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NNTP-Posting-Date: Sat, 13 Aug 2011 16:48:34 -0500
Date: Sat, 13 Aug 2011 14:48:31 -0700
From: Patricia Shanahan <pats@acm.org>
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Subject: Re: Singleton Pattern
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On 8/13/2011 1:56 PM, vbhavsar@gmail.com wrote:
...
> public class Singleton {
>
> 	private static Singleton _instance;
> 	private Singleton(){}
>
> 	private synchronized static void createInstance(){
> 		_instance = new Singleton();
> 	}
>
> 	public static Singleton getInstance(){
> 		if (_instance == null){
> 			createInstance();
> 		}
> 		return _instance;
> 	}
> }
...
> Anyone see any issues with this?

Suppose thread A calls getInstance, sees _instance to be null, calls
createInstance, and some time later thread B calls getInstance and also
sees _instance to be null. Isn't B going to go ahead and re-initialize
_instance?

If you do not think that is possible, please explain why not.

Patricia