SkLazyPtr.h revision 0d03db7446126be6ccce744be9b37ef475142e16
1/* 2 * Copyright 2014 Google Inc. 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 SkLazyPtr_DEFINED 9#define SkLazyPtr_DEFINED 10 11/** Declare a lazily-chosen static pointer (or array of pointers) of type F. 12 * 13 * Example usage: 14 * 15 * Foo* CreateFoo() { return SkNEW(Foo); } 16 * Foo* GetSingletonFoo() { 17 * SK_DECLARE_STATIC_LAZY_PTR(Foo, singleton, CreateFoo); // Clean up with SkDELETE. 18 * return singleton.get(); 19 * } 20 * 21 * These macros take an optional void (*Destroy)(T*) at the end. If not given, we'll use SkDELETE. 22 * This option is most useful when T doesn't have a public destructor. 23 * 24 * void CustomCleanup(Foo* ptr) { ... } 25 * Foo* GetSingletonFooWithCustomCleanup() { 26 * SK_DECLARE_STATIC_LAZY_PTR(Foo, singleton, CreateFoo, CustomCleanup); 27 * return singleton.get(); 28 * } 29 * 30 * If you have a bunch of related static pointers of the same type, you can 31 * declare an array of lazy pointers together: 32 * 33 * Foo* CreateFoo(int i) { return ...; } 34 * Foo* GetCachedFoo(Foo::Enum enumVal) { 35 * SK_DECLARE_STATIC_LAZY_PTR_ARRAY(Foo, Foo::kEnumCount, cachedFoos, CreateFoo); 36 * return cachedFoos[enumVal]; 37 * } 38 * 39 * 40 * You can think of SK_DECLARE_STATIC_LAZY_PTR as a cheaper specialization of 41 * SkOnce. There is no mutex or extra storage used past the pointer itself. 42 * In debug mode, each lazy pointer will be cleaned up at process exit so we 43 * can check that we've not leaked or freed them early. 44 * 45 * We may call Create more than once, but all threads will see the same pointer 46 * returned from get(). Any extra calls to Create will be cleaned up. 47 * 48 * These macros must be used in a global or function scope, not as a class member. 49 */ 50 51#define SK_DECLARE_STATIC_LAZY_PTR(T, name, Create, ...) \ 52 static Private::SkLazyPtr<T, Create, ##__VA_ARGS__> name 53 54#define SK_DECLARE_STATIC_LAZY_PTR_ARRAY(T, name, N, Create, ...) \ 55 static Private::SkLazyPtrArray<T, N, Create, ##__VA_ARGS__> name 56 57 58 59// Everything below here is private implementation details. Don't touch, don't even look. 60 61#include "SkDynamicAnnotations.h" 62#include "SkThread.h" 63#include "SkThreadPriv.h" 64 65// See FIXME below. 66class SkFontConfigInterface; 67class SkTypeface; 68 69namespace Private { 70 71template <typename T> void sk_delete(T* ptr) { SkDELETE(ptr); } 72 73// Set *dst to ptr if *dst is NULL. Returns value of *dst, destroying ptr if not swapped in. 74// Issues the same memory barriers as sk_atomic_cas: acquire on failure, release on success. 75template <typename P, void (*Destroy)(P)> 76static P try_cas(void** dst, P ptr) { 77 P prev = (P)sk_atomic_cas(dst, NULL, ptr); 78 79 if (prev) { 80 // We need an acquire barrier before returning prev, which sk_atomic_cas provided. 81 Destroy(ptr); 82 return prev; 83 } else { 84 // We need a release barrier before returning ptr, which sk_atomic_cas provided. 85 return ptr; 86 } 87} 88 89// This has no constructor and must be zero-initalized (the macro above does this). 90template <typename T, T* (*Create)(), void (*Destroy)(T*) = sk_delete<T> > 91class SkLazyPtr { 92public: 93 T* get() { 94 // If fPtr has already been filled, we need an acquire barrier when loading it. 95 // If not, we need a release barrier when setting it. try_cas will do that. 96 T* ptr = (T*)sk_acquire_load(&fPtr); 97 return ptr ? ptr : try_cas<T*, Destroy>(&fPtr, Create()); 98 } 99 100#ifdef SK_DEVELOPER 101 // FIXME: We know we leak refs on some classes. For now, let them leak. 102 void cleanup(SkFontConfigInterface*) {} 103 void cleanup(SkTypeface*) {} 104 template <typename U> void cleanup(U* ptr) { Destroy(ptr); } 105 106 ~SkLazyPtr() { 107 this->cleanup((T*)fPtr); 108 fPtr = NULL; 109 } 110#endif 111 112private: 113 void* fPtr; 114}; 115 116// This has no constructor and must be zero-initalized (the macro above does this). 117template <typename T, int N, T* (*Create)(int), void (*Destroy)(T*) = sk_delete<T> > 118class SkLazyPtrArray { 119public: 120 T* operator[](int i) { 121 SkASSERT(i >= 0 && i < N); 122 // If fPtr has already been filled, we need an acquire barrier when loading it. 123 // If not, we need a release barrier when setting it. try_cas will do that. 124 T* ptr = (T*)sk_acquire_load(&fArray[i]); 125 return ptr ? ptr : try_cas<T*, Destroy>(&fArray[i], Create(i)); 126 } 127 128#ifdef SK_DEVELOPER 129 ~SkLazyPtrArray() { 130 for (int i = 0; i < N; i++) { 131 Destroy((T*)fArray[i]); 132 fArray[i] = NULL; 133 } 134 } 135#endif 136 137private: 138 void* fArray[N]; 139}; 140 141} // namespace Private 142 143#endif//SkLazyPtr_DEFINED 144