Please Help: Application Hang. Possible Deadlock

[Giesen Giesen <gi...@gmail.com>]

I have an application running on Tomcat 5.5 that periodically hangs in
our production environment. When I try any page in my application, my
web browser just waits for a page indefinitely. I can wait for an hour
and it will never respond (normally responds in 1-3 seconds).

I haven't reproduced this issue on my dev system.  Tomcat Manager
continues to respond correctly during this hang so Tomcat itself is
correctly configured and still functioning.

I see no errors in my log files or catalina.out. On the server status
page, I see this:
Max threads: 150 Min spare threads: 25 Max spare threads: 75 Current
thread count: 150 Current thread busy: 130

Does that imply a deadlock within the web application? My application
is somewhat complicated and not all written by me. This site is low
volume (typically 0-2 users are on at any given time), so I can't
imagine why 130 threads would be busy. How could I test if there is a
deadlock? Ideally I could see a stack trace of those busy threads.

Any other ideas?

Thanks!

Tomcat 5.5
JDK 1.5.08
Linux
JSF/Hibernate/Facelets

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Re: Please Help: Application Hang. Possible Deadlock

[Christopher Schultz <ch...@christopherschultz.net>]

Giesen,

> I haven't reproduced this issue on my dev system.  Tomcat Manager
> continues to respond correctly during this hang so Tomcat itself is
> correctly configured and still functioning.

This suggests that Tomcat and the VM are okay, but your webapp is hosed.
Do you use JDBC connections in your application? If you do, do you pool
those connections? If you have exhausted your connection pool, your
threads will wait forever for a connection (depending on your CP settings).

Chuck's suggestion to obtain a thread dump will be very helpful in
determining what's going on. Look through your thread dump for
Object.wait() before just dumping the entire thing to the list.

-chris

RE: Please Help: Application Hang. Possible Deadlock

["Caldarale, Charles R" <Ch...@unisys.com>]

> From: Giesen Giesen [mailto:giesen2@gmail.com] 
> Subject: Please Help: Application Hang. Possible Deadlock
> 
> Does that imply a deadlock within the web application?

Quite likely.  Take a thread dump (IIRC, kill -3 or kill -QUIT) and see
what they're doing or stuck on.

 - Chuck


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