检测WCF双工合同中的客户端死亡

Question

我正在尝试构建一个SOA，客户端可以在服务器上执行长时间运行的查询，服务器使用回调进行响应。

我希望能够检测客户端是否断开连接（通过用户启动的关闭，未处理的异常或网络连接丢失），以便服务器可以选择取消昂贵的请求。

我正在测试各种失败案例，但我似乎无法启动某些事件处理程序。

经过测试的失败案例： 在请求之后杀死客户端进程。 使用像CurrPorts这样的程序来关闭TCP连接。

测试代码：

using System;
using System.ServiceModel;
using System.Threading;

namespace WCFICommunicationObjectExperiments
{
    class Program
    {
        static void Main(string[] args)
        {
            var binding = new NetTcpBinding(SecurityMode.None);

            var serviceHost = new ServiceHost(typeof (Server));
            serviceHost.AddServiceEndpoint(typeof (IServer), binding, "net.tcp://localhost:5000/Server");
            serviceHost.Open();
            Console.WriteLine("Host is running, press <ENTER> to exit.");
            Console.ReadLine();
        }

    }

    [ServiceContract(CallbackContract = typeof(IClient))]
    public interface IServer
    {
        [OperationContract]
        void StartProcessing(string Query);
    }

    public interface IClient
    {
        [OperationContract]
        void RecieveResults(string Results);
    }

    [ServiceBehavior(ConcurrencyMode = ConcurrencyMode.Multiple)]
    public class Server : IServer
    {

        public void StartProcessing(string Query)
        {
            Thread.Sleep(5000);

            //Callback Channel
            var clientCallback = OperationContext.Current.GetCallbackChannel<IClient>();
            var clientCallbackCommunicationObject = ((ICommunicationObject) clientCallback);
            EventHandler faultedHandlerCallback = (o, s) => Console.WriteLine("Client Channel Faulted.");
            EventHandler closedHandlerCallback = (o, s) => Console.WriteLine("Client Channel Closed.");
            clientCallbackCommunicationObject.Faulted += faultedHandlerCallback;
            clientCallbackCommunicationObject.Closed += closedHandlerCallback;

            //Request Channel
            var requestChannel = OperationContext.Current.Channel;
            EventHandler faultedHandlerRequest = (o, s) => Console.WriteLine("Request Channel Faulted.");
            EventHandler closedHandlerRequest = (o, s) => Console.WriteLine("Request Channel Closed.");
            requestChannel.Faulted += faultedHandlerRequest;
            requestChannel.Closed += closedHandlerRequest;

            try
            {
                clientCallback.RecieveResults("42.");
            }
            catch (CommunicationObjectAbortedException ex)
            {
                Console.WriteLine("Client Aborted the connection");
            }
            catch (CommunicationObjectFaultedException ex)
            {
                Console.WriteLine("Client Died.");
            }
            clientCallbackCommunicationObject.Faulted -= faultedHandlerCallback;
            clientCallbackCommunicationObject.Faulted -= closedHandlerCallback;
            requestChannel.Faulted -= faultedHandlerRequest;
            requestChannel.Closed -= closedHandlerRequest;
        }
    }

    public class ClientToTestStates : IClient
    {
        private IServer m_Server;

        private readonly ManualResetEvent m_ReceivedEvent = new ManualResetEvent(false);
        private readonly ManualResetEvent m_ChannelFaulted = new ManualResetEvent(false);
        private readonly ManualResetEvent m_ChannelClosed = new ManualResetEvent(false);

        public ClientToTestStates()
        {
            var binding = new NetTcpBinding(SecurityMode.None);
            var channelFactory = new DuplexChannelFactory<IServer>(this, binding, new EndpointAddress("net.tcp://localhost:5000/Server"));
            m_Server = channelFactory.CreateChannel();
            ((ICommunicationObject)m_Server).Open();
            ((ICommunicationObject)m_Server).Faulted += ChannelFaulted;
            ((ICommunicationObject)m_Server).Closed += ChannelClosed;

            m_Server.StartProcessing("What is the answer?");

            WaitHandle.WaitAny(new WaitHandle[] {m_ReceivedEvent, m_ChannelFaulted, m_ChannelClosed});
        }

        void ChannelFaulted(object sender, EventArgs e)
        {
            m_ChannelFaulted.Set();
            Console.WriteLine("Channel Faulted.");
        }

        void ChannelClosed(object sender, EventArgs e)
        {
            m_ChannelClosed.Set();
            Console.WriteLine("Channel Closed.");
        }


        public void RecieveResults(string results)
        {
            m_ReceivedEvent.Set();
            Console.WriteLine("Recieved Results {0}", results);
        }
    }
}

处理这类失败案件的最佳做法是什么？我希望能够使用底层的tcp连接来检测其中的一些内容。

Answer 1

在他的“编程WCF服务”一书中，Juval Lowy解释说WCF没有提供管理服务回调的机制，这必须由服务和客户端明确管理。如果服务尝试调用已在客户端关闭的回调，则将在服务通道上抛出ObjectDisposedException。

他建议在服务合同中添加Connect和Disconnect方法 - 因为在调用这些服务时必须向服务提供回调，该服务可以管理客户端回调。然后由客户端确保在不再希望从服务接收回调时调用Disconnect，并且服务必须在调用客户端的回调时处理任何异常。

Answer 2

尝试此操作以检查回调对象是否仍然有效：

(((ICommunicationObject)myCallbackObject).State == CommunicationState.Opened)

在这种情况下，

myCallbackObject是您可以通过其执行回调的对象，即实现回调合同的对象