在设备上运行时，MonoTouch不支持OpenAsync方法打开Web服务连接（在模拟器上工作）

Question

I am using MonoTouch 4.0.7 with MonoDevelop 2.8 Beta 2 and XCode 4 (by the way someone know how to get MonoTouch 4.2 version?). We are trying to call a .Net web service method through classes generated by the slsvcutil proxy generator.

When testing the app on the iPhone simulator, the code is working and we succeed to connect to the server and send web services requests.

However, when testing the app on a device (iPhone 4 with iOS 4.3.5), the app fails to connect to the server when calling OpenAsynch() method (Method called in the code generated by the proxy generator), we get a strange error:

Attempting to JIT compile method '(wrapper delegate-begin-invoke) '(wrapper delegate-begin-invoke) :begin_invoke_IAsyncResult_ this __TimeSpan_AsyncCallback_object (System.TimeSpan,System.AsyncCallback,object)' while running with --aot-only.

My error stack:

Unhandled Exception: System.ExecutionEngineException: Attempting to JIT compile method '(wrapper delegate-begin-invoke) <Module>:begin_invoke_IAsyncResult__this___TimeSpan_AsyncCallback_object (System.TimeSpan,System.AsyncCallback,object)' while running with --aot-only.
at System.ServiceModel.MonoInternal.ClientRuntimeChannel.OnBeginOpen (TimeSpan timeout, System.AsyncCallback callback, System.Object state) [0x00000] in <filename unknown>:0 
at System.ServiceModel.Channels.CommunicationObject.BeginOpen (TimeSpan timeout, System.AsyncCallback callback, System.Object state) [0x00000] in <filename unknown>:0 
at System.ServiceModel.Channels.CommunicationObject.BeginOpen (System.AsyncCallback callback, System.Object state) [0x00000] in <filename unknown>:0 
at System.ServiceModel.ClientBase`1+ChannelBase`1[ICommandMgr,ICommandMgr].System.ServiceModel.ICommunicationObject.BeginOpen (System.AsyncCallback callback, System.Object state) [0x00000] in <filename unknown>:0 
at System.ServiceModel.ClientBase`
1[ICommandMgr].System.ServiceModel.ICommunicationObject.BeginOpen (System.AsyncCallback callback, System.Object state) [0x00000] in <filename unknown>:0 
at CommandMgrClient.OnBeginOpen (System.Object[] inValues, System.AsyncCallback callback, System.Object asyncState) [0x00000] in CommandMgrStaticProxyClient.cs:1156
 at System.ServiceModel.ClientBase`1[ICommandMgr].InvokeAsync (System.ServiceModel.BeginOperationDelegate beginOperationDelegate, System.Object[] inValues, System.ServiceModel.EndOperationDelegate endOperationDelegate, System.Threading.SendOrPostCallback operationCompletedCallback, System.Object userState) [0x00000] in <filename unknown>:0 
at CommandMgrClient.OpenAsync (System.Object userState) [0x00057] in CommandMgrStaticProxyClient.cs:1193 

Someone know if it is a MonoTouch bug or if there is a way to fix this crash? Thanks in advance!

---- EDIT ----

I found a workaround: replace the OpenAsync() call by Open(). Thus, I think it is a limitation/bug of MonoTouch that does not support asynchronous call to open a Web service connection. I'll enter a bug in bugzilla.xamarin.com

 private void DoNotificationMgrOpenAsync(string address, int port)
{
  this.SystemUIHandler.LogInfo(">>>>>> NotificationMgr Open");
  m_notificationMgrClient = new NotificationMgrClient(
    new System.ServiceModel.BasicHttpBinding() { Namespace = "http://schema.dartfish.com/2011/05/RemoteControl" },
    new System.ServiceModel.EndpointAddress(
      string.Format(System.Globalization.CultureInfo.InvariantCulture, "http://{0}:{1}/Dartfish/RemoteControlServices/",
      address, port)));
  //m_notificationMgrClient.OpenCompleted += new System.EventHandler<System.ComponentModel.AsyncCompletedEventArgs>(NotificationMgrClient_OpenCompleted);
  //m_notificationMgrClient.OpenAsync();

  m_notificationMgrClient.Open();
  DoGetLastMessageId();
}

void NotificationMgrClient_OpenCompleted(object sender, System.ComponentModel.AsyncCompletedEventArgs e)
{
  this.SystemUIHandler.LogInfo("<<<<<< NotificationMgr Open");
  System.Diagnostics.Debug.Assert(m_notificationMgrClient != null);
  if (m_notificationMgrClient != null)
  {
    m_notificationMgrClient.OpenCompleted -= NotificationMgrClient_OpenCompleted;
    // init messageId
    DoGetLastMessageId();
  }
}

Answer 1

I believe the specific problem is the same as in this post from the Unity 3D forum:

AOT issue with += event handler syntax

As in this post, the generated async proxy code uses the += event syntax, which requires JIT compilation. I have confirmed that the fix in the post solves that problem.

I haven't tested OpenAsyc, so you may run into additional difficulties after solving the event handler issue.

Answer 2

UPDATE

MonoTouch (itself) is hitting one of the full-AOT limitation of MonoTouch.

The immediate workaround is to use the synchronous Open method (instead of OpenAsync method).

A bug report was opened to track this issue. You can add yourselves on its cc list to be updated on its progress.