C#

//private String _datos;
       Queue _cola = new Queue();

private void bw_DoWork(object sender, DoWorkEventArgs e)
{

    BackgroundWorker bw = sender as BackgroundWorker;
    string port = (string)e.Argument;

    //put all your serial port code here
    SerialPort sprt = new SerialPort(port);
    sprt.BaudRate = 4800;
    sprt.Parity = Parity.None;
    sprt.StopBits = StopBits.One;
    sprt.DataBits = 8;
    sprt.Handshake = Handshake.None;
    try
    {
        sprt.Open();
    }
    catch (Exception)
    {
        MessageBox.Show("Check port");
        return;
    }

    while (!bw.CancellationPending)
    {
        string indata = sprt.ReadLine();

        lock (_cola)
        {
            _cola.Enqueue(indata);

        }
        //update the graph
        BeginInvoke((Action)(() = UpdateGraph(port)));
    }
    //user wants to stop the worker
    sprt.Close();

}

private void UpdateGraph(string port)
{
    //messures is shared by several threads: you must lock it to access it safely
    lock (_cola)
    {

        string text = Leer();

        rtbOutput.AppendText(text );
        rtbOutput.ScrollToCaret();

    }
    //the curve has been updated so refresh the graph
}