UI freezing due to Task.Run activity in async/await Task.Run() scenario (reworded)

Question

UI freezing due to Task.Run activity in async/await Task.Run() scenario (reworded)

Art Hansen 621

[Previously} Help needed understanding C# await Task.Run() and threading

I’m creating a desktop C# Winforms app. If an exception is thrown due to a missing essential component the user can choose an automated fix option that searches the app’s archives for a usable replacement. A progress bar is used . I’m testing the communication between the UI and search progress. For testing purposes there’s a Winforms timer and a while loop in the Task.Run that completes based on elapsed time or a cancellation flag. Currently the timer’s OnTick event is not firing, progress is not being reported and the UI freezes. Since I get a boatload of messages from within the while loop that loop is obviously preventing anything else from occurring.

The code:

public partial class Recovery : Form
{
	private int _elapsed;
	private static bool _running;
	private static CustomProgBar _pBar;
	private static System.Windows.Forms.Timer _winFtimer;

    private void InitWinFtimer()
	{
		_winFtimer = new System.Windows.Forms.Timer();
		_winFtimer.Interval = 100;
		_winFtimer.Tick += WinFtimer_OnTick;
		_winFtimer.Start();
	}
	private void WinFtimer_OnTick(object sender, EventArgs e)
	{
		_elapsed += _winFtimer.Interval;
		
		// not happening
		Console.WriteLine($"in OnTick elapsed = {_elapsed}"); 
	}
	private void StartBTN_Click(object sender, EventArgs e)
	{
		InitWinFtimer();
		_pBar.Maximum = 5;

		_running = true;
		IProgress<int> prog = new Progress<int>(value =>
		{
			ActionLBL.Text = value.ToString();
			_pBar.Value = value / 1000;
			
			// not happening
			Console.WriteLine($"in IProgress<int> _pBar.Value = {_pBar.Value}");
		});
		RunTask(prog);
	}
	private async void RunTask(IProgress<int> prog)
	{
		await Task.Run(() =>
		{
			while (_elapsed < 4010 && _running)
			{
				Console.WriteLine($"in while elapsed = {_elapsed}");

				if (prog != null)
					prog.Report(_elapsed);
			}
		});
		ActionLBL.Text = "Completed.";
	}
	private void CancelBTN_Click(object sender, EventArgs e)
	{
		_running = false;
	}
}

My understanding is that the activity in the TasK.Run occurs on a dedicated thread separate from the UI thread. I must be missing something fundamental. Any help will be appreciated…

Karen Payne MVP 35,606 Reputation points Volunteer Moderator

2023-09-12T13:52:15.9+00:00

If you want a good resource see the following shows do's and dont's and this page.
Art Hansen 621 Reputation points

2023-09-12T14:26:38.0466667+00:00

Hi @Karen Payne MVP thank goodness for any response

I can't get this site to accept my code and the old "preview" isn't showing ... I click on the code block icon, select language (C#) and paste code ... nada ..any idea what's up?

You' helped me before (with coding) some months ago; I'd value your expertise if I could share my code!

UPDATE 2 hrs later code's there ... trick was to not create a code block at all but just paste code as plain text at which point the code block was created correctly containing the code. Not intuitively obvious to me.

3 answers

Your answer

Karen Payne MVP 35,606 Reputation points Volunteer Moderator

2023-09-12T13:52:15.9+00:00

If you want a good resource see the following shows do's and dont's and this page.
Art Hansen 621 Reputation points

2023-09-12T14:26:38.0466667+00:00

Hi @Karen Payne MVP thank goodness for any response

I can't get this site to accept my code and the old "preview" isn't showing ... I click on the code block icon, select language (C#) and paste code ... nada ..any idea what's up?

You' helped me before (with coding) some months ago; I'd value your expertise if I could share my code!

UPDATE 2 hrs later code's there ... trick was to not create a code block at all but just paste code as plain text at which point the code block was created correctly containing the code. Not intuitively obvious to me.

Answer 1

your timer is running on the UI, so will only block durning its callback. but your worker thread is 100% cpu bound and updates a UI component continuously, so these updates will block the UI thread.

if you don't want to use invoke, a common approach is a queue. the background thread inserts entries in a thread safe queue. the UI thread uses a timer to empty and process the queued items. In your case you would need to implement a debounce as there is minimum delay in loading the queue.

note: the timer uses the event loop to dispatch. but I suspect your sending so many UI update requests, there is no loop.

if you add a sleep to the background loop, I suspect your code will work.

            while (_elapsed < 4010 && _running)
			{
				Console.WriteLine($"in while elapsed = {_elapsed}");

                Thread.Sleep(10); // allow window.loop to run before next UI update
				if (prog != null)
					prog.Report(_elapsed);
			}

Answer 2

Karen Payne MVP 35,606 Volunteer Moderator

See my code sample which has a dependency for this class project for Task Dialogs. Both are in the same repository.

formDemo

Art Hansen 621 Reputation points

2023-09-13T16:53:42.05+00:00

Well, you've been busy! I notice your code doesn't use the Task.Run => very much - is that a personal preference or is there more to it than that?
Karen Payne MVP 35,606 Reputation points Volunteer Moderator

2023-09-13T17:10:58.5166667+00:00

In regards to Task.Run, only when needed as shown here. And sorry for the late response, busy at work.
Art Hansen 621 Reputation points

2023-09-20T05:02:39.87+00:00

Not as delayed as mine ... that's what I suspected. Appreciate the pointers (and sprinkling of humor in your code)-- closet code has been bookmarked.

Answer 3

Bruce (SqlWork.com) 83,821

what messy code. also a background thread can not update a UI control value. the update must be done from the UI thread. if you have a current winform then use invoke. also _running should be a cancelation token.

        private void button1_Click(object sender, EventArgs e)
        {
            _cancellationToken = new CancellationTokenSource();
            _pBar.Maximum = 5;
            IProgress<int> prog = new Progress<int>(value =>
		    {
			   ActionLBL.Invoke(() => 
               { 
                     ActionLBL.Text = value.ToString();
			         _pBar.Value = value / 1000; 
               }
		    });

            RunTask(prog, _cancellationToken.Token);
        }

        private async void RunTask(prog, CancellationToken token)
        {
            ActionLBL.Text = "Started";
            await Task.Run(() =>
            {
                for (int i = 0; i < 4010; i = i + 100)
                {
                    if (token.IsCancellationRequested)
                        return;

                    Thread.Sleep(100); // fake work
                    
                    prog?.Report(i);  
                }

            });
            ActionLBL.Text = token.IsCancellationRequested ? "Cancelled" : "Completed";
        }

        private void CancelBTN_Click(object sender, EventArgs e)
        {
            _cancellationToken.Cancel();
        }

Art Hansen 621 Reputation points

2023-09-13T16:40:59.2766667+00:00

Bruce thanx for the response. I do understand a background process like BackgroundWorker or Task,Run cannot directly update a UI control - an intermediary like ProgressChanged or IProgress is necessary (I've been using BackgoundWorker but trying to transition using https://blog.stephencleary.com/2013/09/taskrun-vs-backgroundworker-round-4.html as a guide). What I don't understand is why the while loop in the background process is locking the winforms timer which I understood runs on the UI thread - shouldn't those two things be happening independently?
Art Hansen 621 Reputation points

2023-09-20T04:49:50.44+00:00

Apologies for the delayed response – personal issue.

YES! – inserting the short processing pause with the Sleep( ) did the trick. That implies the while loop was somehow processing too fast for the other code; I was not aware that’s even possible. A handy addition to my toolkit…

Just to clarify for future readers the initially posted code was properly constructed BUT the while loop needed to wait a bit (the Sleep()) on other processing. Also using the Invoke() didn't appear to have any impact.

BTW I’m curious about the “messy code” observation. I’m self-taught so my coding “style” basically emulates various examples I’ve found (primarily MSDN). Is there a style standard provided to people in a traditional educational curriculum?
Anonymous

2023-09-20T09:47:52.88+00:00

Hi @Art Hansen ， If the answer is the right solution, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Art Hansen 621 Reputation points

2023-10-01T08:21:34.22+00:00

@Anonymous I cannot mark Bruce's initial answer as the solution since it did not provide the solution. His comment describing how the while loop was monopolizing the cpu and recommendation to insert a short Sleep is a solution and if the comment is converted to an answer I'll gladly accept it as a solution. It looks like only the comment author can convert the comment to an answer.
Anonymous

2023-10-02T01:11:33.2933333+00:00

Hi @Art Hansen ，Are you referring to Karen's comment? She appears to have posted her answer below. If you tell me which comment it is, I can turn it into an answer.
Art Hansen 621 Reputation points

2023-10-02T08:35:27.0166667+00:00

@Anonymous I'm referring to "Bruce (SqlWork.com)"'s last comment above posted Sep 13 at 7 PM - thx for your help

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UI freezing due to Task.Run activity in async/await Task.Run() scenario (reworded)

3 answers

Your answer