| /* |
| * Copyright 2014 Google Inc. |
| * |
| * Use of this source code is governed by a BSD-style license that can be |
| * found in the LICENSE file. |
| */ |
| |
| #ifndef SkLazyPtr_DEFINED |
| #define SkLazyPtr_DEFINED |
| |
| /** Declare a lazily-chosen static pointer (or array of pointers) of type T. |
| * |
| * Example usage: |
| * |
| * Foo* GetSingletonFoo() { |
| * SK_DECLARE_STATIC_LAZY_PTR(Foo, singleton); // Created with SkNEW, destroyed with SkDELETE. |
| * return singleton.get(); |
| * } |
| * |
| * These macros take an optional T* (*Create)() and void (*Destroy)(T*) at the end. |
| * If not given, we'll use SkNEW and SkDELETE. |
| * These options are most useful when T doesn't have a public constructor or destructor. |
| * Create comes first, so you may use a custom Create with a default Destroy, but not vice versa. |
| * |
| * Foo* CustomCreate() { return ...; } |
| * void CustomDestroy(Foo* ptr) { ... } |
| * Foo* GetSingletonFooWithCustomCleanup() { |
| * SK_DECLARE_STATIC_LAZY_PTR(Foo, singleton, CustomCreate, CustomDestroy); |
| * return singleton.get(); |
| * } |
| * |
| * If you have a bunch of related static pointers of the same type, you can |
| * declare an array of lazy pointers together, and we'll pass the index to Create(). |
| * |
| * Foo* CreateFoo(int i) { return ...; } |
| * Foo* GetCachedFoo(Foo::Enum enumVal) { |
| * SK_DECLARE_STATIC_LAZY_PTR_ARRAY(Foo, Foo::kEnumCount, cachedFoos, CreateFoo); |
| * return cachedFoos[enumVal]; |
| * } |
| * |
| * |
| * You can think of SK_DECLARE_STATIC_LAZY_PTR as a cheaper specialization of |
| * SkOnce. There is no mutex or extra storage used past the pointer itself. |
| * |
| * We may call Create more than once, but all threads will see the same pointer |
| * returned from get(). Any extra calls to Create will be cleaned up. |
| * |
| * These macros must be used in a global scope, not in function scope or as a class member. |
| */ |
| |
| #define SK_DECLARE_STATIC_LAZY_PTR(T, name, ...) \ |
| namespace {} static Private::SkLazyPtrBase<T, ##__VA_ARGS__> name |
| |
| #define SK_DECLARE_STATIC_LAZY_PTR_ARRAY(T, name, N, ...) \ |
| namespace {} static Private::SkLazyPtrArray<T, N, ##__VA_ARGS__> name |
| |
| // namespace {} forces these macros to only be legal in global scopes. Chrome has thread-safety |
| // problems with them in function-local statics because it uses -fno-threadsafe-statics, and even |
| // in builds with threadsafe statics, those threadsafe statics are just unnecessary overhead. |
| |
| // Everything below here is private implementation details. Don't touch, don't even look. |
| |
| #include "SkDynamicAnnotations.h" |
| #include "SkThread.h" |
| #include "SkThreadPriv.h" |
| |
| // See FIXME below. |
| class SkFontConfigInterfaceDirect; |
| |
| namespace Private { |
| |
| // Set *dst to ptr if *dst is NULL. Returns value of *dst, destroying ptr if not swapped in. |
| // Issues the same memory barriers as sk_atomic_cas: acquire on failure, release on success. |
| template <typename P, void (*Destroy)(P)> |
| static P try_cas(void** dst, P ptr) { |
| P prev = (P)sk_atomic_cas(dst, NULL, ptr); |
| |
| if (prev) { |
| // We need an acquire barrier before returning prev, which sk_atomic_cas provided. |
| Destroy(ptr); |
| return prev; |
| } else { |
| // We need a release barrier before returning ptr, which sk_atomic_cas provided. |
| return ptr; |
| } |
| } |
| |
| template <typename T> T* sk_new() { return SkNEW(T); } |
| template <typename T> void sk_delete(T* ptr) { SkDELETE(ptr); } |
| |
| // We're basing these implementations here on this article: |
| // http://preshing.com/20140709/the-purpose-of-memory_order_consume-in-cpp11/ |
| // |
| // Because the users of SkLazyPtr and SkLazyPtrArray will read the pointers |
| // _through_ our atomically set pointer, there is a data dependency between our |
| // atomic and the guarded data, and so we only need writer-releases / |
| // reader-consumes memory pairing rather than the more general write-releases / |
| // reader-acquires convention. |
| // |
| // This is nice, because a sk_consume_load is free on all our platforms: x86, |
| // ARM, MIPS. In contrast, sk_acquire_load issues a memory barrier on non-x86. |
| |
| // This has no constructor and must be zero-initalized (the macro above does this). |
| template <typename T, T* (*Create)() = sk_new<T>, void (*Destroy)(T*) = sk_delete<T> > |
| class SkLazyPtrBase { |
| public: |
| T* get() { |
| // If fPtr has already been filled, we need a consume barrier when loading it. |
| // If not, we need a release barrier when setting it. try_cas will do that. |
| T* ptr = (T*)sk_consume_load(&fPtr); |
| return ptr ? ptr : try_cas<T*, Destroy>(&fPtr, Create()); |
| } |
| |
| protected: |
| void* fPtr; |
| }; |
| |
| template <typename T> T* sk_new_arg(int i) { return SkNEW_ARGS(T, (i)); } |
| |
| // This has no constructor and must be zero-initalized (the macro above does this). |
| template <typename T, int N, T* (*Create)(int) = sk_new_arg<T>, void (*Destroy)(T*) = sk_delete<T> > |
| class SkLazyPtrArray { |
| public: |
| T* operator[](int i) { |
| SkASSERT(i >= 0 && i < N); |
| // If fPtr has already been filled, we need an consume barrier when loading it. |
| // If not, we need a release barrier when setting it. try_cas will do that. |
| T* ptr = (T*)sk_consume_load(&fArray[i]); |
| return ptr ? ptr : try_cas<T*, Destroy>(&fArray[i], Create(i)); |
| } |
| |
| private: |
| void* fArray[N]; |
| }; |
| |
| } // namespace Private |
| |
| // This version is suitable for use as a class member. |
| // It's the same as above except it has a constructor to zero itself and a destructor to clean up. |
| template <typename T, |
| T* (*Create)() = Private::sk_new<T>, |
| void (*Destroy)(T*) = Private::sk_delete<T> > |
| class SkLazyPtr : public Private::SkLazyPtrBase<T, Create, Destroy> { |
| public: |
| SkLazyPtr() { INHERITED::fPtr = NULL; } |
| ~SkLazyPtr() { if (INHERITED::fPtr) { Destroy((T*)INHERITED::fPtr); } } |
| private: |
| typedef Private::SkLazyPtrBase<T, Create, Destroy> INHERITED; |
| }; |
| |
| |
| #endif//SkLazyPtr_DEFINED |