Comment 18 for bug 1518430

Reviewed: https://review.openstack.org/395018
Committed: https://git.openstack.org/cgit/openstack/oslo.messaging/commit/?id=d690cac08ca0f6c18518e7760d8bdcfd14cdee84
Submitter: Jenkins
Branch: stable/mitaka

commit d690cac08ca0f6c18518e7760d8bdcfd14cdee84
Author: John Eckersberg <email address hidden>
Date: Fri Oct 14 11:02:47 2016 -0400

    rabbit: Avoid busy loop on epoll_wait with heartbeat+eventlet

    Calling threading.Event.wait() when using eventlet results in a busy
    loop calling epoll_wait, because the Python 2.x
    threading.Condition.wait() implementation busy-waits by calling
    sleep() with very small values (0.0005..0.05s). Because sleep() is
    monkey-patched by eventlet, this results in many very short timers
    being added to the eventlet hub, and forces eventlet to constantly
    epoll_wait looking for new data unecessarily.

    This utilizes a new Event from eventletutils which conditionalizes the
    event primitive depending on whether or not eventlet is being used.
    If it is, eventlet.event.Event is used instead of threading.Event.
    The eventlet.event.Event implementation does not suffer from the same
    busy-wait sleep problem. If eventlet is not used, the previous
    behavior is retained.

    For Newton backport, this bundles the Event from eventletutils
    directly in oslo.messaging under the _utils module. It is taken from:

    https://review.openstack.org/#/c/389739/

    combined with the followup fix:

    https://review.openstack.org/#/c/394460/

    Change-Id: I5c211092d282e724d1c87ce4d06b6c44b592e764
    Depends-On: Id33c9f8c17102ba1fe24c12b053c336b6d265501
    Closes-bug: #1518430
    (cherry picked from commit a6c193f3eba62cdcbfe04d0fa93e95352bcfb1c3)