Whenever we run into an inline cache miss when we try to set an ivar, we may need to take the global lock, just to be able to lookup inside `shape->edges`. To solve that, when we're in multi-ractor mode, we can treat the `shape->edges` as immutable. When we need to add a new edge, we first copy the table, and then replace it with CAS. This increases memory allocations, however we expect that creating new transitions becomes increasingly rare over time. ```ruby class A def initialize(bool) @a = 1 if bool @b = 2 else @c = 3 end end def test @d = 4 end end def bench(iterations) i = iterations while i > 0 A.new(true).test A.new(false).test i -= 1 end end if ARGV.first == "ractor" ractors = 8.times.map do Ractor.new do bench(20_000_000 / 8) end end ractors.each(&:take) else bench(20_000_000) end ``` The above benchmark takes 27 seconds in Ractor mode on Ruby 3.4, and only 1.7s with this branch. Co-Authored-By: Étienne Barrié <[email protected]>