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/*************************************************************************
> File Name: Singleton.cpp
> Created Time: Tue 31 Oct 2017 10:20:58 PM CST
************************************************************************/
#include <iostream>
using namespace std;
#include <pthread.h>
//懒汉式 (创建的时候采取new实例)以时间换取空间,线程不安全
class singleton_L
{
public:
static singleton_L* getinstance()
{
if(instance == NULL)
{
instance = new singleton_L();
}
return instance;
}
~singleton_L()
{
if(instance != NULL)
{
delete instance;
instance = NULL;
}
}
private:
singleton_L(){}
static singleton_L* instance;
};
singleton_L* singleton_L::instance = NULL;
//饿汉式(在定义实例的时候就去new对象)以空间换时间
class singleton_E
{
public:
static singleton_E* getinstance()
{
return instance;
}
private:
singleton_E(){}
static singleton_E* instance;
};
singleton_E* singleton_E::instance = new singleton_E();
//懒汉式 线程安全式(双检锁)
/*
所谓双重检查加锁机制,指的是:并不是每次进入getInstance方法都需要同步,而是先不
同步,进入方法过后,先检查实例是否存在,如果不存在才进入下面的同步块,这是第一重
检查。进入同步块过后,再次检查实例是否存在,如果不存在,就在同步的情况下创建一个
实例,这是第二重检查。这样一来,就只需要同步一次了,从而减少了多次在同步情况下进
行判断所浪费的时间。
*/
class singleton_L_Lock
{
public:
static singleton_L_Lock* getinstance()
{
if(instance == NULL)
{
pthread_mutex_lock(&mutex);
if(instance == NULL)
instance = new singleton_L_Lock();
pthread_mutex_unlock(&mutex);
}
return instance;
}
~singleton_L_Lock()
{
if(instance != NULL)
{
delete instance;
instance = NULL;
}
}
public:
static pthread_mutex_t mutex;
private:
singleton_L_Lock()
{
pthread_mutex_init(&mutex, NULL);
}
private:
static singleton_L_Lock* instance;
};
singleton_L_Lock* singleton_L_Lock::instance = NULL;
pthread_mutex_t singleton_L_Lock::mutex;
int main()
{
singleton_L* p = singleton_L::getinstance();
singleton_L* p1 = singleton_L::getinstance();
singleton_L* p2 = singleton_L::getinstance();
cout << p << endl;
cout << p1 << endl;
cout << p2 << endl;
cout << "=================" << endl;
singleton_E* E = singleton_E::getinstance();
singleton_E* E1 = singleton_E::getinstance();
singleton_E* E2 = singleton_E::getinstance();
cout << E << endl;
cout << E1 << endl;
cout << E2 << endl;
cout << "=================" << endl;
singleton_L_Lock* L = singleton_L_Lock::getinstance();
singleton_L_Lock* L1 = singleton_L_Lock::getinstance();
singleton_L_Lock* L2 = singleton_L_Lock::getinstance();
cout << L << endl;
cout << L1 << endl;
cout << L2 << endl;
return 0;
}