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https://issues.apache.org/jira/browse/SOLR-13678?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16899236#comment-16899236
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Hoss Man commented on SOLR-13678:
---------------------------------
AFAICT CollectionPropWatcher isn't used internally by solr anywhere, so this
issue will only ipmact solr clients that explicitly register their own watchers.
/cc [~tomasflobbe] & [~prusko] and linking to SOLR-11960 where this was
ntroduced.
> ZkStateReader.removeCollectionPropsWatcher can deadlock with concurrent
> zkCallback thread on props watcher
> ----------------------------------------------------------------------------------------------------------
>
> Key: SOLR-13678
> URL: https://issues.apache.org/jira/browse/SOLR-13678
> Project: Solr
> Issue Type: Bug
> Security Level: Public(Default Security Level. Issues are Public)
> Reporter: Hoss Man
> Priority: Major
> Attachments: collectionpropswatcher-deadlock-jstack.txt
>
>
> while investigating an (unrelated) test bug in CollectionPropsTest I
> discovered a deadlock situation that can occur when calling
> {{ZkStateReader.removeCollectionPropsWatcher()}} if a zkCallback thread tries
> to concurrently fire the watchers set on the collection props.
> {{ZkStateReader.removeCollectionPropsWatcher()}} is itself called when a
> {{CollectionPropsWatcher.onStateChanged()}} impl returns "true" -- meaning
> that IIUC any usage of {{CollectionPropsWatcher}} could potentially result in
> this type of deadlock situation.
> {noformat}
> "TEST-CollectionPropsTest.testReadWriteCached-seed#[D3C6921874D1CFEB]" #15
> prio=5 os_prio=0 cpu=567.78ms elapsed=682.12s tid=0x00007
> fa5e8343800 nid=0x3f61 waiting for monitor entry [0x00007fa62d222000]
> java.lang.Thread.State: BLOCKED (on object monitor)
> at
> org.apache.solr.common.cloud.ZkStateReader.lambda$removeCollectionPropsWatcher$20(ZkStateReader.java:2001)
> - waiting to lock <0x00000000e6207500> (a
> java.util.concurrent.ConcurrentHashMap)
> at
> org.apache.solr.common.cloud.ZkStateReader$$Lambda$617/0x00000001006c1840.apply(Unknown
> Source)
> at
> java.util.concurrent.ConcurrentHashMap.compute([email protected]/ConcurrentHashMap.java:1932)
> - locked <0x00000000eb9156b8> (a
> java.util.concurrent.ConcurrentHashMap$Node)
> at
> org.apache.solr.common.cloud.ZkStateReader.removeCollectionPropsWatcher(ZkStateReader.java:1994)
> at
> org.apache.solr.cloud.CollectionPropsTest.testReadWriteCached(CollectionPropsTest.java:125)
> ...
> "zkCallback-88-thread-2" #213 prio=5 os_prio=0 cpu=14.06ms elapsed=672.65s
> tid=0x00007fa6041bf000 nid=0x402f waiting for monitor ent
> ry [0x00007fa5b8f39000]
> java.lang.Thread.State: BLOCKED (on object monitor)
> at
> java.util.concurrent.ConcurrentHashMap.compute([email protected]/ConcurrentHashMap.java:1923)
> - waiting to lock <0x00000000eb9156b8> (a
> java.util.concurrent.ConcurrentHashMap$Node)
> at
> org.apache.solr.common.cloud.ZkStateReader$PropsNotification.<init>(ZkStateReader.java:2262)
> at
> org.apache.solr.common.cloud.ZkStateReader.notifyPropsWatchers(ZkStateReader.java:2243)
> at
> org.apache.solr.common.cloud.ZkStateReader$PropsWatcher.refreshAndWatch(ZkStateReader.java:1458)
> - locked <0x00000000e6207500> (a
> java.util.concurrent.ConcurrentHashMap)
> at
> org.apache.solr.common.cloud.ZkStateReader$PropsWatcher.process(ZkStateReader.java:1440)
> at
> org.apache.solr.common.cloud.SolrZkClient$ProcessWatchWithExecutor.lambda$process$1(SolrZkClient.java:838)
> at
> org.apache.solr.common.cloud.SolrZkClient$ProcessWatchWithExecutor$$Lambda$253/0x00000001004a4440.run(Unknown
> Source)
> at
> java.util.concurrent.Executors$RunnableAdapter.call([email protected]/Executors.java:515)
> at
> java.util.concurrent.FutureTask.run([email protected]/FutureTask.java:264)
> at
> org.apache.solr.common.util.ExecutorUtil$MDCAwareThreadPoolExecutor.lambda$execute$0(ExecutorUtil.java:209)
> at
> org.apache.solr.common.util.ExecutorUtil$MDCAwareThreadPoolExecutor$$Lambda$140/0x0000000100308c40.run(Unknown
> Source)
> at
> java.util.concurrent.ThreadPoolExecutor.runWorker([email protected]/ThreadPoolExecutor.java:1128)
> at
> java.util.concurrent.ThreadPoolExecutor$Worker.run([email protected]/ThreadPoolExecutor.java:628)
> at java.lang.Thread.run([email protected]/Thread.java:834)
> {noformat}
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