Update ResourceNotificationServiceLogging

[DamianEdwards]

Fixes #4686

Microsoft Reviewers: Open in CodeFlow

[mitchdenny]

Is there any chance that we'll get two resource notifications for a resource being processed in parallel. I'm wondering if there is potential for resource states to rapidly oscillate and then we don't fire them.

[DamianEdwards]

Is there any chance that we'll get two resource notifications for a resource being processed in parallel. I'm wondering if there is potential for resource states to rapidly oscillate and then we don't fire them.

The publish method takes a lock on the state, so all updates for a resource get effectively sequentialized anyway, so while races might result in "extra" transitions being logged, I'm not sure any can be missed, e.g.

1. no state -> state1
2. state2 update comes in
3. state1 update comes in
4. state2 and state1 updates race such that state1 gets the lock first
5. no update is logged for state1 update as resource is already in that state
6. state2 update is logged as transition from state1 to state2

If in step 4 state2 update gets the lock first, then state1 to state2 transition is logged, and then state1 update logs transition from state2 to state1 (the "extra" update).

If we wanted to solve that we could use a Channel or similar but ultimately calls to Publish still race each other until the sync point.