This is what can happen.
This is the potential race.
DrainDispatcher is started via serviceStart() . As a last step, this starts the actual dispatcher thread (eventHandlingThread.start() - and returns immediately - which means the thread may or may not have started up by the time start returns.
UserThread: calls dispatcher.getEventHandler().handle()
This sets drained = false, and a context switch happens.
DispatcherThread: starts running
DispatcherThread drained = queue.isEmpty(); -> This sets drained to true, since Thread1 yielded before putting anything into the queue.
UserThread: actual.handle(event) - which puts the event in the queue for the dispatcher thread to process, and returns control.
UserThread: dispatcher.await() - Since drained is true, this returns immediately - even though there is a pending event to process.