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From "Jean-Daniel Cryans (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2503) PriorityQueue isn't thread safe, KeyValueHeap uses it that way
Date Thu, 29 Apr 2010 21:22:54 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2503?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12862419#action_12862419
] 

Jean-Daniel Cryans commented on HBASE-2503:
-------------------------------------------

Yeah might as well... And it relates even more to 2077 than I thought. So here if a next is
waiting on a close... the result is a bit unclear to me. The user would see this as the end
of a scan as a null would be returned by this.storeHeap.peek()? So adding to the sync'ed methods,
I think we need a "closed' marker on RegionScanner that we would need to verify in next()
and set in close().

> PriorityQueue isn't thread safe, KeyValueHeap uses it that way
> --------------------------------------------------------------
>
>                 Key: HBASE-2503
>                 URL: https://issues.apache.org/jira/browse/HBASE-2503
>             Project: Hadoop HBase
>          Issue Type: Bug
>    Affects Versions: 0.20.3
>            Reporter: Jean-Daniel Cryans
>            Assignee: Jean-Daniel Cryans
>            Priority: Critical
>             Fix For: 0.20.5, 0.21.0
>
>
> In the same spirit as HBASE-2077, but a bit different (at least to me). Dave Latham had
the following NPE killing a RS:
> {code}
> Exception in thread "regionserver/192.168.41.2:60020.leaseChecker" java.lang.NullPointerException
>         at org.apache.hadoop.hbase.regionserver.KeyValueHeap$KVScannerComparator.compare(KeyValueHeap.java:127)
>         at org.apache.hadoop.hbase.regionserver.KeyValueHeap$KVScannerComparator.compare(KeyValueHeap.java:117)
>         at java.util.PriorityQueue.siftDownUsingComparator(PriorityQueue.java:644)
>         at java.util.PriorityQueue.siftDown(PriorityQueue.java:612)
>         at java.util.PriorityQueue.poll(PriorityQueue.java:523)
>         at org.apache.hadoop.hbase.regionserver.KeyValueHeap.close(KeyValueHeap.java:151)
>         at org.apache.hadoop.hbase.regionserver.HRegion$RegionScanner.close(HRegion.java:1862)
>         at org.apache.hadoop.hbase.regionserver.HRegionServer$ScannerListener.leaseExpired(HRegionServer.java:1959)
>         at org.apache.hadoop.hbase.Leases.run(Leases.java:98)
> {code}
> He also has the same stack traces from 2077. The PQ javadoc says this class is not thread
safe, but it is used by the leaseChecker thread and the client threads. We need to use something
like the BlockingPriorityQueue instead.

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