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From "Raghu Angadi (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-3010) ConcurrentModificationException from org.apache.hadoop.ipc.Server$Responder in JobTracker
Date Tue, 01 Apr 2008 20:10:27 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-3010?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

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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