@Override
    synchronized public void registerConfigChangeWatcher(ConfigChangeWatcher watcher) {
        startListening(new WatcherHolder(watcher), new ConfigChangeCallback() {
            @Override
            public synchronized void onSingleValueChanged(final WatcherHolder holder, final ConfigTable.ConfigItem configItem) {
                notifySingleValue(holder.getWatcher(), configItem);
            }

            @Override
            public synchronized void onGroupValuesChanged(final WatcherHolder holder,
                                             final GroupConfigTable.GroupConfigItems groupConfigItems) {
                notifyGroupValues((GroupConfigChangeWatcher) holder.getWatcher(), groupConfigItems);
            }
        });
    }
Implement Config Watcher register using client listening.
oap-server/server-configuration/configuration-api/src/main/java/org/apache/skywalking/oap/server/configuration/api/ListeningConfigWatcherRegister.java