#include <iostream>
#include <mutex>
using namespace std;

//懒汉式
/*
class SingleObject
{
private:
    SingleObject()
    {
        cout << "create SingleObject" << endl;
    }
    static SingleObject *instance;

public:
    static SingleObject *getInstance()
    {
        if (instance == nullptr)
        {
            instance = new SingleObject();
        }
        return instance;
    }
};
SingleObject *SingleObject::instance = nullptr;
*/

//饿汉式
/*
class SingleObject
{
private:
    SingleObject()
    {
        cout << "create SingleObject" << endl;
    }

public:
    static SingleObject *getInstance()
    {
        static SingleObject instance;
        return &instance;
    }
}
*/

//多线程加锁
class SingleObject
{
private:
    SingleObject()
    {
        cout << "create SingleObject" << endl;
    }
    static SingleObject *instance;
    static mutex *my_mutext;

public:
    static SingleObject *getInstance()
    {
        if(instance == nullptr)
        {
            my_mutext->lock();
            instance = new SingleObject();
            my_mutext->unlock();
        }
        return instance;
    }
    void test()
    {
        cout << "hello world" << endl;
    }
};

SingleObject *SingleObject::instance = nullptr;
mutex *SingleObject::my_mutext = new mutex();