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https://issues.apache.org/jira/browse/HDFS-6591?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14047549#comment-14047549
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Liang Xie commented on HDFS-6591:
---------------------------------
Attached v4 should address [[email protected]]'s comments.
[~cnauroth], after a looking, it seems that it's a convention that adding
"future.get()" after "CompletionService#poll", even Future<Void>, see this
example:
https://github.com/apache/hbase/blob/e4138a3a9408193e90dd6cc0db6d61320e370479/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/snapshot/RegionServerSnapshotManager.java#L319
I grep lots of open source code, all have this style, even don't need the
result for further processing:)
I didn't read through JDK FutureTask related impl so far, but my thought is
that the JavaDoc for "CompletionService#poll" probably is not correct enough.
Also i replaced "future.get" with "Thread.sleep(xx)", still got failed result,
so it should not related with: "so this might indicate a race condition that
had been masked by the future.get() taking up a few extra cycles", per my
understanding so far.
> while loop is executed tens of thousands of times in Hedged Read
> ------------------------------------------------------------------
>
> Key: HDFS-6591
> URL: https://issues.apache.org/jira/browse/HDFS-6591
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: hdfs-client
> Affects Versions: 2.4.0
> Reporter: LiuLei
> Assignee: Liang Xie
> Attachments: HDFS-6591-v2.txt, HDFS-6591-v3.txt, HDFS-6591-v4.txt,
> HDFS-6591.txt, LoopTooManyTimesTestCase.patch
>
>
> I download hadoop-2.4.1-rc1 code from
> http://people.apache.org/~acmurthy/hadoop-2.4.1-rc1/, I test the Hedged
> Read. I find the while loop in hedgedFetchBlockByteRange method is executed
> tens of thousands of times.
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