WCF：从客户端回调处理程序调用自托管服务

Question

Problem: getting a deadlock exception message in the WCF client.

Scenario:

1. Service calls a client callback (this call is completely independent and is initiated by some condition on the server).

2. While inside the client callback function, the client calls a function in the service and that's when the deadlock exception is thrown:

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.

I tried to simplify the code as much as I can. I did read this article but still I cant find where the problem is: http://msdn.microsoft.com/en-us/library/cc294424.aspx I'd appreciate any suggestions....

SERVICE:

    [ServiceContract(Namespace = "http://abc.com/Core", SessionMode = SessionMode.Required, CallbackContract = typeof(ISvcCallback))] 
public interface ISvc
{
    // One way only - does not wait until operation completes and returns
    // Can initiate session
    [OperationContract(IsOneWay = true)]
    void Initialize(string appId);

    [OperationContract(IsInitiating = false)]
    Account GetCurrentAccount();

}

public interface ISvcCallback
{
    /// <summary>
    /// Report status of the account
    /// </summary>
    /// <param name="acct"></param>
    [OperationContract(IsOneWay=true)]
    void AccountStatus(Account acct);

}

Service Implementation
[ServiceBehavior(InstanceContextMode = InstanceContextMode.Single, ConcurrencyMode = ConcurrencyMode.Reentrant, UseSynchronizationContext = false)]
public class Svc : ISvc
{
    public Account GetCurrentAccount()
    {
            SipAccount sipAcct = null;
            try
            {
                Account acct = m_MyBusinessObject.GetCurrentAccount();
            }
            catch (Exception ex)
            {

            }

            return Acct;
        }
    }

}

CLIENT:

public class CallbackHandler : WcfSipItfService.IWinSipItfCallback
{
    public void AccountStatus(Account Acct)
    {          
            try
            {
                // display accout status in UI by delegate-wrapped event
                // delegate and event declarations are somewhere else
                // and work fine...
                if (DisplayAccountStatusEvent != null)
                    DisplayAccountStatusEvent(Acct);

            }
            catch (Exception ex)
            {
                ....
            }

    }

    private void OnDisplayAccountStatusEvent(Account acct)
    {
                // call service function results in deadlock
                Account acct = GetCurrentAccount();

    }

}

The service is Duplex - uses WSDualHttpBinding.

Answer 1

The deadlock appears to be due to you making a new out bound call while processing a callback from the previous call.

The error message states that you may be able to solve it by "specify ConcurrencyMode of Reentrant or Multiple on CallbackBehaviorAttribute".

Edit

I missed the code that was off the screen. Couple of things to check:

• Why do you need instance mode single?
• Did you updated the service references after changing the concurrency mode?

Answer 2

What's your client? Is it a UI client? if so, you need to add callbackBehavior UseSynchronizationContext=false to client that implements callback contract.