在非UI线程上调用AsyncWaitHandle.WaitOne时出现NotSupportedException

Question

I try to wait for an HttpWebRequest to finish without writing a dozen AsyncCallbacks. For that I tried to handle the call in a Task and use WaitOne within it --> so the ui thread will not be blocked.

The Problem now is that there appears a NotSupportedException everytime I call it and I don´t understand why. Can someone tell me more about that and maybe how to fix this issue?

Here the code:

    Task.Factory.StartNew((x)=>
            {


            HttpWebRequest request = WebRequest.CreateHttp(baseUri + "/api/" + ControllerName);
            request.Method = "POST";
            request.ContentType = "application/json";
            request.Headers["Session"] = SessionKey;

            IAsyncResult GetRequestStreamResult = request.BeginGetRequestStream(null, null);
            GetRequestStreamResult.AsyncWaitHandle.WaitOne(); //<-- That causes the exception
            using (Stream RequestStream = request.EndGetRequestStream(GetRequestStreamResult))
            {
                DataContractJsonSerializer serializer = new DataContractJsonSerializer(Parameter.GetType());
                serializer.WriteObject(RequestStream, Parameter);
            }

Best regards

Christoph

Answer 1

I found this article . That pointed me to the direction that maybe it is no common silverlight issue, but a Problem with the actual implementation of the IAsyncResult which is of System.Net.Browser.OHWRAsyncResult. And this simply throws a NotSupportedException in any case when accessing the AsyncWaitHandle getter.

I helped me out by writing this small Extension method:

    private static void WaitForIt(this IAsyncResult result)
    {
        while (!result.IsCompleted)
        {
            Thread.Sleep(50);
        }
    }

Not really pretty but it works...

Regards

Christoph

Answer 2

Use this handler...

  while ((GetRequestStreamResult.AsyncWaitHandle.WaitOne(1000, true) == false)
          && (GetRequestStreamResult.IsCompleted == false))
           {
               // Do nothing 
           }