shutdown! (Net::SSH::Gateway)

    # File lib/net/ssh/gateway.rb, line 85
      def shutdown!
        return unless active?

        @session_mutex.synchronize do
          # cancel all active forward channels
          @session.forward.active_locals.each do |lport, host, port|
            @session.forward.cancel_local(lport)
          end
        end

        @active = false

        @thread.join
        @session.close
      end