1 /* 2 * Copyright 2006 The Android Open Source Project 3 * 4 * Use of this source code is governed by a BSD-style license that can be 5 * found in the LICENSE file. 6 */ 7 8 #ifndef SkRefCnt_DEFINED 9 #define SkRefCnt_DEFINED 10 11 #include "../private/SkAtomics.h" 12 #include "../private/SkUniquePtr.h" 13 #include "SkTypes.h" 14 15 /** \class SkRefCntBase 16 17 SkRefCntBase is the base class for objects that may be shared by multiple 18 objects. When an existing owner wants to share a reference, it calls ref(). 19 When an owner wants to release its reference, it calls unref(). When the 20 shared object's reference count goes to zero as the result of an unref() 21 call, its (virtual) destructor is called. It is an error for the 22 destructor to be called explicitly (or via the object going out of scope on 23 the stack or calling delete) if getRefCnt() > 1. 24 */ 25 class SK_API SkRefCntBase : SkNoncopyable { 26 public: 27 /** Default construct, initializing the reference count to 1. 28 */ 29 SkRefCntBase() : fRefCnt(1) {} 30 31 /** Destruct, asserting that the reference count is 1. 32 */ 33 virtual ~SkRefCntBase() { 34 #ifdef SK_DEBUG 35 SkASSERTF(fRefCnt == 1, "fRefCnt was %d", fRefCnt); 36 fRefCnt = 0; // illegal value, to catch us if we reuse after delete 37 #endif 38 } 39 40 #ifdef SK_DEBUG 41 /** Return the reference count. Use only for debugging. */ 42 int32_t getRefCnt() const { return fRefCnt; } 43 #endif 44 45 /** May return true if the caller is the only owner. 46 * Ensures that all previous owner's actions are complete. 47 */ 48 bool unique() const { 49 if (1 == sk_atomic_load(&fRefCnt, sk_memory_order_acquire)) { 50 // The acquire barrier is only really needed if we return true. It 51 // prevents code conditioned on the result of unique() from running 52 // until previous owners are all totally done calling unref(). 53 return true; 54 } 55 return false; 56 } 57 58 /** Increment the reference count. Must be balanced by a call to unref(). 59 */ 60 void ref() const { 61 #ifdef SK_BUILD_FOR_ANDROID_FRAMEWORK 62 // Android employs some special subclasses that enable the fRefCnt to 63 // go to zero, but not below, prior to reusing the object. This breaks 64 // the use of unique() on such objects and as such should be removed 65 // once the Android code is fixed. 66 SkASSERT(fRefCnt >= 0); 67 #else 68 SkASSERT(fRefCnt > 0); 69 #endif 70 (void)sk_atomic_fetch_add(&fRefCnt, +1, sk_memory_order_relaxed); // No barrier required. 71 } 72 73 /** Decrement the reference count. If the reference count is 1 before the 74 decrement, then delete the object. Note that if this is the case, then 75 the object needs to have been allocated via new, and not on the stack. 76 */ 77 void unref() const { 78 SkASSERT(fRefCnt > 0); 79 // A release here acts in place of all releases we "should" have been doing in ref(). 80 if (1 == sk_atomic_fetch_add(&fRefCnt, -1, sk_memory_order_acq_rel)) { 81 // Like unique(), the acquire is only needed on success, to make sure 82 // code in internal_dispose() doesn't happen before the decrement. 83 this->internal_dispose(); 84 } 85 } 86 87 #ifdef SK_DEBUG 88 void validate() const { 89 SkASSERT(fRefCnt > 0); 90 } 91 #endif 92 93 protected: 94 /** 95 * Allow subclasses to call this if they've overridden internal_dispose 96 * so they can reset fRefCnt before the destructor is called. Should only 97 * be called right before calling through to inherited internal_dispose() 98 * or before calling the destructor. 99 */ 100 void internal_dispose_restore_refcnt_to_1() const { 101 #ifdef SK_DEBUG 102 SkASSERT(0 == fRefCnt); 103 fRefCnt = 1; 104 #endif 105 } 106 107 private: 108 /** 109 * Called when the ref count goes to 0. 110 */ 111 virtual void internal_dispose() const { 112 this->internal_dispose_restore_refcnt_to_1(); 113 delete this; 114 } 115 116 // The following friends are those which override internal_dispose() 117 // and conditionally call SkRefCnt::internal_dispose(). 118 friend class SkWeakRefCnt; 119 120 mutable int32_t fRefCnt; 121 122 typedef SkNoncopyable INHERITED; 123 }; 124 125 #ifdef SK_REF_CNT_MIXIN_INCLUDE 126 // It is the responsibility of the following include to define the type SkRefCnt. 127 // This SkRefCnt should normally derive from SkRefCntBase. 128 #include SK_REF_CNT_MIXIN_INCLUDE 129 #else 130 class SK_API SkRefCnt : public SkRefCntBase { }; 131 #endif 132 133 /////////////////////////////////////////////////////////////////////////////// 134 135 /** Helper macro to safely assign one SkRefCnt[TS]* to another, checking for 136 null in on each side of the assignment, and ensuring that ref() is called 137 before unref(), in case the two pointers point to the same object. 138 */ 139 #define SkRefCnt_SafeAssign(dst, src) \ 140 do { \ 141 if (src) src->ref(); \ 142 if (dst) dst->unref(); \ 143 dst = src; \ 144 } while (0) 145 146 147 /** Call obj->ref() and return obj. The obj must not be nullptr. 148 */ 149 template <typename T> static inline T* SkRef(T* obj) { 150 SkASSERT(obj); 151 obj->ref(); 152 return obj; 153 } 154 155 /** Check if the argument is non-null, and if so, call obj->ref() and return obj. 156 */ 157 template <typename T> static inline T* SkSafeRef(T* obj) { 158 if (obj) { 159 obj->ref(); 160 } 161 return obj; 162 } 163 164 /** Check if the argument is non-null, and if so, call obj->unref() 165 */ 166 template <typename T> static inline void SkSafeUnref(T* obj) { 167 if (obj) { 168 obj->unref(); 169 } 170 } 171 172 template<typename T> static inline void SkSafeSetNull(T*& obj) { 173 if (obj) { 174 obj->unref(); 175 obj = nullptr; 176 } 177 } 178 179 /////////////////////////////////////////////////////////////////////////////// 180 181 template <typename T> struct SkTUnref { 182 void operator()(T* t) { t->unref(); } 183 }; 184 185 /** 186 * Utility class that simply unref's its argument in the destructor. 187 */ 188 template <typename T> class SkAutoTUnref : public skstd::unique_ptr<T, SkTUnref<T>> { 189 public: 190 explicit SkAutoTUnref(T* obj = nullptr) : skstd::unique_ptr<T, SkTUnref<T>>(obj) {} 191 192 T* detach() { return this->release(); } 193 operator T*() const { return this->get(); } 194 }; 195 // Can't use the #define trick below to guard a bare SkAutoTUnref(...) because it's templated. :( 196 197 class SkAutoUnref : public SkAutoTUnref<SkRefCnt> { 198 public: 199 SkAutoUnref(SkRefCnt* obj) : SkAutoTUnref<SkRefCnt>(obj) {} 200 }; 201 #define SkAutoUnref(...) SK_REQUIRE_LOCAL_VAR(SkAutoUnref) 202 203 // This is a variant of SkRefCnt that's Not Virtual, so weighs 4 bytes instead of 8 or 16. 204 // There's only benefit to using this if the deriving class does not otherwise need a vtable. 205 template <typename Derived> 206 class SkNVRefCnt : SkNoncopyable { 207 public: 208 SkNVRefCnt() : fRefCnt(1) {} 209 ~SkNVRefCnt() { SkASSERTF(1 == fRefCnt, "NVRefCnt was %d", fRefCnt); } 210 211 // Implementation is pretty much the same as SkRefCntBase. All required barriers are the same: 212 // - unique() needs acquire when it returns true, and no barrier if it returns false; 213 // - ref() doesn't need any barrier; 214 // - unref() needs a release barrier, and an acquire if it's going to call delete. 215 216 bool unique() const { return 1 == sk_atomic_load(&fRefCnt, sk_memory_order_acquire); } 217 void ref() const { (void)sk_atomic_fetch_add(&fRefCnt, +1, sk_memory_order_relaxed); } 218 void unref() const { 219 if (1 == sk_atomic_fetch_add(&fRefCnt, -1, sk_memory_order_acq_rel)) { 220 SkDEBUGCODE(fRefCnt = 1;) // restore the 1 for our destructor's assert 221 delete (const Derived*)this; 222 } 223 } 224 void deref() const { this->unref(); } 225 226 private: 227 mutable int32_t fRefCnt; 228 }; 229 230 #endif 231
