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From "Taras Tielkes (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LOGGING-108) Classloader reference leak on Tomcat 5.5.17 with log4j in webapp
Date Fri, 30 Jun 2006 09:23:30 GMT
    [ http://issues.apache.org/jira/browse/LOGGING-108?page=comments#action_12418592 ] 

Taras Tielkes commented on LOGGING-108:
---------------------------------------

Here's some proof this is happening.

Change the following code (package org.apache.jasper.runtime):
----------------------
    // Logger
    private static Log log = LogFactory.getLog(PageContextImpl.class);
----------------------

to this:

----------------------
    // Logger
    private static Log log;
	    
    static {
	System.err.println(">> CCL loader: " + Thread.currentThread().getContextClassLoader().getClass().getCanonicalName());
	System.err.println(">> our loader: " + PageContextImpl.class.getClassLoader().getClass().getCanonicalName());
	log = LogFactory.getLog(PageContextImpl.class);
	System.err.println(">> log loader: " + log.getClass().getClassLoader().getClass().getCanonicalName());
    }
----------------------

You'll see the following output (on the console) the first time a JSP page is rendered:
----------------------
...
>> CCL loader: org.apache.catalina.loader.WebappClassLoader
>> our loader: org.apache.catalina.loader.StandardClassLoader
>> log loader: org.apache.catalina.loader.WebappClassLoader
...
----------------------
You can see that the current class (PageContextImpl) was loaded by a container classloader
(above the webapp CL).
You also see that commons-logging 1.1 used the context classloader to find an implementation
of Log.

Since the PageContextImpl class will never be unloaded while Tomcat runs, a WebappClassLoader
leak is the result.


> Classloader reference leak on Tomcat 5.5.17 with log4j in webapp
> ----------------------------------------------------------------
>
>          Key: LOGGING-108
>          URL: http://issues.apache.org/jira/browse/LOGGING-108
>      Project: Commons Logging
>         Type: Bug

>     Versions: 1.1 Final
>  Environment: JDK 1.5.0_07, Tomcat 5.5.17
> commons-logging-api-1.1.jar is configured for the Tomcat bootstrap
> commons-logging-adapters-1.1.jar is deployed with a webapp
> log4j-1.2.11 is deployed with webapp
> This is the configuration specifically described in the release notes for 1.1:
> " New jar file commons-logging-adapters-xxx.jar is now provided. This can be
>   used to resolve class cast conflicts where parts of commons-logging are
>   deployed via different classloaders. It is not expected to be frequently
>   used; it is only necessary in situations where a container has deployed
>   commons-logging-api.jar and a webapp wants to bind to a third-party
>   logging implementation such as log4j. In this case, the webapp can
>   experience problems if it deploys commons-logging.jar as this causes
>   duplicates of the core commons-logging classes, but commons-logging-adapters
>   can be safely used."
>     Reporter: Taras Tielkes
>  Attachments: path.gif
>
> Some Tomcat Jasper implementation classes are initialized (that mean static fields and
static initializer) when the current thread has the webapp classloader set as the context
classloader.
> An example of this is org.apache.jasper.runtime.PageContextImpl
> If the first JSP page rendered on a freshly started Tomcat 5.5.17 is for a webapp that
contains the configuration described in the "Environment" section above, a leak will occur:
> The class PageContextImpl (loader by CL above Webapp classloader in delegation chain)
stays loaded for the duration of the JVM
> The "log" field in this class refers to a class loaded from a WebappClassloader.
> This produces a classloader reference leak to the webapp, even after undeployment.

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