WCF InvalidOperationException when calling back in a callback

Question

I have a service like this:

[ServiceContract(SessionMode = SessionMode.Required, CallbackContract=typeof(IMyServiceCallback))]
public interface IMyService
{
    [OperationContract]
    bool CallService();
}

public interface IMyServiceCallback
{
    [OperationContract(IsOneWay = true)]
    void NotifyClient();
}

In the implementation of NotifyClient() I attempt to make a call to CallService(). This results in an InvalidOperationException:

Additional information: This operation would deadlock because the reply cannot be received until the current Message completes processing. If you want to allow out-of-order message processing, specify ConcurrencyMode of Reentrant or Multiple on CallbackBehaviorAttribute.

My service has ServiceBehavior set as follows:

[ServiceBehavior(InstanceContextMode=InstanceContextMode.PerSession, ConcurrencyMode=ConcurrencyMode.Multiple, UseSynchronizationContext=false)]

and my callback has CallbackBehavior as:

[CallbackBehavior(ConcurrencyMode = ConcurrencyMode.Multiple, UseSynchronizationContext=false)]

What could be causing this exception? I have also tried using ConcurrencyMode.Reentrant, but that doesn't help. I am able to get round the problem by invoking CallService() on a worker thread, but I would still like to know what is causing the exception.

Thanks.

Edit: added [OperationContract(IsOneWay = true)], but the problem remains.

score 1 · Answer 1 · answered Oct 28 '12 at 07:44

Have you tried invoking the NotifyClient() callback on a separate thread? This should avoid any possible deadlocks.

public class Service : IMyService
{
     public bool CallService()
     {
           IMyServiceCallback callback = OperationContext.Current.GetCallbackChannel<IMyServiceCallback>();
           Task.Factory.StartNew((cb) => cb.NotifyClient(), callback);
     }
}

score 1 · Answer 2 · answered Aug 15 '11 at 14:34

1

Try setting the operationcontract on your callback to

[OperationContract(IsOneWay = true)]

answered Aug 15 '11 at 14:34

Dominik

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I've tried that also, but it doesn't help. (I should have included that in my description...). – MrNick Aug 15 '11 at 14:49
Can you post your implementations of NotifyClient and CallService? – Dominik Aug 16 '11 at 07:47
Notify client does nothing other than call proxy.CallService(). And the CallSericve method does not have to contain anything for this to exception to occur. The proxy I have created myself, deriving from DuplexClientBase. Since I've been able to overcome the problem by calling CallService on another therad I'm not going to investigate any further for the time being. Thanks for your help though! – MrNick Aug 17 '11 at 09:07
I've found out the cause of the problem. I only put CallbackBehavior on the base class, not the children! – MrNick Aug 23 '11 at 09:32

WCF InvalidOperationException when calling back in a callback

2 Answers2