Question

I am working on a system based on the publisher subscriber pattern. I have a WCF service that is running in a WPF application. There are numerous clients which connect to the service. The client side is also WPF. I am attaching code snippets of my system below:

Service:

[ServiceContract(Namespace = "http://AutoFXProfitsServer", SessionMode = SessionMode.Required, CallbackContract = typeof(ITradeMirrorClientContract))]
    public interface ITradeMirror
    {
        [OperationContract]
        string Subscribe(string userName, string password, int accountID);

        [OperationContract]
        bool Unsubscribe(string userName, string password, int accountID);

        [OperationContract]
        void PublishNewSignal(string signalInformation);
    }

    public interface ITradeMirrorClientContract
    {
        [OperationContract(IsOneWay = true)]
        void NewSignal(string signalInformation);
    }

    public class NewSignalEventArgs : EventArgs
    {
        public string SignalInformation;
    }
.
.
.
.
[ServiceBehavior(InstanceContextMode = InstanceContextMode.PerSession, AutomaticSessionShutdown = false)]
public class TradeMirrorService : DependencyObject, ITradeMirror
{
.
.
.
.

public string Subscribe(string userName, string password, int accountID)
    {
        try
        {
            if (AuthenticationSuccessful)
            {
                _callback = OperationContext.Current.GetCallbackChannel<ITradeMirrorClientContract>();
                _newSignalHandler = new NewSignalEventHandler(NewSignalHandler);
                NewSignalEvent -= _newSignalHandler;
                NewSignalEvent += _newSignalHandler;

                string suffixes = GetSuffixes();
                return suffixes;
            }
            else
            {
                return "FAILED";
            }
        }
        catch (Exception exception)
        {
            return "FAILED";
        }
    }

public bool Unsubscribe(string userName, string password, int accountID)
    {
        try
        {
            if (SearchHelper.UnAuthenticateUserCredentials(userName, password, accountID, _helper))
            {
                _callback = OperationContext.Current.GetCallbackChannel<ITradeMirrorClientContract>();
                _newSignalHandler = new NewSignalEventHandler(NewSignalHandler);
                NewSignalEvent -= _newSignalHandler;
                return true;
            }
            else
            {
                return false;
            }
        }
        catch (Exception exception)
        {
            return false;
        }
    }

public void PublishNewSignal(string signalInformation)
    {
        try
        {
            if (HeartBeatMessage())
            {

            }
            else
            {
                _systemOrderID++;

                signalInformation = TransformSignalInformation(signalInformation, _systemOrderID);
            }

            var e = new NewSignalEventArgs {SignalInformation = signalInformation};
            NewSignalEvent(this, e);
        }
        catch (Exception exception)
        {
        }
    }

And my app.config:

<?xml version="1.0"?>
<configuration>
  <system.serviceModel>
    <bindings>
      <netTcpBinding>
        <binding closeTimeout="23:59:59" openTimeout="23:59:59"     receiveTimeout="23:59:59" sendTimeout="23:59:59" transactionFlow="false" transferMode="Buffered" 
             transactionProtocol="OleTransactions" hostNameComparisonMode="StrongWildcard" listenBacklog="1000" maxBufferPoolSize="524288" maxBufferSize="65536" 
             maxConnections="1000" maxReceivedMessageSize="65536">
          <readerQuotas maxDepth="32" maxStringContentLength="8192" maxArrayLength="16384" maxBytesPerRead="4096" maxNameTableCharCount="16384"/>
          <reliableSession ordered="true" inactivityTimeout="23:59:59" enabled="false"/>
          <security mode="None"/>
        </binding>
      </netTcpBinding>
    </bindings>
    <!--For debugging purposes set the includeExceptionDetailInFaults attribute to true-->
    <behaviors>
      <serviceBehaviors>
        <behavior>
          <serviceMetadata httpGetEnabled="false" httpGetUrl="http://95.138.188.232/autofxprofits/service"/>
         <serviceDebug includeExceptionDetailInFaults="true"/>
    </behavior>
  </serviceBehaviors>
</behaviors>
  </system.serviceModel>
<startup><supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.0"/></startup>    </configuration>

The system works perfectly for long periods without any issues. What happens is that for some reason (about which i am not entirley sure) the service sometimes crashed with the exception:

CommunicationObjectAbortedException OR CommunicationObjectFaultedException

System.ServiceModel.CommunicationObjectAbortedException: The communication object,  System.ServiceModel.Channels.ServiceChannel, cannot be used for communication because it has  been Aborted.

Server stack trace: 
   at System.ServiceModel.Channels.CommunicationObject.ThrowIfDisposedOrNotOpen()
   at System.ServiceModel.Channels.ServiceChannel.Call(String action, Boolean oneway, ProxyOperationRuntime operation, Object[] ins, Object[] outs, TimeSpan timeout)
   at System.ServiceModel.Channels.ServiceChannelProxy.InvokeService(IMethodCallMessage methodCall, ProxyOperationRuntime operation)
   at System.ServiceModel.Channels.ServiceChannelProxy.Invoke(IMessage message)

Exception rethrown at [0]: 
   at System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg)
   at System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData, Int32 type)
   at AutoFXProfitsServer.ITradeMirrorClientContract.NewSignal(String signalInformation)
   at AutoFXProfitsServer.TradeMirrorService.NewSignalHandler(Object sender, NewSignalEventArgs e) in D:\Work\Trade Mirror - Kumar\AutoFXToolsTradeMirror\AutoFXProfitsServer\Service.cs:line 232
   at AutoFXProfitsServer.TradeMirrorService.PublishNewSignal(String signalInformation) in D:\Work\Trade Mirror - Kumar\AutoFXToolsTradeMirror\AutoFXProfitsServer\Service.cs:line 171

OR,

System.ServiceModel.CommunicationObjectFaultedException: The communication object,     System.ServiceModel.Channels.ServiceChannel, cannot be used for communication because it is in the Faulted state.

Server stack trace: 
   at System.ServiceModel.Channels.CommunicationObject.ThrowIfDisposedOrNotOpen()
   at System.ServiceModel.Channels.ServiceChannel.Call(String action, Boolean oneway, ProxyOperationRuntime operation, Object[] ins, Object[] outs, TimeSpan timeout)
   at System.ServiceModel.Channels.ServiceChannelProxy.InvokeService(IMethodCallMessage methodCall, ProxyOperationRuntime operation)
   at System.ServiceModel.Channels.ServiceChannelProxy.Invoke(IMessage message)

Exception rethrown at [0]: 
   at System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg)
   at System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData, Int32 type)
   at AutoFXProfitsServer.ITradeMirrorClientContract.NewSignal(String signalInformation)
   at AutoFXProfitsServer.TradeMirrorService.NewSignalHandler(Object sender, NewSignalEventArgs e) in D:\Work\Trade Mirror - Kumar\AutoFXToolsTradeMirror\AutoFXProfitsServer\Service.cs:line 235
   at AutoFXProfitsServer.TradeMirrorService.NewSignalEventHandler.Invoke(Object sender, NewSignalEventArgs e)
   at AutoFXProfitsServer.TradeMirrorService.PublishNewSignal(String signalInformation) in D:\Work\Trade Mirror - Kumar\AutoFXToolsTradeMirror\AutoFXProfitsServer\Service.cs:line 174

Just to reiterate, these exception occur in the PublishNewSignal method. One reason that i have made out from all the testing is that this happens when a client is abnormally closed. For example, the client process is closed from the task manager etc.

But this issue is a big pain and we can not move forawrd without fixing this stability issue. Does anyone have any idea as to why the communication object becomes faulted and the service crashes?

Hoping to get some positive feedback on this.

Thanks.
Umer

Answer 1

After some research, i have solved this issue myself. The problem was that whenever my client disconnected unexpectedly without properly unsubscribing, and the service was not properly taking care of the dropped client. So the communciation object became faulted. Lee’s answer to this question really helped me think in the right direction. Upon some more research then, i found this discussion pretty useful in solving the problem.