Unlocking Ractors: class instance variables in Ruby

In a previous post about ractors, I explained why I think it’s really unlikely you’d ever be able to run an entire application inside a ractor, but that they could still be situationally very useful to move CPU-bound work out of the main thread, and to unlock some parallel algorithm. But as I mentioned, this is unfortunately not yet viable because there are many known implementation bugs that can lead to interpreter crashes, and that while they are supposed to execute in parallel, the Ruby VM still has one true global lock that Ractors need to acquire to perform certain operations, making them often perform worse than the equivalent single-threaded code. One of these remaining contention points is class instance variables and class variables, and given it’s quite frequent for code to check a class or module instance variable as some sort of configuration, this contention point can have a very sizeable impact on Ractor performance, let me show you with a simple benchmark: module Mod ... Read full article.