make_silence_stream_thread_safe.rb

require 'active_support/core_ext/kernel/reporting'
require 'monitor'

# Monkey patch silence_stream to be thread safe
# -> Pull request on Rails: https://github.com/rails/rails/pull/13139
# -> But this will allow us to continue to see log output when running specs
# -> It could be we just patch ActiveRecord::SessionStore that triggers the `.quietly` calls
#    on logging the `find_session_id` calls.
module Kernel
  # Silences any stream for the duration of the block.
  #
  #   silence_stream(STDOUT) do
  #     puts 'This will never be seen'
  #   end
  #
  def silence_stream(stream)
    @@monitor ||= Monitor.new
    @@monitor.synchronize do
      begin
        old_stream = stream.dup
        stream.reopen(RbConfig::CONFIG['host_os'] =~ /mswin|mingw/ ? 'NUL:' : '/dev/null')
        stream.sync = true
        yield
      ensure
        stream.reopen(old_stream)
      end
    end
  end
end

Thank you so much for figuring this problem out. I was struggling with this for a few hours myself, but never found the source of the problem. Your Gist saved me bigtime!

This method of overloading makes me uncomfortable, with the code copying. I've pushed my version of your fix here: https://gist.github.com/alexmchale/b68a2c72ed1f432418d9

Thanks @alexmchale, Rails has just deprecated the non-threadsafe messages, so should be long until this isn't required. See rails/rails@1fbb5c1...3121412

Thank you. Capybara is behaving again!

Thank you. Capybara is behaving again! [2]