code: @Override
    public PollResult startPoll(PollController conn)
    {
      if (! _lifecycle.isActive()) {
        log.warning(this + " select disabled");
  
        return PollResult.CLOSED;
      }
  
      SocketBar socket = conn.getSocket();
  
      if (socket == null) {
        log.warning(this + " socket empty for " + conn);
  
        return PollResult.CLOSED;
      }
  
      SelectableChannel selChannel = socket.selectableChannel();
  
      if (selChannel == null) {
        log.warning(this + " no channel for " + socket);
  
        return PollResult.CLOSED;
      }
  
      _connectionCount.incrementAndGet();
  
      _activeCount.incrementAndGet();
  
      _registerQueue.offer(conn);
      
      return PollResult.START;
    }
docs: Adds a keepalive connection.
  
  @param conn the connection to register as keepalive
  
  @return true if the connection changes to the keepalive state