code: public List<SchedulerListener> getInternalSchedulerListeners() {
  
      synchronized (internalSchedulerListeners) {
        return java.util.Collections.unmodifiableList(
            new ArrayList<SchedulerListener>(internalSchedulerListeners));
      }
    }
docs: Get a List containing all of the <i>internal</i> <code>{@link SchedulerListener}</code>s
  registered with the <code>Scheduler</code>.