Comment by doomlaser

They put up their editor source code on Github recently (https://github.com/Unity-Technologies/UnityCsReference), and originally it also included the full source to their runtime garbage collector, which ended up being the standard open source C++ boehm collector (https://github.com/ivmai/bdwgc) from the 90s.

Unity should replace it with a reference counting object management system, or update to a newer garbage collection technique to minimize the inadvertent sweeps that cause huge choppy frame rate drops.