Notice that the mere fact that a notify has been executed does not imply anything in particular about the state of the class (e.g., that it has been updated), nor does the notification protocol transmit any useful information other than the class name. Therefore, all notify does is indicate that some backend wishes its peers to examine class_name in some application-specific way.
This event notification is performed through the Libpq protocol and frontend application interface. The application program must explicitly poll a Libpq global variable, PQAsyncNotifyWaiting, and call the routine PQnotifies in order to find out the name of the class to which a given notification corresponds. If this code is not included in the application, the event notification will be queued and never be processed.