The item/fluid selection menu has a text search functionality which performs its text search on a separate thread. While some improvements were made in #556 (use of Future and a thread pool), I realise that more should likely be done regarding thread safety.

Primarily, I want to look at how feasible it is to move the text search to the main thread, including if any relevant optimisations are made.
Failing that, extra care should be taken to guard against potenial threading issues (item list initialization is probably better done on the main thread, for example). It should also be looked at if minecraft provides a thread pool that would be relevant to use.

As the threaded search might be related to a difficult-to-diagnose problem, I'm inclined to take the short route of just getting rid of the threading, and leaving potential optimisations for another day.