code: @Override
    public PollResult startPoll(PollController conn)
    {
      try {
        boolean isNew = conn.enableKeepaliveIfNew(this);
  
        if (! enableKeepalive(conn, isNew)) {
          return PollResult.CLOSED;
        }
  
        if (conn.toKeepaliveStart()) {
          _activeCount.incrementAndGet();
  
          return PollResult.START;
        }
        else {
          return PollResult.DATA;
        }
      } catch (IOException e) {
        conn.onPollReadClose();
  
        throw new IllegalStateException(e);
      }
    }
docs: Adds a keepalive connection.
  
  @param conn the connection to register as keepalive
  
  @return true if the connection changes to the keepalive state