FOSS gamedev and creative worlds

I have an on_shutdown operation that I would like to happen when the game is actually shut down, but often the "shutting down" screen sits there for many seconds, apparently deleting 45 buffers, is there any way to wait for this process to end before the callback is run (rather then as soon as exit is clicked)? or is there a way to speed up the shutdown process?

Which mods are you running while playing ? some lua mapgens can cause game to shutdown slowly.

realterrain, the mod i am working on, which is a mapgen mod. i am waiting until there is no generating happening around me and it still takes forever. how can I identify what is lingering?