static void onGCNotification(final VF1<GarbageCollectionNotificationInfo> theListener) {
  NotificationListener listener = new NotificationListener {
    public void handleNotification(Notification notification, O handback) {
      // extract garbage collection information from notification.
      GarbageCollectionNotificationInfo gcInfo = GarbageCollectionNotificationInfo.from((CompositeData) notification.getUserData());
      pcallF(theListener, gcInfo);
    }
  };

  for (GarbageCollectorMXBean gcBean : ManagementFactory.getGarbageCollectorMXBeans())
    ((NotificationEmitter) gcBean).addNotificationListener(listener, null, null);
}