WCF双工:如何处理双工回调中引发的异常 [英] WCF Duplex: How to handle thrown exception in duplex Callback

问题描述

在WCF双工设置中，如何处理客户端的回调方法中引发的异常?

How do I handle an exception thrown in a callback method on the client in a WCF duplex setup?

当前，客户端似乎没有引发错误事件(除非我监视不正确?)，但随后使用该客户端调用Ping()的任何操作都会失败，并显示CommunicationException:通信对象System.ServiceModel. Channels.ServiceChannel，由于已中止，因此无法用于通信.".

Currently, the client does not appear to raise the faulted event (unless I'm monitoring it incorrectly?) but any subsequent to call Ping() using the the client fails with CommunicationException: "The communication object, System.ServiceModel.Channels.ServiceChannel, cannot be used for communication because it has been Aborted.".

我该如何处理并重新创建客户端等?我的第一个问题是如何找出何时发生.其次，如何最好地应对呢?

How do I deal with this and recreate the client etc? My first question is how to find out when it happens. Secondly, how best to deal with it?

我的服务和回调合同:

[ServiceContract(CallbackContract = typeof(ICallback), SessionMode = SessionMode.Required)]
public interface IService
{
    [OperationContract]
    bool Ping();
}

public interface ICallback
{
    [OperationContract(IsOneWay = true)]
    void Pong();
}

我的服务器实现:

[ServiceBehavior(InstanceContextMode = InstanceContextMode.PerCall, ConcurrencyMode = ConcurrencyMode.Single)]
public class Service : IService
{
    public bool Ping()
    {
        var remoteMachine = OperationContext.Current.GetCallbackChannel<ICallback>();

        remoteMachine.Pong();
    }
}

我的客户实施:

[CallbackBehavior(UseSynchronizationContext = false, ConcurrencyMode = ConcurrencyMode.Single)]
public class Client : ICallback
{
    public Client ()
    {
        var context = new InstanceContext(this);
        var proxy = new WcfDuplexProxy<IApplicationService>(context);

        (proxy as ICommunicationObject).Faulted += new EventHandler(proxy_Faulted);

        //First Ping will call the Pong callback. The exception is thrown
        proxy.ServiceChannel.Ping();
        //Second Ping call fails as the client is in Aborted state
        try
        {
            proxy.ServiceChannel.Ping();
        }
        catch (Exception)
        {
            //CommunicationException here 
            throw;
        }
    }
    void Pong()
    {
        throw new Exception();
    }

    //These event handlers never get called
    void proxy_Faulted(object sender, EventArgs e)
    {
        Console.WriteLine("client faulted proxy_Faulted");
    }
}

推荐答案

事实证明，您不能期望出现Faulted事件.因此，重新建立连接的最佳方法是在后续对Ping()的调用失败时进行连接:

As it turns out, you cannot expect the Faulted event to be raised. So, the best way to re-establish the connection is to do it when the subsequent call to Ping() fails:

我将在此处简化代码:

public class Client : ICallback
{
    public Client ()
    {
        var context = new InstanceContext(this);
        var proxy = new WcfDuplexProxy<IApplicationService>(context);

        (proxy.ServiceChannel as ICommunicationObject).Faulted +=new EventHandler(ServiceChannel_Faulted);

        //First Ping will call the Pong callback. The exception is thrown
        proxy.ServiceChannel.Ping();
        //Second Ping call fails as the client is in Aborted state
        try
        {
            proxy.ServiceChannel.Ping();
        }
        catch (Exception)
        {
            //Re-establish the connection and try again
            proxy.Abort();
            proxy = new WcfDuplexProxy<IApplicationService>(context);
            proxy.ServiceChannel.Ping();
        }
    }
    /*
    [...The rest of the code is the same...]
    //*/
}

很显然，在我的示例代码中，将再次引发Exception，但我希望这对使人们了解如何重新建立连接很有用.

Obviously, in my example code, the Exception will be thrown again but I hope this is useful to give people an idea of how to re-establish the connection.

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