Issue #19112 has been updated by luke-gru (Luke Gruber). Pull request is here if you're interested: https://github.com/ruby/ruby/pull/7184 ---------------------------------------- Bug #19112: Ractor garbage collection breaks/disables all active tracepoints https://bugs.ruby-lang.org/issues/19112#change-101477 * Author: ivoanjo (Ivo Anjo) * Status: Open * Priority: Normal * 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/