C++单例模式

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本文介绍了一种使用C++实现线程安全的单例模式的方法。通过互斥锁确保实例创建过程中的线程安全性，并提供了getInstance和destroy方法来获取单例对象和释放资源。

//
// Created by fengxb on 18-7-28.
//

#ifndef SINGLETON_SINGLETON_H
#define SINGLETON_SINGLETON_H

#include <pthread.h>

class Singleton{
public:
    static Singleton* getInstance();
    static void destroy();
private:
    Singleton();
    ~Singleton();

private:
    static pthread_mutex_t mutex;
    static Singleton* singleton_ptr;
};

#endif //SINGLETON_SINGLETON_H

//
// Created by fengxb on 18-7-28.
//
#include <iostream>
#include "Singleton.h"

Singleton* Singleton::singleton_ptr= nullptr;
pthread_mutex_t Singleton::mutex;

Singleton* Singleton::getInstance()  {
    if(singleton_ptr== nullptr){
        pthread_mutex_init(&mutex, nullptr);
        pthread_mutex_lock(&mutex);
        if(singleton_ptr== nullptr){
            singleton_ptr=new Singleton();
        }
        pthread_mutex_unlock(&mutex);
        pthread_mutex_destroy(&mutex);
    }
    return singleton_ptr;
}

Singleton::Singleton() {
    std::cout<<"constructor"<<std::endl;
}

Singleton::~Singleton() {
    std::cout<<"destructor"<<std::endl;
    singleton_ptr= nullptr;
}

void Singleton::destroy() {
    if(singleton_ptr){
        pthread_mutex_init(&mutex, nullptr);
        pthread_mutex_lock(&mutex);
        if(singleton_ptr){
            delete singleton_ptr;
            singleton_ptr= nullptr;
        }
        pthread_mutex_unlock(&mutex);
        pthread_mutex_destroy(&mutex);
    }
}

#include <iostream>
#include "Singleton.cpp"
int main() {
    Singleton *a=Singleton::getInstance();
    Singleton *b=Singleton::getInstance();
    if(a==b) {
        std::cout<<"a==b"<<std::endl;
    }
    Singleton *c=Singleton::getInstance();
    std::cout<<a<<std::endl;
    std::cout<<b<<std::endl;
    std::cout<<c<<std::endl;
    a->destroy();
//    b->destroy();
    a= nullptr;
    std::cout<<a<<std::endl;
    std::cout<<b<<std::endl;
    std::cout<<c<<std::endl;
    return 0;
}