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https://issues.apache.org/jira/browse/HADOOP-951?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12468437
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Konstantin Shvachko commented on HADOOP-951:
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chooseTargets() iterates over the heartbeats list. Looks like somebody else
modified the list during iteration.
chooseTargets() should synchronize on the heartbeats list, since we have the
heartbeats lock separate from
the global namespace lock now.
We should also check other places where heartbeats is used, and make sure both
locks are enforced.
> java.util.ConcurrentModificationException in FSNamesystem.chooseTargets
> -------------------------------------------------------------------------
>
> Key: HADOOP-951
> URL: https://issues.apache.org/jira/browse/HADOOP-951
> Project: Hadoop
> Issue Type: Bug
> Components: dfs
> Affects Versions: 0.10.1
> Reporter: Koji Noguchi
>
> 2007-01-26 01:14:37,509 INFO org.apache.hadoop.ipc.Server: IPC Server handler
> 7 on 8020 call error: java.io.IOException:
> java.util.ConcurrentModificationException
> java.io.IOException: java.util.ConcurrentModificationException
> at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:449)
> at java.util.AbstractList$Itr.next(AbstractList.java:420)
> at org.apache.hadoop.dfs.FSNamesystem.chooseTargets(FSNamesystem.java:2282)
> at org.apache.hadoop.dfs.FSNamesystem.startFile(FSNamesystem.java:484)
> at org.apache.hadoop.dfs.NameNode.create(NameNode.java:238)
> at sun.reflect.GeneratedMethodAccessor60.invoke(Unknown Source)
> at
> sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
> at java.lang.reflect.Method.invoke(Method.java:585)
> at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:337)
> at org.apache.hadoop.ipc.Server$Handler.run(Server.java:538)
> Not sure if it's related, but this exception happend when namenode was
> replicating many blocks.
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