Comment 11 for bug 1988311

Reviewed: https://review.opendev.org/c/openstack/oslo.concurrency/+/855714
Committed: https://opendev.org/openstack/oslo.concurrency/commit/ee3f73a13379a79282325906787aae7da0f6ac27
Submitter: "Zuul (22348)"
Branch: master

commit ee3f73a13379a79282325906787aae7da0f6ac27
Author: Balazs Gibizer <email address hidden>
Date: Sat Sep 3 15:35:35 2022 +0200

    Fix fair internal lock used from eventlet.spawn_n

    The fasteners lib in version 0.15.0 removed the
    threading.current_thread workaround for eventlet[1] because eventlet
    seemed to fixed the current_thread issues tracked in [2]. However the
    fix for [2] only fixed half of the problem. The threading.current_thread
    call works if it is called from thread created by eventlet.spawn.
    However if the thread is created with eventlet.spawn_n then
    threading.current_thread is still broken and returns the ID of the
    python native thread.

    The fasteners' ReaderWriterLock depends heavily on
    threading.current_thread to decide which thread holds a lock and to
    allow re-entry of that thread. This leads to the situation that
    multiple threads created from spawn_n could take the same
    ReaderWriterLock at the same time.

    The fair internal lock in oslo.concurrency uses ReaderWriterLock and
    as a result such lock is broken for threads created with spawn_n.

    Note that this issue was raised with eventlet in [3] when the nova team
    detected it via a direct usage of ReaderWriterLock in the nova test
    code. As [3] did not lead to a solution in eventlet nova implemented a
    nova local fix for the test code in [4].

    However now we detected that oslo.concurrency is affected by this issue
    as well.

    This patch restores the workaround that was removed by [1].

    Note that a fasteners issue [5] also opened to restore the
    workaround[1].

    [1] https://github.com/harlowja/fasteners/commit/467ed75ee1e9465ebff8b5edf452770befb93913
    [2] https://github.com/eventlet/eventlet/issues/172
    [3] https://github.com/eventlet/eventlet/issues/731
    [4] https://review.opendev.org/c/openstack/nova/+/813114
    [5] https://github.com/harlowja/fasteners/issues/96

    Closes-Bug: #1988311
    Change-Id: Ia873bcc6b07121c9bd0b94c593567d537b4c1112