docs: synchronized void addInterestedByClass(Class<?> clazz, Collection<ProbeListener> newListeners) {
          Set<ProbeListener> currentListeners = listenersByClass.get(clazz);
          if (currentListeners == null) {
              currentListeners = new HashSet<ProbeListener>();
              listenersByClass.put(clazz, currentListeners);
          }
          currentListeners.addAll(newListeners);
      }