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https://issues.apache.org/jira/browse/HDFS-3616?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13482105#comment-13482105
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Jing Zhao commented on HDFS-3616:
---------------------------------
Also got this exception in HDFS-4106. Seems like the exception happens because
a thread is iterating the hashmap bpSlices (FsVolumeImpl#shutdown) while
another thread is remove entries from the same hashMap
(FsVolumeImpl#shutdownBlockPool). A quick fix can be changing bpSlices from a
HashMap to a ConcurrentHashMap.
> TestWebHdfsWithMultipleNameNodes fails with ConcurrentModificationException
> in DN shutdown
> ------------------------------------------------------------------------------------------
>
> Key: HDFS-3616
> URL: https://issues.apache.org/jira/browse/HDFS-3616
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: data-node
> Affects Versions: 2.0.0-alpha, 3.0.0
> Reporter: Uma Maheswara Rao G
>
> I have seen this in precommit build #2743
> {noformat}
> java.util.ConcurrentModificationException
> at java.util.HashMap$HashIterator.nextEntry(HashMap.java:793)
> at java.util.HashMap$EntryIterator.next(HashMap.java:834)
> at java.util.HashMap$EntryIterator.next(HashMap.java:832)
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsVolumeImpl.shutdown(FsVolumeImpl.java:209)
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsVolumeList.shutdown(FsVolumeList.java:168)
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl.shutdown(FsDatasetImpl.java:1214)
> at
> org.apache.hadoop.hdfs.server.datanode.DataNode.shutdown(DataNode.java:1105)
> at
> org.apache.hadoop.hdfs.MiniDFSCluster.shutdownDataNodes(MiniDFSCluster.java:1324)
> at
> org.apache.hadoop.hdfs.MiniDFSCluster.shutdown(MiniDFSCluster.java:1304)
> at
> org.apache.hadoop.hdfs.web.TestWebHdfsWithMultipleNameNodes.shutdownCluster(TestWebHdfsWithMultipleNameNodes.java:100)
> {noformat}
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