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From sebb <seb...@gmail.com>
Subject Re: svn commit: r819141 - in /commons/proper/lang/trunk/src: java/org/apache/commons/lang/concurrent/LazyInitializer.java test/org/apache/commons/lang/concurrent/ test/org/apache/commons/lang/concurrent/LazyInitializerTest.java
Date Mon, 28 Sep 2009 10:52:20 GMT
On 28/09/2009, Stephen Colebourne <scolebourne@btopenworld.com> wrote:
> sebb wrote:
>
> > Where is that described? The first reference I found says that the
> > local variable is a performance optimisation; it's the volatile
> > keyword that makes it thread-safe:
> >
> >
> http://technology.amis.nl/blog/4384/the-double-checked-locking-confusion
> > also
> >
> http://jeremymanson.blogspot.com/2008/05/double-checked-locking.html
> >
> > But of course these could be wrong...
> >
>
> http://java.sun.com/developer/technicalArticles/Interviews/bloch_effective_08_qa.html
>
>  "The idiom is very fast but also complicated and delicate, so don't be
> tempted to modify it in any way"
>

That does not necessarily mean that the version without the temporary
variable is wrong.

As I see it, the fact that the variable is volatile is enough to
ensure as-sequential operation, because the write of the volatile
variable happens-before the read.

>  Stephen
>
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