Issue #20485 has been reported by skhrshin (Shintaro Sakahara). ---------------------------------------- Bug #20485: Simple use of Mutex and Fiber makes GC leak objects with singleton method https://bugs.ruby-lang.org/issues/20485 * Author: skhrshin (Shintaro Sakahara) * Status: Open * ruby -v: ruby 3.2.3 (2024-01-18 revision 52bb2ac0a6) [x86_64-linux] * Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN ---------------------------------------- I found a possible memory leak which occurs only when several conditions are met. The code to reproduce the problem is below: ``` class Work def add_method singleton_class.define_method(:f) {} end end Mutex.new.synchronize { Fiber.new {}.resume } work = Work.new work.add_method work = nil GC.start num_objs = ObjectSpace.each_object.select { |o| o.is_a?(Work) rescue false }.size unless num_objs.zero? raise "NG" end ``` Expected result: The script exits normally. Actual result: RuntimeError "NG" is raised. If I remove `Mutex.new.synchronize { Fiber.new {}.resume }` or `work.add_method`, GC works as expected. Is there any problem at the way to use Mutex and Fiber in this code, or is it a bug due to Ruby? I tested ruby 3.3.1 (2024-04-23 revision c56cd86388) [x86_64-linux] too and the result was same. -- https://bugs.ruby-lang.org/