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From Kris Schneider <k...@dotech.com>
Subject Re: <c:set> and runtime expressions
Date Wed, 05 Apr 2006 12:26:53 GMT
The implication that the example singleton class causes a memory leak just 
because "...it creates a hard reference to a class instance into the class 
itself" is hard to believe. There are plenty of other ways to pin classes 
loaded by the web app's class loader, but the singleton pattern isn't one 
of them.

One common way to pin classes is through the JavaBeans Introspector. Since 
the Introspector caches information about the classes it processes, those 
references will keep the web app's class loader from becoming eligible for 
collection. If you're using a container that doesn't take this into 
account, the common solution is to create a ServletContextListener that 
calls Introspector.flushCaches in its contextDestroyed method.

If your singleton is really causing a performance issue, there's probably 
something else going on. If it's released open source, you might want to 
post a link to the code so someone can take a look at it.

Luca Passani wrote:
> Tarek Nabil wrote:
> 
>> Thanks a lot Luca for pointing this out. I must say it's completely new
>> information to me. I wonder if it's really accurate and relevant to all
>> containers.
>>
>> For example, in Oracle Containers for Java (OC4J), when you redeploy an
>> application, the OC4J instance is restarted. You can reload an
>> application without restarting the OC4J instance. Do you think that
>> would make it immune against this kind of problem? I'm also going to the
>> Oracle forums with that question.  
>>
> can you post (or send me off-line) a pointer to your post on the Oracle 
> forum?
> 
> I am interested in this for a bit of open source that I have released 
> and where I have used a Singleton.
> If I restart the application, it takes increasingly more time for the 
> app-server to recover each time the Singleton is rebuilt.
> This is a problem I want to fix for the first release.
> 
> Luca

-- 
Kris Schneider <mailto:kris@dotech.com>
D.O.Tech       <http://www.dotech.com/>

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