[concurrency-interest] a question regarding thedouble-checke dlocking

Bill Pugh pugh at cs.umd.edu
Mon Jun 19 10:26:51 EDT 2006


On Jun 19, 2006, at 5:29 AM, Yechiel Feffer wrote:

> I am concerned with general correctness of my code,
> want to avoid the price of volatile, here is a quote from jsr133 FAQ
> "However, for fans of double-checked locking (and we really hope  
> there are none left), the news is still not good. The whole point  
> of double-checked locking was to avoid the performance overhead of  
> synchronization. Not only has brief synchronization gotten a LOT  
> less expensive since the Java 1.0 days, but under the new memory  
> model, the performance cost of using volatile goes up, almost to  
> the level of the cost of synchronization. So there's still no good  
> reason to use double-checked-locking"
>


That is not from the JSR 133 FAQ.

The person who wrote that doesn't know what they are talking about.

The cost of a volatile read is significantly less than synchronization.
In fact, you would be hard pressed to find an increase over the cost of
a normal read in a double checked locking usage.

	Bill


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