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https://issues.apache.org/jira/browse/HBASE-8539?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13660873#comment-13660873
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Ted Yu commented on HBASE-8539:
-------------------------------
Looking at ArrayList source code, Arrays.copyOf() is used internally.
So getListeners() doesn't have to change.
> Double(or tripple ...) ZooKeeper listeners of the same type when Master
> recovers from ZK SessionExpiredException
> ----------------------------------------------------------------------------------------------------------------
>
> Key: HBASE-8539
> URL: https://issues.apache.org/jira/browse/HBASE-8539
> Project: HBase
> Issue Type: Bug
> Components: master
> Affects Versions: 0.98.0, 0.94.7, 0.95.0
> Reporter: Jeffrey Zhong
> Assignee: Jeffrey Zhong
> Fix For: 0.98.0, 0.94.8, 0.95.1
>
> Attachments: 8539-addendum-v2.patch, double-registered listeners.png,
> hbase-8539-0.94-addendum-03.patch, hbase-8539-0.94.patch,
> hbase-8539-addendum-03.patch, hbase-8539.patch, hbase-8539.patch
>
>
> When Master tries to recover from zookeeper session expired exceptions, we
> don't clean old registered listener instances. Therefore, it may end up we
> have two(or more) listeners to double handling same events. Attached a screen
> shot from debugger to show the issue.
> I considered to limit one listener per class while I think that would limit
> the listener usage so I choose to clear exiting listeners during recovery for
> the fix.
> (This issue is unrelated to the issue HBASE-8365 because I verified there is
> no dup-listeners when HBASE-8365 happened)
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