Comment 4 for bug 1622865

Reviewed: https://review.openstack.org/371012
Committed: https://git.openstack.org/cgit/openstack/congress/commit/?id=3785f810b5c59ff2ad2666de794c067e3733c90e
Submitter: Jenkins
Branch: master

commit 3785f810b5c59ff2ad2666de794c067e3733c90e
Author: Masahito Muroi <email address hidden>
Date: Fri Sep 16 02:20:35 2016 +0900

    control_bus service has only 1 heartbeat thread

    control_service class expects to have only one heartbeat thread.
    But the service launchs a heartbeat thread everytime when
    control_bus.start() is called. Thus control_bus has 3 methods
    and sends 3 heartbeat messages always.

    This adds a barrier to stop creating extra heartbeat threads in the class.

    Change-Id: I28f06eef3548e07367a3c3757892112a87391ce5
    Closes-Bug: #1622865