Issue #19376 has been updated by luke-gru (Luke Gruber). Tracker changed from Bug to Misc Subject changed from Ability to read ivars of non-frozen classes/modules across ractors is not thread-safe to (Please close) Ability to read ivars of non-frozen classes/modules across ractors is not thread-safe Backport deleted (2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN) Nevermind this is actually safe, I ran into a separate segfault that this example was giving that's unrelated to that thread-safety issue. I'll file separate bug. ---------------------------------------- Misc #19376: (Please close) Ability to read ivars of non-frozen classes/modules across ractors is not thread-safe https://bugs.ruby-lang.org/issues/19376#change-101472 * Author: luke-gru (Luke Gruber) * Status: Open * Priority: Normal ---------------------------------------- This segfaults: ```ruby class C class << self attr_accessor :val end end GO = false rs = 100.times.map do Ractor.new do Thread.pass until GO 1000.times do val = C.val p val end end end ts = 100.times.map do |i| Thread.new do Thread.pass until GO 1000.times do C.val = Object.new.freeze end end end GO = true ts.each(&:join) rs.each(&:take) ``` It looks like a silly example, but it can crash even if the main thread doesn't spawn any more threads. Getting/setting ivars on objects in parallel without VM lock isn't safe, so for non-frozen shareable objects (basically classes and modules), it's unsafe to access their instance variables even if the values are shareable. -- https://bugs.ruby-lang.org/