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From "Benjamin Reed (JIRA)" <j...@apache.org>
Subject [jira] Commented: (ZOOKEEPER-767) Submitting Demo/Recipe Shared / Exclusive Lock Code
Date Thu, 03 Jun 2010 17:57:00 GMT

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-767?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12875221#action_12875221
] 

Benjamin Reed commented on ZOOKEEPER-767:
-----------------------------------------

-1 there are a couple of problems with the implementation:

1) shouldn't you check to see if you already have a lock before you do the create? that will
remove the code right after the create in the getXXXXLock() methods.

2) if you already have an exclusive lock, shouldn't that also count as a shared lock?

3) the error handling is a bit problematic. a connection loss exception or an interrupt can
leave a process holding a lock without knowing it.

4) when you go through the children, you may end up checking for the existence of every znode
before you, which could be wasteful.

i think it may be better to expand the current locking code to handle shared lock rather than
add a new lock implementation. the current lock recipe implementation only does exclusive
locks, but it is implemented in a way that makes it easy to support shared locks as well and
it takes care of the above problems.

> Submitting Demo/Recipe Shared / Exclusive Lock Code
> ---------------------------------------------------
>
>                 Key: ZOOKEEPER-767
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-767
>             Project: Zookeeper
>          Issue Type: Improvement
>          Components: recipes
>    Affects Versions: 3.3.0
>            Reporter: Sam Baskinger
>            Assignee: Sam Baskinger
>            Priority: Minor
>             Fix For: 3.4.0
>
>         Attachments: ZOOKEEPER-767.patch, ZOOKEEPER-767.patch
>
>
> Networked Insights would like to share-back some code for shared/exclusive locking that
we are using in our labs.

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