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POcurrent OperationContext is null in WCF Windows Service
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2013-03-04T15:42:50.137
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I am trying to set up a Publish/Subscribe system using WCF and where the WCF server is in a Windows service. The binding is net.TCP. The service is providing a "Subscribe" method to the client so the client can register a callback handler to an event that will be raised from a DLL linked to the server. In the Subscribe method I attempt to get the callback channel using the OperationContext.Current.GetCallbackChannel method. When I attempt this the OperationContext.Current property returns NULL. Can anyone tell me under what circumstances this property would return null?? Have I missed setting something up? I will include the service code and the interface code below. I am using c# in Visual Studio 2012 and targeting framework 4.5. Service: <pre><code>namespace WService { [ServiceBehavior(InstanceContextMode = InstanceContextMode.PerSession)] public class WcfPublisherService : IWcfPublisherContract { IOALogic logic = new OAControlExample(); IWcfSubscriberContract _callback = null; public void Subscribe() { _callback = OperationContext.Current.GetCallbackChannel<IWcfSubscriberContract>(); logic.BarriersChanged += logic_BarriersChanged; } public void UnSubscribe() { logic.BarriersChanged -= logic_BarriersChanged; } void logic_BarriersChanged(object sender, BarriersChangedEventArgs e) { _callback.BarriersChanged(e.BarrierLines); } } } </code></pre> Interface: <pre><code>namespace WService { [ServiceContract(SessionMode = SessionMode.Required, CallbackContract = typeof(IWcfSubscriberContract))] public interface IWcfPublisherContract { [OperationContract(IsOneWay=false, IsInitiating=true)] void Subscribe(); [OperationContract(IsOneWay = false, IsTerminating=true)] void UnSubscribe(); } public interface IWcfSubscriberContract { [OperationContract(IsOneWay = true)] void BarriersChanged(BarrierLines barrierLines); } } </code></pre> Client: <pre><code>namespace TestClient { public partial class Form1 : Form { WcfPublisherService myService = new WcfPublisherService(); ServiceCallback serviceCallback = new ServiceCallback(); public Form1() { InitializeComponent(); serviceCallback.NewMessage += serviceCallback_NewMessage; } private delegate void serviceCallback_NewMessageDelegate(object sender, NewMessageEventArgs e); void serviceCallback_NewMessage(object sender, NewMessageEventArgs e) { if (textBox1.InvokeRequired) { textBox1.Invoke(new serviceCallback_NewMessageDelegate(serviceCallback_NewMessage), new object[] {sender, e}); } else { if (textBox1.Text.Trim().Length > 1) { textBox1.Text += Environment.NewLine; } textBox1.Text += e.Msg; } } private void button1_Click(object sender, EventArgs e) { myService.Subscribe(); } private void button2_Click(object sender, EventArgs e) { myService.UnSubscribe(); } } [CallbackBehaviorAttribute(UseSynchronizationContext = false)] class ServiceCallback : IWcfSubscriberContract { public delegate void NewMessageEventHandler(object sender, NewMessageEventArgs e); public event NewMessageEventHandler NewMessage; protected virtual void OnNewMessage(string msg) { if (NewMessage != null) { NewMessage(this, new NewMessageEventArgs(msg)); } } public void BarriersChanged(OA.BarrierLines barrierLines) { OnNewMessage("new barrier lines"); } } public class NewMessageEventArgs : EventArgs { public NewMessageEventArgs(string msg) { this.Msg = msg; } public string Msg { get; set; } } } </code></pre> ********* New Edit *************** Thanks to SalientBrain's suggestions, I have made considerable changes to my project because I realized the service had to be long running and continually running even if no clients are connected so I changed it to a singleton. Even so, my original problem still persists. SalientBrain has asked to see my config file so I will include it below along with all the other pertinent files. I've stripped it out to conserve space, but I don't think I removed anything important. The error occurs in Subscribe method of the PulisherService class. I hope it is something stupid I did in the config file. Well, here it is: Config: <pre><code> <configuration> <startup> <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" /> </startup> <system.serviceModel> <behaviors> <serviceBehaviors> <behavior name="WService.WCFPublisherServiceBehavior"> <serviceMetadata httpGetEnabled="false" httpsGetEnabled="false" /> <serviceDebug includeExceptionDetailInFaults="false" /> </behavior> </serviceBehaviors> </behaviors> <services> <service behaviorConfiguration="WService.WCFPublisherServiceBehavior" name="WService.WcfPublisherService"> <endpoint address="" binding="netTcpBinding" bindingConfiguration="" name="NetTcpBindingEndpoint" contract="WService.IWcfPublisherContract"> <identity> <dns value="localhost" /> </identity> </endpoint> <endpoint address="mex" binding="mexTcpBinding" bindingConfiguration="" name="MexTcpBindingEndpoint" contract="IMetadataExchange" /> <host> <baseAddresses> <add baseAddress="net.tcp://localhost:8523/Publisher" /> </baseAddresses> </host> </service> </services> </system.serviceModel> </configuration> </code></pre> WcfContracts: <pre><code> namespace WService { [ServiceContract(SessionMode = SessionMode.Allowed, CallbackContract = typeof(IWcfSubscriberContract))] public interface IWcfPublisherContract { [OperationContract(IsOneWay=false)] void Subscribe(string key); [OperationContract(IsOneWay = false)] void UnSubscribe(string key); } public interface IWcfSubscriberContract { [OperationContract(IsOneWay = true)] void BarriersChanged(BarrierLines barrierLines); } } </code></pre> WcfService: <pre><code> namespace WService { [ServiceBehavior(InstanceContextMode = InstanceContextMode.Single, ConcurrencyMode = ConcurrencyMode.Multiple)] public class WcfPublisherService : IWcfPublisherContract { private static WcfPublisherService _instance = null; private IOALogic _logic = null; private Dictionary<string, IWcfSubscriberContract> _callbacks = new Dictionary<string, IWcfSubscriberContract>(); private ReaderWriterLock _callbacksLock = new ReaderWriterLock(); private WcfPublisherService() { } public static WcfPublisherService TheInstance() { if (_instance == null) { _instance = new WcfPublisherService(); } return _instance; } public void StopWcf() { _logic.StopRequest(); } public void StartWcf(IOALogic logic) { _logic = logic; _logic.BarriersChanged += logic_BarriersChanged; ThreadPool.QueueUserWorkItem(new WaitCallback(StartWork), null); } public void StartWork(object state) { _logic.Run(); } public void Subscribe(string key) { OperationContext context = OperationContext.Current; // The above line returns null *********************************************** _callbacksLock.AcquireWriterLock(2000); if (_callbacksLock.IsWriterLockHeld) { _callbacks.Add(key, context.GetCallbackChannel<IWcfSubscriberContract>()); // The above line throws a null execption because context is null ******** _callbacksLock.ReleaseWriterLock(); } } public void UnSubscribe(string key) { _callbacksLock.AcquireWriterLock(2000); if (_callbacksLock.IsWriterLockHeld) { _callbacks.Remove(key); _callbacksLock.ReleaseWriterLock(); } } void logic_BarriersChanged(object sender, BarriersChangedEventArgs e) { _callbacksLock.AcquireReaderLock(1000); if (_callbacksLock.IsReaderLockHeld) { try { foreach (IWcfSubscriberContract callback in _callbacks.Values) { callback.BarriersChanged(e.BarrierLines); } } finally { _callbacksLock.ReleaseReaderLock(); } } } } } </code></pre> WindowsService: <pre><code> namespace WService { public partial class WService : ServiceBase { internal static ServiceHost _serviceHost = null; internal static IOALogic _logic = new OAControlExample(); public WService() { InitializeComponent(); } protected override void OnStart(string[] args) { if (_serviceHost != null) { _serviceHost.Close(); } _serviceHost = new ServiceHost(WcfPublisherService.TheInstance()); WcfPublisherService.TheInstance().StartWcf(_logic); _serviceHost.Open(); } protected override void OnStop() { if (WcfPublisherService.TheInstance() != null) { WcfPublisherService.TheInstance().StopWcf(); } if (_serviceHost != null) { _serviceHost.Close(); _serviceHost = null; } } } } </code></pre> TestForm: <pre><code> namespace TestClient { public partial class Form1 : Form { ServiceCallback serviceCallback = new ServiceCallback(); public Form1() { InitializeComponent(); serviceCallback.NewMessage += serviceCallback_NewMessage; } private delegate void serviceCallback_NewMessageDelegate(object sender, NewMessageEventArgs e); void serviceCallback_NewMessage(object sender, NewMessageEventArgs e) { if (textBox1.InvokeRequired) { textBox1.Invoke(new serviceCallback_NewMessageDelegate(serviceCallback_NewMessage), new object[] {sender, e}); } else { if (textBox1.Text.Trim().Length > 1) { textBox1.Text += Environment.NewLine; } textBox1.Text += e.Msg; } } private void button1_Click(object sender, EventArgs e) { serviceCallback.Subscribe(); } private void button2_Click(object sender, EventArgs e) { serviceCallback.Unsubscribe(); } } } </code></pre> TestCallbackClass: <pre><code> namespace TestClient { [CallbackBehaviorAttribute(UseSynchronizationContext = true)] class ServiceCallback : IWcfSubscriberContract { WcfPublisherService myService = WcfPublisherService.TheInstance(); string callbackKey = Guid.NewGuid().ToString(); public delegate void NewMessageEventHandler(object sender, NewMessageEventArgs e); public event NewMessageEventHandler NewMessage; protected virtual void OnNewMessage(string msg) { if (NewMessage != null) { NewMessage(this, new NewMessageEventArgs(msg)); } } public void Subscribe() { try { myService.Subscribe(callbackKey); } catch (Exception ex) { OnNewMessage("exception: " + ex.Message); } } public void Unsubscribe() { try { myService.UnSubscribe(callbackKey); } catch (Exception ex) { OnNewMessage("exception: " + ex.Message); } } public void BarriersChanged(OAInterface.BarrierLines barrierLines) { OnNewMessage("new barrier lines"); } } public class NewMessageEventArgs : EventArgs { public NewMessageEventArgs(string msg) { this.Msg = msg; } public string Msg { get; set; } } } </code></pre>
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<c#><wcf><callback><operationcontext>
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current OperationContext is null in WCF Windows Service
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