c# - 异步死锁？

Question

我相当确定我在我的应用程序中造成了死锁，但我不确定如何解决该问题。我有一些事件部件并且是 async 和 await 的新手，所以请多多包涵。

我有一个客户端上传文件如下:

public static async Task<string> UploadToService(HttpPostedFile file, string authCode, int id)
{
    var memoryStream = new MemoryStream();
    file.InputStream.CopyTo(memoryStream);

    var requestContent = new MultipartFormDataContent();
    var fileContent = new ByteArrayContent(memoryStream.ToArray());
    fileContent.Headers.ContentType = MediaTypeHeaderValue.Parse(file.ContentType);
    requestContent.Add(fileContent, "file", file.FileName);

    using (var httpClient = new HttpClient())
    {
        httpClient.BaseAddress = new Uri(BaseUrl);
        httpClient.DefaultRequestHeaders.Accept.Clear();

        var message =
            await
                httpClient.PostAsync(
                    string.Format("Upload?authCode={0}&id={1}", authCode, id),
                    requestContent);

        return await message.Content.ReadAsStringAsync();
    }
}

接收文件的piece:

[HttpPost]
public Task<HttpResponseMessage> Upload(string authCode, int id)
{
    var request = Request;

    var provider = new CustomMultipartFormDataStreamProvider(root);

    var task =
        request.Content.ReadAsMultipartAsync(provider)
            .ContinueWith(o =>
            {
                // ...
                // Save file
                // ...

                return new HttpResponseMessage()
                {
                    Content = new StringContent("File uploaded successfully"),
                    StatusCode = HttpStatusCode.OK
                };
            });

    return task;
}

一切从以下开始:

protected void Page_Load(object sender, EventArgs e)
{
    if (IsPostBack)
    {
        var file = HttpContext.Current.Request.Files[0];

        var response = UploadToService(file, hiddenAuthCode.Value, int.Parse(hiddenId.Value));
    }
}

除了 PostAsync 从未识别出 task 已返回外，一切似乎都正常。我可以看到 await ... PostAsync ... 任务的状态是 WaitingForActivation 但我不完全确定那是什么意思(记住，我对这东西一窍不通)。我的文件已保存到正确的位置，但应用程序始终无法识别来 self 的服务的响应。

如果有人能指出正确的方向，我将不胜感激。

Answer 1

我认为问题在于您只需调用 UploadToService内部以即发即弃的方式Page_Load .请求处理在此任务完成之前简单地结束。

你应该使用 <%@ Page Async="true" ...>在此 WebForms 页面中并包含 <add key="aspnet:UseTaskFriendlySynchronizationContext" value="true" />在你的web.config那里。

然后使用RegisterAsyncTask ，代码将如下所示:

protected void Page_Load(object sender, EventArgs e)
{
    if (IsPostBack)
    {
        var file = HttpContext.Current.Request.Files[0];

        RegisterAsyncTask(new PageAsyncTask(() => UploadToService(file, 
            hiddenAuthCode.Value, int.Parse(hiddenId.Value))));
    }
}

附带说明一下，您可以改进这部分:

file.InputStream.CopyTo(memoryStream);

像这样:

await file.InputStream.CopyToAsync(memoryStream);

并替换ContinueWith与 async/await :

[HttpPost]
public async Task<HttpResponseMessage> Upload(string authCode, int id)
{
    var request = Request;

    var provider = new CustomMultipartFormDataStreamProvider(root);

    await request.Content.ReadAsMultipartAsync(provider);

    return new HttpResponseMessage()
    {
        Content = new StringContent("File uploaded successfully"),
        StatusCode = HttpStatusCode.OK
    };
}

相关:"Using Asynchronous Methods in ASP.NET 4.5" .