StreamSocket.InputStreamOptions.ReadAsync hangs when using Wait()

Question

This is the smallest possible scenario, I was able to prepare:

• This code connects to imap.gmail.com
• Reads the initial server greeting (using Read method)
• Sends NOOP command (NO Operation)
• Reads NOOP command response (again using Read method)

The problem is that the second Read hangs . It works perfectly if 'await ReadAsync' is used.

When I break the program I can see the Call Stack starts at task.Wait() and ends on System.Threading.Monitor.Wait().

If I debug this step by step, it does not hang. I must admit it looks like a .NET framework bug, but maybe I'm missing something obvious.

private static async Task<byte[]> ReadAsync(StreamSocket socket)
{
    // all responses are smaller that 1024
    IBuffer buffer = new byte[1024].AsBuffer();
    await socket.InputStream.ReadAsync(
            buffer, buffer.Capacity, InputStreamOptions.Partial);
    return buffer.ToArray();
}

private static byte[] Read(StreamSocket socket)
{
    Task<byte[]> task = ReadAsync(socket);
    task.Wait();
    return task.Result;
}

private async void Button_Click(object sender, RoutedEventArgs e)
{
    Encoding encoding = Encoding.GetEncoding("Windows-1250");

    using (StreamSocket socket = new StreamSocket())
    {
        await socket.ConnectAsync(
            new HostName("imap.gmail.com"), "993", SocketProtectionLevel.Ssl);

        // notice we are using Wait() version here without any problems:
        byte[] serverGreetings = Read(socket);              

        await socket.OutputStream.WriteAsync(
            encoding.GetBytes("A0001 NOOP\r\n").AsBuffer());
        await socket.OutputStream.FlushAsync();

        //byte[] noopResponse = await ReadAsync(socket);    // works
        byte[] noopResponse = Read(socket);                 // hangs
    }
}

Answer 1

I explain the cause of this deadlock in my recent MSDN article as well as on my blog .

The short answer is that you're not supposed to call Wait or Result on async code; you should use await all the way.