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https://issues.apache.org/jira/browse/HDFS-6788?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14081278#comment-14081278
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Arpit Agarwal commented on HDFS-6788:
-------------------------------------
The reentrant behavior of ReentrantReadWriteLock is different from
synchronized. A synchronized method can always call another synchronized
method, however a read lock holder will block if it attempts to get the write
lock. From a quick look I did not find any issues with this patch however I
have not reviewed it carefully enough yet.
> Improve synchronization in BPOfferService with read write lock
> --------------------------------------------------------------
>
> Key: HDFS-6788
> URL: https://issues.apache.org/jira/browse/HDFS-6788
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode
> Affects Versions: 2.5.0
> Reporter: Yongjun Zhang
> Assignee: Yongjun Zhang
> Attachments: HDFS-6788.001.patch
>
>
> Threads in DN (DataXceiver, PacketResponder, Async disk worker etc) may block
> at BPOfferService.getBlockPoolId() when calling BPOfferService.checkBlock(),
> though they are just reading the same blockpool id. This is unnecessary
> overhead and may cause performance hit when many threads compete. Filing this
> jira to replace synchronized method with read write lock
> (ReentrantReadWriteLock).
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