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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 >> >> _______________________________________________ >> thredds mailing list >> thredds@xxxxxxxxxxxxxxxx >> For list information or to unsubscribe, visit: http://www.unidata.ucar.edu/mailing_lists/ >
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