Web API-异步模块或处理程序已完成，而异步操作仍处于挂起状态

Question

无法理解这一点。想法？

[控制器]

await _imageRepo.Resize(name, width, height, queryParams, (image) =>
{
    response = createResponse(image);
});

[储存库]

public async Task Resize(string name, string width, string height, ImageOptions options, Action<Images> callback)
{
    var actionName = "resized";
    var newWidth = Convert.ToInt32(width);
    var newHeight = string.IsNullOrEmpty(height) ? newWidth : Convert.ToInt32(height);
    var resizedName = ApplyOptionName(string.Format("{0}-{3}-{1}x{2}", name, newWidth, newHeight, actionName), options);
    await Get(resizedName, null, async (previousImage) =>
    {
        if (previousImage != null)
        {
            callback(previousImage);
            return;
        }
        await Get(name, null, image =>
        {
            if (image == null)
            {
                callback(null);
                return;
            }
            using (ImageFactory imageFactory = new ImageFactory())
            {
                imageFactory.Load(image.ToStream());
                imageFactory.Resize(new ResizeLayer(new Size(newWidth, newHeight), ResizeMode.Max, AnchorPosition.Left));
                ProcessImageOptions(imageFactory, options);
                using (MemoryStream ms = new MemoryStream())
                {
                    imageFactory.Image.Save(ms, System.Drawing.Imaging.ImageFormat.Png);
                    var newImage = Create(new Images(ms) { Name = resizedName });
                    callback(newImage);
                }
            }
        });
    });
}

【例外】

[InvalidOperationException: An asynchronous module or handler completed while an asynchronous operation was still pending.]

所有这些回调都让我感到不舒服，但为什么我会犯这个错误？

Answer 1

虽然回调并不好。我们决定继续使用这种模式。这意味着要弄清楚如何使这些lambda的返回任务。

这很容易。

正如Stephen Cleary所写"将它们更改为Func<…，任务>…"。

这就是最终的实施。

public async Task Resize(string name, string width, string height, ImageOptions options, Func<Images, Task> callback)
{
    var actionName = "resized";
    var newWidth = Convert.ToInt32(width);
    var newHeight = string.IsNullOrEmpty(height) ? newWidth : Convert.ToInt32(height);
    var resizedName = ApplyOptionName(string.Format("{0}-{3}-{1}x{2}", name, newWidth, newHeight, actionName), options);
    await Get(resizedName, null, async (previousImage) =>
    {
        Images resizedImage = null;
        if (previousImage != null)
        {
            resizedImage = previousImage;
        }
        else
        {
            await Get(name, null, async (image) =>
            {
                if (image == null)
                {
                    resizedImage = null;
                    return;
                }
                using (ImageFactory imageFactory = new ImageFactory())
                {
                    imageFactory.Load(image.ToStream());
                    imageFactory.Resize(new ResizeLayer(new Size(newWidth, newHeight), ResizeMode.Max, AnchorPosition.Left));
                    ProcessImageOptions(imageFactory, options);
                    using (MemoryStream ms = new MemoryStream())
                    {
                        imageFactory.Image.Save(ms, System.Drawing.Imaging.ImageFormat.Png);
                        resizedImage = await CreateAsync(new Images(ms) { Name = resizedName });
                    }
                }
            });
        }
        await callback(resizedImage);
    });
}

一个次要的因素。。。但没有造成任何伤害。

谢谢你的帮助！