[C++知识库]多线程单例模式一则

多线程单例创建对象时，需要加锁保护。

其示例代码如下：

#include <atomic>
#include <chrono>
#include <iostream>
#include <mutex>
#include <thread>


class TSingleton
{
public:
   static TSingleton* ins()
    {
        if (__instance != NULL)
            return  __instance;

        locker.lock();
        if (__instance == NULL)
            __instance =   new TSingleton; //注意没有指定atomic，可能导致CPU乱序执行导致异常
        locker.unlock();

        return __instance;
    }

   static void release()
   {
       if (__instance == NULL)
           return;

       locker.lock();
        if (__instance != NULL)
        {
            delete __instance;
            __instance = NULL;
        }
        locker.unlock();
   }

    void speak()
    {
        std::cout << "Welcome to Shanghai !" << std::endl;
    }

    void cry()
    {
        std::cout << "oh, I am seeking you !" << std::endl;
    }

private:
    TSingleton() {};
    static std::atomic<TSingleton*> __instance;
    static std::mutex locker;
};

std::atomic<TSingleton*> TSingleton::__instance = NULL;
std::mutex TSingleton::locker;
bool bExit = false;

int main()
{
    std::thread thr1([=]()
        {
            while (!bExit)
            {
                TSingleton::ins()->speak();
                std::this_thread::sleep_for(std::chrono::seconds(1));
            }
        });

    std::thread thr2([=]()
        {
            while (!bExit)
            {
                TSingleton::ins()->cry();
                std::this_thread::sleep_for(std::chrono::seconds(2));
            }
        });


    thr1.detach();
    thr2.detach();

    char c;
    std::cin >> c;
    bExit = true;
    std::this_thread::sleep_for(std::chrono::seconds(3));
    TSingleton::release();
    return 0;
}

运行效果如下：