SkRefCnt.h revision 733418f91e4d90f4ec250d9a97120618a5a89b49
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 "SkDynamicAnnotations.h" 14#include "SkThread.h" 15#include "SkInstCnt.h" 16#include "SkTemplates.h" 17 18/** \class SkRefCntBase 19 20 SkRefCntBase is the base class for objects that may be shared by multiple 21 objects. When an existing owner wants to share a reference, it calls ref(). 22 When an owner wants to release its reference, it calls unref(). When the 23 shared object's reference count goes to zero as the result of an unref() 24 call, its (virtual) destructor is called. It is an error for the 25 destructor to be called explicitly (or via the object going out of scope on 26 the stack or calling delete) if getRefCnt() > 1. 27*/ 28class SK_API SkRefCntBase : SkNoncopyable { 29public: 30 SK_DECLARE_INST_COUNT_ROOT(SkRefCntBase) 31 32 /** Default construct, initializing the reference count to 1. 33 */ 34 SkRefCntBase() : fRefCnt(1) {} 35 36 /** Destruct, asserting that the reference count is 1. 37 */ 38 virtual ~SkRefCntBase() { 39#ifdef SK_DEBUG 40 SkASSERTF(fRefCnt == 1, "fRefCnt was %d", fRefCnt); 41 fRefCnt = 0; // illegal value, to catch us if we reuse after delete 42#endif 43 } 44 45 /** Return the reference count. Use only for debugging. */ 46 int32_t getRefCnt() const { return fRefCnt; } 47 48 /** May return true if the caller is the only owner. 49 * Ensures that all previous owner's actions are complete. 50 */ 51 bool unique() const { 52 // We believe we're reading fRefCnt in a safe way here, so we stifle the TSAN warning about 53 // an unproctected read. Generally, don't read fRefCnt, and don't stifle this warning. 54 bool const unique = (1 == SK_ANNOTATE_UNPROTECTED_READ(fRefCnt)); 55 if (unique) { 56 // Acquire barrier (L/SL), if not provided by load of fRefCnt. 57 // Prevents user's 'unique' code from happening before decrements. 58 //TODO: issue the barrier. 59 } 60 return unique; 61 } 62 63 /** Increment the reference count. Must be balanced by a call to unref(). 64 */ 65 void ref() const { 66 SkASSERT(fRefCnt > 0); 67 sk_atomic_inc(&fRefCnt); // No barrier required. 68 } 69 70 /** Decrement the reference count. If the reference count is 1 before the 71 decrement, then delete the object. Note that if this is the case, then 72 the object needs to have been allocated via new, and not on the stack. 73 */ 74 void unref() const { 75 SkASSERT(fRefCnt > 0); 76 // Release barrier (SL/S), if not provided below. 77 if (sk_atomic_dec(&fRefCnt) == 1) { 78 // Acquire barrier (L/SL), if not provided above. 79 // Prevents code in dispose from happening before the decrement. 80 sk_membar_acquire__after_atomic_dec(); 81 internal_dispose(); 82 } 83 } 84 85#ifdef SK_DEBUG 86 void validate() const { 87 SkASSERT(fRefCnt > 0); 88 } 89#endif 90 91protected: 92 /** 93 * Allow subclasses to call this if they've overridden internal_dispose 94 * so they can reset fRefCnt before the destructor is called. Should only 95 * be called right before calling through to inherited internal_dispose() 96 * or before calling the destructor. 97 */ 98 void internal_dispose_restore_refcnt_to_1() const { 99#ifdef SK_DEBUG 100 SkASSERT(0 == fRefCnt); 101 fRefCnt = 1; 102#endif 103 } 104 105private: 106 /** 107 * Called when the ref count goes to 0. 108 */ 109 virtual void internal_dispose() const { 110 this->internal_dispose_restore_refcnt_to_1(); 111 SkDELETE(this); 112 } 113 114 // The following friends are those which override internal_dispose() 115 // and conditionally call SkRefCnt::internal_dispose(). 116 friend class GrTexture; 117 friend class SkWeakRefCnt; 118 119 mutable int32_t fRefCnt; 120 121 typedef SkNoncopyable INHERITED; 122}; 123 124#ifdef SK_REF_CNT_MIXIN_INCLUDE 125// It is the responsibility of the following include to define the type SkRefCnt. 126// This SkRefCnt should normally derive from SkRefCntBase. 127#include SK_REF_CNT_MIXIN_INCLUDE 128#else 129class SK_API SkRefCnt : public SkRefCntBase { }; 130#endif 131 132/////////////////////////////////////////////////////////////////////////////// 133 134/** Helper macro to safely assign one SkRefCnt[TS]* to another, checking for 135 null in on each side of the assignment, and ensuring that ref() is called 136 before unref(), in case the two pointers point to the same object. 137 */ 138#define SkRefCnt_SafeAssign(dst, src) \ 139 do { \ 140 if (src) src->ref(); \ 141 if (dst) dst->unref(); \ 142 dst = src; \ 143 } while (0) 144 145 146/** Call obj->ref() and return obj. The obj must not be NULL. 147 */ 148template <typename T> static inline T* SkRef(T* obj) { 149 SkASSERT(obj); 150 obj->ref(); 151 return obj; 152} 153 154/** Check if the argument is non-null, and if so, call obj->ref() and return obj. 155 */ 156template <typename T> static inline T* SkSafeRef(T* obj) { 157 if (obj) { 158 obj->ref(); 159 } 160 return obj; 161} 162 163/** Check if the argument is non-null, and if so, call obj->unref() 164 */ 165template <typename T> static inline void SkSafeUnref(T* obj) { 166 if (obj) { 167 obj->unref(); 168 } 169} 170 171template<typename T> static inline void SkSafeSetNull(T*& obj) { 172 if (NULL != obj) { 173 obj->unref(); 174 obj = NULL; 175 } 176} 177 178/////////////////////////////////////////////////////////////////////////////// 179 180/** 181 * Utility class that simply unref's its argument in the destructor. 182 */ 183template <typename T> class SkAutoTUnref : SkNoncopyable { 184public: 185 explicit SkAutoTUnref(T* obj = NULL) : fObj(obj) {} 186 ~SkAutoTUnref() { SkSafeUnref(fObj); } 187 188 T* get() const { return fObj; } 189 190 T* reset(T* obj) { 191 SkSafeUnref(fObj); 192 fObj = obj; 193 return obj; 194 } 195 196 void swap(SkAutoTUnref* other) { 197 T* tmp = fObj; 198 fObj = other->fObj; 199 other->fObj = tmp; 200 } 201 202 /** 203 * Return the hosted object (which may be null), transferring ownership. 204 * The reference count is not modified, and the internal ptr is set to NULL 205 * so unref() will not be called in our destructor. A subsequent call to 206 * detach() will do nothing and return null. 207 */ 208 T* detach() { 209 T* obj = fObj; 210 fObj = NULL; 211 return obj; 212 } 213 214 /** 215 * BlockRef<B> is a type which inherits from B, cannot be created, 216 * cannot be deleted, and makes ref and unref private. 217 */ 218 template<typename B> class BlockRef : public B { 219 private: 220 BlockRef(); 221 ~BlockRef(); 222 void ref() const; 223 void unref() const; 224 }; 225 226 /** If T is const, the type returned from operator-> will also be const. */ 227 typedef typename SkTConstType<BlockRef<T>, SkTIsConst<T>::value>::type BlockRefType; 228 229 /** 230 * SkAutoTUnref assumes ownership of the ref. As a result, it is an error 231 * for the user to ref or unref through SkAutoTUnref. Therefore 232 * SkAutoTUnref::operator-> returns BlockRef<T>*. This prevents use of 233 * skAutoTUnrefInstance->ref() and skAutoTUnrefInstance->unref(). 234 */ 235 BlockRefType *operator->() const { 236 return static_cast<BlockRefType*>(fObj); 237 } 238 operator T*() { return fObj; } 239 240private: 241 T* fObj; 242}; 243// Can't use the #define trick below to guard a bare SkAutoTUnref(...) because it's templated. :( 244 245class SkAutoUnref : public SkAutoTUnref<SkRefCnt> { 246public: 247 SkAutoUnref(SkRefCnt* obj) : SkAutoTUnref<SkRefCnt>(obj) {} 248}; 249#define SkAutoUnref(...) SK_REQUIRE_LOCAL_VAR(SkAutoUnref) 250 251#endif 252