ACE的Double-checked-locking的Singleton

 1 class Singleton
 2 {
 3 private:
 4     static Singleton* volatile instance_;
 5     static ACE_Recursive_Thread_Mutex lock_;
 6 protected:
 7     Singleton() {}
 8 public:
 9     static Singleton* Instance()
10     {
11         if (instance_ == 0)
12         {
13             ACE_Guard<ACE_Recursive_Thread_Mutex> guard(lock_);
14             if (instance_ == 0)
15                 instance_ = new Singleton;
16         }
17         return instance_;
18     }
19     
20 };
21 
22 Singleton* volatile Singleton::instance_ = 0;