Comment 4 for bug 1533787

Reviewed: https://review.openstack.org/267625
Committed: https://git.openstack.org/cgit/openstack/ceilometer/commit/?id=e84a10882a9b682ff41c84e8bf4ee2497e7e7a31
Submitter: Jenkins
Branch: master

commit e84a10882a9b682ff41c84e8bf4ee2497e7e7a31
Author: gordon chung <email address hidden>
Date: Thu Jan 14 09:47:33 2016 -0500

    better support notification coordination

    when launching multiple agents at same time, there is a chance that
    agents will miss the registry of another agent. this is possible
    because there is a lot of overhead involved when starting up agents,
    specifically with initialising managers.

    this change makes it so the agent only joins the group AFTER it has
    done all setup that does not require coordination. after it joins,
    we start listening right away for other changes to group membership

    additionally, this adds a lock to pipeline queue setup so only one
    event at any time can trigger a reconfiguration.

    Change-Id: I8100160a3aa83a190c4110e6e8be9b26aef8fd1c
    Closes-Bug: #1533787