Most single-process implementations of event-driven programming are handled as soon as they appear in a serial fashion. Whether it is a callback-based style GUI application or full-fledged signaling in the style of the blinker library, an event-driven application usually maintains some kind of mapping between events and lists of handlers to execute whenever one of these events happens.
This style of information passing in distributed applications is usually realized through a request-response communication. A request-response is a bidirectional and obviously synchronous way of communication between services. It can definitely be a basis for simple event handling, but has many downsides that make it really inefficient ...
