1.1 --- a/src/Pure/Concurrent/future.ML	Thu Jul 30 23:23:52 2009 +0200
     1.2 +++ b/src/Pure/Concurrent/future.ML	Thu Jul 30 23:37:53 2009 +0200
     1.3 @@ -269,7 +269,11 @@
     1.4      (*canceled groups*)
     1.5      val _ =
     1.6        if null (! canceled) then ()
     1.7 -      else (change canceled (filter_out (Task_Queue.cancel (! queue))); broadcast_work ());
     1.8 +      else
     1.9 +       (Multithreading.tracing 1 (fn () =>
    1.10 +          string_of_int (length (! canceled)) ^ " canceled groups");
    1.11 +        change canceled (filter_out (Task_Queue.cancel (! queue)));
    1.12 +        broadcast_work ());
    1.13  
    1.14      (*delay loop*)
    1.15      val _ = wait_interruptible next_round scheduler_event