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From Jordan Zimmerman <jor...@jordanzimmerman.com>
Subject Re: LeaderSelector edge case - preventing timely leadership withdrawal
Date Tue, 10 Sep 2013 21:55:03 GMT
https://issues.apache.org/jira/browse/CURATOR-54

On Sep 9, 2013, at 10:32 AM, Arie Zilberstein <azilberstein@salesforce.com> wrote:

> 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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