I got back to this problem today and have some initial ideas.

I did some profiling and the profiler clearly shows that most CPU time was in macfont_list and CTFontDescriptorCreateMatchingFontDescriptors. (screenshot attached below) So yes, it’s a Mac-only problem.

macfont_list will call CTFontDescriptorCreateMatchingFontDescriptors for n times, where n is the number of installed fonts. It seems CTFontDescriptorCreateMatchingFontDescriptors is very expensive, and we should minimize the use of it.

I did a quick proof-of-concept patch (attached) that removes the outer loop (utilizing CTFontDescriptorCreateMatchingFontDescriptors itself to search for fonts). And now I no longer experience long delays. It’s not complete as I haven’t adapted & incorporated mac_font_create_preferred_family_for_attributes yet.

I don’t see noticeable font differences after the change on the files I’m working on. I would like to gather some feedback from the more experienced on whether this is a promising solution or not. If it is, I will refine it into a formal patch.