C++實現一個線程安全的單例工廠

C++實現一個線程安全的單例工廠

我們見到經常有人用 static 局部對象的方式實現了類似單例模式,最近發現一篇文章明確寫明 編譯器在處理 static局部變量的時候 並不是線程安全的 ！！！

於是實現了一個單例工廠 並且是線程安全的

#ifndef SINGLETONFACTORY_H
#define SINGLETONFACTORY_H
#include windows.h
#include 
namespace Tools
{
templateclass SingletonFactory
{
public:
    virtual ~SingletonFactory()
    {
      ::DeleteCriticalSection(&__criticalSection);
    }
    std::auto_ptr& GetInstance();
    static SingletonFactory* CreateSingletonFactory();
private:
    SingletonFactory()
    {
       ::InitializeCriticalSection(&__criticalSection);
    }
    std::auto_ptr __singletonObj;
    CRITICAL_SECTION __criticalSection;
};

//初始化創建  後續在多線程中使用
//還有另一種寫法是單獨的函數直接返回內部單例包裝靜態成員在 多線程情況下不安全
//SingletonFactory::CreateSingletonFactory().GetInstance();
template SingletonFactory* SingletonFactory::CreateSingletonFactory(){
    static SingletonFactory temObj;
    return &temObj;
}
//工廠實例
template std::auto_ptr&  SingletonFactory::GetInstance()
{
    if(__singletonObj.get()==0)
    {
        ::EnterCriticalSection(&__criticalSection);
        if(__singletonObj.get()==0)
            __singletonObj=std::auto_ptr(new T);
        ::LeaveCriticalSection(&__criticalSection);
    }
    return  __singletonObj;
}
}

#endif // SINGLETONFACTORY_H

測試代碼

    SingletonFactory*singleton1=SingletonFactory::CreateSingletonFactory();
    singleton1->GetInstance()->x=100;
    cout<GetInstance()->x<GetInstance()->y=200;
    cout<GetInstance()->x<GetInstance()->y<*singleton2=SingletonFactory::CreateSingletonFactory();
    singleton2->GetInstance()->x=100;
    cout<GetInstance()->x<GetInstance()->y=200;
    cout<GetInstance()->x<GetInstance()->y<