SkRefCnt.h revision 91208922687a33df1d5253928b8d5d7d4685c7ac 
1
2/*
3 * Copyright 2006 The Android Open Source Project
4 *
5 * Use of this source code is governed by a BSD-style license that can be
6 * found in the LICENSE file.
7 */
8
9
10#ifndef SkRefCnt_DEFINED
11#define SkRefCnt_DEFINED
12
13#include "SkThread.h"
14#include "SkInstCnt.h"
15#include "SkTemplates.h"
16
17/** \class SkRefCnt
18
19    SkRefCnt is the base class for objects that may be shared by multiple
20    objects. When an existing owner wants to share a reference, it calls ref().
21    When an owner wants to release its reference, it calls unref(). When the
22    shared object's reference count goes to zero as the result of an unref()
23    call, its (virtual) destructor is called. It is an error for the
24    destructor to be called explicitly (or via the object going out of scope on
25    the stack or calling delete) if getRefCnt() > 1.
26*/
27class SK_API SkRefCnt : SkNoncopyable {
28public:
29    SK_DECLARE_INST_COUNT_ROOT(SkRefCnt)
30
31    /** Default construct, initializing the reference count to 1.
32    */
33    SkRefCnt() : fRefCnt(1) {}
34
35    /** Destruct, asserting that the reference count is 1.
36    */
37    virtual ~SkRefCnt() {
38#ifdef SK_DEBUG
39        SkASSERT(fRefCnt == 1);
40        fRefCnt = 0;    // illegal value, to catch us if we reuse after delete
41#endif
42    }
43
44    /** Return the reference count.
45    */
46    int32_t getRefCnt() const { return fRefCnt; }
47
48    /** Increment the reference count. Must be balanced by a call to unref().
49    */
50    void ref() const {
51        SkASSERT(fRefCnt > 0);
52        sk_atomic_inc(&fRefCnt);  // No barrier required.
53    }
54
55    /** Decrement the reference count. If the reference count is 1 before the
56        decrement, then delete the object. Note that if this is the case, then
57        the object needs to have been allocated via new, and not on the stack.
58    */
59    void unref() const {
60        SkASSERT(fRefCnt > 0);
61        // Release barrier (SL/S), if not provided below.
62        if (sk_atomic_dec(&fRefCnt) == 1) {
63            // Aquire barrier (L/SL), if not provided above.
64            // Prevents code in dispose from happening before the decrement.
65            sk_membar_aquire__after_atomic_dec();
66            internal_dispose();
67        }
68    }
69
70    void validate() const {
71        SkASSERT(fRefCnt > 0);
72    }
73
74protected:
75    /**
76     *  Allow subclasses to call this if they've overridden internal_dispose
77     *  so they can reset fRefCnt before the destructor is called. Should only
78     *  be called right before calling through to inherited internal_dispose()
79     *  or before calling the destructor.
80     */
81    void internal_dispose_restore_refcnt_to_1() const {
82#ifdef SK_DEBUG
83        SkASSERT(0 == fRefCnt);
84        fRefCnt = 1;
85#endif
86    }
87
88private:
89    /**
90     *  Called when the ref count goes to 0.
91     */
92    virtual void internal_dispose() const {
93        this->internal_dispose_restore_refcnt_to_1();
94        SkDELETE(this);
95    }
96
97    friend class SkWeakRefCnt;
98    friend class GrTexture;     // to allow GrTexture's internal_dispose to
99                                // call SkRefCnt's & directly set fRefCnt (to 1)
100
101    mutable int32_t fRefCnt;
102
103    typedef SkNoncopyable INHERITED;
104};
105
106///////////////////////////////////////////////////////////////////////////////
107
108/** Helper macro to safely assign one SkRefCnt[TS]* to another, checking for
109    null in on each side of the assignment, and ensuring that ref() is called
110    before unref(), in case the two pointers point to the same object.
111 */
112#define SkRefCnt_SafeAssign(dst, src)   \
113    do {                                \
114        if (src) src->ref();            \
115        if (dst) dst->unref();          \
116        dst = src;                      \
117    } while (0)
118
119
120/** Check if the argument is non-null, and if so, call obj->ref()
121 */
122template <typename T> static inline void SkSafeRef(T* obj) {
123    if (obj) {
124        obj->ref();
125    }
126}
127
128/** Check if the argument is non-null, and if so, call obj->unref()
129 */
130template <typename T> static inline void SkSafeUnref(T* obj) {
131    if (obj) {
132        obj->unref();
133    }
134}
135
136///////////////////////////////////////////////////////////////////////////////
137
138/**
139 *  Utility class that simply unref's its argument in the destructor.
140 */
141template <typename T> class SkAutoTUnref : SkNoncopyable {
142public:
143    explicit SkAutoTUnref(T* obj = NULL) : fObj(obj) {}
144    ~SkAutoTUnref() { SkSafeUnref(fObj); }
145
146    T* get() const { return fObj; }
147
148    void reset(T* obj) {
149        SkSafeUnref(fObj);
150        fObj = obj;
151    }
152
153    /**
154     *  Return the hosted object (which may be null), transferring ownership.
155     *  The reference count is not modified, and the internal ptr is set to NULL
156     *  so unref() will not be called in our destructor. A subsequent call to
157     *  detach() will do nothing and return null.
158     */
159    T* detach() {
160        T* obj = fObj;
161        fObj = NULL;
162        return obj;
163    }
164
165    /**
166     * BlockRef<B> is a type which inherits from B, cannot be created,
167     * and makes ref and unref private.
168     */
169    template<typename B> class BlockRef : public B {
170    private:
171        BlockRef();
172        void ref() const;
173        void unref() const;
174    };
175
176    /** If T is const, the type returned from operator-> will also be const. */
177    typedef typename SkTConstType<BlockRef<T>, SkTIsConst<T>::value>::type BlockRefType;
178
179    /**
180     *  SkAutoTUnref assumes ownership of the ref. As a result, it is an error
181     *  for the user to ref or unref through SkAutoTUnref. Therefore
182     *  SkAutoTUnref::operator-> returns BlockRef<T>*. This prevents use of
183     *  skAutoTUnrefInstance->ref() and skAutoTUnrefInstance->unref().
184     */
185    BlockRefType *operator->() const {
186        return static_cast<BlockRefType*>(fObj);
187    }
188    operator T*() { return fObj; }
189
190private:
191    T*  fObj;
192};
193
194class SkAutoUnref : public SkAutoTUnref<SkRefCnt> {
195public:
196    SkAutoUnref(SkRefCnt* obj) : SkAutoTUnref<SkRefCnt>(obj) {}
197};
198
199class SkAutoRef : SkNoncopyable {
200public:
201    SkAutoRef(SkRefCnt* obj) : fObj(obj) { SkSafeRef(obj); }
202    ~SkAutoRef() { SkSafeUnref(fObj); }
203private:
204    SkRefCnt* fObj;
205};
206
207/** Wrapper class for SkRefCnt pointers. This manages ref/unref of a pointer to
208    a SkRefCnt (or subclass) object.
209 */
210template <typename T> class SkRefPtr {
211public:
212    SkRefPtr() : fObj(NULL) {}
213    SkRefPtr(T* obj) : fObj(obj) { SkSafeRef(fObj); }
214    SkRefPtr(const SkRefPtr& o) : fObj(o.fObj) { SkSafeRef(fObj); }
215    ~SkRefPtr() { SkSafeUnref(fObj); }
216
217    SkRefPtr& operator=(const SkRefPtr& rp) {
218        SkRefCnt_SafeAssign(fObj, rp.fObj);
219        return *this;
220    }
221    SkRefPtr& operator=(T* obj) {
222        SkRefCnt_SafeAssign(fObj, obj);
223        return *this;
224    }
225
226    T* get() const { return fObj; }
227    T& operator*() const { return *fObj; }
228    T* operator->() const { return fObj; }
229
230    typedef T* SkRefPtr::*unspecified_bool_type;
231    operator unspecified_bool_type() const {
232        return fObj ? &SkRefPtr::fObj : NULL;
233    }
234
235private:
236    T* fObj;
237};
238
239#endif
240
241