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From Nick Williams <nicho...@nicholaswilliams.net>
Subject Re: [jira] [Commented] (LOG4J2-406) JMX MBeans are not being unregistered when a tomcat web application that uses log4j is undeployed, leading to a permgen memory leak.
Date Fri, 20 Sep 2013 00:02:34 GMT
Thanks, Remko.

Team: should this method Remko added be called automatically from LoggerContext#stop()?

N

On Sep 19, 2013, at 6:51 PM, Remko Popma (JIRA) wrote:

> 
>    [ https://issues.apache.org/jira/browse/LOG4J2-406?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13772489#comment-13772489
] 
> 
> Remko Popma commented on LOG4J2-406:
> ------------------------------------
> 
> Nick, I did't have much time to work on this but I've added a way to unregister all MBeans
associated with a LoggerContext.
> {{org.apache.logging.log4j.core.jmx.Server#unregisterContext(String loggerContextName)}}
> 
> 
> Next step would be calling this method when a web application is undeployed.
> 
>> JMX MBeans are not being unregistered when a tomcat web application that uses log4j
is undeployed, leading to a permgen memory leak.
>> ------------------------------------------------------------------------------------------------------------------------------------
>> 
>>                Key: LOG4J2-406
>>                URL: https://issues.apache.org/jira/browse/LOG4J2-406
>>            Project: Log4j 2
>>         Issue Type: Bug
>>         Components: Core, JMX
>>   Affects Versions: 2.0-beta9
>>        Environment: Java 1.7.0_17-b02, tomcat 7.0.34.0, NetBeans 7.3, Windows 7 (64
bit)
>>           Reporter: Kerrigan Joseph
>>        Attachments: PermGen.zip
>> 
>> 
>> When the log4j2 library is being used with a tomcat web application (included in
the web application's libraries, not in the container's libraries), tomcat correctly discovers
and initializes the Log4jServletContainerInitializer and adds the Log4JServletContextListener
as described in the [manual|http://logging.apache.org/log4j/2.x/manual/webapp.html] (after
removing "log4j*.jar" from the jarsToSkip property as described on that page). However, two
MBeans that log4j registers (ContextSelector and StatusLogger) are never unregistered when
the web application is undeployed. This prevents the entire web application from being garbage
collected and leads to a permgen memory leak and causes an OutOfMemoryError after a few undeploy/redeploy
cycles*.
>> We could work around this by taking the following steps:
>> # Added a context parameter to the web.xml file specifying a value for the log4jContextName
parameter. This seems to prevent java.lang.ApplicationShutdownHooks from keeping a refernce
to the log4j LoggerContext, which was part of why the memory leak was occuring**.
>> # In addition, took one of the following measures:
>> #* Added the log4j2 libraries to tomcat's classpath. Regardless of whether or not
the libraries were in the web application's classpath, this seemed to circumvent the entire
issue.
>> #* Disabled jmx entirely, by adding -Dlog4j.disable.jmx=true to the JVM options for
tomcat.
>> #* Added a custom ServletContextListener which manually unregisters all log4j MBeans
upon the destruction of the context.
>> Any of the steps from 2 worked equally well, but none of them worked unless we also
took step 1.
>> \* We used jmap and jhat to confirm that the application was not being unloaded from
memory after being undeployed, and were able to narrow the cause down to those MBeans by tracing
a reference path from the StandardClassloader through them to the WebappClassLoader.
>> \** We're unsure of what role ApplicationShutdownHooks plays in this scenario, but
we observed in jhat that the reference path between log4j and ApplicationShutdownHooks disappeared
after adding the log4jContextName parameter, and that this was necessary to stop the permgen
memory leak.
> 
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