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From Len Popp <len.p...@gmail.com>
Subject Re: Tomcat/JVM hangs in session.getAttribute / HashMap.get()
Date Thu, 08 Sep 2005 16:56:11 GMT
On 9/7/05, Caldarale, Charles R <Chuck.Caldarale@unisys.com> wrote:
> > From: Len Popp [mailto:len.popp@gmail.com]
> > Subject: Re: Tomcat/JVM hangs in session.getAttribute / HashMap.get()
> >
> > So if I want to *safely* call session.setAttribute or
> session.getAttribute
> > I have to make sure the calls are synchronized on session.attributes.
> 
> Actually no - if you can find _all_ the events that can trigger
> references or udpates to session attributes, you can synchronize on any
> object you like.  The synchronize blocks internal to Tomcat then become
> redundant, but they cause no harm.

It would take me quite a while to look at all the possible code paths
inside Tomcat to figure that out. :-(

> Another option (as suggested by the HashMap javadoc) is to modify
> StandardSession to use a HashMap wrappered by
> Collections.synchronizedMap().  No idea what kind of performance impact
> that would have, but at least it would limit the changes needed to just
> one place in one file.
> 
>  - Chuck

That would be easier, but I was hoping I wouldn't have to use a hacked
version of Tomcat.

Thanks for your explanations.
-- 
Len

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