设计模式之-单例模式

单例在资源管理相关等方面 基本上是必须使用的。


代码：

#include<iostream>
#include <pthread.h>
#include <stdlib.h>
using namespace std;
class noncopyable {
protected:
    noncopyable(){};
    ~noncopyable(){};
private:
    noncopyable(const noncopyable&);
    const noncopyable& operator=(const noncopyable&);
};

template <typename T>
class Singleton : public noncopyable {
public:
    static T* instance() {
        pthread_once(&ponce_, &Singleton::Init);
        return value_;
    }

private:
    Singleton();
    ~Singleton();

    static void Init() {
        value_ = new T();
        ::atexit(Destroy);
    }
    static void  Destroy() {
        delete value_;
    }

private:

    static pthread_once_t ponce_;
    static T* value_;


};

template <typename T>
pthread_once_t Singleton<T>::ponce_ = PTHREAD_ONCE_INIT;

template <typename T>
T* Singleton<T>::value_ = NULL;


class AA {
public:
    void show() { cout << "a" ;}
};

int main(int argc, char* argv[]) {

    AA *pa = Singleton<AA>::instance();
    pa->show();
    return 0;
}