139 lines
3.0 KiB
C++
139 lines
3.0 KiB
C++
#ifndef BASE_FRAMEWORK_OBSERVER_LIST_H_
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#define BASE_FRAMEWORK_OBSERVER_LIST_H_
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#include <assert.h>
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#include <vector>
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#include <algorithm>
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/*
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* 这个类主要解决一个问题：
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* 当MessagePump在遍历ObserverList的时候，
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* 允许从一个Observer内部调用RemoveObserver来移除自己或者别的Observer而不会导致接下来的遍历崩溃（iterator被erase）
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*
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* Google Chrome的做法是重载iterator，这里采用lazy erase技术。下面是示例代码：
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*
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* ObserverList<Observer> observers;
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* ...
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* observers.AquireLazyErase(); // aquire lazy erase
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* size_t index = 0;
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* for (;;)
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* {
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* Observer *observer = observers.GetObject(index++);
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* if (observer == NULL)
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* break;
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* // use observer here
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* }
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* observers.ReleaseLazyErase(); // release lazy erase
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* observer.Compact(); // compact the list
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*/
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class LazyEraser
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{
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public:
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LazyEraser() : lazy_erase_(0) {}
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/* NOTE: calling 'ApplyLasyErase' increases the reference count, calling 'ReleaseLasyErase' decreases the reference count */
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int AquireLazyErase() { return ++lazy_erase_; }
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int ReleaseLazyErase() { assert(lazy_erase_ > 0); return --lazy_erase_; }
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virtual void Compact() = 0;
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protected:
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int lazy_erase_;
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};
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class AutoLazyEraser
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{
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public:
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AutoLazyEraser(LazyEraser* lazy_eraser) : ptr_(lazy_eraser)
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{
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if (ptr_)
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ptr_->AquireLazyErase();
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}
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AutoLazyEraser(AutoLazyEraser &lazy_eraser)
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{
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if (lazy_eraser.ptr_)
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lazy_eraser.ptr_->AquireLazyErase();
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ptr_ = lazy_eraser.ptr_;
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}
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void operator=(AutoLazyEraser &lazy_eraser)
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{
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if (lazy_eraser.ptr_)
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lazy_eraser.ptr_->AquireLazyErase();
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ptr_ = lazy_eraser.ptr_;
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}
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~AutoLazyEraser()
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{
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if (ptr_)
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{
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if (ptr_->ReleaseLazyErase() < 1)
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ptr_->Compact();
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}
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}
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private:
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LazyEraser *ptr_;
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};
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template<typename ObserverType>
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class ObserverList : public LazyEraser
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{
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public:
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void AddObserver(ObserverType *observer)
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{
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assert(observer);
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if (std::find(observers_.begin(), observers_.end(), observer) == observers_.end())
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observers_.push_back(observer);
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}
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void RemoveObserver(ObserverType *observer)
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{
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typename std::vector<ObserverType *>::iterator pos = std::find(observers_.begin(), observers_.end(), observer);
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if (pos == observers_.end())
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return;
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/* this method may be called within a traversal of the list */
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if (lazy_erase_ > 0)
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*pos = NULL;
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else
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observers_.erase(pos);
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}
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void Compact()
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{
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if (lazy_erase_ > 0 || observers_.empty())
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return;
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ObserverType **src = &observers_[0];
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ObserverType **target = src;
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ObserverType **end = src + observers_.size();
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/* fast compacting algorithm */
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while (src < end)
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{
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if (*src != NULL)
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{
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if (target != src)
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*target = *src;
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target++;
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}
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src++;
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}
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observers_.resize(target - &observers_[0]);
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}
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ObserverType* GetObserver(size_t index) const
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{
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if (index >= GetObserverCount())
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return NULL;
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return observers_[index];
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}
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size_t GetObserverCount() const { return observers_.size(); };
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private:
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std::vector<ObserverType *> observers_;
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};
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#endif // BASE_FRAMEWORK_OBSERVER_LIST_H_
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