Question

I got the code below from a website,and this way of serial port reading is my only option because DataReceived event often doesn’t work.but this code has a problem,if I close the application while transfering the application hangs forever,but I can’t see why?neither freezing nor aborting the thread work.actually aborting the thread causes the program to crash.

public class CommPort
{
    SerialPort _serialPort;
    Thread _readThread;
    bool _keepReading;

    //begin Singleton pattern
    static readonly CommPort instance = new CommPort();

    // Explicit static constructor to tell C# compiler
    // not to mark type as beforefieldinit
    static CommPort()
    {
    }

    CommPort()
    {
        _serialPort = new SerialPort();
        _readThread = null;
        _keepReading = false;
    }

    public static CommPort Instance
    {
        get
        {
            return instance;
        }
    }
    //end Singleton pattern

    //begin Observer pattern
    public delegate void EventHandler(string param);
    public EventHandler StatusChanged;
    public EventHandler DataReceived;

    private void StartReading()
    {
        if (!_keepReading)
        {
            _keepReading = true;
            _readThread = new Thread(new ThreadStart(ReadPort));
            _readThread.Start();
        }
    }
    private void StopReading()
    {
        if (_keepReading)
        {
            _keepReading = false;
            _serialPort.Close();
            //_readThread.Join();   //block until exits
            _readThread.Abort();
            //_readThread = null;
        }
    }
    private void ReadPort()
    {
        while (_keepReading)
        {
            if (_serialPort.IsOpen)
            {
                byte[] readBuffer = new byte[_serialPort.ReadBufferSize + 1];
                try
                {
                    // If there are bytes available on the serial port,
                    // Read returns up to "count" bytes, but will not block (wait)
                    // for the remaining bytes. If there are no bytes available
                    // on the serial port, Read will block until at least one byte
                    // is available on the port, up until the ReadTimeout milliseconds
                    // have elapsed, at which time a TimeoutException will be thrown.
                    int count = _serialPort.Read(readBuffer, 0, _serialPort.ReadBufferSize);
                    String SerialIn = System.Text.Encoding.ASCII.GetString(readBuffer, 0, count);
                    DataReceived(SerialIn);
                }
                catch (TimeoutException)
                {
                }
            }
            else
            {
                TimeSpan waitTime = new TimeSpan(0, 0, 0, 0, 50);
                Thread.Sleep(waitTime);
            }
        }
    }


    /// <summary> Open the serial port with current settings. </summary>
    public void Open()
    {
        Close();

        try
        {
            _serialPort.PortName = Properties.Settings.Default.COMPort;
            _serialPort.BaudRate = Properties.Settings.Default.BPS;
            _serialPort.Parity = Properties.Settings.Default.Parity;
            _serialPort.DataBits = Properties.Settings.Default.DataBit;
            _serialPort.StopBits = Properties.Settings.Default.StopBit;
            _serialPort.Handshake = Properties.Settings.Default.HandShake;

            // Set the read/write timeouts
            _serialPort.ReadTimeout = 50;
            _serialPort.WriteTimeout = 50;

            _serialPort.Open();
            StartReading();
        }
        catch (IOException)
        {
            StatusChanged(String.Format("{0} does not exist", Properties.Settings.Default.COMPort));
        }
        catch (UnauthorizedAccessException)
        {
            StatusChanged(String.Format("{0} already in use", Properties.Settings.Default.COMPort));
        }
        catch (Exception ex)
        {
            StatusChanged(String.Format("{0}", ex.ToString()));
        }

        // Update the status
        if (_serialPort.IsOpen)
        {
            string p = _serialPort.Parity.ToString().Substring(0, 1); //First char
            string h = _serialPort.Handshake.ToString();
            if (_serialPort.Handshake == Handshake.None)
                h = "no handshake"; // more descriptive than "None"

            StatusChanged(String.Format("{0}: {1} bps, {2}{3}{4}, {5}",
            _serialPort.PortName, _serialPort.BaudRate,
            _serialPort.DataBits, p, (int)_serialPort.StopBits, h));
        }
        else
        {
            StatusChanged(String.Format("{0} already in use", Properties.Settings.Default.COMPort));
        }
    }

    /// <summary> Close the serial port. </summary>
    public void Close()
    {
        StopReading();
        StatusChanged("connection closed");
    }
    public bool IsOpen
    {
        get
        {
            return _serialPort.IsOpen;
        }
    }
}

Answer 1

When you close the Port in StopReading() it will cause an Exception in _serialPort.Read(…).

Not sure which one exactly but it’s not a TimeOut. Your current code lets that escape and that’s when your thread and your App are killed.

So add a catch(Exceptiopn ex) around the while loop in ReadPort().