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https://issues.apache.org/jira/browse/POOL-161?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12874126#action_12874126
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Mark Thomas commented on POOL-161:
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I wonder if we want to support this use case. The simple solution would be to
package commons-pool in each web application. Disk is cheap, memory is cheap.
Is the memory and disk space saved worth the additional complexity?
I am currently looking to fix a related issue in Tomcat's use of commons-dbcp
and commons-pool. I believe I'll be able to fix that entirely within Tomcat but
if not, it will likely impact this fix. I'll report back here with any progress
on the Tomcat issue.
> 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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