[jira] [Resolved] (LOG4J2-406) JMX MBeans are not being unregistered when a tomcat web application that uses log4j is undeployed, leading to a permgen memory leak.

["Remko Popma (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/LOG4J2-406?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Remko Popma resolved LOG4J2-406.
--------------------------------

       Resolution: Fixed
    Fix Version/s: 2.0
                   2.0-rc1

Changes:
* MBeans are now re-registered every time the Configuration is modified (previously there were some code paths where MBeans  were not registered).
* _All_ MBeans are now unregistered when the LoggerContext is stopped. This includes the MBeans for the StatusLogger and ContextSelector.
* Cleaned up the o.a.l.l.c.jmx.Server class (mixing format changes with logic changes, sorry about that).

This _should_ solve the problem but when using jhat to view the heap after undeploying the example PermGen application I still see the log4j classes loaded. (Not sure that I did this right...) With another test program I've verified that MBeans are unregistered when the LoggerContext is stopped, though, so is it possible that the problem is caused by something other than the MBeans?

Note also that this is a stopgap solution. It unregisters _all_ MBeans, so unloading one webapp will unload the MBeans for all other webapps as well. This is clearly not ideal but seemed a lesser evil than causing the app server to crash with an OutOfMemoryError. I will create a separate Jira issue for the permanent solution.

Fixed in revision 1557654.
Please verify and close.

> 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
>            Assignee: Remko Popma
>             Fix For: 2.0-rc1, 2.0
>
>         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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