src/Pure/System/swing_thread.scala

   }
 
 
   /* delayed actions */
 
-  private def delayed_action(first: Boolean)(time: Time)(action: => Unit): () => Unit =
+  private def delayed_action(first: Boolean)(time: Time)(action: => Unit): Boolean => Unit =
   {
     val listener = new ActionListener {
       override def actionPerformed(e: ActionEvent) { Swing_Thread.assert(); action }
     }
     val timer = new Timer(time.ms.toInt, listener)
     timer.setRepeats(false)
 
     def invoke() { later { if (first) timer.start() else timer.restart() } }
-    invoke _
+    def revoke() { timer.stop() }
+
+    (active: Boolean) => if (active) invoke() else revoke()
   }
 
   // delayed action after first invocation
   def delay_first = delayed_action(true) _