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https://issues.apache.org/jira/browse/HADOOP-3010?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Raghu Angadi updated HADOOP-3010:
---------------------------------
Attachment: HADOOP-3010.patch
Patch attached. Server synchronizes on selector.keys() when it iterates over it
once every few seconds. JavaDoc for Selector says we need to synchronize on
these sets while accessing them. In this perticular case, IPC handler could
enqueue more connections (thus modifying selector.keys()) while Responder
iterates over them.
With some artificial sleeps I verified these exceptions show up before the
patch and disappear after.
Regd unit test, I think this was straight forward incorrect access of an object
and we are correcting it. I don't think this requires a unit test, as such it
is not easy to trigger this reliably.
> ConcurrentModificationException from org.apache.hadoop.ipc.Server$Responder
> in JobTracker
> -----------------------------------------------------------------------------------------
>
> Key: HADOOP-3010
> URL: https://issues.apache.org/jira/browse/HADOOP-3010
> Project: Hadoop Core
> Issue Type: Bug
> Components: ipc
> Affects Versions: 0.16.1
> Reporter: Amar Kamat
> Assignee: Raghu Angadi
> Fix For: 0.17.0
>
> Attachments: HADOOP-3010.patch
>
>
> I see lot of these in my JobTracker log
> {noformat}
> WARN org.apache.hadoop.ipc.Server: Exception in Responder
> java.util.ConcurrentModificationException
> at java.util.HashMap$HashIterator.nextEntry(HashMap.java:793)
> at java.util.HashMap$KeyIterator.next(HashMap.java:827)
> at
> java.util.Collections$UnmodifiableCollection$1.next(Collections.java:1010)
> at org.apache.hadoop.ipc.Server$Responder.run(Server.java:475)
> {noformat}
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