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From "james strachan (JIRA)" <j...@apache.org>
Subject [jira] Commented: (ZOOKEEPER-78) added a high level protocol/feature - for easy Leader Election or exclusive Write Lock creation
Date Fri, 18 Jul 2008 11:52:32 GMT

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-78?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12614703#action_12614703

james strachan commented on ZOOKEEPER-78:

Thanks Flavio! 

Totally agreed on 1. Strictly speaking we should catch all exceptions and handle them properly
(which may mean throwing some, or responding properly to others or whatever).

One of the main reasons for the retry logic was to avoid errors like trying to create a znode
that already exists or loosing connection to the ZK server etc - but we should go through
all possible exceptions and handle them much cleaner.

In particular we really need test cases that show the server closing and restarting during
the process of acquiring the lock or after a lock owner has the lock etc.  

I figured I'd send a patch first and see if anyone else had a better implementation lying
around - or knew a neater way to solve this - before I spent too much time getting it totally
correct etc. 

For 2) I just added that so that when running the unit tests you could see INFO or DEBUG level
logging etc (particularly when running in your IDE)

> added a high level protocol/feature - for easy Leader Election or exclusive Write Lock
> -----------------------------------------------------------------------------------------------
>                 Key: ZOOKEEPER-78
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-78
>             Project: Zookeeper
>          Issue Type: New Feature
>          Components: java client
>    Affects Versions: 3.0.0
>            Reporter: james strachan
>            Assignee: james strachan
>         Attachments: writeLock_protocol.patch
> Here's a patch which adds a little WriteLock helper class for performing leader elections
or creating exclusive locks in some directory znode. Note its an early cut; am sure we can
improve it over time. The aim is to avoid folks having to use the low level ZK stuff but provide
a simpler high level abstraction.

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