Unhandled C # callback exception error

Question

I have a three-tier architecture and send some data at the transport level (TCP Client) using tcp sockets, this is asynchronous using the BeginSend method.

public void TransportData(Stream stream) { try { SetTransporterState(StateObject.State.SendingData); if (clientSock.Connected) { ASCIIEncoding asen = new ASCIIEncoding(); stream.Position = 0; byte[] ba = GetStreamAsByteArray(stream); if (clientSock.Connected) clientSock.BeginSend(ba, 0, ba.Length, SocketFlags.None, new AyncCallback(SendData), clientSock); else throw new SockCommunicationException("Socket communication failed"); } catch (SocketException sex) { throw sex; } catch (SockCommunicationException comex) { bool rethrow = ExceptionPolicy.HandleException(comex, "TransportLayerPolicy"); if (rethrow) { throw; } } } } catch (SocketException soex) { throw soex; } catch (SockCommunicationException comex) { bool rethrow = ExceptionPolicy.HandleException(comex, "TransportLayerPolicy"); if (rethrow) { throw; } } catch (Exception ex) { LoggingMessageHelper.LogDeveloperMessage(ex.Message + Environment.NewLine + ex.StackTrace, 1, TraceEventType.Critical); bool rethrow = ExceptionPolicy.HandleException(ex, "TransportLayerPolicy"); if (rethrow) { throw; } } } 

SendData () callback code is below

  private void SendData(IAsyncResult iar) { Socket remote = null; try { remote = (Socket)iar.AsyncState; try { int sent = remote.EndSend(iar); } catch (Exception ex) { throw ex; } if (remote.Connected ) { remote.BeginReceive(data, 0, size, SocketFlags.None, new AsyncCallback(ReceiveData), remote); } else throw new SockCommunicationException("Communication Failed"); } catch (SocketException soex) { throw new SockCommunicationException("Communication Failed"); } catch (SockCommunicationException comex) { bool rethrow = ExceptionPolicy.HandleException(comex, "TransportLayerPolicy"); if (rethrow) { throw; } } 

When the server shuts down, the client does not know until it sends some data, so the Connected property is true. Then the line remote.BeginReceive () throws a SocketException which I am trying to catch and throw a custom exception (sockCommunicationException).

However, when I do this, I get an unhandled exception. I would like to create this error for the user interface through the business layer. When a similar exception occurs in a callback method, where does it rise to?

How can I avoid this unhandled exception and throw this exception out of the user interface level.

Please, help.

Thanks in advance!

Answer 1

Yes, it doesn’t work. The callback is executed in the threadpool thread, there is no one there to catch the exception. You need to, say, raise an event that the user interface can subscribe to. Marshaling is required, the UI code should use something like Control.BeginInvoke () if it needs to update the interface.

Answer 2

This is a common requirement.

Typically, the SendData solution has access to the local method to notify the client of the result of the operation and possibly display it in the user interface.

Now you need to achieve this at an average level that is different . Your client calls the server, which in turn calls the asynchronous method and starts the operation. If the client needs to know about the result and its exceptions, it must poll the server and check the result - and you will need to save the result (on the server or in some database) until the client retrieves it or throws it out after a timeout - cleaning itself becomes complicated.

Alternatively, he can use the Duplex method for the server to communicate with the Client. This decision sounds great, but being fair is awful for various reasons that go beyond this.