Threadsafe singleton using volatile,synchonized

[BLS]

Thanks Sean, indeed a very interesting thread.
>From 2004;It is really worth to browse the archives!
What is the reason/rationale for using volatile in this way ?
 
Another Question:
Is something like this available 

CriticalSectionBegin()
{
// Your Single thread code goes here
}
CriticalSectionEnd()

Bjoern 

Sean Kelly Wrote:

> BLS wrote:
> > Probabely I should use D-Learn instead but due to the fact that it is about compiler optimizing ... blah, blah ; Simple question : Is this singleton implementation thread safe ?  Makes : 
> > static volatile Singleton _instance
> > sense ?
> > 
> > module pattern.singleton
> > 
> > class Singleton 
> > {
> > public:
> > 	static Singleton getInstance()
> > 	{
> > 		// double check lock
> >         if (_instance is null)
> > 		{
> > 			synchronized {
> >                 if (_instance is null) 
> > 				{
> >                     _instance = new Singleton();
> >                 }
> >             }
> >         }
> >         return _instance;      
> >     }
> > private:
> > 	this() {} 
> > 	
> > 	// do not optimize  
> > 	static volatile Singleton _instance;
> > }
> 
> 
> No.  The 'volatile' qualifier is applied to a statement, not a variable. 
>   You need to do something like this:
> 
> # class Singleton
> # {
> #     static Singleton s;
> #
> #     Singleton instance()
> #     {
> #         volatile Singleton tmp = s;
> #         if(!tmp)
> #         {
> #            synchronized
> #            {
> #                tmp = s;
> #                if(!tmp)
> #                {
> #                   volatile tmp = new Singleton();
> #                   s = tmp;
> #                }
> #            }
> #         }
> #         return s;
> #     }
> # }
> 
> This is from:
> 
> http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digitalmars.D&artnum=9260
> 
> in thread:
> 
> http://www.digitalmars.com/d/archives/digitalmars/D/9149.html#N9231
> 
> 
> Sean