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From "Phil Steitz (JIRA)" <j...@apache.org>
Subject [jira] Commented: (POOL-161) ContextClassLoader problems for the Evictor thread
Date Sun, 06 Jun 2010 14:33:54 GMT

    [ https://issues.apache.org/jira/browse/POOL-161?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12876046#action_12876046
] 

Phil Steitz commented on POOL-161:
----------------------------------

Thanks, Sylvain.  My mistake on 2.

I am on the fence as to whether to apply Sylvain's patch for 1.5.x or wait until 2.0 to fully
fix the issue.  Does anyone see any risk in applying the patch in 1.5.5?  If we don't apply
it, we should at least update the docs to make it clear that the evictor is nailed to the
loader used to load the library.

> 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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