Pulled this off yesterday.

Finally at a place where my branch of Eternity with a multithreaded renderer is far enough along that I released a public beta. Thread: https://www.doomworld.com/forum/topic/135380-multithreaded-renderer-beta/

The only thing left is to add load balancing, and try look into ways to maybe reduce sync costs as thread count increases.

I've been working on clearing out multithreading bugs from the Doom source port I work on (of which there are far too many), and my first fix for spectre fuzz had some quirks which could result in some pretty neat effects.