Issue #22419 has been reported by yahonda (Yasuo Honda). ---------------------------------------- Bug #22419: [BUG] "rb_objspace_reachable_objects_from_local: set is owned by another Ractor" when a non-main Ractor reads a class instance variable since f0439cdfa7 https://bugs.ruby-lang.org/issues/22419 * Author: yahonda (Yasuo Honda) * Status: Open * ruby -v: ruby 4.1.0dev (2026-10-06T22:31:56Z master f0439cdfa7) +PRISM [x86_64-linux] * Backport: 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN ---------------------------------------- The Rails nightly CI against Ruby master started crashing with `[BUG] rb_objspace_reachable_objects_from_local: set is owned by another Ractor` in Action Pack and Action View on all of master, YJIT and master-debug. It bisects to f0439cdfa7 ("Remove VM lock from Ractor.make_shareable()", https://github.com/ruby/ruby/pull/19145): reading a class instance variable that holds a frozen `Set` created on the main Ractor from a non-main Ractor crashes. The crash happens where a non-main Ractor reads class-level state such as `AbstractController::Base.action_methods` (a frozen `Set` memoized in a class instance variable) and `Mime::Type`'s registry: https://buildkite.com/rails/rails-nightly/builds/4809#01a11d51-060e-49c8-bdc... The full log of that Action Pack job is attached (rails-nightly_build_4809_actionpack-master.log.zip). It can be reproduced with a single Action Pack test: ``` cd actionpack && bin/test test/controller/base_test.rb -i test_action_methods_is_ractor_safe_by_default ``` ## Steps to reproduce ```ruby class C @s = Set[1, 2].freeze class << self; attr_reader :s; end end p Ractor.new { C.s.include?(1) }.value ``` ## Expected behavior ``` $ ruby -v ruby 4.1.0dev (2026-10-06T21:11:37Z master e8964f3aa3) +PRISM [x86_64-linux] $ ruby rep.rb rep.rb:5: warning: Ractor API is experimental and may change in future versions of Ruby. true ``` ## Actual behavior ``` $ ruby -v ruby 4.1.0dev (2026-10-06T22:31:56Z master f0439cdfa7) +PRISM [x86_64-linux] $ ruby rep.rb rep.rb:5: warning: Ractor API is experimental and may change in future versions of Ruby. rep.rb:5: [BUG] rb_objspace_reachable_objects_from_local: set is owned by another Ractor ruby 4.1.0dev (2026-10-06T22:31:56Z master f0439cdfa7) +PRISM [x86_64-linux] -- Ruby level backtrace information ---------------------------------------- rep.rb:5:in 'block in <main>' -- Threading information --------------------------------------------------- Total ractor count: 2 Ruby thread count for this ractor: 1 -- C level backtrace information ------------------------------------------- ruby(rb_print_backtrace+0x11) vm_dump.c:1117 ruby(rb_vm_bugreport) vm_dump.c:1483 ruby(rb_bug_without_die_internal+0xbe) error.c:1150 ruby(rb_bug) error.c:1168 ruby(...) gc.c:5948 ruby(obj_traverse_reachable+0x2b) ractor.c:1687 ruby(obj_traverse_i) ractor.c:1825 ruby(rb_obj_traverse+0x2c) ractor.c:1875 ruby(rb_ractor_shareable_p_continue) ractor.c:2081 ruby(rb_ractor_shareable_p+0x1b) ./include/ruby/ractor.h:280 ruby(rb_ractor_shareable_p) ./include/ruby/ractor.h:269 ruby(rb_ivar_lookup) variable.c:1626 ruby(vm_sendish+0xae) vm_insnhelper.c:6285 ... ``` ---Files-------------------------------- rails-nightly_build_4809_actionpack-master.log.zip (168 KB) -- https://bugs.ruby-lang.org/