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From "Colin Patrick McCabe (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6803) Documenting DFSClient#DFSInputStream expectations reading and preading in concurrent context
Date Wed, 13 Aug 2014 18:30:13 GMT

    [ https://issues.apache.org/jira/browse/HDFS-6803?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14095874#comment-14095874
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Colin Patrick McCabe commented on HDFS-6803:
--------------------------------------------

bq. Should we require the implementations of FSInputStream should be thread-safe (or at least
for PositionedReadable)? And modify some implementations such as WebHDFS to make pread concurrently?

I think stack's point 2.1 and 2.2 imply that pread can safely be called from multiple threads
concurrently.  I guess we should document this too so that there's no confusion.

> Documenting DFSClient#DFSInputStream expectations reading and preading in concurrent
context
> --------------------------------------------------------------------------------------------
>
>                 Key: HDFS-6803
>                 URL: https://issues.apache.org/jira/browse/HDFS-6803
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: hdfs-client
>    Affects Versions: 2.4.1
>            Reporter: stack
>         Attachments: DocumentingDFSClientDFSInputStream (1).pdf
>
>
> Reviews of the patch posted the parent task suggest that we be more explicit about how
DFSIS is expected to behave when being read by contending threads. It is also suggested that
presumptions made internally be made explicit documenting expectations.
> Before we put up a patch we've made a document of assertions we'd like to make into tenets
of DFSInputSteam.  If agreement, we'll attach to this issue a patch that weaves the assumptions
into DFSIS as javadoc and class comments. 



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