wxWidgets has QueueEvent and ProcessEvent and AddPendingEvent for this sort of thing - does Qt force you to emit a signal without being able to queue it first?
Qt offers both signals/slots and a lower level (but still cross platform) event system with the usual post event (async) and send event (blocking) methods.
Signals/slots provide a connection abstraction on top of events, and blocking vs queued behavior is a per-connection attribute. So, in cases where the emitter wants to control blocking vs async behavior, you might use the event system with post or send directly.
