lockutils - native threads support

[Mark McLoughlin]

https://review.openstack.org/14139

This piece of code:

            sem = _semaphores.get(name, semaphore.Semaphore())
            if name not in _semaphores:
                # this check is not racy - we're already holding ref locally
                # so GC won't remove the item and there was no IO switch
                # (only valid in greenthreads)
                _semaphores[name] = sem

assumes that we're using greenthreads and not native threads

We should support native threads soon

This:

  http://stackoverflow.com/questions/5390569/dynamically-allocating-and-destroying-mutexes

shows how we can fix that by protecting the semaphores dict with a lock

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/54581

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/54581
Committed: http://github.com/openstack/oslo-incubator/commit/79e6bc6cbb2288b82c587ae3a19a41540647886d
Submitter: Jenkins
Branch: master

commit 79e6bc6cbb2288b82c587ae3a19a41540647886d
Author: Victor Stinner <email address hidden>
Date: Wed Oct 30 17:26:21 2013 +0100

    fix lockutils.lock() to make it thread-safe

    lockutils.lock() is currenctly safe when used with greenthreads, but it is not
    safe when used with classic threads. This change uses a lock to protect
    _semaphores dictionary.

    Change-Id: Ia18e6e9f9a1353640729ac57d7225c660159cd55
    Closes-Bug: 1065529