concurrency problem in non-block calls to probes

[Simon Poirier]

Making multiple non-blocking calls to probes makes breaks data probe model integrity. I.E. subsequent calls to install/uninstall will generate unpredictable behaviour.

Steps:
someaction = addons.Create('someaction')
ProbeMgr.install(someaction, block=False)
# ... do something...
ProbeMgr.uninstall(someaction, block=False)
ProbeMgr.install(someaction, block=False)

Final state of probe varies between having 2 times the same installed action, without it being uninstallable... to not having any actions installed at all. Making blocking calls seems to enforce the correct behaviour.

It could be documented as a limitation, but I fear it might backfire in the future if we don't do any validation/locking in the probe while playing with it from multiple processes