templateclass ObjectPool { enum { nPollSize = 4 }; //最多三个对象 protected: struct _Node { _Node* next; }; _Node* front; //头 _Node* rear; //尾 private: void ReFillPool() //填充 { size_t total = sizeof(_Node) + sizeof(_Ty); for (int i = 0; i < nPoolSize; ++i) { _Node* s = (_Node*)malloc(total); //_Node 和 对象大小都开辟出来 new(s + 1) _Ty(); //在指针后面构造对象 s->next = nullptr; rear->next = s; rear = s; } } void InitPool() //初始化 { if (rear != nullptr) return; _Node* head = (_Node*)malloc(sizeof(_Node)); head->next = nullptr; front = rear = head; } public: ObjectPool() :front(nullptr), rear(nullptr) { InitPool(); } ~ObjectPool() { clear(); } _Ty* allocObjMemory() //获得对象池 { if (front == rear) //为空 注入对象 { ReFillPool(); } _Node* s = front->next; //不为空 取第一个结点 front->next = s->next; if (s == rear) { rear = front; } return (_Ty*)(s + 1); //返回 _Ty 对象 } void freeObjectMemory(void* pobj) { _Node* q = (_Node*)((char*)pobj - sizeof(_Node)); //减去4，回到_Node链表 q->next = rear->next; //将q 归还给链表 尾插 rear->next = q; rear = q; } };
在构造链表的过程中，尽管链表只有一个next成员，但是由于在链表填充的过程中，多分配了一个对象的空间大小
则该链表结构变成，前面4字节为Node指针，后面的为对象的内存
再看下面的代码
templateclass ObjectPool { private: enum { nPoolSize = 4 }; protected: struct _Node { _Node* next; }; _Node* front; _Node* rear; void InitPool() //初始化 { _Node* s = (_Node*)malloc(sizeof(_Node)); s->next = nullptr; front = rear = s; ReFillPool(); } void ReFillPool() //填充 { int total = sizeof(_Node) + sizeof(_Ty); for (int i = 0; i < nPoolSize; ++i) { _Node* s = (_Node*)malloc(total); s->next = nullptr; rear->next = s; rear = s; } } void Clear() { _Node* p = nullptr; while (front->next != nullptr) { p = front->next; front->next = p->next; free p; } free front; front = rear = nullptr; } public: ObjectPool() :front(nullptr), rear(nullptr) { InitPool(); } ~ObjectPool() { Clear(); } ObjectPool(const ObjectPool&) = delete; ObjectPool& opertaor = (const ObjectPool&) = delete; _Ty* allocObjMemory() { if (front == rear) { ReFillPool(); } _Node* s = front->next; front->next = s->next; if (s == rear) rear = front; return (_Ty*)((char*)s + sizeof(_Node)); } void freeObjMemory(void* q) { _Node* p = (_Node*)(char*)q - sizeof(_Node); p->next = nullptr; rear->next = p; rear = p; } }; class Point { private: float _x; float _y; public: Point(float x = 0.0f, float y = 0.0f) :_x(x), _y(y) {} Point(const Point&) = default; Point& operator = (const Point&) = default; ~Point() {} public: void* operator new(size_t sz) //静态方法 没有this指针 { return malloc(sz); } //1. 计算大小 //2. 分配空间 //3. 返回地址 调用构造函数 void operator delete(void* p) //size_t sz { free(p); } //自动计算指针所指之物的大小，传递给delete //系统将new delete默认定义为静态 }; int main() { Point* pa1 = new Point(1, 2); delete pa1; }
系统对象operator new 和 operator delete 的重载进行了作弊行为，系统会将他们自动定义为静态函数，并且会自动计算类型的大小进行传入
- operator new
- 计算大小
- 分配空间
- 返回地址 调用构造函数
- delete
- 自动计算指针所指之物的大小，传递给delete
根据下面代码，我们在operator new 与 operator delete 调度ObjectPool，但是这样并不属于我们将对象创建好再直接去使用，而是一个一个去构建
templateclass ObjectPool { private: enum { nPoolSize = 4 }; protected: struct _Node { _Node* next; }; _Node* front; _Node* rear; void InitPool() //初始化 { _Node* s = (_Node*)malloc(sizeof(_Node)); s->next = nullptr; front = rear = s; ReFillPool(); } void ReFillPool() //填充 { int total = sizeof(_Node) + sizeof(_Ty); for (int i = 0; i < nPoolSize; ++i) { _Node* s = (_Node*)malloc(total); s->next = nullptr; rear->next = s; rear = s; } } void Clear() { _Node* p = nullptr; while (front->next != nullptr) { p = front->next; front->next = p->next; free p; } free front; front = rear = nullptr; } public: ObjectPool() :front(nullptr), rear(nullptr) { InitPool(); } ~ObjectPool() { Clear(); } ObjectPool(const ObjectPool&) = delete; ObjectPool& opertaor = (const ObjectPool&) = delete; _Ty* allocObjMemory() { if (front == rear) { ReFillPool(); } _Node* s = front->next; front->next = s->next; if (s == rear) rear = front; return (_Ty*)((char*)s + sizeof(_Node)); } void freeObjMemory(void* q) { _Node* p = (_Node*)(char*)q - sizeof(_Node); p->next = nullptr; rear->next = p; rear = p; } }; class Point { private: static ObjectPool PointPool; private: float _x; float _y; public: Point(float x = 0.0f, float y = 0.0f) :_x(x), _y(y) {} Point(const Point&) = default; Point& operator = (const Point&) = default; ~Point() {} public: void* operator new(size_t sz) //静态方法 没有this指针 { return PointPool.allocObjMemory(); //函数本身没用this指针，成员属于私有成员，需要指针指向成员 //PointPool设计为静态对象 } void operator delete(void* p) //size_t sz { PointPool.freeObjMemory(p); } }; int main() { Point* pa1 = new Point(1, 2); Point* pa2 = new Point(3, 4); delete pa1; delete pa2; return 0; }
templateclass ObjectPool { private: enum { nPoolSize = 4 }; protected: struct _Node { _Node* next; }; _Node* front; _Node* rear; void InitPool() //初始化 { _Node* s = (_Node*)malloc(sizeof(_Node)); s->next = nullptr; new(s + 1) _Ty(); //构建对象 front = rear = s; ReFillPool(); } void ReFillPool() //填充 { int total = sizeof(_Node) + sizeof(_Ty); for (int i = 0; i < nPoolSize; ++i) { _Node* s = (_Node*)malloc(total); s->next = nullptr; rear->next = s; rear = s; } } void Clear() { _Node* p = nullptr; while (front->next != nullptr) { p = front->next; front->next = p->next; free(p); } free(front); front = rear = nullptr; } public: ObjectPool() :front(nullptr), rear(nullptr) { InitPool(); } ~ObjectPool() { Clear(); } ObjectPool(const ObjectPool&) = delete; ObjectPool& operator=(const ObjectPool&) = delete; _Ty* allocObjMemory() { if (front == rear) { ReFillPool(); } _Node* s = front->next; front->next = s->next; if (s == rear) rear = front; return (_Ty*)((char*)s + sizeof(_Node)); } void freeObjMemory(void* q) { _Node* p = (_Node*)(char*)q - sizeof(_Node); p->next = nullptr; rear->next = p; rear = p; } }; template class ObjectPoolBase { public: _Ty* GetObject() //获得对象 { return objpool.allocObjMemory(); } void RetObject(_Ty* p) //归还对象 { objpool.freeObjMemory(p); } static ObjectPoolBase<_Ty>& instance() { static ObjectPoolBase<_Ty> objbase; return objbase; } private: using ClassTypePool = ObjectPool<_Ty>; ClassTypePool objpool; }; class Point { private: static ObjectPool PointPool; private: float _x; float _y; public: Point(float x = 0.0f, float y = 0.0f) :_x(x), _y(y) {} Point(const Point&) = default; Point& operator = (const Point&) = default; ~Point() {} public: void* operator new(size_t) = delete; void operator delete(void*) = delete; }; int main() { ObjectPoolBase & pointpool = ObjectPoolBase ::instance(); Point* ap = pointpool.GetObject(); pointpool.RetObject(ap); return 0; }
这里添加ObjectPoolBase类型，使用单例模式来添加一个中间类，提供调用接口
templateclass ObjectPool { private: enum { nPoolSize = 4 }; protected: struct _Node { _Node* next; }; _Node* front; _Node* rear; void InitPool() //初始化 { if (rear != nullptr) return; _Node* s = (_Node*)malloc(sizeof(_Node)); s->next = nullptr; front = rear = s; ReFillPool(); } void ReFillPool() //填充 { int total = sizeof(_Node) + sizeof(_Ty); for (int i = 0; i < nPoolSize; ++i) { _Node* s = (_Node*)malloc(total); new(s + 1) _Ty();//构造对象 s->next = nullptr; rear->next = s; rear = s; } } void Clear() { _Node* p = nullptr; while (front->next != nullptr) { p = front->next; front->next = p->next; free(p); } free(front); front = rear = nullptr; } public: ObjectPool() :front(nullptr), rear(nullptr) { InitPool(); } ~ObjectPool() { Clear(); } ObjectPool(const ObjectPool&) = delete; ObjectPool& operator=(const ObjectPool&) = delete; _Ty* allocObjMemory() { if (front == rear) { ReFillPool(); } _Node* s = front->next; front->next = s->next; if (s == rear) rear = front; return (_Ty*)((char*)s + sizeof(_Node)); } void freeObjMemory(void* q) { _Node* p = (_Node*)((char*)q - sizeof(_Node)); p->next = nullptr; rear->next = p; rear = p; } }; template class ObjectPoolBase { public: _Ty* GetObject() //获得对象 { return objpool.allocObjMemory(); } void RetObject(_Ty* p) //归还对象 { objpool.freeObjMemory(p); } static ObjectPoolBase<_Ty>& instance() { static ObjectPoolBase<_Ty> objbase; return objbase; } private: using ClassTypePool = ObjectPool<_Ty>; ClassTypePool objpool; }; class Point { private: static ObjectPool PointPool; private: float _x; float _y; public: Point(float x = 0.0f, float y = 0.0f) :_x(x), _y(y) {} Point(const Point&) = default; Point& operator = (const Point&) = default; ~Point() {} public: void operator delete(void*) = delete; }; int main() { ObjectPoolBase & pointpool = ObjectPoolBase ::instance(); Point* ap = pointpool.GetObject(); pointpool.RetObject(ap); return 0; }
