Tests cause ThreadError: already initialized with Ruby 2.6.0

[shirosaki]

Steps to reproduce

Test like this causes ThreadError: already initialized after updating Ruby 2.6.0.

class EmployeesControllerTest < ActionController::TestCase
  def test_list_markup
    get :list
    assert_response(:success)
  end
  ...
end

EmployeesControllerTest#test_edit_markup:
ThreadError: already initialized
    /home/shirosaki/.rbenv/versions/2.6.0/lib/ruby/2.6.0/monitor.rb:259:in `mon_initialize'
    /home/shirosaki/.rbenv/versions/2.6.0/lib/ruby/2.6.0/monitor.rb:252:in `initialize'
    /home/shirosaki/.rbenv/versions/2.6.0/lib/ruby/gems/2.6.0/gems/actionpack-4.2.11/lib/action_dispatch/http/response.rb:119:in `initialize'
    /home/shirosaki/.rbenv/versions/2.6.0/lib/ruby/gems/2.6.0/gems/actionpack-4.2.11/lib/action_controller/test_case.rb:277:in `recycle!'
    /home/shirosaki/.rbenv/versions/2.6.0/lib/ruby/gems/2.6.0/gems/actionpack-4.2.11/lib/action_controller/test_case.rb:617:in `process'
    /home/shirosaki/.rbenv/versions/2.6.0/lib/ruby/gems/2.6.0/gems/actionpack-4.2.11/lib/action_controller/test_case.rb:67:in `process'
    /home/shirosaki/.rbenv/versions/2.6.0/lib/ruby/gems/2.6.0/gems/actionpack-4.2.11/lib/action_controller/test_case.rb:514:in `get'
    /home/shirosaki/work/master/test/functional/employees_controller_test.rb:24:in `test_edit_markup'

Expected behavior

Not raise ThreadError.

Actual behavior

Raise ThreadError.

System configuration

Rails version:
4.2.11
Ruby version:
2.6.0

The error would be related to this issue.
https://bugs.ruby-lang.org/issues/15000

If I remove raise ThreadError, "already initialized" in lib/monitor.rb, tests pass.

[y-yagi]

Rails 4.2 is only supported for severe security issues.
Can you check whether this issue occurs even with the latest version?

[vinistock]

The error occurs in Rails 4.2.11 and it seems to be only in controller specs.

You can see the error at this travis job output for a gem I test against multiple Rails/Ruby versions.

[y-yagi]

Thanks for your information.
As described above, 4.2 only support severe security issues.
If this only occurs in 4.2, we do nothing. So I close. Thanks.

[markets]

Hi @y-yagi @vinistock, I confirm this only happens with Ruby 2.6 and Rails 4.2.

It only happened to me in controller tests too, while upgrading the CI matrix in https://github.com/markets/maily.

The weird thing is that those tests were passing for me 1 week ago using ruby-head (at that point was 2.6) in Travis. So, to be honest, it seems more a Ruby (or even Travis or RVM) change rather than Rails ...

[y-yagi]

Hi, @markets
I checked maily's CI. It seems tests were already failed in 1 week ago.
https://travis-ci.org/markets/maily/jobs/470573918#L556-L563

It seems that it was allowed failures.
https://travis-ci.org/markets/maily/builds/470573898

[markets]

Oh! you're totally right @y-yagi, last time it passed (ruby 2.6 + rails 4.2) was in October 12: https://travis-ci.org/markets/maily/jobs/440759767. But I didn't commit anything between October 12 and December 20, so I'm not sure at which point started to fail (at that time, unreleased ruby 2.6 was in allowed failures). Did you know whether this is only a problem in controller tests or rails 4.2 doesn't run in ruby 2.6? Thanks!

[Vasfed]

@markets this is caused by rails reusing ActionController::TestResponse object in tests, can be fixed by this monkeypatch:

if RUBY_VERSION>='2.6.0'
  if Rails.version < '5'
    class ActionController::TestResponse < ActionDispatch::TestResponse
      def recycle!
        # hack to avoid MonitorMixin double-initialize error:
        @mon_mutex_owner_object_id = nil
        @mon_mutex = nil
        initialize
      end
    end
  else
    puts "Monkeypatch for ActionController::TestResponse no longer needed"
  end
end

[markets]

@Vasfed thanks for the workaround 👍, I think a lot of people will need it (or something smilar at least) to continue supporting rails the 4.2 + ruby 2.6 combo in their CIs, I was allowing failures, but this is of course not ideal: markets/maily@9857a98