# File lib/rack/session/redis.rb, line 22
      def generate_unique_sid(session)
        return generate_sid if session.empty?
        loop do
          sid = generate_sid
          first = with do |c|
            [*c.setnx(sid, session, @default_options)].first
          end
          break sid if [1, true].include?(first)
        end
      end