proof_class_attribute_not_threadsafe.rb

# This file demonstrates that attributes created by class_attribute (in Rails' ActiveSupport) are not thread-safe.
# On my system, the test fails sometimes when setting count to 1_000 and always with a count of 10_000.
# Expected exception: NameError: Undefined method setting for 'BugTest::MyClass'
# Note: Occurs on jruby only.
# See issue https://github.com/rails/rails/issues/26758

begin
  require 'bundler/inline'
rescue LoadError => e
  $stderr.puts 'Bundler version 1.10 or later is required. Please update your Bundler'
  fail e
end

gemfile(true) do
  source 'https://rubygems.org'
  gem 'rails', github: 'rails/rails'
end

require 'active_support'
require 'active_support/core_ext/object/blank'
require 'minitest/autorun'

class BugTest < Minitest::Test
  # Boot phase: Single-threaded
  class MyClass
    class_attribute :setting
  end

  def test_multithreaded
    puts "Ruby version: #{RUBY_VERSION}"
    puts "Ruby engine: #{RUBY_ENGINE}"
    puts "ActiveSupport: #{ActiveSupport::VERSION::STRING}"

    # Program up and running: This must be allowed to be multi-threaded IMHO
    # On my system, failure occurs sometimes with 1'000 and always with 10'000 threads.
    count = 10_000
    ts = []
    count.times do |i| # Spawning threads
      ts << Thread.new do
        sleep(rand)  # Random sleep (0-1 sec.) to avoid accidental sequential behavior
        MyClass.setting = i  # Exception occurs on this line.
        sleep(rand)
      end
    end
    count.times do |i|
      ts[i].join  # Joining threads and termination
    end
  end
end