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From Mark Eggers <its_toas...@yahoo.com>
Subject Re: Tomcat memory leak error launching web app in NetBeans 6.9.1
Date Mon, 18 Oct 2010 17:05:32 GMT
I saw a mention of this on the Quartz forums. People there seem to think it's a 
race condition between Quartz's scheduler shutdown and Tomcat's thread memory 
leak reporting.

I wrote a quick Quartz scheduler (1.8.3) application. It does the following:

1. Uses the supplied listener to put a scheduler factory in the servlet context 
   (org.quartz.ee.servlet.QuartzInitializerListener)
2. Uses another listener to add a job that writes to a log file every 5 minutes
3. Uses the provided listener (org.quartz.ee.servlet.QuartzInitializerListener) 
to shut down 
   all schedulers

The supplied listener is configured via parameters to start the scheduler on 
startup, and shut down the scheduler on application termination.

When I watch this using visualvm (1.3.1) on Tomcat 6.0.18 and 6.0.29, I see the 
four threads that are started by Quartz vanish when the application is 
undeployed. Tomcat reports the SEVERE error for some of these threads in 
catalina.out. I ran the test twice and I think that Tomcat reported different 
threads on each run (didn't save the log files). I also didn't look for any 
stray classes left after the application was undeployed.

The supplied listener can be configured to not start or shut down the scheduler. 
Starting and shutting down the scheduler can then be managed by the second 
listener (that adds the job). I've not tried this yet.

Finally, there are two ways to shut down the scheduler. The default (graceful) 
way waits for any pending jobs to complete. Calling shutdown(false) immediately 
terminates the scheduler. This doesn't seem to be configurable using the 
supplied listener, so the scheduler would have to be managed by the second 
listener.

Environment:

OS:      Fedora 13 2.6.34.7-56.fc13.i686
Java:    Oracle/Sun Java JRE/JDK 1.6.0_22
IDE:     NetBeans 6.9.1 / Maven 2.2.1
Tomcat:  6.0.29
         6.0.18
Quartz:  1.8.3
Monitor: VisualVM 1.3.1 (https://visualvm.dev.java.net/)

If I have some time today, I'll try some variations.

. . . . just my two cents.

/mde/
----- Original Message ----
From: Martin O'Shea <appy74@dsl.pipex.com>
To: Tomcat Users List <users@tomcat.apache.org>
Sent: Mon, October 18, 2010 5:52:08 AM
Subject: RE: Tomcat memory leak error launching web app in NetBeans 6.9.1

You're probably correct and assuming this is to do with Quartz which it seems to 
be, are you aware of any similar cases or remedies?

-----Original Message-----
From: Christopher Schultz [mailto:chris@christopherschultz.net] 
Sent: 18 Oct 2010 13 49
To: Tomcat Users List
Subject: Re: Tomcat memory leak error launching web app in NetBeans 6.9.1

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Martin,

On 10/16/2010 11:11 AM, Martin O'Shea wrote:
> Definitely seems to be when the web application in question is terminated, 
>rather than Tomcat itself. And all indications are the listener that handles the 
>scheduler.
> 
> And I've tried another similar application which gives messages of the same 
>kind.
> 
> And yet both apps have worked under other environments.

Note that the leak detection has been added and improved in recent
Tomcat versions. It's possible that this problem has always been there,
you're just never been notified about it.

- -chris
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