I am considering using deferred messages as a delay/timeout alerting mechanism within my Saga. I would do this by sending a deferred message at the same time as sending a message to a handler to do some time-consuming work.
If that handler fails to publish a response within the deferred timespan the Saga is alerted to the timeout/delay via the deferred message arrival. This is different to a handler failure as its still running, just slower than expected.
The issue comes if everything runs as expected, its possible that the Saga will complete all of its steps and you'd find many deferred messages waiting to be delivered to a Saga that no longer exists. Is there a way to clean up the deferred messages you know are no longer required?
Perhaps there is a nicer way of implementing this functionality in Rebus?
Once sent, deferred messages cannot be cancelled.
But Rebus happens to ignore messages that cannot be correlated with a saga instance, and the saga handler does not allow for that particular message type to initiate a new saga, so if the saga instance is gone, the message will simply be swallowed.
That's the difference between using IHandleMessages<CanBeIgnored> and IAmInitiatedBy<CannotBeIgnored> on your saga. 🙂