访问Collection时是否ArgumentOutOfRangeException，即使索引未超出范围？

Question

我有一个应用程序，该应用程序通过一个线程中的一系列图像过滤器处理图像，并在另一个线程中的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，这些派生类因要在GPU上执行的HLSL着色器程序而异。 图像处理线程遍历那些过滤器实例的集合。 仅当需要将图像从视频内存下载到系统内存时，才调用GetEffectResult（）。 我使用Monitor.Enter（this），因为保证每个过滤器实例在过滤器链中仅存在一次。

为了设置和配置过滤器，我有一个UI，它显示过滤器链中每个过滤器的输出。 筛选器实例由筛选器模型封装，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线程通过计时器重复调用每个过滤器模型实例的Refresh（）方法。

不时地，我在下面的行上收到ArgumentOutOfRangeException：

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

但是，当我检查LastResults属性时，它就像应该包含一个元素。 即使调试器说Collection实际上确实包含一个项目，而我始终访问该集合中的第一个项目，也可能引发ArgumentOutOfRangeException？

Answer 1

调试器的属性被重新评估异常后已被抛出之后 。 元素可能是在Visual Studio暂停调试器的所有操作时由另一个线程插入的。

HTH