Comment 5 for bug 1624538

Reviewed: https://review.openstack.org/372550
Committed: https://git.openstack.org/cgit/openstack/heat/commit/?id=4695f47f68031195b23857a1fce827c39c626faa
Submitter: Jenkins
Branch: stable/newton

commit 4695f47f68031195b23857a1fce827c39c626faa
Author: Zane Bitter <email address hidden>
Date: Fri Sep 16 17:05:25 2016 -0400

    Don't acquire the lock when cancelling a stack

    We used to try to acquire the stack lock in order to find out which engine
    to cancel a running update on, in the misguided belief that it could never
    succeed. Accordingly, we never released the lock.

    Since it is entirely possible to encounter a race where the lock has
    already been released, use the get_engine_id() method instead to look up
    the ID of the engine holding the lock without attempting to acquire it.

    Change-Id: I1d026f8c67dddcf840ccbc2f3f1537693dc266fb
    Closes-Bug: #1624538
    (cherry picked from commit e2ba3390cda4d7bfcf8397da097ac5358ead1ca5)