Windows support for parallelization and instrumenter

[gmcgibbon]

Summary

Fixes #34374.

Adds Windows support for ActiveSupport::Testing::Parallelization and ActiveSupport::Notifications::Instrumenter.

Unsure of how I can adequately test this aside from adding a Windows build to CI.

r? @eileencodes since you added test parallelization and event CPU time to Rails 😄

[ahorek]

Suggested change

	! RUBY_PLATFORM =~ /bccwin|cygwin|emx|mingw|mswin|wince/
	!Gem.win_platform?

[ahorek]

doesn't work for me, you should skip it at
https://github.com/rails/rails/blob/master/activesupport/lib/active_support/test_case.rb#L14

'drb/unix' is not available
Traceback (most recent call last):
        22: from bin/test:5:in `<main>'
        21: from bin/test:5:in `require_relative'
        20: from C:/rails/tools/test.rb:26:in `<top (required)>'
        19: from C:/rails/railties/lib/rails/test_unit/runner.rb:39:in `run'
        18: from C:/rails/railties/lib/rails/test_unit/runner.rb:50:in `load_tests'
        17: from C:/rails/railties/lib/rails/test_unit/runner.rb:50:in `each'
        16: from C:/rails/railties/lib/rails/test_unit/runner.rb:50:in `block in load_tests'
        15: from C:/rails/railties/lib/rails/test_unit/runner.rb:50:in `require'
        14: from C:/rails/actionpack/test/abstract/callbacks_test.rb:3:in `<top (required)>'
        13: from C:/rails/actionpack/test/abstract/callbacks_test.rb:3:in `require'
        12: from C:/rails/actionpack/test/abstract_unit.rb:428:in `<top (required)>'
        11: from C:/rails/actionpack/test/abstract_unit.rb:428:in `new'
        10: from C:/rails/actionpack/test/abstract_unit.rb:385:in `initialize'
         9: from C:/Ruby25-x64/lib/ruby/2.5.0/drb/drb.rb:1710:in `start_service'
         8: from C:/Ruby25-x64/lib/ruby/2.5.0/drb/drb.rb:1710:in `new'
         7: from C:/Ruby25-x64/lib/ruby/2.5.0/drb/drb.rb:1404:in `initialize'
         6: from C:/Ruby25-x64/lib/ruby/2.5.0/drb/drb.rb:772:in `open_server'
         5: from C:/Ruby25-x64/lib/ruby/2.5.0/drb/drb.rb:804:in `auto_load'
         4: from C:/rails/activesupport/lib/active_support/dependencies.rb:297:in `require'
         3: from C:/rails/activesupport/lib/active_support/dependencies.rb:263:in `load_dependency'
         2: from C:/rails/activesupport/lib/active_support/dependencies.rb:297:in `block in require'
         1: from C:/rails/activesupport/lib/active_support/dependencies.rb:297:in `require'
C:/Ruby25-x64/lib/ruby/2.5.0/drb/unix.rb:6:in `<top (required)>': UNIXServer is required (LoadError)

[gmcgibbon]

Ok, I was able to run tests with a dummy app on Ruby 2.5.3 on Windows 10 using this code, but removing parallelization when on Windows is likely a cleaner solution if DRb isn't properly supported. I'll see what I can do!

[eileencodes]

We can flip it to use threads by default in Windows like we do for JRuby

[gmcgibbon]

Great idea! I assume CRuby on Windows won't get the same threading advantages as JRuby, but it should still work. I edited the test_helper template to use threads when on Windows.

[gmcgibbon]

This seems to be working on my setup with paralellize(workers: 2, with: :threads), but I get circular autoload errors when running parallelized tests. Do we want to recommend eager loading when parallelizing with threads?

[eileencodes]

Does eager loading fix the circular autoload errors?

[gmcgibbon]

It does. I got one or two SQLite busy exceptions between a few test runs once I eager loaded but I think that's a separate threading issue. I talked to @rafaelfranca about the circular autoload errors and he mentioned @matthewd's work on https://github.com/rails/rails/blob/master/activesupport/lib/active_support/dependencies/interlock.rb. Maybe this can be avoided without eager load somehow?