对象大小固定的单线程内存池设计

超、凢脫俗 2022-09-23 03:54 84阅读 0赞

类Rational通过重载new和delete以实现高效的内存分配，提高程序性能。  
具体设计方案如下：

class Rational
    {
    public:
        Rational(int a = 0, int b = 1)
            :n(a), d(b)
        {}
    
        void* operator new(size_t size){
            return memPool->alloc(size);
        }
    
        void operator delete(void* doomed, size_t size){
            memPool->free(doomed);
        }
    
    private:
        int n;
        int d;
        static MemoryPool<Rational>* memPool;
    };
    
    
    /*
        以下为内存分配与回收类## 标题 ##的实现
    */
    
    template <class T>
    class MemoryPool
    {
    public:
        MemoryPool(size_t size = EXPANSION_SIZE);
        ~MemoryPool();
    
    
        inline void* alloc(size_t size);
    
        inline void free(void* someElement);
    private:
        //空闲列表的下一个元素
        MemoryPool<T>* next;
    
        //如果空闲列表为空，就按该大小扩展它
        enum{ EXPANSION_SIZE = 32};
    
        //添加空闲元素至空闲列表
        void expandTheFreeList(inthowMany = EXPANSION_SIZE);
    };
    
    
    template <class T>
    MemoryPool<T>::MemoryPool(size_t size)
    {
        expandTheFreeList(size);
    }
    
    
    //析构函数  遍历空间列表，并删除所有元素
    template <class T>
    MemoryPool<T>::~MemoryPool()
    {
        MemoryPool* nextPtr = next;
        for (nextPtr = next; nextPtr != NULL; nextPtr = next){
            next = next->next;
            delete[] nextPtr;
        }
    }
    
    //分配内存
    template <class T>
    inline
    void* MemoryPool<T>::alloc(size_t)
    {
        if (!next){
       //内存用尽则调用expandTheFreeList扩充
            expandTheFreeList();
        }
    
        MemoryPool<T>* head = next;
        next = head->next;
    
        return head;
    }
    
    //将内存回收到空闲列表
    template <class T>
    inline
    void MemoryPool<T>::free(void* doomed)
    {
        MemoryPool<T>* head = static_cast<MemoryPool<T>*>(doomed);
        head->next = next;
        next = head;
    }
    
    
    //expandTheFreeList向堆中分配新元素，然后将它们连接到空闲列表中
    //当空闲列表被用尽时调用
    template <class T>
    void MemoryPool<T>::expandTheFreeList(int howMany)
    {
        //分配足够大的对象已包含下一个指针
        size_t size = (sizeof(T) > sizeof(MemoryPool<T>*)) ?
            sizeof(T) : sizeof(MemoryPool<T>*);
    
        MemoryPool<T>* runner = static_cast<MemoryPool<T>*>(new char[size]);
        next = runner;
        for (int i = 0; i < howMany; i++){
            runner->next = static_cast<MemoryPool<T>*>new char[size];
            runner = runner->next;
        }
        runner->next = 0;
    }

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读书笔记：《提高C++性能的编程技术》