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From "Sylvain Laurent (JIRA)" <j...@apache.org>
Subject [jira] Commented: (POOL-161) ContextClassLoader problems for the Evictor thread
Date Sat, 05 Jun 2010 17:51:54 GMT

    [ https://issues.apache.org/jira/browse/POOL-161?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12875921#action_12875921
] 

Sylvain Laurent commented on POOL-161:
--------------------------------------

1. Correct

2. No. Mark's patch fixes the CCL when the TimerThread is started. The patch I provided allows
to have the ObjectFactory called with a different CCL just for the duration of the call. So
there are no leak problems involved here for case #2, just a use case in a multi-classloader
environment

3. The issue I raised did not ask to review the whole commons-pool usage in multi-classloader
environment, I just proposed to fix a use case I encountered. Actually I first discovered
the leak and then found out about the issue about multi-classloader usage...

So, If my patch were applied, I would consider the issue as totally fixed.

> ContextClassLoader problems for the Evictor thread
> --------------------------------------------------
>
>                 Key: POOL-161
>                 URL: https://issues.apache.org/jira/browse/POOL-161
>             Project: Commons Pool
>          Issue Type: Bug
>    Affects Versions: 1.5.4
>            Reporter: Sylvain Laurent
>             Fix For: 2.0
>
>         Attachments: patch_Evictor_CCL.txt, TestGenericObjectPoolClassLoader.patch.txt
>
>
> Since a single Timer is used for several GenericObjectPool instances, this may create
classloader issues and a memory leak of one classloader :
> Let's imagine the following scenario :
> - commons-pool.jar is in the classpath of a webapp container (e.g. tomcat).
> - 2 webapps A and B are deployed, each creating an instance of GenericObjectPool for
its own usage.
> - each webapp makes use of the idle object evictor and sets a positive number for minIdle
> - first, webapp A instantiates its GenericObjectPool. Since this is the first TimerTask
to be created, the Timer instance is created, thus creating a Thread whose ContextClassLoader
is the current one, that is webapp A's ContextClassLoader.
> The TimerTask properly creates instances of idle objects in the pool, making use of the
ObjectFactory provided by A.
> - then B instantiates its GenericObjectPool. A new TimerTask is created, and it tries
to invoke the ObjectFactory provided by B. But when it needs a class that only exists in B
webapp, it cannot find it because the ContextClassLoader of the Timer Thread is A's classloader.
> Other side effect : if webapp A is undeployed, but B is still running, then A's webappClassLoader
cannot be GCed because the Timer Thread keeps a strong reference to A's classloader (as its
context classloader).

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