src/Pure/Concurrent/future.ML

     (*shutdown*)
     val continue = not (! do_shutdown andalso null (! workers));
     val _ = if continue then () else scheduler := NONE;
 
     val _ = notify_all ();
-    val _ = interruptible (fn () => wait_timeout (Time.fromSeconds 1)) ()
+    val _ = interruptible (fn () =>
+        wait_timeout (Time.fromMilliseconds (if null (! canceled) then 1000 else 50))) ()
       handle Exn.Interrupt => List.app do_cancel (Task_Queue.cancel_all (! queue));
   in continue end;
 
 fun scheduler_loop () =
   while SYNCHRONIZED "scheduler" scheduler_next do ();