Async operation completes, but result is not send to browser

Question

I want to implement a webchat.

The backend is a dual WCF channel. Dual channel works in the console or winforms, and it actually works on the web. I can at least send and receive messages.

As a base I used this blog post so, the async operation completes.

When i debug the result, I see that the messages are all ready to send to the browser.

[AsyncTimeout(ChatServer.MaxWaitSeconds * 1020)] // timeout is a bit longer than the internal wait
public void IndexAsync()
{
  ChatSession chatSession = this.GetChatSession();
  if (chatSession != null)
  {
    this.AsyncManager.OutstandingOperations.Increment();
    try
    {
      chatSession.CheckForMessagesAsync(msgs =>
      {
        this.AsyncManager.Parameters["response"] = new ChatResponse { Messages = msgs };
        this.AsyncManager.OutstandingOperations.Decrement();
      });
    }
    catch (Exception ex)
    {
      Logger.ErrorException("Failed to check for messages.", ex);
    }
  }
}

public ActionResult IndexCompleted(ChatResponse response)
{
  try
  {
    if (response != null)
    {
      Logger.Debug("Async request completed. Number of messages: {0}", response.Messages.Count);
    }
    JsonResult retval = this.Json(response);
    Logger.Debug("Rendered response: {0}", retval.);
    return retval;
  }
  catch (Exception ex)
  {
    Logger.ErrorException("Failed rendering the response.", ex);
    return this.Json(null);
  }
}

But nothing is actually sent.

Checking Fiddler, I see the request but I never get a response.

[SessionState(SessionStateBehavior.ReadOnly)]  
public class ChatController : AsyncController

I also had to set the SessionStateBehaviour to Readonly, otherwise the async operation would block the whole page.

EDIT: Here is the CheckForMessagesAsync:

public void CheckForMessagesAsync(Action<List<ChatMessage>> onMessages)
{
  if (onMessages == null)
    throw new ArgumentNullException("onMessages");

  Task task = Task.Factory.StartNew(state =>       
  {
    List<ChatMessage> msgs = new List<ChatMessage>();
    ManualResetEventSlim wait = new ManualResetEventSlim(false);
    Action<List<ChatMessage>> callback = state as Action<List<ChatMessage>>;
    if (callback != null)
    {
      IDisposable subscriber = m_messages.Subscribe(chatMessage =>
      {
        msgs.Add(chatMessage);
        wait.Set();
      });
      bool success;
      using (subscriber)
      {
        // Wait for the max seconds for a new msg
        success = wait.Wait(TimeSpan.FromSeconds(ChatServer.MaxWaitSeconds));              
      }
      if (success) this.SafeCallOnMessages(callback, msgs);
      else this.SafeCallOnMessages(callback, null);
    }        
  }, onMessages);
}
private void SafeCallOnMessages(Action<List<ChatMessage>> onMessages, List<ChatMessage> messages)
{
  if (onMessages != null)
  {
    if (messages == null)
      messages = new List<ChatMessage>();
    try
    {
      onMessages(messages);
    }
    catch (Exception ex)
    {
      this.Logger.ErrorException("Failed to call OnMessages callback.", ex);
    }
  }
}

it`s the same idea as the in the refered blog post

EDIT2: Btw, when nothing is received, so the wait timeout comes into play, the reponse returns. so it seems to crash somewhere. any idea how to log this?

Answer 1

I changed the jQUERY request (see original blog post) from POST to GET. That fixes it.