Re: comment #21 and gating; if this is fully async, then gating is only
going to tighten the race, but not eliminate it. i.e. code like:
if is_leader():
leader_set(...)
can still error as the leadership could be lost between the two calls.
The only safe way of doing leadership code is probably something like:
if is_leader():
try:
# do things you have to do before calling leader_set()
leader_set(...) # if this passes, we are the leader
# do other things that depend on being the leader
except NotImplementedError: # because that's what bizarrely is
returned by charmhelpers
# we're not the leader after all (or something else ... can't
really tell)
if not is_leader():
# we're not the leader any more, undo any damage
else:
raise # something else went wrong
except OtherErrorsTheCodeMayHaveThrownIfWeAreInterested:
# etc
Anyone spot any problems? If this is a pattern, we should try to get it
into charmhelpers as a context manager or similar.
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https://bugs.launchpad.net/bugs/1654116
Title:
Attempts to write leadership settings when not the leader during
relation-changed hooks
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