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From "Suresh Srinivas (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-1865) Share LeaseChecker thread among DFSClients
Date Fri, 06 May 2011 21:34:03 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1865?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13030151#comment-13030151

Suresh Srinivas commented on HDFS-1865:

# DFSClient.java
#* DFSClient#filesBeingWritten - worth adding a comment that a file can be opened for write
by a DFSClient only once.
# LeaseRenewer.java
#* In the class document, it is good to describe lease mechanism briefly. This would help
people understand the code better. Adding additional comments on how LeaseRenewer works would
also be good. Adding information about synchronization will also help understand the code
#* Please throw HadoopIllegalArgumentException instead of NullPointerException.
#* Please do not access DFSClient#filesBeingWritten in this class. Add methods to DFSClient
to do this.
#* Factory#remove - please avoid adding synchronized on renewer. Instead call a method on
renewer, that is synchronized.
#* Minor: Simplify the code in in LeaseRenewer#get(). If map returns empty then add it to
map and return it. You do not not need if else. You can do it with just if and can get rid
of "r".
#* Copy on array list for DFSClients as an alternative to making a copy every time in renew()?
#* Why do you check {if (r == stored) } in Factory#remove()?
#* Why did we choose to use volatile for sleepPeriod and synchronized for gracePeriod and
other periods?

> Share LeaseChecker thread among DFSClients
> ------------------------------------------
>                 Key: HDFS-1865
>                 URL: https://issues.apache.org/jira/browse/HDFS-1865
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: hdfs client
>            Reporter: Tsz Wo (Nicholas), SZE
>            Assignee: Tsz Wo (Nicholas), SZE
>         Attachments: h1865_20110503.patch, h1865_20110504.patch
> Each {{DFSClient}} runs a {{LeaseChecker}} thread within a JVM.  The number threads could
be reduced by sharing the threads.

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