LazyInstance

1，栈上分配内存

 

private:int8_t buf_[sizeof(_Ty)];_Ty *instance_;DISALLOW_COPY_AND_ASSIGN(LazyInstance);}; 

2. 惰性初始化，在真正用到时才调用构造函数

_Ty* getPtr() {if (!Traits::kAllowedToAccessOnNonjoinableThread)ThreadRestrictions::assertSingletonAllowed();if ((NoBarrier_Load(&state_) != STATE_CREATED) &&needsInstance()) {instance_ = Traits::New(buf_);completeInstance(instance_, Traits::Delete);}return instance_;} 

3. 线程安全

bool LazyInstanceHelper::needsInstance() {if (Acquire_CompareAndSwap(&state_, STATE_EMPTY, STATE_CREATING) == STATE_EMPTY) {return true;} else {while (NoBarrier_Load(&state_) != STATE_CREATED) {ThreadData::yieldCurrentThread();}}return false;} 

4. 用法

static LazyInstance<MyClass> my_instance(base::LINKER_INITIALIZED); void SomeMethod() { my_instance.Get().SomeMethod(); MyClass::SomeMethod() MyClass* ptr = my_instance.Pointer(); ptr->DoDoDo(); }