private static final int DEFAULT_WITNESS_PORT = 135;  // RPC endpoint mapper
    
    public interface WitnessNotificationListener {
        void onWitnessNotification(WitnessNotification notification);
        void onRegistrationFailed(WitnessRegistration registration, Exception error);
        void onRegistrationExpired(WitnessRegistration registration);
    }
    

    public interface WitnessNotificationListener {
        /**
         * Called when a witness notification is received.
         *
         * @param notification the witness notification
         */
        void onWitnessNotification(WitnessNotification notification);

        /**
         * Called when a witness registration fails.
         *
         * @param registration the failed registration
         * @param error the error that occurred

        private final CountDownLatch notificationLatch = new CountDownLatch(1);
        private volatile WitnessNotification lastNotification;

        @Override
        public void onWitnessNotification(WitnessNotification notification) {
            this.lastNotification = notification;
            notificationLatch.countDown();
        }

        @Override