code: public RootChannelList getRootChannels(long fromId, int maxPageSize) {
      List<InternalInstrumented<ChannelStats>> channelList
          = new ArrayList<>();
      Iterator<InternalInstrumented<ChannelStats>> iterator
          = rootChannels.tailMap(fromId).values().iterator();
  
      while (iterator.hasNext() && channelList.size() < maxPageSize) {
        channelList.add(iterator.next());
      }
      return new RootChannelList(channelList, !iterator.hasNext());
    }
docs: Returns a {@link RootChannelList}.