file_to_require.rb

$scratch << :con_pre
$con1_ready = true
sleep 0.5
if $con1_raise
  $con1_raise = false
  raise "con1"
end
sleep 0.5
$scratch << :con_post

test.rb

        start = false
        fin = false

        $scratch = []
        $con1_ready = false
        $con1_raise = true
        path = "path/to/content/below.rb"

        t1_res = nil
        t2_res = nil

        t1 = Thread.new do

          begin
            require(path)
          rescue RuntimeError
          end

          # This hits the bug. Because MRI removes it's internal lock from a table
          # when the exception is raised, this #require doesn't see that t2 is
          # in the middle of requiring the file, so this #require runs when it should
          # not.
          #
          # Sometimes this raises a ThreadError also, but I'm not sure why.
          t1_res = require(path)

          Thread.pass until fin
          $scratch << :t1_post
        end

        t2 = Thread.new do
          Thread.pass until $con1_ready
          begin
            t2_res = require(path)
            $scratch << :t2_post
          ensure
            fin = true
          end
        end

        t1.join
        t2.join

        raise "bug" unless t1_res == false
        raise "bug" unless t2_res == true

        $scratch == [:con_pre, :con_pre, :con_post, :t2_post, :t1_post]