c# - 有一个待处理的异步操作，并且只能同时处理一个异步操作

Question

在我的开发机器上运行它时没有任何问题，效果很好。当部署到我的服务器时，我总是收到错误。

System.IO.IOException: Error reading MIME multipart body part. ---> System.InvalidOperationException: There is a pending asynchronous operation, and only one asynchronous operation can be pending concurrently. at System.Web.Hosting.IIS7WorkerRequest.BeginRead(Byte[] buffer, Int32 offset, Int32 count, AsyncCallback callback, Object state)

我正在尝试上传图像。当我在本地计算机上运行它时，没有错误并且文件确实被上传。

        public async Task<HttpResponseMessage> PostFile(int TaskID)
    {
        // Check if the request contains multipart/form-data. 
        if (!Request.Content.IsMimeMultipartContent())
        {
            throw new HttpResponseException(HttpStatusCode.UnsupportedMediaType);
        }

        try
        {
            StringBuilder sb = new StringBuilder(); // Holds the response body 
            string root = HttpContext.Current.Server.MapPath("~/App_Data");
            var provider = new MultipartFormDataStreamProvider(root);

            //// Read the form data and return an async task. 
            await Request.Content.ReadAsMultipartAsync(provider);

错误发生在以await 开头的代码的最后一行。

Answer 1

需要添加以下代码行。

Request.Content.LoadIntoBufferAsync().Wait();

这是在出错的行之前添加的。

现在看起来像这样。

            var provider = new MultipartFormDataStreamProvider(root);

            Request.Content.LoadIntoBufferAsync().Wait();

            //// Read the form data and return an async task. 
            await Request.Content.ReadAsMultipartAsync(provider);