docs: public synchronized void registerNeighborConcurrent(String groupName, NeighborConcurrentGroup neighborConcurrentGroup) {
          verifyCanScheduleState();
          if (neighborConcurrentGroupMap == null) {
              neighborConcurrentGroupMap = new ConcurrentHashMap<String, NeighborConcurrentGroup>(); // just in case
              neighborConcurrentGroupList = new CopyOnWriteArrayList<NeighborConcurrentGroup>(); // just in case
          }
          neighborConcurrentGroupMap.put(groupName, neighborConcurrentGroup);
          neighborConcurrentGroupList.add(neighborConcurrentGroup);
      }