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Date: Tue, 2 Jun 2015 06:26:18 +0000 (UTC)
From: "Rakesh R (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Message-ID: <JIRA.12829468.1431499514000.90925.1433226378005@Atlassian.JIRA>
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 <JIRA.12829468.1431499514014@arcas>
Subject: [jira] [Commented] (HDFS-8386) Improve synchronization of
 'streamer' reference in DFSOutputStream - accessed inconsistently with
 respect to synchronization
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    [ https://issues.apache.org/jira/browse/HDFS-8386?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14568620#comment-14568620 ] 

Rakesh R commented on HDFS-8386:
--------------------------------

Thank you [~andrew.wang] for the interest.

{{streamer}} is used by the erasure coding element [DFSStripedOutputStream.java#L283|https://github.com/apache/hadoop/blob/HDFS-7285/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSStripedOutputStream.java#L283]. Considering this usage, can we keep the visibility same as {{protected}}. But I feel it is possible to to make the visibility to {{private}}, following is one proposal to make it {{private}}. I hope the below code snippet will be helpful to know about the proposed changes. If you agree I'm happy to do the changes accordingly. Any thoughts?
# Expose update and getter API in DFSOutputStream.java:
{code}
  protected synchronized void updateStreamer(DataStreamer streamer) {
    this.streamer = streamer;
  }

  protected synchronized DataStreamer getStreamer() {
    return streamer;
  }
{code}
# Modify the logic to access {{streamer}} in DFSStripedOutputStream.java like,
{code}
  private synchronized StripedDataStreamer getCurrentStreamer() {
    return (StripedDataStreamer)super.getStreamer();
  }

  private synchronized StripedDataStreamer setCurrentStreamer(int i) {
    super.updateStreamer(streamers.get(i));
    return getCurrentStreamer();
  }
{code}

> Improve synchronization of 'streamer' reference in DFSOutputStream - accessed inconsistently with respect to synchronization
> ----------------------------------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-8386
>                 URL: https://issues.apache.org/jira/browse/HDFS-8386
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: hdfs-client
>            Reporter: Rakesh R
>            Assignee: Rakesh R
>         Attachments: HDFS-8386-00.patch
>
>
> Presently {{DFSOutputStream#streamer}} object reference is accessed inconsistently with respect to synchronization. It would be good to improve this part. This has been noticed when implementing the erasure coding feature.
> Please refer the related [discussion thread|https://issues.apache.org/jira/browse/HDFS-8294?focusedCommentId=14541411&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14541411] in the jira HDFS-8294 for more details.


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