Singleton pattern in Ruby

The following is the singleton pattern in Ruby:

ruby 代码

 

1. class Singleton  
2.     private_class_method :new  
3.     @@instance = nil  
4.       
5.       
6.     def Singleton.instance  
7.         if(@instance == nil)  
8.             @instance = new  
9.         end  
10.         return @instance  
11.     end  
12. end  

and you can define two instances of this class by the instance method like this:

ruby 代码

1. s = Singleton.instance  
2. s2 = Singleton.instance  

then you can use this code to test whether the two instances are the same reference or not:

ruby 代码

1. puts s.equal?(s2)  

If you run these codes,you can get 'true' in your console.

But there is a problem,this class can't work in mutl-thread environment,is it right?