C# Winform freezing on SerialPort.Close

Question

I have a winform program that does some asynchronous IO on a SerialPort. However, I\'m periodically running into an issue with the program freezing on the SerialPo

Answer 1

The reason it would hang when you close it is because in the event handler of your SerialPort object

You're synchronizing a call with the main thread (typically by calling invoke). SerialPort's close method waits for its EventLoopRunner thread which fires DataReceived/Error/PinChanged events to terminate. but since your own code in the event is also waiting for main thread to respond, you run into a dead lock situation.

solution: use begininvoke instead of invoke: https://connect.microsoft.com/VisualStudio/feedback/details/202137/serialport-close-hangs-the-application

reference: http://stackoverflow.com/a/3176959/146622

EDIT: the Microsoft link is broken as they have retired Connect. try web.archive.org: https://web.archive.org/web/20111210024101/https://connect.microsoft.com/VisualStudio/feedback/details/202137/serialport-close-hangs-the-application

Answer 2

Workaround by nobugz user from here:

1) add System.Threading.Thread CloseDown; field to form with serial port serialPort1;

2) implement method CloseSerialOnExit() with serialPort1 close steps:

private void CloseSerialOnExit()
{

    try
    {
        serialPort1.DtrEnable = false;
        serialPort1.RtsEnable = false;
        serialPort1.DiscardInBuffer();
        serialPort1.DiscardOutBuffer();
        serialPort1.Close();
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message);

    }
}

3) when you need to close serialPort1 (e.g. on button click) call CloseSerialOnExit() in new thread to avoid hang:

...
CloseDown = new System.Threading.Thread(new System.Threading.ThreadStart(CloseSerialOnExit)); 
CloseDown.Start();
...

and that's it!

Answer 3

I had a same problem. I solved this problem by using SerialPortStrem library. You can install by Nuget Pageckage Installer.

SerialportStream libary has the following advantages.

• An independent implementation of System.IO.Ports.SerialPort and SerialStream for better reliability and maintainability.

After using SerialPortStream library, I hadn't UI freezing problem such as deadlock in WPF. I think the same issue in Windows forms. so, use the SerialPortStream library.

This library is obviously a solution to solve the UI Freezing.

Answer 4

Thank you also for answers. I faced similar issue until today. I used the Andrii Omelchenko solution and helped a lot but not 100%. I saw that the cause for hanging serial port is the reception event handler. Before stopping serial port, uninstall reception event handler.

try
        {
            serialPort.DtrEnable = false;
            serialPort.RtsEnable = false;
            serialPort.DataReceived -= serialPort_DataReceived;
            Thread.Sleep(200);
            if (serialPort.IsOpen == true)
            {
                serialPort.DiscardInBuffer();
                serialPort.DiscardOutBuffer();
                serialPort.Close();
            }
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
        }