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Date: Tue, 23 May 2017 05:08:04 +0000 (UTC)
From: "Anoop Sam John (JIRA)" <jira@apache.org>
To: issues@hbase.apache.org
Message-ID: <JIRA.13073537.1495220648000.269290.1495516084068@Atlassian.JIRA>
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Subject: [jira] [Commented] (HBASE-18085) Prevent parallel purge in
 ObjectPool
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archived-at: Tue, 23 May 2017 05:08:08 -0000


    [ https://issues.apache.org/jira/browse/HBASE-18085?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16020668#comment-16020668 ] 

Anoop Sam John commented on HBASE-18085:
----------------------------------------

In ur test method for tryLock, there is no logic other than just try lock and release.  If that is been removed as dead code by compiler?  One way to avoid that is using the return value.  See BlackHole in JMH and its usage.. The diff in numbers that reported by JMH benchmark is so huge!  The impl of tryLock is having a volatile read and all.   So this huge diff in numbers looks strange no? That was my doubt. 

> Prevent parallel purge in ObjectPool
> ------------------------------------
>
>                 Key: HBASE-18085
>                 URL: https://issues.apache.org/jira/browse/HBASE-18085
>             Project: HBase
>          Issue Type: Bug
>            Reporter: Yu Li
>            Assignee: Yu Li
>         Attachments: e89l05465.st3.jstack, HBASE-18085.patch
>
>
> Parallel purge in ObjectPool is meaningless and will cause contention issue since {{ReferenceQueue#poll}} has synchronization (source code shown below)
> {code}
>     public Reference<? extends T> poll() {
>         if (head == null)
>             return null;
>         synchronized (lock) {
>             return reallyPoll();
>         }
>     }
> {code}
> We observed threads blocking on the purge method while using offheap bucket cache, and we could easily reproduce this by testing the 100% cache hit case in bucket cache with enough reading threads.
> We propose to add a purgeLock and use tryLock to avoid parallel purge.


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