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Date: Thu, 22 Nov 2012 07:42:58 +0000 (UTC)
From: "Hiroshi Ikeda (JIRA)" <jira@apache.org>
To: issues@hbase.apache.org
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Subject: [jira] [Updated] (HBASE-7160) Improve IdLock and remove its minor
 defects
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     [ https://issues.apache.org/jira/browse/HBASE-7160?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Hiroshi Ikeda updated HBASE-7160:
---------------------------------

    Attachment: HBASE-7160-V3.patch

Patch v3 from review board.
                
> Improve IdLock and remove its minor defects
> -------------------------------------------
>
>                 Key: HBASE-7160
>                 URL: https://issues.apache.org/jira/browse/HBASE-7160
>             Project: HBase
>          Issue Type: Improvement
>            Reporter: Hiroshi Ikeda
>            Assignee: Hiroshi Ikeda
>            Priority: Minor
>         Attachments: HBASE-7160.patch, HBASE-7160-V2.patch, HBASE-7160-V3.patch
>
>
> Combination of synchronizations and concurrent collections complicates the code, and it is hard to trace the code and to confirm its correctness. We should re-create the class and make it more understandable.
> In the current code, I find the following minor defects:
> (1) In the case that there is a waiting thread for a lock in getLockEntry() and another thread is releasing the lock by calling releaseLockEntry(), trying to get the lock with a 3rd thread by calling getLockEntry() falls into a busy loop until the waiting thread wakes up and gets the lock.
> Even if notify() wakes up the blocked thread and causes a context switch to the waked thread immediately, synchronization might block the waked thread and cause another context switch, and the busy loop might continue for a while.
> (2) In the same case as (1), since releasing the lock is merely notifying without removing the lock-entry from the map, interrupting the waiting thread might leave an unused lock-entry (entry.numWaiters == 0) in the map. This is a memory leak unless the id of the lock is used again.

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