This is usually not a problem because using globals and taking locks unnecessarily is unidiomatic Rust. You have to go out of your way to write more code when y

This is usually not a problem because using globals and taking locks unnecessarily is unidiomatic Rust. You have to go out of your way to write more code when you use mutexes, so most people don't unless they truly need to. We have experience with this. For a long time, WebRender rasterized glyphs and other resources sequentially. Switching it to parallelize was painless: Glenn just added a parallel for loop from Rayon and we got speedups.