Computing project-files in another thread

[Tassilo Horn]

Hi all,

I started using Raven [1] which is something similar to Helm.  I.e., you
have a list of sources like buffers and recent files and get a nice
completion UI for switching buffers and finding files.

I added another source for project files which calls `project-files' in
projects recognized by project.el.  That blocked the UI for large
projects because `project-files' essentially uses find using
`shell-command-to-string', and that might take a while.

So I tried computing `project-files' in another thread which initially
keeps the UI responsive, but as soon as the new thread becomes the
active one, the UI blocks again.

I assume that's because below `shell-command-to-string' there's no
`thread-yield' call, right?  Does anyone know a strategically good place
to put a `thread-yield', or do we need to rewrite `project-files'
somehow to make thread-switching during a call to it possible?

Thanks for any pointers!
Tassilo

[1] https://github.com/chameco/raven