Issue #19112 has been updated by jhawthorn (John Hawthorn). I think there are a couple problems interacting here. * First is that the GC hooks were being registered specifically on one Ractor, which doesn't make sense as GC could be run inside an arbitrary Ractor (and is global) * Second is that when a hook was disabled (or I believe a Ractor GC'd) we'd change the global flags for which events were being listened to without considering other Ractors might still be subscribed I've just merged https://github.com/ruby/ruby/pull/15396 which tracks the objspace events in a global list fixing the first issue, and in most cases will avoid clobbering the global flags (though that fix is incomplete and we'll want something like Luke's proper fix to handle the per-Ractor events). ---------------------------------------- Bug #19112: Ractor garbage collection breaks/disables all active tracepoints https://bugs.ruby-lang.org/issues/19112#change-115512 * Author: ivoanjo (Ivo Anjo) * Status: Assigned * Assignee: ractor * ruby -v: ruby 3.2.0dev (2022-11-08T08:08:48Z master cdb3ec3af8) [x86_64-linux] * Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN ---------------------------------------- Howdy 👋! I work for Datadog [on the `ddtrace` gem](https://github.com/DataDog/dd-trace-rb) and I found an issue with Ractors + TracePoint. ### Background For tracking time spent in Garbage Collection on our Ruby profiler, we use a tracepoint that listens to the internal GC events. While doing other experiments around Ractors and profiling, I noticed that our tracepoint would suddenly stop working after Ractors were used in the application. I was able to reduce this down to the testcase below. ### How to reproduce (Ruby version & script) I was able to reproduce this on any Ruby 3 version, including master (`ruby 3.2.0dev (2022-11-08T08:08:48Z master cdb3ec3af8) [x86_64-linux]`). ```ruby puts RUBY_DESCRIPTION if ENV['RUN_RACTOR'] == 'true' Ractor.new { 10 }.take puts "Ractor ran!" else puts "Ractor DID NOT ran!" end puts "Enabling tracepoint" tracepoint = TracePoint.new(:line) { |tp| p [tp.path, tp.lineno, tp.event] }.tap(&:enable) 5.times { puts "Triggering gc!"; GC.start } puts "Tracepoint state is enabled? #{tracepoint.enabled?}" puts "Re-enabling tracepoint" tracepoint.enable puts "Finished!" ``` ### Expectation and result Without the Ractor, the tracepoint works as intended: ``` # RUN_RACTOR=false ./ruby ../ruby-3.1.2/triggergc.rb ruby 3.2.0dev (2022-11-08T08:08:48Z master cdb3ec3af8) [x86_64-linux] Ractor DID NOT ran! Enabling tracepoint ["<internal:kernel>", 91, :line] ["../ruby-3.1.2/triggergc.rb", 14, :line] ["../ruby-3.1.2/triggergc.rb", 14, :line] Triggering gc! ["<internal:gc>", 34, :line] ["../ruby-3.1.2/triggergc.rb", 14, :line] Triggering gc! ["<internal:gc>", 34, :line] ["../ruby-3.1.2/triggergc.rb", 14, :line] Triggering gc! ["<internal:gc>", 34, :line] ["../ruby-3.1.2/triggergc.rb", 14, :line] Triggering gc! ["<internal:gc>", 34, :line] ["../ruby-3.1.2/triggergc.rb", 14, :line] Triggering gc! ["<internal:gc>", 34, :line] ["../ruby-3.1.2/triggergc.rb", 16, :line] ["<internal:trace_point>", 257, :line] Tracepoint state is enabled? true ["../ruby-3.1.2/triggergc.rb", 17, :line] Re-enabling tracepoint ["../ruby-3.1.2/triggergc.rb", 18, :line] ["<internal:trace_point>", 213, :line] ["../ruby-3.1.2/triggergc.rb", 20, :line] ["../ruby-3.1.2/triggergc.rb", 20, :line] Finished! ``` ...but once the Ractor runs and is garbage collected, we see that the tracepoint breaks: ``` # RUN_RACTOR=true ./ruby ../ruby-3.1.2/triggergc.rb ruby 3.2.0dev (2022-11-08T08:08:48Z master cdb3ec3af8) [x86_64-linux] ../ruby-3.1.2/triggergc.rb:5: warning: Ractor is experimental, and the behavior may change in future versions of Ruby! Also there are many implementation issues. Ractor ran! Enabling tracepoint ["<internal:kernel>", 91, :line] ["../ruby-3.1.2/triggergc.rb", 14, :line] ["../ruby-3.1.2/triggergc.rb", 14, :line] Triggering gc! ["<internal:gc>", 34, :line] Triggering gc! Triggering gc! Triggering gc! Triggering gc! Tracepoint state is enabled? true Re-enabling tracepoint ["../ruby-3.1.2/triggergc.rb", 20, :line] ["../ruby-3.1.2/triggergc.rb", 20, :line] Finished ``` ### Additional notes This is a somewhat annoying bug, because it can break all gems that use tracepoints, including `ddtrace`. In particular for `ddtrace`, our plan is to disable the feature that uses tracepoints for Ruby 3 users, to avoid any issues from our tracepoints getting disabled. -- https://bugs.ruby-lang.org/