its (virtual)
28 destructor is called. It is an error for the destructor to be called
29 explicitly (or via the object going out of scope on the stack or calling
30 delete) if getRefCnt() > 1.
31 */
32 class SkRefCnt : SkNoncopyable {
33 public:
34 /** Default construct, initializing the reference count to 1.
35 */
SkRefCnt()36 SkRefCnt() : fRefCnt(1) {}
37
38 /** Destruct, asserting that the reference count is 1.
39 */
~SkRefCnt()40 virtual ~SkRefCnt() { SkASSERT(fRefCnt == 1); }
41
42 /** Return the reference count.
43 */
getRefCnt()44 int32_t getRefCnt() const { return fRefCnt; }
45
46 /** Increment the reference count. Must be balanced by a call to unref().
47 */
ref()48 void ref() const {
49 SkASSERT(fRefCnt > 0);
50 sk_atomic_inc(&fRefCnt);
51 }
52
53 /** Decrement the reference count. If the reference count is 1 before the
54 decrement, then call delete on the object. Note that if this is the
55 case, then the object needs to have been allocated via new, and not on
56 the stack.
57 */
unref()58 void unref() const {
59 SkASSERT(fRefCnt > 0);
60 if (sk_atomic_dec(&fRefCnt) == 1) {
61 fRefCnt = 1; // so our destructor won't complain
62 SkDELETE(this);
63 }
64 }
65
66 /** Helper version of ref(), that first checks to see if this is not null.
67 If this is null, then do nothing.
68 */
safeRef()69 void safeRef() const {
70 if (this) {
71 this->ref();
72 }
73 }
74
75 /** Helper version of unref(), that first checks to see if this is not null.
76 If this is null, then do nothing.
77 */
safeUnref()78 void safeUnref() const {
79 if (this) {
80 this->unref();
81 }
82 }
83
84 private:
85 mutable int32_t fRefCnt;
86 };
87
88 /** \class SkAutoUnref
89
90 SkAutoUnref is a stack-helper class that will automatically call unref() on
91 the object it points to when the SkAutoUnref object goes out of scope.
92 If obj is null, do nothing.
93 */
94 class SkAutoUnref : SkNoncopyable {
95 public:
SkAutoUnref(SkRefCnt * obj)96 SkAutoUnref(SkRefCnt* obj) : fObj(obj) {}
97 ~SkAutoUnref();
98
get()99 SkRefCnt* get() const { return fObj; }
100
101 /** If the hosted object is null, do nothing and return false, else call
102 ref() on it and return true
103 */
104 bool ref();
105
106 /** If the hosted object is null, do nothing and return false, else call
107 unref() on it, set its reference to null, and return true
108 */
109 bool unref();
110
111 /** If the hosted object is null, do nothing and return NULL, else call
112 unref() on it, set its reference to null, and return the object
113 */
114 SkRefCnt* detach();
115
116 private:
117 SkRefCnt* fObj;
118 };
119
120 ///////////////////////////////////////////////////////////////////////////////
121
122 /** Helper macro to safely assign one SkRefCnt[TS]* to another, checking for
123 null in on each side of the assignment, and ensuring that ref() is called
124 before unref(), in case the two pointers point to the same object.
125 */
126 #define SkRefCnt_SafeAssign(dst, src) \
127 do { \
128 if (src) src->ref(); \
129 if (dst) dst->unref(); \
130 dst = src; \
131 } while (0)
132
133
134 /** Check if the argument is non-null, and if so, call obj->ref()
135 */
SkSafeRef(T * obj)136 template <typename T> static inline void SkSafeRef(T* obj) {
137 if (obj) {
138 obj->ref();
139 }
140 }
141
142 /** Check if the argument is non-null, and if so, call obj->unref()
143 */
SkSafeUnref(T * obj)144 template <typename T> static inline void SkSafeUnref(T* obj) {
145 if (obj) {
146 obj->unref();
147 }
148 }
149
150 #endif
151
152