多线程安全单例模式学习代码 c++11

// Singleton.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <mutex>        
#include <iostream>
#include <windows.h>

using namespace std;

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std::mutex gPrintMtx;    // 多线程下 用于打印的互斥量
std::mutex gSingletonmtx;        // Singleton类的互斥量
std::mutex gSamplemtx;        // 示例类的互斥量

// 单例模式类 模板为实际单例类
template<typename T>
class Singleton {
public:
    // 多线程下使用互斥量 注意死锁
    Singleton() {
        std::lock_guard<std::mutex> lck(gSingletonmtx);
        count++;
        if (p == NULL) {
            p = new T();
        }
        std::lock_guard<std::mutex> lock(gPrintMtx);
        //cout << "Singleton ..." << endl;
    }

    T* GetInstance() {
        return p;
    }
    ~Singleton() {
        //    使用计数来决定是否删除实际单例类
        std::lock_guard<std::mutex> lck(gSingletonmtx);
        count--;
        if (p != NULL&&count == 0)
        {
            delete p;
            p = NULL;
            count = 0;
            std::lock_guard<std::mutex> lock(gPrintMtx);
            cout << "~Singleton delete" << endl;
        }
        std::lock_guard<std::mutex> lock(gPrintMtx);
        //cout << "~Singleton ..." << endl;
    }
private:
    static int count;
    static T* p;

};

template<typename T>
T* Singleton<T>::p = NULL;

template<typename T>
int Singleton<T>::count = 0;


// 单例模式的示例类
class Sample {
public:
    // 多线程下使用互斥量 注意死锁
    Sample() { 
        std::lock_guard<std::mutex> lck(gSamplemtx);
        std::lock_guard<std::mutex> lock(gPrintMtx);
        count++; cout << "Sample..." << endl; 
    }
    void GetCount(){ 
        std::lock_guard<std::mutex> lck(gSamplemtx);
        std::lock_guard<std::mutex> lock(gPrintMtx);
        cout << "****Sample::cout = " << count << endl; 
    }
    ~Sample() { 
        std::lock_guard<std::mutex> lck(gSamplemtx);
        std::lock_guard<std::mutex> lock(gPrintMtx);
        cout << "~Sample..." << endl; 
    }
private:
    static int count ;
};

int Sample::count = 0;

void ThreadFunc() {
    //    多个Sample类 单例模式
    Singleton<Sample> a;
    Singleton<Sample> b;
    Singleton<Sample> c;

    // 查看Sample类的计数 验证
    a.GetInstance()->GetCount();
    b.GetInstance()->GetCount();
    c.GetInstance()->GetCount();
}


int main()
{
    const int threadCount = 20; //线程数目 可更改
    std::thread threads[threadCount];

    // 多线程执行函数
    for (int i = 0; i < threadCount; i++)
    {
        threads[i] = std::thread(ThreadFunc);
    }

    // join() 等待
    for (auto& th : threads)
        th.join();

    return 0;
}

运行显示：

Sample...
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
****Sample::cout = 1
~Sample...
~Singleton delete
请按任意键继续. . .