我们见到经常有人用 static 局部对象的方式实现了类似单例模式,最近发现一篇文章明确写明 编译器在处理 static局部变量的时候 并不是线程安全的 !!!
http://blogs.msdn.com/b/oldnewthing/archive/2004/03/08/85901.aspx
https://blog.csdn.net/yue7603835/article/details/49704423
于是实现了一个单例工厂 并且是线程安全的
- #ifndef SINGLETONFACTORY_H
- #define SINGLETONFACTORY_H
- #include "windows.h"
- #include <memory>
- namespace Tools
- {
- template<class T>class SingletonFactory
- {
- public:
- virtual ~SingletonFactory()
- {
- ::DeleteCriticalSection(&__criticalSection);
- }
- std::auto_ptr<T>& GetInstance();
- static SingletonFactory<T>* CreateSingletonFactory();
- private:
- SingletonFactory()
- {
- ::InitializeCriticalSection(&__criticalSection);
- }
- std::auto_ptr<T> __singletonObj;
- CRITICAL_SECTION __criticalSection;
- };
- //初始化创建 后续在多线程中使用
- //还有另一种写法是单独的函数直接返回内部单例包装静态成员在 多线程情况下不安全
- //SingletonFactory::CreateSingletonFactory().GetInstance();
- template<class T> SingletonFactory<T>* SingletonFactory<T>::CreateSingletonFactory(){
- static SingletonFactory<T> temObj;
- return &temObj;
- }
- //工厂实例
- template<class T> std::auto_ptr<T>& SingletonFactory<T>::GetInstance()
- {
- if(__singletonObj.get()==0)
- {
- ::EnterCriticalSection(&__criticalSection);
- if(__singletonObj.get()==0)
- __singletonObj=std::auto_ptr<T>(new T);
- ::LeaveCriticalSection(&__criticalSection);
- }
- return __singletonObj;
- }
- }
- #endif // SINGLETONFACTORY_H
测试代码
- SingletonFactory<Data1>*singleton1=SingletonFactory<Data1>::CreateSingletonFactory();
- singleton1->GetInstance()->x=100;
- cout<<singleton1->GetInstance()->x<<endl;
- singleton1->GetInstance()->y=200;
- cout<<singleton1->GetInstance()->x<<endl;
- cout<<singleton1->GetInstance()->y<<endl;
- SingletonFactory<Data2>*singleton2=SingletonFactory<Data2>::CreateSingletonFactory();
- singleton2->GetInstance()->x=100;
- cout<<singleton2->GetInstance()->x<<endl;
- singleton2->GetInstance()->y=200;
- cout<<singleton2->GetInstance()->x<<endl;
- cout<<singleton2->GetInstance()->y<<endl;