Hi Jon, Heiko,
I'm having a hard time reproducing the problem reliably. I've only seen
it twice so far. And haven't been able to catch it in action. I did get
the IllegalStateException from the Jasper JspFactoryImpl both times:
"java.lang.IllegalStateException: Cannot create a session
after the response has been committed"
Googling on the above exception message brings up a fair number of hits
but none of them seem totally relevant. Or when they sound somewhat
relevant, there isn't a solution.
More tomorrow.
Ethan
On 3/16/2010 9:05 AM, Jonathan Blower wrote:
> Hi Heiko, Ethan,
>
> I've been trying to figure out what might be going on here - thanks for
> your great diagnosis Heiko. I'm not sure what can be done in the
> THREDDS/WMS code to prevent this, but I've modified some code in the
> ncWMS WmsController class to attempt to catch exceptions that are thrown
> when clients disconnect:
>
> http://www.resc.rdg.ac.uk/trac/ncWMS/browser/branches/tds-refactor-2010-
> 01-09/src/java/uk/ac/rdg/resc/ncwms/controller/WmsController.java#L250
>
> Heiko - you mentioned that it's possible that poor exception handling
> could cause a tomcat thread to be left in an invalid state. I can't
> reproduce your problem reliably so I can't test this myself, but I
> wonder if you could find out whether this is happening in your setup?
> The VisualVM tool
> (http://java.sun.com/javase/6/docs/technotes/guides/visualvm/) can give
> a thread dump from your running Tomcat system - perhaps you could run
> this when an error occurs and see if anything is suspicious?
>
> Ethan - are you able to reproduce Heiko's problem?
>
> Cheers, Jon
>
>
> -----Original Message-----
> From: Ethan Davis [mailto:edavis@xxxxxxxxxxxxxxxx]
> Sent: 05 March 2010 23:32
> To: Heiko Klein
> Cc: Jonathan Blower; thredds@xxxxxxxxxxxxxxxx
> Subject: Re: [thredds] ncWMS GetCapabilities return sometimes empty
> document
>
> Hi Heiko,
>
> That is great. Thanks.
>
> I'm a bit swamped through next week but I will jump on this the
> following week before I get to some other WMS work.
>
> Thanks,
>
> Ethan
>
> On 3/5/2010 4:44 AM, Heiko Klein wrote:
>> Hi,
>>
>> finally, I managed to generate a simple case how to reproduce this
> error:
>>
>> a) start tomcat
>> b) abort fetching some maps (3-4 times on a tomcat with
>> 10thredds/HTTP1.1 connector), i.e. call
>> GET
>>
> 'http://localhost:8081/thredds/wms/data/met.no/hirlam12/wam_nsea.fc.2009
> 0604.nc?REQUEST=GetMap&LAYERS=significant_wave_height&PALETTE=redblue&SE
> RVICE=WMS&FORMAT=image/png&VERSION=1.3.0&CRS=EPSG:4326&BBOX=-30,-60,30,9
> 0&WIDTH=400&HEIGHT=400&STYLES=BOXFILL/ncview'
>>> /dev/null
>> and abort this call before it is finished. (Ctrl-C)
>> c) get some 'getCapabilities' documents:
>> while [ 1 ]; do GET
>>
> 'http://localhost:8081/thredds/wms/data/met.no/hirlam12/wam_nsea.fc.2009
> 0604.nc?service=WMS&version=1.3.0&request=GetCapabilities'
>>> testCap.xml; ls -l testCap.xml; done
>> ...
>> -rw-r--r-- 1 heikok heikok 172126 2010-03-05 12:11 testCap.xml
>> -rw-r--r-- 1 heikok heikok 172126 2010-03-05 12:11 testCap.xml
>> -rw-r--r-- 1 heikok heikok 172126 2010-03-05 12:11 testCap.xml
>> -rw-r--r-- 1 heikok heikok 0 2010-03-05 12:11 testCap.xml
>> -rw-r--r-- 1 heikok heikok 172126 2010-03-05 12:11 testCap.xml
>> -rw-r--r-- 1 heikok heikok 172126 2010-03-05 12:11 testCap.xml
>>
>>
>> When the capabilites document with 0 byte size is fetched, the earlier
>> mentioned exception is thrown.
>>
>>
>> Since step b) is the crucial step to reproduce the 0 byte document, I
>> guess there is somewhere a badly caught
> ClientAbortException/IOException
>> when writing to the responses OutputStream, leaving a tomcat-thread in
>> an invalid state.
>>
>>
>> We can solve this problem currently by adding a proxy in front of
>> thredds (apache mod_proxy) which seems to swallow all
>> client-connection-aborts before they reach tomcat.
>>
>> Best regards,
>>
>> Heiko
>>
>> On 2010-02-19 16:54, Heiko Klein wrote:
>>> Hi,
>>>
>>> I'm still trying to track down this problem, so here a short update:
>>>
>>> The ncWMS/TDS crashes seems to be connected to concurrency: The
> problem
>>> occurs when reloading the wms-client (openlayers in firefox), that
> means
>>> GetCapabilites and GetMap are run in parallel. We're downloading
> tiles,
>>> so reloading will fetch one capability doc + approx 12 maps.
>>>
>>> * If I configure tomcat to only use one thread, and use the default
>>> 'HTTP/1.1' connector, the problem disappears (but response-times are
>>> very slow).
>>> * Using 4 threads + 'HTTP/1.1', the problem appears very fast. (one
> or
>>> two reloads)
>>> * Using the 'Nio' connector and 4 threads, the problem appears, but
> not
>>> so fast (3-4 reloads)
>>> * Using the 'Nio' connector with only one thread, is about the same
> as
>>> Nio with several threads.
>>>
>>>
>>> Best regards,
>>>
>>> Heiko
>>>
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>>
