[ 
https://issues.apache.org/jira/browse/SOLR-13393?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16815790#comment-16815790
 ] 

ASF subversion and git services commented on SOLR-13393:
--------------------------------------------------------

Commit c58787d045d5ab0f463ccd09e76eb8d66e14ee96 in lucene-solr's branch 
refs/heads/branch_8x from Chris M. Hostetter
[ https://gitbox.apache.org/repos/asf?p=lucene-solr.git;h=c58787d ]

SOLR-13393: Fixed ZkClientClusterStateProvider to prevent risk of leaking 
ZkStateReader/threads when processing concurrent requests during shutdown.

This primarily affected tests, but may have also caused odd errors/delays when 
restart/shutting down solr nodes.

(cherry picked from commit 980fd7d5c56349570b2202dedcf7b454216a61b8)


> ZkClientClusterStateProvider can leak ZkStateReader (and associated watcher 
> threads) if background threads attempt to use it after close() .
> --------------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: SOLR-13393
>                 URL: https://issues.apache.org/jira/browse/SOLR-13393
>             Project: Solr
>          Issue Type: Bug
>      Security Level: Public(Default Security Level. Issues are Public) 
>            Reporter: Hoss Man
>            Assignee: Hoss Man
>            Priority: Major
>         Attachments: SOLR-13393.patch, SOLR-13393.patch, SOLR-13393.patch
>
>
> while digging into some test failures related to leaked ZkStateReader 
> objects, i noticed a pattern which i beleive can be explained by the fact 
> that ZkClientClusterStateProvider does not complain/fail if some caller tries 
> to connect()/use it after it's already been closed – in this situation it 
> will just re-create a new ZkStateReader (which is later leaked)
> So in in situations where background/timer threads use a 
> SolrClientCloudManager/ZkClientClusterStateProvider, we might see...
> {noformat}
> T1 : start shutdown...
> T1 :  ...SolrClientCloudManager.close()...
> T1 :   ...ZkClientClusterStateProvider.close()...
> T1 :    ...ZkStateReader.close()
> T1 :    ...zkStateReader = null;
> T 2: run background thread/task/trigger...
> T 2:  ...get ZkClientClusterStateProvider
> T 2:  ...call ZkClientClusterStateProvider.connect()
> T 2:   ...zkStateReader = new ZkStateReader()                 /* LEAKED */
> T 2:  ... do something with ZkClientClusterStateProvider
> T 2:  ...finish background thread/task/trigger
> T1 :  ...finish shutdown of ZkClientClusterStateProvider / 
> SolrClientCloudManager
> {noformat}



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