Coherence objects not released when undeploying application?

Question

Hi
Part of our continuous integration build is deploying our application to a Weblogic server and running some selenium test cases against it. We have usually about 15 builds running each day.
Our problem is that we seem to be experiencing a memory leak in that process; each new build takes more and more memory until weblogic starts throwing out-of-memory errors (as a workaround we'r restarting weblogic every night).
After spending some time using a profiler (we'r using YourKit Java Profiler) it appears that the calls to Coherence libraries cause references to our objects not being properly released and GC is not able to get rid of them properly. If the calls to the Coherence libraries are removed teh GC correctly releases all our application objects.
To confirm this I have created this simle test scenario:
1. Created an empty web application (war) that has only one class in it:
package com.test;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import com.tangosol.net.CacheFactory;
public class TestServletContextListener implements ServletContextListener {
     public void contextDestroyed(ServletContextEvent arg0) {
          CacheFactory.shutdown();          
     public void contextInitialized(ServletContextEvent arg0) {}
2. Modified the web.xml to register the ContextListener:
<listener>
<listener-class>com.test.TestServletContextListener</listener-class>
</listener>
3. Created empty EAR that has only two libraries in it: coherence.jar & tangosol.jar (version 3.3.1)
5. included the test web application in the EAR (no other classes, projects or libraries are included; no other configuration settings are adjusted from defaults)
6. While using the profiler I was performing deployemnt and undeployment of teh EAR against the Weblogic server. With each new deployment a new set of com.tangosol* classes is created. Those classes are not released even when GC is forced from the profiler.
I'm not able to attach a screenshot from the profiler to this post, but with each redeployment I can see the following objects created (ordered with number of objects created in a descending order):
com.tangosol.util.Base$ComonMonitor: 1024 new objects
com.tangosol.run.xml.XmlToken: 16 new Objects
com.tangosol.util.ListMap: 11 new Objects
com.tangosol.util.RecyclingLingedList$Node: 5 new Objects
etc.
Am I doing something wrong or is there really a problem with the object references not properly released in Coherence?
thank you
s.

Answer 1

Hello Robert
I have double checked that the two coherence libs don’t exist anywhere on the server class path. I have also tried calling shutdown from preStop instead of postStop but it made no difference.
(Please note that I'm not really looking for the right place to shutdown Coherence; instead I'm trying to demonstrate that calls to Coherence libraries causes object references not to be released properly. I have chosen to use the shutdown method only because it's nicely visible when it's being invoked and also it is something that our application is calling during shutdowns).
To make sure that I'm not overlooking something with the Weblogic setup I have tried it with Tomcat:
1. Downloaded and installed Tomcat 6.0.14
2. Create new WAR project and put coherence.jar & tangosol.jar in WEB-INF/lib
3. Created one class:
package com.test;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import com.tangosol.net.CacheFactory;
public class TestServletContextListener implements ServletContextListener {
     public void contextDestroyed(ServletContextEvent arg0) {
          CacheFactory.shutdown();
     public void contextInitialized(ServletContextEvent arg0) {}
4. modified web.xml:
<listener>
     <listener-class>com.test.TestServletContextListener</listener-class>
</listener>
5. deployed the WAR to the tomcat server with profiler connected to it
After that I have used Tomcat Web Application Manager (http://localhost:8088/manager/html/list) to Stop & Start the application repeatedly.
The behavior is the same as on weblogic. Each stop of the application creates another set of tangosol objects that do not get released by GC.
Am I correct when I say that there is some problem with the Coherence libraries causing memory leaks by not allowing GC to release old objects?
Thank you
s.