winforms: updating progress with a parallel.foreach

问题

I haven't seen any posts pertaining to my issue, so I apologize if I post a question already asked.

I have a windows form program, c#, that checks stocks and does analysis. The main form launches another form, via a new thread and ShowDialog. While it's loading, it's running a parallel.foreach. In that parallel.foreach, I'd like to show progress on the main form.

I've run into cross-threading issues, and added invoke, although it doesn't appear to be thread-safe as it seems to be deadlocking toward the end of the parallel.foreach. I've tried delegates, events, no luck. Help me Obi-Wans, you're my only hope!

Stripped down version:

Main form

private void button1_Click(object sender, EventArgs e)
    {
        YearLows yearLows = new YearLows();
        Thread yearLowsThread = new Thread(() => StartYearLows(yearLows));
        yearLowsThread.Start();
        btnGetYearLows.Enabled = false;
    }

    private void StartYearLows(YearLows yearLows)
    {
        yearLows.ShowDialog();
    }

    public void UpdateProgress(string text)
    {
        lblProgress.Text = text;
    }

2nd form dialog

    public partial class YearLows : Form
    {
        private void YearLows_Load(object sender, EventArgs e)
        {
            // work
            Parallel.ForEach(responseStocks, new ParallelOptions { MaxDegreeOfParallelism = MaxThreads }, x =>
            {
              // more work
              Interlocked.Increment(stocksProcessed);
              UpdateProgress($"{stocksProcessed} / {stocksTotal} Researched");
            });
        }

        private void UpdateProgress(string text)
        {
            Invoke(new Action(() => frmMain.UpdateProgress(text)));
        }
    }

Update 1: If I move the progress update label to the child form, it appears I am getting all the progress updates. I had to move from the Load event to the Shown event so that the form renders, so users can see the progress updates. I had to follow SLaks advice though and run Task.Run(() => Parallel.ForEach. This will work for me. Would still like to figure out why it still locks up toward the end if I wanted the progress updates on the main form. (I've always read async void was bad, but I guess no way around this in these defined method signatures in winforms)

    public partial class YearLows : Form
    {
        private async void YearLows_Shown(object sender, EventArgs e)
        {
            await AnalyzeStocks();
        }

        private async Task AnalyzeStocks(object sender, EventArgs e)
        {
            // work
            await Task.Run(() => Parallel.ForEach(responseStocks, new ParallelOptions { MaxDegreeOfParallelism = MaxThreads }, x =>
            {
                // more work
                Interlocked.Increment(stocksProcessed);
                UpdateProgress($"{stocksProcessed} / {stocksTotal} Researched");
            }));
        }

        private void UpdateProgress(string text)
        {
            Invoke(new Action(() => lblProgress.UpdateProgress(text)));
        }
    }

回答1:

Parallel.ForEach is a blocking call; it runs delegates on the calling thread too. Therefore, the UI cannot update until it finishes.

Instead, you should use await with Task.WhenAll (if you're doing async work) or Task.Run(() => Parallel.ForEach(...)) (if it's CPU-bound) so that you leave the UI thread idle and able to update.

回答2:

you can use Async Await function for this puprose... this link can be more useful to you...

PictureBox animation freezing while Task running

来源：https://stackoverflow.com/questions/51092054/winforms-updating-progress-with-a-parallel-foreach

标签

multithreading

winforms

parallel.foreach