Hi Zecas,
As Sebastian said, the DispatcherThread is just used to find and execute Async Job and Timer. It won't affect process engine.
The process engine is very simple. When you called service method, like executionService.startProcessInstanceById(), process engine will invoke related Command to execute process, the process will run through process definition until it arrival a wating Activity(StateActivity or TaskActivity) or arrival EndActivity. Whatever it turn to wait or end state, ther service will return and we could get the process instance. One request, One response.