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https://issues.apache.org/jira/browse/WW-4058?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13641925#comment-13641925
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Rene Gielen commented on WW-4058:
---------------------------------
Lukasz, your patch won't work since the ContainerHolder-ThreadLocal is bound
per request thread, while the destroy method is bound to the shutdown thread
which most likely never served a request before. Thus you will not be clearing
the actual request ThreadLocal instances in the destroy phase when calling
clear.
That said, we need to cleanup those ThreadLocals by the end of the request. To
me best candidate seems to be Dispatcher.cleanupRequest. I'm not entirely sure
this gets called no matter what, though. A bit annoying when dealing with
ThreadLocals like these is the lazy initialization via Dispatcher.getContainer,
which has a massive call hierarchy. Usually we would want to have ThreadLocals
initialized with a predictable lifecycle, that is init exactly once at the
beginning and destroy guarantied exactly once at the end of the cycle. Also I'm
wondering if we would better be off to use the Request to store the Container
rather than a ThreadLocal. But I'm not sure about the implication at that stage.
Anyway, to clean up ThreadLocals we should call remove() (since 1.6) rather
than set null. I'm going to change this now as a first step
> ContainerHolder causes ThreadLocal memory leak
> ----------------------------------------------
>
> Key: WW-4058
> URL: https://issues.apache.org/jira/browse/WW-4058
> Project: Struts 2
> Issue Type: Bug
> Components: Core Actions
> Affects Versions: 2.3.14
> Environment: Tomcat 7.0.39
> java version "1.7.0_15"
> OpenJDK Runtime Environment (IcedTea7 2.3.7) (7u15-2.3.7-0ubuntu1~12.04.1)
> OpenJDK 64-Bit Server VM (build 23.7-b01, mixed mode)
> Reporter: Boris Morris
> Assignee: Lukasz Lenart
> Fix For: 2.3.15
>
> Attachments: hprof_2.png, hprof.png
>
>
> The localContext ThreadLocal is not cleaned up properly when stopping /
> undeploying / redeploying a S2 application. This will in most cases cause the
> web application ClassLoader not to be garbage collected, thus leaving a
> redeployment memory leak.
> I am using Tomcat 7.0.39 and when I undeploy my application the following is
> reported in the logs:
> {noformat}
> 2013-04-23 12:00:31,082 [request-worker-4] ERROR
> org.apache.catalina.loader.WebappClassLoader- The web application [/dev]
> created a ThreadLocal with key of type [java.lang.ThreadLocal] (value
> [java.lang.ThreadLocal@7f2283e1]) and a value of type
> [com.opensymphony.xwork2.inject.ContainerImpl] (value
> [com.opensymphony.xwork2.inject.ContainerImpl@330069fc]) but failed to remove
> it when the web application was stopped. Threads are going to be renewed over
> time to try and avoid a probable memory leak.
> 2013-04-23 12:00:31,083 [request-worker-4] ERROR
> org.apache.catalina.loader.WebappClassLoader- The web application [/dev]
> created a ThreadLocal with key of type [java.lang.ThreadLocal] (value
> [java.lang.ThreadLocal@7f2283e1]) and a value of type
> [com.opensymphony.xwork2.inject.ContainerImpl] (value
> [com.opensymphony.xwork2.inject.ContainerImpl@330069fc]) but failed to remove
> it when the web application was stopped. Threads are going to be renewed over
> time to try and avoid a probable memory leak.
> 2013-04-23 12:00:31,101 [request-worker-4] ERROR
> org.apache.catalina.loader.WebappClassLoader- The web application [/dev]
> created a ThreadLocal with key of type [java.lang.ThreadLocal] (value
> [java.lang.ThreadLocal@7f2283e1]) and a value of type
> [com.opensymphony.xwork2.inject.ContainerImpl] (value
> [com.opensymphony.xwork2.inject.ContainerImpl@330069fc]) but failed to remove
> it when the web application was stopped. Threads are going to be renewed over
> time to try and avoid a probable memory leak.
> 2013-04-23 12:00:31,101 [request-worker-4] ERROR
> org.apache.catalina.loader.WebappClassLoader- The web application [/dev]
> created a ThreadLocal with key of type [java.lang.ThreadLocal] (value
> [java.lang.ThreadLocal@7f2283e1]) and a value of type
> [com.opensymphony.xwork2.inject.ContainerImpl] (value
> [com.opensymphony.xwork2.inject.ContainerImpl@330069fc]) but failed to remove
> it when the web application was stopped. Threads are going to be renewed over
> time to try and avoid a probable memory leak.
> 2013-04-23 12:00:31,101 [request-worker-4] ERROR
> org.apache.catalina.loader.WebappClassLoader- The web application [/dev]
> created a ThreadLocal with key of type [java.lang.ThreadLocal] (value
> [java.lang.ThreadLocal@7f2283e1]) and a value of type
> [com.opensymphony.xwork2.inject.ContainerImpl] (value
> [com.opensymphony.xwork2.inject.ContainerImpl@330069fc]) but failed to remove
> it when the web application was stopped. Threads are going to be renewed over
> time to try and avoid a probable memory leak.
> 2013-04-23 12:00:31,101 [request-worker-4] ERROR
> org.apache.catalina.loader.WebappClassLoader- The web application [/dev]
> created a ThreadLocal with key of type [java.lang.ThreadLocal] (value
> [java.lang.ThreadLocal@7f2283e1]) and a value of type
> [com.opensymphony.xwork2.inject.ContainerImpl] (value
> [com.opensymphony.xwork2.inject.ContainerImpl@330069fc]) but failed to remove
> it when the web application was stopped. Threads are going to be renewed over
> time to try and avoid a probable memory leak.
> 2013-04-23 12:00:31,102 [request-worker-4] ERROR
> org.apache.catalina.loader.WebappClassLoader- The web application [/dev]
> created a ThreadLocal with key of type [java.lang.ThreadLocal] (value
> [java.lang.ThreadLocal@7f2283e1]) and a value of type
> [com.opensymphony.xwork2.inject.ContainerImpl] (value
> [com.opensymphony.xwork2.inject.ContainerImpl@330069fc]) but failed to remove
> it when the web application was stopped. Threads are going to be renewed over
> time to try and avoid a probable memory leak.
> 2013-04-23 12:00:31,102 [request-worker-4] ERROR
> org.apache.catalina.loader.WebappClassLoader- The web application [/dev]
> created a ThreadLocal with key of type [java.lang.ThreadLocal] (value
> [java.lang.ThreadLocal@7f2283e1]) and a value of type
> [com.opensymphony.xwork2.inject.ContainerImpl] (value
> [com.opensymphony.xwork2.inject.ContainerImpl@330069fc]) but failed to remove
> it when the web application was stopped. Threads are going to be renewed over
> time to try and avoid a probable memory leak.
> 2013-04-23 12:00:31,103 [request-worker-4] ERROR
> org.apache.catalina.loader.WebappClassLoader- The web application [/dev]
> created a ThreadLocal with key of type [java.lang.ThreadLocal] (value
> [java.lang.ThreadLocal@7f2283e1]) and a value of type
> [com.opensymphony.xwork2.inject.ContainerImpl] (value
> [com.opensymphony.xwork2.inject.ContainerImpl@330069fc]) but failed to remove
> it when the web application was stopped. Threads are going to be renewed over
> time to try and avoid a probable memory leak.
> 2013-04-23 12:00:31,103 [request-worker-4] ERROR
> org.apache.catalina.loader.WebappClassLoader- The web application [/dev]
> created a ThreadLocal with key of type [java.lang.ThreadLocal] (value
> [java.lang.ThreadLocal@7f2283e1]) and a value of type
> [com.opensymphony.xwork2.inject.ContainerImpl] (value
> [com.opensymphony.xwork2.inject.ContainerImpl@330069fc]) but failed to remove
> it when the web application was stopped. Threads are going to be renewed over
> time to try and avoid a probable memory leak.
> 2013-04-23 12:00:31,103 [request-worker-4] ERROR
> org.apache.catalina.loader.WebappClassLoader- The web application [/dev]
> created a ThreadLocal with key of type [java.lang.ThreadLocal] (value
> [java.lang.ThreadLocal@7f2283e1]) and a value of type
> [com.opensymphony.xwork2.inject.ContainerImpl] (value
> [com.opensymphony.xwork2.inject.ContainerImpl@330069fc]) but failed to remove
> it when the web application was stopped. Threads are going to be renewed over
> time to try and avoid a probable memory leak.
> 2013-04-23 12:00:31,103 [request-worker-4] ERROR
> org.apache.catalina.loader.WebappClassLoader- The web application [/dev]
> created a ThreadLocal with key of type [java.lang.ThreadLocal] (value
> [java.lang.ThreadLocal@7f2283e1]) and a value of type
> [com.opensymphony.xwork2.inject.ContainerImpl] (value
> [com.opensymphony.xwork2.inject.ContainerImpl@330069fc]) but failed to remove
> it when the web application was stopped. Threads are going to be renewed over
> time to try and avoid a probable memory leak.
> {noformat}
> After poking around in the heap dump it would seem that Tomcat is correct.
> There is indeed a GC root at the ThreadLocal used by the ContainerImpl.
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