One common OOP pattern is Model-View-Controller where one object (the controller) is a dependant of the model. Every time the model changes it notifies all of its dependants. In this case the model has a dictionary of dependants and iterates through those.
Another common pattern is NotificationCenter wherein an object emits a notification and clients can register functions that will be executed when that notification happens.
A Server emits a \newAllocators notification when it creates new node and bus allocators which it does when it quits or boots.
You can listen for this:
The Buffer class register a function to clear its info cache whenever a server restarts. The server is emitting changed messages quite often (every 0.4 secs for the status updates), and the Buffer class is only interested in boot/quit events, so this is a more lightweight system for this purpose.
The object emits a message and may also pass extra args.
An interested client can register the action function for the object/message notification. A listener may only register one action per object/message notification.
Remove the registrations.
After the notification has been emitted and handled, automatically unregister.
Simply confirms if a registration is already in place.