Need a way to abort charm execution

As a charmer, I’d like a way to abort charm execution from anywhere. Use case: I have a charm with many event handlers, but regardless of which event we’re in, I want the charm to do nothing and exit with blocked state if a certain precondition is not met, say, a certain config value is provided. Right now I have to, for each event handler, add a check:

if not self.condition():
    self.unit.status = ...
    return

I could raise an exception in __init__, but that would leave the charm in error state.

I propose to add a Framework.abort() method that raises an exception that gets caught in main and terminates charm execution without committing any state (status will pass through because that’s committed synchronously).

With that, I would only need to add these three lines:

# in MyCharm.__main__:
if not self.condition():
    self.unit.status=...
    self.framework.abort()

[beliaev-maksim]

@benhoyt I will add it as part of sdk tutorial and also add “how to” section on juju.is

I will let you review it once ready

[PietroPasotti]

@benhoyt for my best understanding of what happens when in terms of syncing with juju: see the second section of this doc https://discourse.charmhub.io/t/talking-to-a-workload-control-flow-from-a-to-z/6161

The logic of the code you wrote above is what we need, the issue is: do we want to expose a high-level callable that abstracts it, or do we leave it to the charmers to remember to call framework.commit() before they exit?