public static void addRegistrationListener(RegistrationListener l) {
    synchronized (listenersSync) {
      Set<RegistrationListener> newSet = new HashSet<>(listeners);
      newSet.add(l);
      listeners = newSet;
    }
  }
Adds a {@code RegistrationListener} that will receive callbacks when {@code DataSerializer}s
and {@code Instantiator}s are registered.
geode-core/src/main/java/org/apache/geode/internal/InternalDataSerializer.java