c语言设计模式之单例模式中的饿汉与懒汉详解

#define _CRT_SECURE_NO_WARNINGS 1
#include <iostream>
using namespace std;
class Singleton
{
public:
	//提供静态公有方法，可以类名加域名访问，返回对象指针
	static Singleton* GetInstance()
	{
		return m_instance;
	}
	class GCarbo
	{
	public:
		~GCarbo()
		{
			cout << "delete instance" << endl;
			if (nullptr != m_instance){
				delete Singleton::m_instance;
				m_instance = nullptr;
			}
		}
	};
private:
	//构造函数私有
	Singleton(){
		cout << "Singleton" << endl;
	};
	//防拷贝
	//C++98
	//Singleton(Singleton const&);
	//Singleton& operator=(Singleton const&);
	//C++11
	Singleton(Singleton const&) = delete;
	Singleton& operator=(Singleton const&) = delete;
	static Singleton *m_instance;
	static GCarbo Carbo;
};
//在程序入口之前完成单例对象的初始化
Singleton* Singleton::m_instance = new Singleton;
Singleton::GCarbo Carbo;
int main()
{
	cout << "main begin" << endl;
	//均无法创建实例
	//Singleton s;
	//Singleton* p = new Singleton;
	//调用共有静态成员方法
	Singleton* p1= Singleton::GetInstance();
	Singleton* p2 = Singleton::GetInstance();
	if (p1 == p2){
		cout << "yes" << endl;
	}
	else{
		cout << "no" << endl;
	}
	system("pause");
	return 0;
}

static Singleton* GetInstance()
{
	if (nullptr == m_instance){
			m_instance = new Singleton();
	}
	return m_instance;
}

#define _CRT_SECURE_NO_WARNINGS 1
#include <iostream>
using namespace std;
class Singleton
{
public:
	static Singleton* GetInstance()
	{
		if (nullptr == m_instance){
			m_instance = new Singleton();
		}
		return m_instance;
	}
	//内嵌垃圾回收类
	class CGarbo{
	public:
   		~CGarbo(){
			cout << "delete instance" << endl;
			if (nullptr != Singleton::m_instance){
				delete Singleton::m_instance;
				m_instance = nullptr;
			}
		}
	};
	//定义一个静态成员变量，程序结束后自动调用其析构函数释放单例对象
	static CGarbo Garbo;
private:
	//构造函数私有
	Singleton() {
		printf("Singleton\n");
	};
	//防拷贝
	Singleton(Singleton const&);
	Singleton& operator=(Singleton const&);
	//单例对象指针
	static Singleton* m_instance;
};
Singleton* Singleton::m_instance = nullptr;
Singleton::CGarbo Garbo;
int main()
{
	cout << "main begin" << endl;
	cout << Singleton::GetInstance() << endl;
	cout << Singleton::GetInstance() << endl;
	system("pause");
	return 0;
}

static Singleton* GetInstance()
	{
		//Double-Check方式加锁保证效率和线程安全
		//保证效率
		if (nullptr == m_instance){
			//保证线程安全
			m_mtx.lock();
			//正常检查
			if (nullptr == m_instance){
				m_instance = new Singleton();
			}
			m_mtx.unlock();
		}
		return m_instance;
	}

class Singleton
{
public:
	static volatile Singleton* GetInstance()
	{
		//Double-Check方式加锁保证效率和线程安全
		//保证效率
		if (nullptr == m_instance){
			//保证线程安全
			m_mtx.lock();
			//正常检查
			if (nullptr == m_instance){
				m_instance = new Singleton();
			}
			m_mtx.unlock();
		}
		return m_instance;
	}
	//内嵌垃圾回收类
	class CGarbo{
	public:
		~CGarbo(){
			cout << "delete instance" << endl;
			if (nullptr != Singleton::m_instance){
				delete Singleton::m_instance;
				m_instance = nullptr;
			}
		}
	};
	//定义一个静态成员变量，程序结束后自动调用其析构函数释放单例对象
	static CGarbo Garbo;
private:
	//构造函数私有
	Singleton() {
		//cout原型operator <<() 连续的cout相当于是函数的递归调用过程
		//cout.operator<<(c1);
		//由于线程的特性会导致输出乱序
		printf("Singleton\n");
	};
	//防拷贝
	Singleton(Singleton const&);
	Singleton& operator=(Singleton const&);
	//单例对象指针
	static volatile Singleton* m_instance;
	static mutex m_mtx;
};
volatile Singleton* Singleton::m_instance = nullptr;
Singleton::CGarbo Garbo;
mutex Singleton::m_mtx;
void func(int n)
{
	printf("%d: %p\n", n, Singleton::GetInstance());
	//cout << Singleton::GetInstance() << " " << n << endl;
}
int main()
{
	cout << "main begin" << endl;
	thread t1(func, 1);
	thread t2(func, 2);
	t1.join();
	t2.join();
	printf("%p\n", Singleton::GetInstance());
	printf("%p\n", Singleton::GetInstance());
	system("pause");
	return 0;
}