@Override
 public Scheduled schedule(Duration initialDelay, Duration interval, Runnable callback) {
   Scheduled task = parent.schedule(initialDelay, interval, callback);
   tasks.add(task);
   return task;
 }
 @Override
 public Scheduled schedule(Duration delay, Runnable callback) {
   Scheduled task = parent.schedule(delay, callback);
   tasks.add(task);
   return task;
 }