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From "Hiroshi Ikeda (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-16648) [JDK8] Use computeIfAbsent instead of get and putIfAbsent
Date Tue, 20 Sep 2016 05:41:20 GMT

    [ https://issues.apache.org/jira/browse/HBASE-16648?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15505655#comment-15505655
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Hiroshi Ikeda commented on HBASE-16648:
---------------------------------------

My bad, I didn't realized that the default implementation is overridden by the interface.
Although CopyOnWriteArrayMap.putIfAbsent is wrongly implemented, it seems computeIfAbsent
works well.

bq. Lock does not reduce performance, the problem is contention.

Generally speaking, lock can reduce performance by context switches when contention occurs,
while CAS doesn't block. Moreover the implementation is not so trivial and causes overhead
to ensure atomicity in ConcurretHashMap.

> [JDK8] Use computeIfAbsent instead of get and putIfAbsent
> ---------------------------------------------------------
>
>                 Key: HBASE-16648
>                 URL: https://issues.apache.org/jira/browse/HBASE-16648
>             Project: HBase
>          Issue Type: Sub-task
>          Components: Performance
>    Affects Versions: 2.0.0
>            Reporter: Duo Zhang
>            Assignee: Duo Zhang
>             Fix For: 2.0.0
>
>         Attachments: HBASE-16648-v1.patch, HBASE-16648-v2.patch, HBASE-16648.patch
>
>




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