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From "Steffen Heil" <>
Subject RE: Blocking threads in Tomcat
Date Tue, 01 Jul 2008 11:08:55 GMT

If you are on linux, do the following:

  killall -3 java

Then look into catalina.out. 

It will print all stack traces, including monitors being hold and waited for.


> -----Original Message-----
> From: Fredrik Tolf [] 
> Sent: Tuesday, July 01, 2008 6:11 AM
> To: Tomcat Users List
> Subject: Blocking threads in Tomcat
> Hi list!
> I've had some issues with requests not being carried out in 
> parallel by Tomcat. My problem is that I haven't been able to 
> figure out when a worker thread blocks and when it does not.
> To try and pin down the behavior, I did a little experiment. 
> I took a servlet that I had, that handles to separate URLs; 
> let's call them "/a"
> and "/b". To try out the parallelism, I added a little delay 
> in the servlet code by calling Thread.sleep(10000). I then 
> tried them out in two browser tabs, and I find the results 
> much enigmatic.
> When I try to access "/a" in one tab and "/b" in another, 
> they both load in 10 seconds each -- that is, if I start the 
> request for "/a" at 12:00:10 and the request for "/b" at 
> 12:00:15, the request for "/a" will finish at 12:00:20, and 
> the request for "/b" will finish at 12:00:25. As one would expect.
> However, when I request "/a" in both tabs, the requests seem 
> to be carried out in sequence -- that is, if I again st´╗┐art 
> the request in tab
> 1 for "/a" at 12:00:10 and the request for in tab 2 for, also 
> for "/a", at 12:00:15, the request for tab 1 will finish at 
> 12:00:20, and the request for tab 2 will finish at 12:00:30.
> Why is this? Is Tomcat explicitly not handling two requests 
> for the exact same URL in parallel? It is the only 
> explanation I can think of, but I cannot figure out how or 
> why it would make sense. If it is indeed the case, can I 
> somehow tell Tomcat to not do that?
> Thanks for your attention!
> Fredrik Tolf
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