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From "Jordan Zimmerman (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CURATOR-54) No reliable way to cancel leadership in LeaderSelector when connection fails due to edge cases
Date Tue, 10 Sep 2013 21:54:51 GMT
Jordan Zimmerman created CURATOR-54:
---------------------------------------

             Summary: 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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