Question

我有一个应用程序，它通过一个线程中的一系列图像过滤器处理图像，并在另一个线程的UI中显示图像。简化的图像过滤器类如下所示：

// This class represents a filter operation on the GPU.
// Process() is repeatedly called by the filter processing thread.
class ShaderFilterBase : IFilter
{
    // This variable holds the result of the image operation.
    private ImageInfo resultImageInfo;

    // Indicates whether the image has been updated by a call to Render()
    bool hasChanged = true;

    public ICollection<ImageInfo> LastResults
    {
        get
        {
            ICollection<ImageInfo> results = new Collection<ImageInfo>();
            results.Add(GetEffectResult());
            return results;
        }
    }

    public ICollection<ImageInfo> Process(ICollection<ImageInfo> images)
    {
        // We only process the image if we have exactly one image.
        // If more than one image has to be processed by the GPU, this method
        // should be overridden in a derived class.
        if (images.Count == 1)
        {
            ImageInfo firstImage = images.First();

            // If the supplied image is already a shader resource on the GPU,
            // we don't need to upload the texture to the GPU again. We just
            // set the output texture of the supplied image to the input texture
            // of the current image.
            if (firstImage.IsShaderResource)
                SetResource(firstImage.ShaderResourceView);
            else
                UploadInputTexture(firstImage);

            Render();

            firstImage.ShaderResourceView = OutputShaderResourceView;
        }

        return images;
    }

    public virtual void Render()
    {
        Monitor.Enter(this);

        // Perform texture operations on the GPU            

        hasChanged = true;

        Monitor.Exit(this);
    }

    public ImageInfo GetEffectResult()
    {
        Monitor.Enter(this);

        if (hasChanged)
        {
            // Download image from GPU and store it in resultImageInfo

            hasChanged = false;
        }

        Monitor.Exit(this);

        return resultImageInfo;
    }
}

此外，我有各种派生类，它们在GPU上执行的HLSL着色器程序不同。图像处理线程迭代这些过滤器实例的集合。只有在需要将图像从视频内存下载到系统内存时才会调用GetEffectResult（）。我使用Monitor.Enter（this），因为每个过滤器实例都保证在过滤器链中只存在一次。

要设置和配置过滤器，我有一个UI，显示过滤器链中每个过滤器的输出。过滤器实例由过滤器模型封装，由WPF UI使用。

internal abstract class FilterModelBase : DependencyObject
{
    private WriteableBitmap preview;

    private static readonly DependencyPropertyKey PreviewPropertyKey = DependencyProperty.RegisterReadOnly("Preview",
        typeof(ImageSource), typeof(FilterModelBase), new PropertyMetadata());

    // The WPF window contains an Image control, which binds to this property.
    public static readonly DependencyProperty PreviewProperty = PreviewPropertyKey.DependencyProperty;

    public ImageSource Preview
    {
        get { return (ImageSource)GetValue(PreviewProperty); }
        private set { SetValue(PreviewPropertyKey, value); }
    }

    // The underlying filter.
    public IFilter Filter
    {
        get { return this.filter; }
    }

    protected FilterModelBase(IEventAggregator eventAggregator, IFilter filter)
    {
        Check.NotNull(filter, "filter");
        this.EventAggregator = eventAggregator;

        this.filter = filter;
    }

    // Updates the filter output preview.
    public virtual void Refresh(Dispatcher dispatcher)
    {
        if (!dispatcher.CheckAccess())
            dispatcher.Invoke(new Action(() => Refresh(dispatcher)));
        else
        {
            ImageInfo filterImage = null;

            Monitor.Enter(this.filter);

            if (this.filter != null && this.filter.LastResults.Count > 0)
                filterImage = this.filter.LastResults.ElementAtOrDefault(0);

            if (filterImage != null)
            {
                this.preview.WritePixels(new Int32Rect(0, 0, filterImage.Width, filterImage.Height),
                    filterImage.ImageBytes, filterImage.Width * filterImage.Channels, 0);
            }

            Monitor.Exit(this.filter);
        }
    }

UI线程通过Timer重复调用每个过滤器模型实例的Refresh（）方法。

我不时会在以下行中收到ArgumentOutOfRangeException：

filterImage = this.filter.LastResults.ElementAtOrDefault(0);

但是，当我检查LastResults属性时，它包含一个元素，就像它应该的那样。怎么可能引发ArgumentOutOfRangeException，即使调试器说集合确实只包含一个项目而且我总是访问集合中的第一个项目？

Answer 1

调用器在抛出异常后重新评估该属性。可视元素已被另一个线程插入，而visual studio正在停止调试器的所有内容。

HTH

访问Collection时ArgumentOutOfRangeException，即使索引不在范围之外？

1 个答案: