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https://issues.apache.org/jira/browse/HDFS-3787?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13433530#comment-13433530
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Eli Collins commented on HDFS-3787:
-----------------------------------
I kicked the pre-commit build manually.
> BlockManager#close races with ReplicationMonitor#run
> ----------------------------------------------------
>
> Key: HDFS-3787
> URL: https://issues.apache.org/jira/browse/HDFS-3787
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: name-node
> Affects Versions: 2.0.0-alpha
> Reporter: Andy Isaacson
> Assignee: Andy Isaacson
> Priority: Minor
> Attachments: hdfs-3787-2.txt, hdfs-3787-2.txt, hdfs-3787.txt
>
>
> We saw {{TestDirectoryScanner}} fail during shutdown:
> {code}
> 2012-08-09 12:17:19,844 WARN datanode.DataNode
> (BPServiceActor.java:run(683)) - Ending block pool service for: Block pool
> BP-610123021-172.29.121.238-1344539835759 (storage id
> DS-1581877160-172.29.121.238-43609-1344539837880) service to
> localhost/127.0.0.1:40012
> ...
> 2012-08-09 12:17:19,876 FATAL blockmanagement.BlockManager
> (BlockManager.java:run(3039)) - ReplicationMonitor thread received Runtime
> exception.
> java.lang.NullPointerException
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlocksMap.getBlockCollection(BlocksMap.java:101)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.computeReplicationWorkForBlocks(BlockManager.java:1141)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.computeReplicationWork(BlockManager.java:1116)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.computeDatanodeWork(BlockManager.java:3070)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager$ReplicationMonitor.run(BlockManager.java:3032)
> at java.lang.Thread.run(Thread.java:662)
> {code}
> Inspecting the code, it appears that {{BlockManager#close ->
> BlocksMap#close}} can set {{blocks}} to {{null}} while
> {{computeDatanodeWork}} is running.
> The fix seems simple -- have {{close}} just set an exit flag, and have
> {{ReplicationMonitor#run}} call {{BlocksMap#close}}.
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