[Bug 1588462] Related fix merged to charm-glance (master)

[OpenStack Infra]

Reviewed:  https://review.openstack.org/325650
Committed: https://git.openstack.org/cgit/openstack/charm-glance/commit/?id=1ab2c809ad7251f6d8a30c053d8c7818ac051547
Submitter: Jenkins
Branch:    master

commit 1ab2c809ad7251f6d8a30c053d8c7818ac051547
Author: Alex Kavanagh <alex at ajkavanagh.co.uk>
Date:   Sun Jun 5 12:57:53 2016 +0000

    Fix for status-set race - related to bug 1588462
    
    This change fixes the obvious race for a status_set() between
    check_optional_interfaces() and assess_status() as the later calls the former
    which calls status_set(), returns the status, which is then potentially set
    again by the assess_status() function.  This cleans up the code so that only a
    single status_set() is performed when calling assess_status().
    
    Change-Id: I06efbcaade8f0c99b5931104e6887d24cb10e35a
    Related-Bug:#1588462

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https://bugs.launchpad.net/bugs/1588462

Title:
  Status set race condition in OpenStack charms with optional relations

Status in ceph-radosgw package in Juju Charms Collection:
  New
Status in cinder package in Juju Charms Collection:
  New
Status in glance package in Juju Charms Collection:
  New
Status in keystone package in Juju Charms Collection:
  New
Status in neutron-api package in Juju Charms Collection:
  New
Status in neutron-gateway package in Juju Charms Collection:
  New
Status in nova-cloud-controller package in Juju Charms Collection:
  New

Bug description:
  In charms that call assess_status() on every hook execution and that have
  optional relations there are two places where status_set() is called in
  set_os_workload_status() and make_assess_status_func()'s _assess_status_func()
  leading to a race condition in which a status may be overwritten.

  For charms like nova-cloud-controller where strangely we call
  set_os_workload_status() on each hook execution instead of assess_status() we
  only see this during pause and resume actions which do call assess_status().

  Regardless of __if__ you hit the race condition you can see the problem simply
  using print statements and an update-status hook run:
  'STATUS SET IN set_os_workload_status', 'active', 'Unit is ready'
  'STATUS SET IN _assess_status_func()', 'active', 'Unit is ready'

  If the first happened to be different the second would clobber it.

  In the set_os_workload_status() stack a comparison is made against the current
  status before setting status. The assess_status() stack needs to do the same
  possibly by calling set_os_workload_status() itself.

  The goal should be to have a single canonical source for status_set.

  This will affect all OpenStack charms that have optional relations.

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