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https://issues.apache.org/jira/browse/HDFS-7854?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14358357#comment-14358357
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Li Bo commented on HDFS-7854:
-----------------------------
hi, Jing
we may encounter some problems in your way of handling of
{{queueCurrentPacket}} and {{waitAndQueueCurrentPacket}}, and also
{{waitForAckedSeqno}}.
{{DFSOutputStream#closed}} is different with {{DataStreamer#streamClosed}}. If
we move these three methods to DataStreamer and replace
{{DFSOutputStream#closed}} with {{DataStreamer#streamClosed}}, we have changed
some logic of the original code. For example, two threads(t1, t2) share the
same DFSOutputStream, if t1 call {{ DFSOutputStream #close()}}, and an
exception is thrown in this function before closing streamer, then
{{DFSOutputStream#closed}} is true and {{DataStreamer#streamClosed}} is still
false. If t2 calls {{ waitForAckedSeqno }}, originally it will immediately quit
this function because {{DFSOutputStream#closed}} is true; if we call
{{streamer. waitForAckedSeqno ()}}, now {{DataStreamer#streamClosed}} is still
false, so t2 will wait for the while loop to exit. I remember that I have
encountered such kinds of problems before.
Because DFSOutputStream also generates packets, I think it’s not bad for
DFSOutputStream to maintain a queue shared with a DataStreamer, and it gives
less changes to the original code.
> Separate class DataStreamer out of DFSOutputStream
> --------------------------------------------------
>
> Key: HDFS-7854
> URL: https://issues.apache.org/jira/browse/HDFS-7854
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Reporter: Li Bo
> Assignee: Li Bo
> Attachments: HDFS-7854-001.patch, HDFS-7854-002.patch,
> HDFS-7854-003.patch
>
>
> This sub task separate DataStreamer from DFSOutputStream. New DataStreamer
> will accept packets and write them to remote datanodes.
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