Pointers on diagnosing session and thread hangs

[Pete Helgren]

We are having a devil of a time tracking down why a web app is hanging 
while running in Tomcat.  We are running version 5.5.27 in Windows XP 
with 2Gb RAM.  The symptom is that randomly a user will report that they 
cannot log into the application.  When we view the Tomcat application 
using Lambda Probe we see many sessions that are persisting long after 
their session expirations should have removed them and the number of 
threads steadily increasing.  The assumption is that we have some 
objects that are getting created that are not being destroyed and 
causing the session to persist or there is some object locked that is 
waiting on another process or thread  somewhere.  I am not an expert by 
any stretch in Tomcat internals so what I need is a way to determine 
what is causing the sessions to "hang" and the threads to begin to grow 
beyond the maximum (650 in our case). 

Is there a "step by step" FAQ somewhere that would allow us to 
systematically analyze the running servlet and determine where the 
"hang" is?  I'd love to see what instruction the code is executing when 
the hang is occurring.  Any pointers/tools you could suggest would be 
helpful.

Thanks,
Pete


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