A non-queued bus implementation that executes subscribers immediately in the main thread. This bus also supports "propagating" events along to any other connected buses. Such behavior is useful, e.g., if we want to have a semi-isolated request- level bus whose events still reach the global EventBus instance.
Collection of subscribers, by their events.
Build an EventSubscription object for the subscriber of the given ID.
Register the given bus to receive events fired on this bus.