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From Chris Eldredge <>
Subject Re: request hangs
Date Thu, 22 Mar 2007 14:10:06 GMT

Thanks for the response.  The thread accepting UDP packets has a timeout 
of 100ms after which it waits again for a packet.  Anyway, this is 
happening in its own thread, executing asynchronously from Tomcat's http 
request processing threads.  I'm not aware of any limitations where 
accepting UDP packets should prevent another thread from accepting TCP 
connections... are you?

Thanks again,


Martin Gainty wrote:
> Hi Chris-
> what happens when you log these events?
> start of UDP loop
> Accepting UDP packets on the loopback address.
> log the buffer from UDP accept 
> goto start of UDP loop
> start of loop to write to temp file
> Reading standard out from a child process 
> log the buffer which is read from standard out
> writing it to a temp file.
> go start of loop to write to temp file
> Im guessing the UDP packet accept logic *may possibly* be blocking as it waits for the
socket to read
> (and hanging the thread)
> Martin --
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> ----- Original Message ----- 
> From: "Chris Eldredge" <>
> To: <>
> Sent: Wednesday, March 21, 2007 6:30 PM
> Subject: request hangs
>> I'm working on a web application which sometimes has several daemon 
>> threads doing I/O processing in the background.  The application seems 
>> to be fine except when several tasks are running, sometimes Tomcat gets 
>> a request and doesn't seem to process it.  The request seems to time out 
>> without ever being passed into my application for processing.
>> My index page has an auto-refresh meta tag so I see this problem 
>> frequently.  The really strange thing is if I click reload once, the 
>> next request also hangs, but if I click reload a 2nd time, this request 
>> is processed very quickly.  This behavior is very consistent, and 
>> doesn't seem to have anything to do with the state of the background 
>> tasks (they are still running).
>> I mention the background tasks because I only see this hanging behavior 
>> when the background tasks are active.  When my application is idle, I 
>> never see the behavior.  Beyond that, I can't figure out what the 
>> background tasks might be doing which would prevent Tomcat from 
>> processing incoming requests:
>> * Accepting UDP packets on the loopback address.
>> * Reading standard out from a child process and writing it to a temp file.
>> Neither of these activities seem like they should interfere with Tomcat 
>> request processing.
>> I have placed some logging calls on a filter I configured in my 
>> application and for the hung requests, the filter never logs a request. 
>>  This seems to indicate that the request is getting stuck before my 
>> application gets a chance to process it.
>> Has anybody seen anything like this before?
>> Any advice for troubleshooting?
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