WCF Callback Timer

Question

I have a WCF service hosted in a Windows service. This uses the Publish Subscribe pattern to post events to multiple subscribers. However, I am finding that after a length of inactivity, the connection fails and I get reliable session was faulted errors. I have tried to fix this by changing the inactivity timeout and receive timout settings but it makes no difference. It's driving me mad to be honest.

A solution I have seen mentioned is to "ping" all the subscribers every so often. (for example half the length of the timeout).

What would be the best way of setting up a "ping" like this? i.e. how do I add a timer to the service and how to get that timer to call a ping function?

EDIT:

I am not totally happy with the ping solution and would like to investigate further why my reliable session keeps timing out. Below is the binding configuration for this service

Server app.config

<binding name="WSDualHttpBinding_IError" receiveTimeout="24.20:31:23.6470000">
    <reliableSession inactivityTimeout="24.20:31:23.6470000" />
</binding>

Client app.config

<binding name="WSDualHttpBinding_IError" closeTimeout="00:01:00"
    openTimeout="00:01:00" receiveTimeout="24.20:31:23.6470000"
    sendTimeout="00:01:00" bypassProxyOnLocal="false" transactionFlow="false"
    hostNameComparisonMode="StrongWildcard" maxBufferPoolSize="524288"
    maxReceivedMessageSize="65536" messageEncoding="Text" textEncoding="utf-8"
    useDefaultWebProxy="true">
    <readerQuotas maxDepth="32" maxStringContentLength="8192" maxArrayLength="16384"
        maxBytesPerRead="4096" maxNameTableCharCount="16384" />
    <reliableSession ordered="true" inactivityTimeout="24.20:31:23.6470000" />
    <security mode="Message">
        <message clientCredentialType="Windows" negotiateServiceCredential="true"
            algorithmSuite="Default" />
    </security>
</binding>

I tried "infinite" rather then this value but it didn't like it. Said the value was invalid even though several pages from a Google search suggested doing this. I can only assume this was valid in an earlier version of WCF/.NET

EDIT2:

Here is the exception log. It definitely does seem to be a random amount of time.

************** Exception Text **************
System.TimeoutException: The operation did not complete within the allotted timeout of 00:00:59.4979498. The time allotted to this operation may have been a portion of a longer timeout.

Server stack trace: 
   at System.ServiceModel.Channels.InterruptibleWaitObject.Wait(TimeSpan timeout, Boolean throwTimeoutException)
   at System.ServiceModel.Channels.ReliableInputConnection.Close(TimeSpan timeout)
   at System.ServiceModel.Channels.ReliableDuplexSessionChannel.OnClose(TimeSpan timeout)
   at System.ServiceModel.Channels.ClientReliableDuplexSessionChannel.OnClose(TimeSpan timeout)
   at System.ServiceModel.Channels.CommunicationObject.Close(TimeSpan timeout)
   at System.ServiceModel.Channels.ServiceChannel.OnClose(TimeSpan timeout)
   at System.ServiceModel.Channels.CommunicationObject.Close(TimeSpan timeout)

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 System.ServiceModel.ICommunicationObject.Close(TimeSpan timeout)
   at System.ServiceModel.ClientBase`1.System.ServiceModel.ICommunicationObject.Close(TimeSpan timeout)
   at System.ServiceModel.ClientBase`1.Close()
   at MyApp.Form1.buttonError_Click(Object sender, EventArgs e)
   at System.Windows.Forms.Control.OnClick(EventArgs e)
   at System.Windows.Forms.Button.OnClick(EventArgs e)
   at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
   at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at System.Windows.Forms.ButtonBase.WndProc(Message& m)
   at System.Windows.Forms.Button.WndProc(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

Answer 1

For implementing the pinging of your clients you may want to follow this list of steps:

1. Extend your callback contract with a Ping method (you should have already a callback contract because you wrote you use the publish subscribe pattern, havn't you?):

   [OperationContract]
   void Ping();
   

2. In the operation the clients call first after connecting, store a reference to the clients operation context in a collection:

   List<OperationContext> _clientCtxList = new List<OperationContext>();
   
   void IMyService.InitSession() {
       _clientCtxList.Add(OperationContext.Current);
   }
   

3. Define a function, called by your timer to ping all the clients:

   void tmrPing (object state) {
       foreach (var ctx in _clientCtxList)
       {
           // todo: catch exceptions and remove client context 
           //       from list in case of failure
           ctx.GetCallbackChannel<IMyCallbackContract>().Ping();
       }
   
       // restart timer
       _timer.Change(10000, Timeout.Infinite);
   }
   

4. Define and start a timer when your service starts up (i'm not aware of IIS hosting, so you have to find the right location for this yourself):

   System.Threading.Timer _timer;
   
   void Startup() {
       // call my function in 10 seconds
       _timer = new System.Threading.Timer(
                       tmrPing, null, 10000, Timeout.Infinte);
   }
   

Remarks:

• This is notepad code - it might contain syntactic errors and might not compile.
• Exception handling is not included
• locking of the _clineCtxList is not included but highly recommended