From: "ko1 (Koichi Sasada) via ruby-core" <ruby-core@...>
Date: 2026-09-09T02:41:56+00:00
Subject: [ruby-core:126604] [Ruby Bug#20158] Ractor affects Coverage results

Issue #20158 has been updated by ko1 (Koichi Sasada).

Status changed from Assigned to Closed

Re-checked: this is fixed, and it was fixed as #19112.

I ran mame's rspec reproduction from #note-3 on four builds. The absolute event counts
differ between versions because they load different numbers of files; what matters is
the with/without-Ractor pair inside one version:

    ruby      TracePoint :line events   no Ractor / with Ractor
    3.3.2                                  22741 / 8112    <- reproduces, stops inside rubygems
    3.4.4                                  35621 / 12738   <- reproduces
    4.0.2                                  52294 / 52325   <- fine
    master 4d185cce78                       5432 / 5455    <- fine

GH-15468 (`4fb537b1ee`, "Make tracepoints with set_trace_func or TracePoint.new ractor
local", Fixes [Bug #19112]) is what fixed it: before that, GC'ing any Ractor object
cleared the global event flags and every enabled tracepoint with them, which is exactly
the "TracePoint stops firing part-way through" symptom here.

Closing as a duplicate of #19112.

Note that Coverage still does not record code executed inside a Ractor -- that is
#20167, which is a different cause (the coverage hook is registered on the Ractor that
called Coverage.start, and hook lists are per-Ractor) and stays open.


----------------------------------------
Bug #20158: Ractor affects Coverage results
https://bugs.ruby-lang.org/issues/20158#change-118836

* Author: janosch-x (Janosch M�ller)
* Status: Closed
* Assignee: ractor
* ruby -v: ruby 3.3.0preview1 (2023-05-12 master a1b01e7701) [arm64-darwin22]
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN
----------------------------------------
I have a large rspec test suite. I found that if I call a Ractor, the Coverage results are strongly affected, i.e. almost all files appear to be uncovered. This happens even if I only ever call a Ractor before the library or rspec are required.

Unfortunately, I was not able to build a simple repro yet.

I assume it is a timing thing and only affects larger suites, or it only happens if there are multiple files, and maybe if the library lazily requires its sub-modules?

However, I guess this should produce the same results when added to the spec_helper.rb of other large suites:

```ruby
# Ractor.new { nil } # uncomment this to affect coverage results

require 'coverage'
Coverage.start

# require library, set up rspec etc. 

RSpec.configuration.after(:suite) do
  # this number is greatly reduced and unstable when calling Ractor above
  p Coverage.result.values.sum { |arr| arr.sum(&:to_i) }
end
```

I had this problem in [this library](https://github.com/jaynetics/character_set/). The problem affects simplecov users as well, as described [here](https://github.com/simplecov-ruby/simplecov/issues/1058).



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