[COCOON-2173] AbstractCachingProcessingPipeline: Two requests can deadlock each other

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 2.1.9, 2.1.10, 2.1.11, 2.2
• Component/s: - Components: Sitemap
• Urgency: Normal
• Other Info: Patch available
• Affects version (Component): Components: Pipeline
• Assignee: Unassigned
• Reporter: Alexander Daniel
• Created: 14/Mar/08 14:20
• Updated: 29/Jan/09 09:57

Description

Two requests can deadlock each other when they depend on the same resources which they acquire in a different order. I can reproduce that in Cocoon 2.1.11 and Cocoon 2.2-RC3-SNAPSHOT:
* request A: generating lock for 55933
* request B: generating lock for 58840
* request B: waiting for lock 55933 which is hold by request A
* request A: waiting for lock 58840 which is hold by request B


I can reproduce this behaviour with Apache Bench and following pipeline:
* terminal 1: Apache Bench request A (ab -k -n 10000 -c 25 http://localhost:8888/samples/reproduceMultipleThreads/productOfferForDevice/55933/)
* terminal 2: Apache Bench request B (ab -k -n 10000 -c 25 http://localhost:8888/samples/reproduceMultipleThreads/productOfferForDevice/58840/)
* terminal 3: touching the two data files every second to invalidate the cache (while true; do echo -n "."; touch 55933.xml 58840.xml; sleep 1; done)

* pipeline:
<map:pipeline type="caching">
  <map:match pattern="productOfferForDevice*/*/">
    <map:generate src="cocoon:/exists/{2}.xml" label="a"/>
    <map:transform type="xsltc" src="productOfferIncludeDevice.xsl" label="b">
        <map:parameter name="noInc" value="{1}"/>
    </map:transform>
    <map:transform type="include" label="c"/>
    <map:serialize type="xml"/>
</map:match>

  <map:match pattern="exists/**">
    <map:act type="resource-exists">
        <map:parameter name="url" value="{1}" />
        <map:generate src="{../1}" />
        <map:serialize type="xml" />
    </map:act>
    <!-- not found -->
    <map:generate src="dummy.xml" />
    <map:serialize type="xml" />
  </map:match>
</map:pipeline>


After some seconds the deadlock occurs ==>
* Apache Bench requests run into a timeout

* I can see following pipe locks in the default transient store:
PIPELOCK:PK_G-file-cocoon://samples/reproduceMultipleThreads/exists/55933.xml?pipelinehash=-910770960103935149_T-xsltc-file:///Users/alex/dev/cocoon/cocoon-2.1.11/build/webapp/samples/reproduceMultipleThreads/productOfferIncludeDevice.xsl;noInc=_T-include-I_S-xml-1 (class: org.mortbay.util.ThreadPool$PoolThread)
PIPELOCK:PK_G-file-cocoon://samples/reproduceMultipleThreads/exists/58840.xml?pipelinehash=-4996088883111986478_T-xsltc-file:///Users/alex/dev/cocoon/cocoon-2.1.11/build/webapp/samples/reproduceMultipleThreads/productOfferIncludeDevice.xsl;noInc=_T-include-I_S-xml-1 (class: org.mortbay.util.ThreadPool$PoolThread)
PIPELOCK:PK_G-file-file:///Users/alex/dev/cocoon/cocoon-2.1.11/build/webapp/samples/reproduceMultipleThreads/55933.xml (class: org.mortbay.util.ThreadPool$PoolThread)
PIPELOCK:PK_G-file-file:///Users/alex/dev/cocoon/cocoon-2.1.11/build/webapp/samples/reproduceMultipleThreads/58840.xml (class: org.mortbay.util.ThreadPool$PoolThread)


I added some logging to AbstractCachingProcessingPipeline.java which reconfirms the explanations above:
INFO (2008-03-13) 13:50.16:072 [sitemap] (/samples/reproduceMultipleThreads/productOfferForDevice/55933/) PoolThread-47/AbstractCachingProcessingPipeline: generating lock PIPELOCK:PK_G-file-cocoon://samples/reproduceMultipleThreads/exists/55933.xml?pipelinehash=-910770960103935149_T-xsltc-file:///Users/alex/dev/cocoon/cocoon-2.1.11/build/webapp/samples/reproduceMultipleThreads/productOfferIncludeDevice.xsl;noInc=_T-include-I_S-xml-1
INFO (2008-03-13) 13:50.16:074 [sitemap] (/samples/reproduceMultipleThreads/productOfferForDevice/55933/) PoolThread-47/AbstractCachingProcessingPipeline: generating lock PIPELOCK:PK_G-file-file:///Users/alex/dev/cocoon/cocoon-2.1.11/build/webapp/samples/reproduceMultipleThreads/55933.xml
INFO (2008-03-13) 13:50.16:075 [sitemap] (/samples/reproduceMultipleThreads/productOfferForDevice/58840/) PoolThread-6/AbstractCachingProcessingPipeline: generating lock PIPELOCK:PK_G-file-cocoon://samples/reproduceMultipleThreads/exists/58840.xml?pipelinehash=-4996088883111986478_T-xsltc-file:///Users/alex/dev/cocoon/cocoon-2.1.11/build/webapp/samples/reproduceMultipleThreads/productOfferIncludeDevice.xsl;noInc=_T-include-I_S-xml-1
INFO (2008-03-13) 13:50.16:075 [sitemap] (/samples/reproduceMultipleThreads/productOfferForDevice/58840/) PoolThread-6/AbstractCachingProcessingPipeline: generating lock PIPELOCK:PK_G-file-file:///Users/alex/dev/cocoon/cocoon-2.1.11/build/webapp/samples/reproduceMultipleThreads/58840.xml
INFO (2008-03-13) 13:50.16:281 [sitemap] (/samples/reproduceMultipleThreads/productOfferForDevice/58840/) PoolThread-6/AbstractCachingProcessingPipeline: waiting for lock PIPELOCK:PK_G-file-file:///Users/alex/dev/cocoon/cocoon-2.1.11/build/webapp/samples/reproduceMultipleThreads/55933.xml
INFO (2008-03-13) 13:50.16:304 [sitemap] (/samples/reproduceMultipleThreads/productOfferForDevice/55933/) PoolThread-47/AbstractCachingProcessingPipeline: waiting for lock PIPELOCK:PK_G-file-file:///Users/alex/dev/cocoon/cocoon-2.1.11/build/webapp/samples/reproduceMultipleThreads/58840.xml


Reproduce yourself with Cocoon 2.1.11:
* download and extract Cocoon 2.1.11
* cd $CocoonHome
* ./build.sh
* cd build/webapp/samples
* tar -xzf $DownloadFolder/reproduceMultipleThreads.tar.gz
* cd ../../..
* ./cocoon.sh
* open 3 terminals and cd into $CocoonHome/build/webapp/samples/reproduceMultipleThreads in each

* dry run without invalidating the cache to see that everything is working:
  - terminal 1: ./terminal1.sh
  - terminal 2: ./terminal2.sh

* run with invalidating the cache every seconds:
  - terminal 1: ./terminal1.sh
  - terminal 2: ./terminal2.sh
  - terminal 3: ./terminal3.sh
* When Apache Bench has run into a timeout you can view the pipelocks with http://localhost:8888/samples/reproduceMultipleThreads/pipelocks


Reproduce yourself with Cocoon 2.2RC3-SNAPSHOT:
* svn checkout http://svn.apache.org/repos/asf/cocoon/trunk
* mvn clean install
* ./cocoon.sh
* cd core/cocoon-webapp/target/work/blocks/cocoon-core-main-sample
* tar -xzf $DownloadFolder/reproduceMultipleThreads2.2RC3-SNAPSHOT.tar.gz

* open 3 terminals and cd into $CocoonTrunk/core/cocoon-webapp/target/work/blocks/cocoon-core-main-sample/reproduceMultipleThreads/ in each

* dry run without invalidating the cache to see that everything is working:
  - terminal 1: ./terminal1.sh
  - terminal 2: ./terminal2.sh

* run with invalidating the cache every second:
  - terminal 1: ./terminal1.sh
  - terminal 2: ./terminal2.sh
  - terminal 3: ./terminal3.sh
* When Apache Bench has run into a timeout you can view the pipelocks with http://localhost:8888/samples/core/reproduceMultipleThreads/pipelocks


Since we are currently facing this issue on our production servers I would appreciate a hint on how to fix that issue in a good way.