Comment 4 for bug 1856312

Reviewed: https://review.opendev.org/698954
Committed: https://git.openstack.org/cgit/openstack/oslo.config/commit/?id=e3e2ba55eeeb86a9bc0624bb2592e46583e839e7
Submitter: Zuul
Branch: master

commit e3e2ba55eeeb86a9bc0624bb2592e46583e839e7
Author: Stephen Finucane <email address hidden>
Date: Fri Dec 13 16:18:33 2019 +0000

    Ensure option groups don't change during logging

    oslo.config allows us to configure groups and options dynamically. This
    can cause a race with our logging as we attempt to iterate through
    option groups that are changing under our feet. This wouldn't be a huge
    issue, since these are just logs are we can always log again, if needed,
    but we store groups in a dictionary and Python doesn't like us changing
    the size of a dict it's iterating through:

      RuntimeError: dictionary changed size during iteration

    Given that we're only reading through this option group and don't need
    to worry about a group _disappearing_, the solution is pretty simple:
    create a copy of our option group names ahead of time so we don't need
    to worry about new ones coming and messing things up.

    No tests are included since this is a race and the only way I see to
    reproduce this would involve lots of ugly threading.

    Change-Id: Id3b28465d645a24f0fcebff2dd68a9bd30e21594
    Signed-off-by: Stephen Finucane <email address hidden>
    Closes-Bug: #1856312