src/Pure/System/tty_loop.scala

       }
     }
     catch { case e: IOException => case Exn.Interrupt() => }
   }
 
-  def join: Unit = { console_output.join; console_input.join }
+  def join(): Unit = { console_output.join; console_input.join }
 
   def cancel(): Unit = console_input.cancel()
 }