def setup_io_restoration
        @finalizers ||= []
        [STDIN, STDOUT, STDERR].each do |io|
          dup = io.dup
          @finalizers.push(
            lambda do
              a = io.respond_to?(:stat) && io.stat
              b = dup.respond_to?(:stat) && dup.stat
              unchanged = (a&&b && a.dev==b.dev && a.ino==b.ino)
              unchanged ? dup.close : io.reopen(dup)
            end
          )
        end
      end