【设计模式】单例模式

总结一下单例模式便于自己之后的复习

1.懒汉模式【版本1：线程不安全】

class Singleton
{
    private:
        Singleton(){}
        static Singleton* instance;
    public:
        int a;
        static Singleton* getInstance();
};

Singleton* Singleton::instance = NULL;

Singleton* Singleton::getInstance()
{
    if(instance == NULL)   
        instance = new Singleton();
    return instance;
}

2.懒汉模式【版本2：加锁来保证线程安全】

使用线程库pthread，linux平台下是支持的，windows下需要配置：配置链接

#include<bits/stdc++.h>
#include<pthread.h>
using namespace std;

class Singleton
{	
	private:	
		 Singleton(){}
		 static Singleton* instance;
	 public:
		 int a;
		 static pthread_mutex_t mutex_lock;
		 static Singleton* getInstance();
};

//初始化静态变量
pthread_mutex_t Singleton::mutex_lock = PTHREAD_MUTEX_INITIALIZER;
Singleton* Singleton::instance = NULL;	

Singleton* Singleton::getInstance()
{	
	pthread_mutex_lock(&mutex_lock);
	    if(instance == NULL)   
		  instance = new Singleton();
	pthread_mutex_unlock(&mutex_lock); 
	return instance;
}

int main()
{
	Singleton* p = Singleton::getInstance();
	p->a = 10;
	cout<<p->a<<endl;
	return 0;
} 

编译g++ -lpthread -o app singleton.cpp
结果：

3.饿汉模式

class Singleton
{
private:
    Singleton(){}
    static Singleton* instance;
public:
    int a;
    ~Singleton(){   instance = NULL;}
    static Singleton* getInstance();
};
Singleton* Singleton::instance = new Singleton();
Singleton* Singleton::getInstance()
{
    return instance;
}