fix(robot-server): clear ChangeNotifier's internal event immediately after waiting #15103
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…ting ChangeNotifier is the interface for alerting robot-server of notification updates deriving from Protocol Engine. Protocol Engine notify()ies, and the PublisherNotifier wait()s. After the event flag is set() in notify(), the PublisherNotifier no longer waits (correctly). However, the event flag isn't cleared immediately on receiving a new event...it's cleared after PublisherNotifer fires all its registered callbacks. This causes some events to be dropped if Protocol Engine tries setting the flag before PublisherNotifier has gotten around to clearing it... woops. The reason we haven't seen this problem earlier is because we currently don't have too many immediately back-to-back events firing, but in the specific scenario mentioned in the ticket, the following is happening: A play action hits PE, and PE sets the event flag via notify(). PublisherNotifier starts firing through its registered callbacks. The command succeeded & next running command updates hit PE very shortly after the play action, and the set event flag is set from True to True redundantly. PublisherNotifier finishes its callbacks then sets the event flag to False...dropping these new events. The fix: simply clear the event flag immediately after waiting.
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Closes RQA-2677
Overview
ChangeNotifier is the interface for alerting robot-server of notification updates deriving from Protocol Engine. Protocol Engine
notify()ies, and the PublisherNotifierwait()s. After the event flag is set() innotify(), the PublisherNotifier no longer waits (correctly). However, the event flag isn't cleared immediately on receiving a new event...it's cleared after PublisherNotifer fires all its registered callbacks. This causes some events to be dropped if Protocol Engine tries setting the flag before PublisherNotifier has gotten around to clearing it... woops.The reason we haven't seen this problem earlier is because we currently don't have too many immediately back-to-back events firing with publishers that would be interested in those events, but in the specific scenario mentioned in the ticket, the following is happening:
notify().TruetoTrueredundantly.False...dropping these new events.The fix: simply clear the event flag immediately after waiting.
Test Plan
Changelog
Risk assessment
low