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https://issues.apache.org/jira/browse/HDFS-6428?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14002416#comment-14002416
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Yongjun Zhang commented on HDFS-6428:
-------------------------------------

HI Colin, 

Yes, I think I understood what you were talking about. My thinking is that 
adding synchronized syntax to all the methods that access {{bpSplices}} seem to 
have slowed down things (in one attempt I did), and I suspect it is the other 
accesses (not the shutdownBlockPool) that caused the run to be slow.

What about I will post result after testing out my original change + the 
addition you suggested (the test has been running for some time), and we then 
decide whether we want to change to reader-writer lock?  Thanks.







> TestWebHdfsWithMultipleNameNodes failed with ConcurrentModificationException
> ----------------------------------------------------------------------------
>
>                 Key: HDFS-6428
>                 URL: https://issues.apache.org/jira/browse/HDFS-6428
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: webhdfs
>            Reporter: Yongjun Zhang
>            Assignee: Yongjun Zhang
>         Attachments: HDFS-6428.001.patch
>
>
> TestWebHdfsWithMultipleNameNodes failed as follows:
> {code}
> Running org.apache.hadoop.hdfs.web.TestWebHdfsWithMultipleNameNodes
> Tests run: 2, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 8.643 sec <<< 
> FAILURE! - in org.apache.hadoop.hdfs.web.TestWebHdfsWithMultipleNameNodes
> org.apache.hadoop.hdfs.web.TestWebHdfsWithMultipleNameNodes  Time elapsed: 
> 3.771 sec  <<< ERROR!
> java.util.ConcurrentModificationException: null
>         at java.util.HashMap$HashIterator.nextEntry(HashMap.java:894)
>         at java.util.HashMap$EntryIterator.next(HashMap.java:934)
>         at java.util.HashMap$EntryIterator.next(HashMap.java:932)
>         at 
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsVolumeImpl.shutdown(FsVolumeImpl.java:251)
>         at 
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsVolumeList.shutdown(FsVolumeList.java:249)
>         at 
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl.shutdown(FsDatasetImpl.java:1389)
>         at 
> org.apache.hadoop.hdfs.server.datanode.DataNode.shutdown(DataNode.java:1304)
>         at 
> org.apache.hadoop.hdfs.MiniDFSCluster.shutdownDataNodes(MiniDFSCluster.java:1555)
>         at 
> org.apache.hadoop.hdfs.MiniDFSCluster.shutdown(MiniDFSCluster.java:1530)
>         at 
> org.apache.hadoop.hdfs.MiniDFSCluster.shutdown(MiniDFSCluster.java:1514)
>         at 
> org.apache.hadoop.hdfs.web.TestWebHdfsWithMultipleNameNodes.shutdownCluster(TestWebHdfsWithMultipleNameNodes.java:99)
> {code}



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