| |
| /* |
| * Copyright 2011 Google Inc. |
| * |
| * Use of this source code is governed by a BSD-style license that can be |
| * found in the LICENSE file. |
| */ |
| |
| |
| |
| #ifndef SkTLazy_DEFINED |
| #define SkTLazy_DEFINED |
| |
| #include "SkTypes.h" |
| #include <new> |
| |
| template <typename T> class SkTLazy; |
| template <typename T> void* operator new(size_t, SkTLazy<T>* lazy); |
| |
| /** |
| * Efficient way to defer allocating/initializing a class until it is needed |
| * (if ever). |
| */ |
| template <typename T> class SkTLazy { |
| public: |
| SkTLazy() : fPtr(NULL) {} |
| |
| explicit SkTLazy(const T* src) : fPtr(NULL) { |
| if (src) { |
| fPtr = new (fStorage) T(*src); |
| } |
| } |
| |
| SkTLazy(const SkTLazy<T>& src) : fPtr(NULL) { |
| if (src.isValid()) { |
| fPtr = new (fStorage) T(*src->get()); |
| } else { |
| fPtr = NULL; |
| } |
| } |
| |
| ~SkTLazy() { |
| if (this->isValid()) { |
| fPtr->~T(); |
| } |
| } |
| |
| /** |
| * Return a pointer to a default-initialized instance of the class. If a |
| * previous instance had been initialized (either from init() or set()) it |
| * will first be destroyed, so that a freshly initialized instance is |
| * always returned. |
| */ |
| T* init() { |
| if (this->isValid()) { |
| fPtr->~T(); |
| } |
| fPtr = new (SkTCast<T*>(fStorage)) T; |
| return fPtr; |
| } |
| |
| /** |
| * Copy src into this, and return a pointer to a copy of it. Note this |
| * will always return the same pointer, so if it is called on a lazy that |
| * has already been initialized, then this will copy over the previous |
| * contents. |
| */ |
| T* set(const T& src) { |
| if (this->isValid()) { |
| *fPtr = src; |
| } else { |
| fPtr = new (SkTCast<T*>(fStorage)) T(src); |
| } |
| return fPtr; |
| } |
| |
| /** |
| * Destroy the lazy object (if it was created via init() or set()) |
| */ |
| void reset() { |
| if (this->isValid()) { |
| fPtr->~T(); |
| fPtr = NULL; |
| } |
| } |
| |
| /** |
| * Returns true if a valid object has been initialized in the SkTLazy, |
| * false otherwise. |
| */ |
| bool isValid() const { return SkToBool(fPtr); } |
| |
| /** |
| * Returns the object. This version should only be called when the caller |
| * knows that the object has been initialized. |
| */ |
| T* get() const { SkASSERT(this->isValid()); return fPtr; } |
| |
| /** |
| * Like above but doesn't assert if object isn't initialized (in which case |
| * NULL is returned). |
| */ |
| T* getMaybeNull() const { return fPtr; } |
| |
| private: |
| friend void* operator new<T>(size_t, SkTLazy* lazy); |
| |
| T* fPtr; // NULL or fStorage |
| char fStorage[sizeof(T)]; |
| }; |
| |
| // Use the below macro (SkNEW_IN_TLAZY) rather than calling this directly |
| template <typename T> void* operator new(size_t, SkTLazy<T>* lazy) { |
| SkASSERT(!lazy->isValid()); |
| lazy->fPtr = reinterpret_cast<T*>(lazy->fStorage); |
| return lazy->fPtr; |
| } |
| |
| // Skia doesn't use C++ exceptions but it may be compiled with them enabled. Having an op delete |
| // to match the op new silences warnings about missing op delete when a constructor throws an |
| // exception. |
| template <typename T> void operator delete(void*, SkTLazy<T>*) { SK_CRASH(); } |
| |
| // Use this to construct a T inside an SkTLazy using a non-default constructor. |
| #define SkNEW_IN_TLAZY(tlazy_ptr, type_name, args) (new (tlazy_ptr) type_name args) |
| |
| /** |
| * A helper built on top of SkTLazy to do copy-on-first-write. The object is initialized |
| * with a const pointer but provides a non-const pointer accessor. The first time the |
| * accessor is called (if ever) the object is cloned. |
| * |
| * In the following example at most one copy of constThing is made: |
| * |
| * SkTCopyOnFirstWrite<Thing> thing(&constThing); |
| * ... |
| * function_that_takes_a_const_thing_ptr(thing); // constThing is passed |
| * ... |
| * if (need_to_modify_thing()) { |
| * thing.writable()->modifyMe(); // makes a copy of constThing |
| * } |
| * ... |
| * x = thing->readSomething(); |
| * ... |
| * if (need_to_modify_thing_now()) { |
| * thing.writable()->changeMe(); // makes a copy of constThing if we didn't call modifyMe() |
| * } |
| * |
| * consume_a_thing(thing); // could be constThing or a modified copy. |
| */ |
| template <typename T> |
| class SkTCopyOnFirstWrite { |
| public: |
| SkTCopyOnFirstWrite(const T& initial) : fObj(&initial) {} |
| |
| // Constructor for delayed initialization. |
| SkTCopyOnFirstWrite() : fObj(NULL) {} |
| |
| // Should only be called once, and only if the default constructor was used. |
| void init(const T& initial) { |
| SkASSERT(NULL == fObj); |
| SkASSERT(!fLazy.isValid()); |
| fObj = &initial; |
| } |
| |
| /** |
| * Returns a writable T*. The first time this is called the initial object is cloned. |
| */ |
| T* writable() { |
| SkASSERT(fObj); |
| if (!fLazy.isValid()) { |
| fLazy.set(*fObj); |
| fObj = fLazy.get(); |
| } |
| return const_cast<T*>(fObj); |
| } |
| |
| /** |
| * Operators for treating this as though it were a const pointer. |
| */ |
| |
| const T *operator->() const { return fObj; } |
| |
| operator const T*() const { return fObj; } |
| |
| const T& operator *() const { return *fObj; } |
| |
| private: |
| const T* fObj; |
| SkTLazy<T> fLazy; |
| }; |
| |
| #endif |