Process triggered event when other event finishes
I've got an event calling a menu (displaying it). This menu, however should not be shown before its items have been generated. This generation of items takes some time because it depends on a database connection. One should be allowed to call the menu before its items have been generated but the actual display of the menu should be done as soon as the items are ready.
The problems with trying to display the menu right away only happens during launch time. Once the items have been generated they will remain available.
What would be a good approach to handle this situation? How could one prevent the triggered even from being processed until the item generation is ready?