收到C＃SerialPort数据并冻结WPF UI

Question

My goal is to spy a gsm module RX/TX communication on a custom system. For this, I use 2 serial ports on my computer and a WPF c# app. On specific commands, the comunnication between the gsm module and the system is able to change for 9600bds, 57600bds or 125000bds. With 9600 and 57600, no problem. But when the com speed is 125000, my UI freeze. I have read a lot of posts about UI freezing with Action, Delegate, dispatcher but it doesn't work and I don't understand how to solve my issue.

Here, what I'm doing for now:

1. I have 2 serial ports from System.IO.Ports;
2. the 2 serial ports use the same SerialDataReceivedEventHandler
3. inside the SerialDataReceivedEventHandler, I build a custom class instance of "QueueElement" with serialPort name, the bytes received and the hour when the event occurs. This QueueElement is push in a Queue from
4. every 100ms, a timer tick event read the Queue to display all item from it to the UI ListBox.

Here some code to explain how I proceed:

// queue to store data read on serial port before display
Queue<QueueElement> queueList;

private void Window_Loaded(object sender, RoutedEventArgs e)
{
    initPorts();
    queueList = new Queue<QueueElement>();
    QueueConsumerProcessRunning = false;
    queueConsumer();
}

private void initPorts()
{                  
    mySerialPort1.DataReceived += new SerialDataReceivedEventHandler(SerialPort_DataReceived);         
    mySerialPort2.DataReceived += new SerialDataReceivedEventHandler(SerialPort_DataReceived);
    // ...
}

// data on serial port
private void SerialPort_DataReceived(object sender, SerialDataReceivedEventArgs e)
{
    Monitor.Enter(queueList);
    try
    {
        // create a queue element and add it to the queue
        // ...
        queueList.Enqueue(queueSingleElement);
    }
    finally
    {
        Monitor.Exit(queueList);
    }
}


private void queueConsumer()
{
    Thread backgroundThread = new Thread(
        new ThreadStart(() =>
        {
            while (true) // always alive
            {
                if ((QueueConsumerProcessRunning == false) && (queueList.Count > 0))
                {

                    Dispatcher.Invoke(() => { QueueCount.Text = queueList.Count.ToString(); });

                    QueueConsumerProcessRunning = true;
                    QueueElement Qelem;// = new QueueElement();

                    Monitor.Enter(queueList);
                    try
                    {
                        // get alodest element
                        Qelem = queueList.Peek();

                        // remove oldest element
                        queueList.Dequeue();
                    }
                    finally
                    {
                        Monitor.Exit(queueList);
                    }

                    // call method to display data    
                    AddDataMethod(buildSerialElement(Qelem.SerialPortName, Qelem.ReadBytes, Qelem.EventHour));

                    QueueConsumerProcessRunning = false;
                }
                Thread.Sleep(100);
            }
        }
    )); // backgroundThread
    backgroundThread.IsBackground = true;
    backgroundThread.Start();            
}


// display received data
// when incoming data is from the same serial port of last received data: add data on last written row except if it's a carriage return
private void AddDataMethod(SerialElement elem)
{
    if (!Dispatcher.CheckAccess()) // CheckAccess returns true if you're on the dispatcher thread       this.ListBoxSpy.Disp...
   {
        Dispatcher.Invoke(new AddDataDelegate(AddDataMethod), elem);
        return;
    }

    // update List<SerialElement>
    // ...
    // and call the function to update item displayed on UI
    refreshDisplay();
}

// refresh display
private void refreshDisplay()
{
    // create a list of ListBoxRowItem
    // ...
    // and display the list on ListBox UI

    ListBoxSpy.ItemsSource = myListBoxRows;   
}

And the xaml part for the ListBox:

<ListBox Name="ListBoxSpy" HorizontalAlignment="Stretch" Margin="0,100,0,0" VerticalAlignment="Stretch" FontFamily="Courier New" >
    <ListBox.ItemTemplate>
        <DataTemplate>
            <TextBlock Text="{Binding Message}" Foreground="{Binding MessageColor}" VirtualizingPanel.IsVirtualizing="True" VirtualizingPanel.VirtualizationMode="Recycling" />                
        </DataTemplate>
    </ListBox.ItemTemplate>
</ListBox>

I use Visual Studio Community 2017.

Answer 1

I think you've got a race condition with the Queue. I assume QueueConsumerTimedEvent is running on the UI thread. The while loop may be running forever because it is checking if queueList.Count > 0 but while processing the top item the DataReceived thread is adding more items to the queue. So it never reaches zero and thus holds up the UI thread.

You should at least move the Monitor.Enter to accomodate but then you run the risk of missing or delaying incoming data. Probably should dequeue first so you can release the Monitor quickly then process the dequeued item.