code: func (tcpConn *TCPConn) Write(b []byte) {
  	tcpConn.Lock()
  	defer tcpConn.Unlock()
  	if tcpConn.closeFlag || b == nil {
  		return
  	}
  
  	tcpConn.doWrite(b)
  }
docs: // b must not be modified by the others goroutines