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https://issues.apache.org/jira/browse/SOLR-8914?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15218529#comment-15218529
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Scott Blum commented on SOLR-8914:
----------------------------------

Correct, the refreshCollectionListLock solves the same class of bug for the 
collections list as we needed to solve for live_nodes.  However, the 
implementation is simpler since we don't need to hold getUpdateLock() and 
therefore there's no deadlock potential.

The code to check this.legacyClusterStateVersion >= stat.getVersion() solves 
that class of bug for clusterstate.json; we already have version guarding code 
for stateformat 2 collections, it was an oversight not to have it for this also.

Net-net: my intent (hope?) is this patch should fix this category of race 
condition for all the major pieces of ZkStateReader.

> ZkStateReader's refreshLiveNodes(Watcher) is not thread safe
> ------------------------------------------------------------
>
>                 Key: SOLR-8914
>                 URL: https://issues.apache.org/jira/browse/SOLR-8914
>             Project: Solr
>          Issue Type: Bug
>            Reporter: Hoss Man
>         Attachments: SOLR-8914.patch, SOLR-8914.patch, SOLR-8914.patch, 
> SOLR-8914.patch, jenkins.thetaphi.de_Lucene-Solr-6.x-Solaris_32.log.txt, 
> live_node_mentions_port56361_with_threadIds.log.txt, 
> live_nodes_mentions.log.txt
>
>
> Jenkin's encountered a failure in TestTolerantUpdateProcessorCloud over the 
> weekend....
> {noformat}
> http://jenkins.thetaphi.de/job/Lucene-Solr-6.x-Solaris/32/consoleText
> Checking out Revision c46d7686643e7503304cb35dfe546bce9c6684e7 
> (refs/remotes/origin/branch_6x)
> Using Java: 64bit/jdk1.8.0 -XX:+UseCompressedOops -XX:+UseG1GC
> {noformat}
> The failure happened during the static setup of the test, when a 
> MiniSolrCloudCluster & several clients are initialized -- before any code 
> related to TolerantUpdateProcessor is ever used.
> I can't reproduce this, or really make sense of what i'm (not) seeing here in 
> the logs, so i'm filing this jira with my analysis in the hopes that someone 
> else can help make sense of it.



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