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From "Jordan Zimmerman (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CURATOR-54) No reliable way to cancel leadership in LeaderSelector when connection fails due to edge cases
Date Tue, 10 Sep 2013 23:01:53 GMT

    [ https://issues.apache.org/jira/browse/CURATOR-54?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13763661#comment-13763661
] 

Jordan Zimmerman commented on CURATOR-54:
-----------------------------------------

FYI - the website doc and example code has also been updated (the website should be regenerated
when this is released)
                
> No reliable way to cancel leadership in LeaderSelector when connection fails due to edge
cases
> ----------------------------------------------------------------------------------------------
>
>                 Key: CURATOR-54
>                 URL: https://issues.apache.org/jira/browse/CURATOR-54
>             Project: Apache Curator
>          Issue Type: Bug
>          Components: Recipes
>    Affects Versions: 2.2.0-incubating
>            Reporter: Jordan Zimmerman
>            Assignee: Jordan Zimmerman
>             Fix For: 2.3.0-incubating
>
>
> From a post to user@
> "Hi,
> I'm fairly new with Zookeeper and Curator. I want to achieve a simple leader election
process.
> But, I ran into trouble implementing the interruption behavior. I could not find a reliable
way to stop the leader (withdraw from leadership).
> I think even the schoolbook example that Curator brings is flawed.
> In leader.ExampleClient:
>  @Override
>     public void stateChanged(CuratorFramework client, ConnectionState newState)
>     {
>         // you MUST handle connection state changes. This WILL happen in production code.
>         if ( (newState == ConnectionState.LOST) || (newState == ConnectionState.SUSPENDED)
)
>         {
>             if ( ourThread != null )
>             {
>                 ourThread.interrupt();
>             }
>         }
>     }
> So in case of lost leadership, the ourThread thread is interrupted. However, ourThread
is set in the 2nd line of the takeLeadership() method. Until then, it is null.
> What happens if the connection is lost immediately after it is established, and ourThread
stays null? Won't it be the case that the thread will go on, thinking that it is the leader,
despite it being supposed to withdraw?
> Thanks,
> Arie"

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