Now that class fields have been deletated to a T_IMEMO/class_fields when we're in multi-ractor mode, we can read and write class instance variable in an atomic way using Read-Copy-Update (RCU). Note when in multi-ractor mode, we always use RCU. In theory we don't need to, instead if we ensured the field is written before the shape is updated it would be safe. Benchmark: ```ruby Warning[:experimental] = false class Foo @foo = 1 @bar = 2 @baz = 3 @egg = 4 @spam = 5 class << self attr_reader :foo, :bar, :baz, :egg, :spam end end ractors = 8.times.map do Ractor.new do 1_000_000.times do Foo.bar + Foo.baz * Foo.egg - Foo.spam end end end if Ractor.method_defined?(:value) ractors.each(&:value) else ractors.each(&:take) end ``` This branch vs Ruby 3.4: ```bash $ hyperfine -w 1 'ruby --disable-all ../test.rb' './miniruby ../test.rb' Benchmark 1: ruby --disable-all ../test.rb Time (mean ± σ): 3.162 s ± 0.071 s [User: 2.783 s, System: 10.809 s] Range (min … max): 3.093 s … 3.337 s 10 runs Benchmark 2: ./miniruby ../test.rb Time (mean ± σ): 208.7 ms ± 4.6 ms [User: 889.7 ms, System: 6.9 ms] Range (min … max): 202.8 ms … 222.0 ms 14 runs Summary ./miniruby ../test.rb ran 15.15 ± 0.47 times faster than ruby --disable-all ../test.rb ```