TPL Dataflow 管道中的图像刷新问题

Question

我正在使用 TPL Dataflow 从路径加载视频（我正在使用 Emgu.CV 库进行加载），并通过 TPL Dataflow 首先将其绘制在 Windows 窗体应用程序中（之后将在与木板）。我有另一篇文章对 TPL Dataflow 帮助很大： Asynchronous Task, video buffering

但是在设置 TPL 数据流之后，第一张图像只加载到 GUI 中，之后（虽然块似乎正在运行，因为打印显示在 cmd 中）图像没有刷新......我不明白出了什么问题?它与调度程序或 TPL 数据流有关吗？ 下面是代码：

public async void CreateVideoProcessingNetwork()
{
    string video_path = @"C:\.......\video_640x360_360p.mp4";

    /* displayVideo Block*/
    var display_video = new ActionBlock<Bitmap>(async received_bitmap =>
    {
        Console.WriteLine("Inside display_video");

        PicturePlot2.Refresh();
        PicturePlot2.Image = received_bitmap;
        Console.WriteLine("Image size = " + received_bitmap.Size);
        Console.WriteLine("Image width = " + received_bitmap.Width);

        await Task.Delay(30);
   });

    var loadVideo = new ActionBlock<string>(async path =>
    {
        capture = new VideoCapture(path);
        Mat matrix = new Mat();
        capture.Read(matrix);
        var mem_stream = new MemoryStream();
        Bitmap HWimage;

        while (matrix.Rows != 0 && matrix.Width != 0)
        {
            Console.WriteLine("Inside LoadVideo");
            matrix = new Mat();
            capture.Read(matrix);
            Bitmap bitmap = new Bitmap(matrix.Width, matrix.Rows);
            bitmap = matrix.ToBitmap();
            bitmap.Save(mem_stream, System.Drawing.Imaging.ImageFormat.Jpeg);
            byte[] image_array = mem_stream.ToArray();
            Console.WriteLine("image_array = " + image_array.Length);
            using (var mem_stream_hw = new MemoryStream(image_array)) HWimage = new Bitmap(mem_stream_hw);
            var accepted = await display_video.SendAsync(HWimage);
            if (!accepted) break;
            await Task.Delay(25);
        }
    });

    PropagateCompletion(loadVideo, display_video);

    loadVideo.Post(video_path);
    loadVideo.Complete();
    await display_video.Completion;
}

我理解错了吗？我想通过 TPL Dataflow 在视频显示中进行某种流水线操作。

更新：

在我完成上述更改后，视频播放。但是还有一个问题。 “生产者”的数据创建速度更快（实际上它取决于 TransformManyBlock 中的 Thread.Sleep 时间），并且在播放视频几秒钟后，应用程序崩溃并出现以下错误：

Unhandled Exception: System.Runtime.InteropServices.ExternalException: A generic error occurred in GDI+.
   at System.Drawing.Graphics.MeasureString(String text, Font font, SizeF layoutArea, StringFormat stringFormat)
   at System.Drawing.Graphics.MeasureString(String text, Font font, Int32 width)
   at System.Windows.Forms.ThreadExceptionDialog..ctor(Exception t)
   at System.Windows.Forms.Application.ThreadContext.OnThreadException(Exception t)
   at System.Windows.Forms.Control.WndProcException(Exception e)
   at System.Windows.Forms.Control.ControlNativeWindow.OnThreadException(Exception e)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
   at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
   at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData)
   at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
   at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
   at System.Windows.Forms.Application.Run(Form mainForm)
   at ntComlabGUI.Program.Main()

例如，如果 Thread.Sleep 被删除，错误几乎立即发生（在前 1-2 秒内）。有人怎么能做流量控制？在 Asynchronous Task, video buffering 帖子中提到了 BoundedCapacity 方法。但我试过了，错误仍然存​​在。下面是代码：

public async void CreateVideoProcessingNetwork()
{
    //string video_path = @"C:\Projects_Repo\ComlabDMA_Ethernet_video\ntComlabGUI_Ultrascale_ethernet\ntComlabGUI\video_640x360_360p.mp4";
    string video_path = @"C:\Projects_Repo\ComlabDMA_Ethernet_video\ntComlabGUI_Ultrascale_ethernet\ntComlabGUI\video_640x360_360p.mp4";


    /* Video Loading TPL Block */
    var video_loader = new TransformManyBlock<string, Bitmap>(load_video,
        new ExecutionDataflowBlockOptions { BoundedCapacity = 128 });

    IEnumerable<Bitmap> load_video(string path)
    {

        capture = new VideoCapture(path);
        Mat matrix = new Mat();
        capture.Read(matrix);
        var mem_stream = new MemoryStream();


        while (matrix.Rows != 0 && matrix.Width != 0)
        {
            capture.Read(matrix);
            Bitmap bitmap = new Bitmap(matrix.Width, matrix.Rows);

            bitmap = matrix.ToBitmap();

            yield return bitmap;
            //Thread.Sleep(1);

        }
        yield break;
    }



    /* Video Loading TPL Block */

    var display_video = new ActionBlock<Bitmap>(async received_image =>
    {
        PicturePlot2.Image = received_image;
        await Task.Delay(33);
    },
    new ExecutionDataflowBlockOptions()
    {
        TaskScheduler = TaskScheduler.FromCurrentSynchronizationContext(),
        BoundedCapacity = 128
    });



    var linkOptions = new DataflowLinkOptions { PropagateCompletion = true };

    video_loader.LinkTo(display_video, linkOptions);
    video_loader.Post(video_path);
    video_loader.Complete();
    await display_video.Completion;


}

也许以下链接是解决方案？ ：How do I arrange flow control in TPL Dataflows?

提前感谢您的帮助， 也为了快速响应， 非常感谢！

Answer 1

问题很可能是PicturePlot2 组件不喜欢被非UI 线程操作。为确保ActionBlock的委托将在UI线程上被调用，您可以像这样配置块的TaskScheduler选项：

var display_video = new ActionBlock<Bitmap>(async received_bitmap =>
{
    Console.WriteLine("Inside display_video");

    PicturePlot2.Refresh();
    PicturePlot2.Image = received_bitmap;
    Console.WriteLine("Image size = " + received_bitmap.Size);
    Console.WriteLine("Image width = " + received_bitmap.Width);

    await Task.Delay(30);
}, new ExecutionDataflowBlockOptions()
{
    TaskScheduler = TaskScheduler.FromCurrentSynchronizationContext()
});

为此，需要在 UI 线程上实例化块。这是因为 Windows 窗体应用程序在启动时会在 UI 线程上安装specialSynchronizationContext，我们希望TaskScheduler.FromCurrentSynchronizationContext 方法能够捕获此上下文。