How to run Task which is not freezing the UI

Question

I'm trying to make an application with GUI (WinForms) that reads data from an FTDI chip via USB and doesn't cause the UI to freeze while reading.

The application window is no longer responsive. The buttons I added to the window don't work, nor does minimize, maximize, close with a cross.... nothing related to the window works. But I can see in the application debugging window in Visual Studio that data is being received.

The data reading is based on an Event from the FTDI driver: ftHandle.SetEventNotification(FTDI.FT_EVENTS.FT_EVENT_RXCHAR, receivedDataEvent);.

It would be appropriate for the reception of this data to work in a separate thread, so as not to block the GUI. I have read that in 90% of cases the best way to handle threads is Tasks. Unfortunately, the following code snippet reads the data, but the UI blocks during this time. How to solve this problem?

This code is executed once, right after the FTDI is initialized to work:

var receivedDataEvent = new AutoResetEvent(false);

ftHandle.SetEventNotification(FTDI.FT_EVENTS.FT_EVENT_RXCHAR, receivedDataEvent);

// Create a new task to receive data
Task dataReceiveTask = new Task(async () =>
{
    while (true)
    {
        // Wait for the FT_EVENT_RXCHAR event
        receivedDataEvent.WaitOne();

        await Task.Run(() =>
        {
            ReadDataAvailableInFtdiBuffer();
        });                    
    }
});

// Start the data receive task
dataReceiveTask.Start();

And the ReadDataAvailableInFtdiBuffer(); is:

void ReadDataAvailableInFtdiBuffer()
{
    ftStatus = ftHandle.GetRxBytesAvailable(ref numBytesAvailable);
    if (numBytesAvailable < 1)
        return;
    System.Diagnostics.Debug.WriteLine(ftStatus + "  bytes available: " + numBytesAvailable.ToString());

    byte[] bytes = new byte[numBytesAvailable];
    UInt32 numBytesRead = 0;
    ftHandle.Read(bytes, numBytesAvailable, ref numBytesRead);

    // --------------------------------------------------------------------------------------------
    // Calling Received Data Event with passing data to the event subscriber (USB)
    // OnFtdiBytesReceived?.Invoke(this, new FtdiBytesReceivedEventArgs(bytes, numBytesAvailable));
    // --------------------------------------------------------------------------------------------
}

EDIT: using Task.Run as suggested in comments:

var receivedDataEvent = new AutoResetEvent(false);          
ftHandle.SetEventNotification(FTDI.FT_EVENTS.FT_EVENT_RXCHAR, receivedDataEvent);

// Create a new task to receive data
Task dataReceiveTask = Task.Run(() =>
{
    while (true)
    {
         // Wait for the FT_EVENT_RXCHAR event
         receivedDataEvent.WaitOne();
         ReadDataAvailableInFtdiBuffer();                                
    }
});

But the UI behaviour is the same.

EDIT2:

Answer 1

. I have read that in 90% of cases the best way to handle threads is Tasks.

The other advice is to never write to the screen, or any variables which were not, or are not, in the same thread as the thread/task. In other words, the gui thread is different from the running thread. Attempting to write to data to the screen or or other memory locations is problematic.

In your case, you want to pass the data, or status to a specific variable which is "locked" and cannot be written to/accessed by either thread concurrently.

I suspect the issue is here

ftStatus = ftHandle.GetRxBytesAvailable(ref numBytesAvailable);

and that the ftStatus was created on a different thread. You will need to figure out a way to safely write or push messages to the status operation in a different way.

---

I ran into something similar and blogged about it ten years ago

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