Why doesn't my NamedPipeServerStream wait?

Question

I'm working with a NamedPipeServerStream to communicate between two processes. Here is the code where I initialize and connect the pipe:

void Foo(IHasData objectProvider)
{
    Stream stream = objectProvider.GetData();
    if (stream.Length > 0)
    {
        using (NamedPipeServerStream pipeServer = new NamedPipeServerStream("VisualizerPipe", PipeDirection.Out, 1, PipeTransmissionMode.Byte, PipeOptions.Asynchronous))
        {
            string currentDirectory = Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location);
            string uiFileName = Path.Combine(currentDirectory, "VisualizerUIApplication.exe");
            Process.Start(uiFileName);
            if(pipeServer.BeginWaitForConnection(PipeConnected, this).AsyncWaitHandle.WaitOne(5000))
            {
                while (stream.CanRead)
                {
                    pipeServer.WriteByte((byte)stream.ReadByte());
                }
            }
            else
            {
                throw new TimeoutException("Pipe connection to UI process timed out.");
            }
        }
    }
}

private void PipeConnected(IAsyncResult e)
{
}

But it never seems to wait. I constantly get the following exception:

System.InvalidOperationException: Pipe hasn't been connected yet. at System.IO.Pipes.PipeStream.CheckWriteOperations() at System.IO.Pipes.PipeStream.WriteByte(Byte value) at PeachesObjectVisualizer.Visualizer.Show(IDialogVisualizerService windowService, IVisualizerObjectProvider objectProvider)

I would think that after the wait returns everything should be ready to go.

If I use pipeServer.WaitForConnection() everything works fine, but hanging the application if the pipe doesn't connect is not an option.

Answer 1

You need to call EndWaitForConnection.

var asyncResult = pipeServer.BeginWaitForConnection(PipeConnected, this);

if (asyncResult.AsyncWaitHandle.WaitOne(5000))
{
    pipeServer.EndWaitForConnection(asyncResult);

    // ...
}

See: IAsyncResult design pattern.