WCF: Callback is not asynchronous

Question

Hi, I'm trying to program a client server based on the callback infrastructure provided by WCF but it isn't working asynchronously.

My client connects to the server calling a login method, where I save the clients callback channel by doing

MyCallback callback = OperationContext.Current.GetCallbackChannel()

After that the server does some processing and uses the callback object to communicate with the client.

All this works, the problem resides on the fact that even though I've set the method in the OperationContract as IsOneWay=true, the server still hangs when doing the call to the client.

I've tested this by launching the server for debug in the visual studio, detaching it, launching the client, calling the above mentioned login method, putting a break point in the implemented callback method of the client, and making the server send a response to the client. The server stops doing what it's supposed to do, waiting for the response of the client.

Any help is appreciated.

Answer 1

I think the sollution to your problem is to properly set the 'ConcurecyMode' and 'Instance ContextMode' attributes for your service. To do that you must decorate your service declaration with those attributes as shown in the exemple below:

  [ServiceBehavior(InstanceContextMode = InstanceContextMode.Single, ConcurrencyMode = ConcurrencyMode.Reentrant)]
    public class SubscriberService: ISubscriberServiceContract
{...}

InstanceContextMode.Single builds your service as a Singleton object so there is only one instance of your service running for all clients;

ConcurencyMode.Reentrant or ConcurencyMode.Multiple enables multithreaded work for the service instance. For 'Multiple' you must take care of thread syncronization in your service.

Answer 2

Did you try to set

[CallbackBehavior(UseSynchronizationContext = false)]

on the client side object implementing the callback interface ?