Duplex WCF + Static Collection of COM objects - wcf

I am trying to build a WCF service that exposes the functionality of a particular COM object that I do not have the original source for. I am using duplex binding so that each client has their own instance as there are events tied to each particular instance which are delivered through a callback (IAgent). It appears there is a deadlock or something because after the first action, my service blocks at my second action's lock. I have tried implementing these custom STA attribute and operation behaviors (http://devlicio.us/blogs/scott_seely/archive/2009/07/17/calling-an-sta-com-object-from-a-wcf-operation.aspx) but my OperationContext.Current is always null. Any advice is much appreciated.
Service
Collection:
private static Dictionary<IAgent, COMAgent> agents = new Dictionary<IAgent, COMAgent>();
First action:
public void Login(LoginRequest request)
{
IAgent agent = OperationContext.Current.GetCallbackChannel<IAgent>();
lock (agents)
{
if (agents.ContainsKey(agent))
throw new FaultException("You are already logged in.");
else
{
ICOMClass startup = new ICOMClass();
string server = ConfigurationManager.AppSettings["Server"];
int port = Convert.ToInt32(ConfigurationManager.AppSettings["Port"]);
bool success = startup.Logon(server, port, request.Username, request.Password);
if (!success)
throw new FaultException<COMFault>(new COMFault { ErrorText = "Could not log in." });
COMAgent comAgent = new COMAgent { Connection = startup };
comAgent.SomeEvent += new EventHandler<COMEventArgs>(comAgent_COMEvent);
agents.Add(agent, comAgent);
}
}
}
Second Action:
public void Logoff()
{
IAgent agent = OperationContext.Current.GetCallbackChannel<IAgent>();
lock (agents)
{
COMAgent comAgent = agents[agent];
try
{
bool success = comAgent.Connection.Logoff();
if (!success)
throw new FaultException<COMFault>(new COMFault { ErrorText = "Could not log off." });
agents.Remove(agent);
}
catch (Exception exc)
{
throw new FaultException(exc.Message);
}
}
}

Take a look at this very similar post: http://www.netfxharmonics.com/2009/07/Accessing-WPF-Generated-Images-Via-WCF
You have to use an OperationContextScope to have access to the current OperationContext from the newly generated thread:
System.Threading.Thread thread = new System.Threading.Thread(new System.Threading.ThreadStart(delegate
{
using (System.ServiceModel.OperationContextScope scope = new System.ServiceModel.OperationContextScope(context))
{
result = InnerOperationInvoker.Invoke(instance, inputs, out staOutputs);
}
}));

Related

Accessing HttpContext.Session from static method

I am getting following error when accessing HttpContext.Session from static method placed in separate task:
Session has not been configured for this application or request.
I used this article to implement access to HttpContext outside the controller
From controller I invoke this static method that used to retrieve image data:
public static void CreateDummyGallery(Gallery gallery)
{
Logger.LogDebug(LogModule.Dummy, $"Starting gallery creation.");
Task.Factory.StartNew(() =>
{
try
{
List<DummyPicture> pictures;
using (var context = new MyzeumContext())
{
int top = 10;
pictures = context.DummyPictures.FromSql($"SELECT * FROM dummypictures ORDER BY RAND() LIMIT {top}").ToList();
}
Logger.LogDebug(LogModule.Dummy, $"Starting retrieving images.");
Parallel.ForEach(pictures, picture => {
using (WebClient client = new WebClient())
{
}
});
Logger.LogDebug(LogModule.Dummy, $"Done retrieving images.");
}
catch(Exception e)
{
Logger.LogError(LogModule.Server, e.Message, e);
}
});
}
The problem occurs in Logger.LogDebug() because this is where I access HttpContext:
public void LogDebug(LogModule module, string message, Exception stackTrace = null)
{
Log record = new Log();
record.Module = module;
record.ThreadId = Environment.CurrentManagedThreadId;
record.SessionId = HttpContextHelper.Current?.Session?.Id;
record.Message = message;
record.Logged = DateTime.UtcNow;
if(stackTrace != null)
{
record.Message += $" :{stackTrace.StackTrace}";
}
queue.Enqueue(record);
}
The problem 99% occurs in the first call inside task:
Logger.LogDebug(LogModule.Dummy, $"Starting retrieving images.");
BUT, right after application starts this whole task block works fine and does not throw any exception. Problem starts after following requests.

Callback is not invoked on the client

I have a self-hosted service that processes long running jobs submitted by a client over net.tcp binding. While the job is running (within a Task), the service will push status updates to the client via a one-way callback. This works fine, however when I attempt to invoke another callback to notify the client the job has completed (also one-way), the callback is never received/invoked on the client. I do not receive any exceptions in this process.
My Callback contract looks like this:
public interface IWorkflowCallback
{
[OperationContract(IsOneWay = true)]
[ApplySharedTypeResolverAttribute]
void UpdateStatus(WorkflowJobStatusUpdate StatusUpdate);
[OperationContract(IsOneWay = true)]
[ApplySharedTypeResolverAttribute]
void NotifyJobCompleted(WorkflowJobCompletionNotice Notice);
}
Code from the service that invokes the callbacks: (not in the service implementation itself, but called directly from the service implementation)
public WorkflowJobTicket AddToQueue(WorkflowJobRequest Request)
{
if (this.workflowEngine.WorkerPoolFull)
{
throw new QueueFullException();
}
var user = ServiceUserManager.CurrentUser;
var context = OperationContext.Current;
var workerId = this.workflowEngine.RunWorkflowJob(user, Request, new Object[]{new DialogServiceExtension(context)});
var workerjob = this.workflowEngine.FindJob(workerId);
var ticket = new WorkflowJobTicket()
{
JobRequestId = Request.JobRequestId,
JobTicketId = workerId
};
user.RegisterTicket<IWorkflowCallback>(ticket);
workerjob.WorkflowJobCompleted += this.NotifyJobComplete;
workerjob.Status.PropertyChanged += this.NotifyJobStatusUpdate;
this.notifyQueueChanged();
return ticket;
}
protected void NotifyJobStatusUpdate(object sender, PropertyChangedEventArgs e)
{
var user = ServiceUserManager.GetInstance().GetUserWithTicket((sender as WorkflowJobStatus).JobId);
Action<IWorkflowCallback> action = (callback) =>
{
ICommunicationObject communicationCallback = (ICommunicationObject)callback;
if (communicationCallback.State == CommunicationState.Opened)
{
try
{
var updates = (sender as WorkflowJobStatus).GetUpdates();
callback.UpdateStatus(updates);
}
catch (Exception)
{
communicationCallback.Abort();
}
}
};
user.Invoke<IWorkflowCallback>(action);
}
protected void NotifyJobComplete(WorkflowJob job, EventArgs e)
{
var user = ServiceUserManager.GetInstance().GetUserWithTicket(job.JobId);
Action<IWorkflowCallback> action = (callback) =>
{
ICommunicationObject communicationCallback = (ICommunicationObject)callback;
if (communicationCallback.State == CommunicationState.Opened)
{
try
{
var notice = new WorkflowJobCompletionNotice()
{
Ticket = user.GetTicket(job.JobId),
RuntimeOptions = job.RuntimeOptions
};
callback.NotifyJobCompleted(notice);
}
catch (Exception)
{
communicationCallback.Abort();
}
}
};
user.Invoke<IWorkflowCallback>(action);
}
In the user.Invoke<IWorkflowCallback>(action) method, the Action is passed an instance of the callback channel via OperationContext.GetCallbackChannel<IWorkflowCallback>().
I can see that the task that invokes the job completion notice is executed by the the service, yet I do not receive the call on the client end. Further, the update callback is able to be invoked successfully after a completion notice is sent, so it does not appear that the channel is quietly faulting.
Any idea why, out of these two callbacks that are implemented almost identically, only one works?
Thanks in advance for any insight.

WCF ChannelFactory and channels - caching, reusing, closing and recovery

I have the following planned architecture for my WCF client library:
using ChannelFactory instead of svcutil generated proxies because
I need more control and also I want to keep the client in a separate
assembly and avoid regenerating when my WCF service changes
need to apply a behavior with a message inspector to my WCF
endpoint, so each channel is able to send its
own authentication token
my client library will be used from a MVC front-end, so I'll have to think about possible threading issues
I'm using .NET 4.5 (maybe it has some helpers or new approaches to implement WCF clients in some better way?)
I have read many articles about various separate bits but I'm still confused about how to put it all together the right way. I have the following questions:
as I understand, it is recommended to cache ChannelFactory in a static variable and then get channels out of it, right?
is endpoint behavior specific to the entire ChannelFactory or I can apply my authentication behavior for each channel separately? If the behavior is specific to the entire factory, this means that I cannot keep any state information in my endpoint behavior objects because the same auth token will get reused for every channel, but obviously I want each channel to have its own auth token for the current user. This means, that I'll have to calculate the token inside of my endpoint behavior (I can keep it in HttpContext, and my message inspector behavior will just add it to the outgoing messages).
my client class is disposable (implements IDispose). How do I dispose the channel correctly, knowing that it might be in any possible state (not opened, opened, failed ...)? Do I just dispose it? Do I abort it and then dispose? Do I close it (but it might be not opened yet at all) and then dispose?
what do I do if I get some fault when working with the channel? Is only the channel broken or entire ChannelFactory is broken?
I guess, a line of code speaks more than a thousand words, so here is my idea in code form. I have marked all my questions above with "???" in the code.
public class MyServiceClient : IDisposable
{
// channel factory cache
private static ChannelFactory<IMyService> _factory;
private static object _lock = new object();
private IMyService _client = null;
private bool _isDisposed = false;
/// <summary>
/// Creates a channel for the service
/// </summary>
public MyServiceClient()
{
lock (_lock)
{
if (_factory == null)
{
// ... set up custom bindings here and get some config values
var endpoint = new EndpointAddress(myServiceUrl);
_factory = new ChannelFactory<IMyService>(binding, endpoint);
// ???? do I add my auth behavior for entire ChannelFactory
// or I can apply it for individual channels when I create them?
}
}
_client = _factory.CreateChannel();
}
public string MyMethod()
{
RequireClientInWorkingState();
try
{
return _client.MyMethod();
}
catch
{
RecoverFromChannelFailure();
throw;
}
}
private void RequireClientInWorkingState()
{
if (_isDisposed)
throw new InvalidOperationException("This client was disposed. Create a new one.");
// ??? is it enough to check for CommunicationState.Opened && Created?
if (state != CommunicationState.Created && state != CommunicationState.Opened)
throw new InvalidOperationException("The client channel is not ready to work. Create a new one.");
}
private void RecoverFromChannelFailure()
{
// ??? is it the best way to check if there was a problem with the channel?
if (((IChannel)_client).State != CommunicationState.Opened)
{
// ??? is it safe to call Abort? won't it throw?
((IChannel)_client).Abort();
}
// ??? and what about ChannelFactory?
// will it still be able to create channels or it also might be broken and must be thrown away?
// In that case, how do I clean up ChannelFactory correctly before creating a new one?
}
#region IDisposable
public void Dispose()
{
// ??? is it how to free the channel correctly?
// I've heard, broken channels might throw when closing
// ??? what if it is not opened yet?
// ??? what if it is in fault state?
try
{
((IChannel)_client).Close();
}
catch
{
((IChannel)_client).Abort();
}
((IDisposable)_client).Dispose();
_client = null;
_isDisposed = true;
}
#endregion
}
I guess better late then never... and looks like author has it working, this might help future WCF users.
1) ChannelFactory arranges the channel which includes all behaviors for the channel. Creating the channel via CreateChannel method "activates" the channel. Channel factories can be cached.
2) You shape the channel factory with bindings and behaviors. This shape is shared with everyone who creates this channel. As you noted in your comment you can attach message inspectors but more common case is to use Header to send custom state information to the service. You can attach headers via OperationContext.Current
using (var op = new OperationContextScope((IContextChannel)proxy))
{
var header = new MessageHeader<string>("Some State");
var hout = header.GetUntypedHeader("message", "urn:someNamespace");
OperationContext.Current.OutgoingMessageHeaders.Add(hout);
}
3) This is my general way of disposing the client channel and factory (this method is part of my ProxyBase class)
public virtual void Dispose()
{
CloseChannel();
CloseFactory();
}
protected void CloseChannel()
{
if (((IChannel)_client).State == CommunicationState.Opened)
{
try
{
((IChannel)_client).Close();
}
catch (TimeoutException /* timeout */)
{
// Handle the timeout exception
((IChannel)innerChannel).Abort();
}
catch (CommunicationException /* communicationException */)
{
// Handle the communication exception
((IChannel)_client).Abort();
}
}
}
protected void CloseFactory()
{
if (Factory.State == CommunicationState.Opened)
{
try
{
Factory.Close();
}
catch (TimeoutException /* timeout */)
{
// Handle the timeout exception
Factory.Abort();
}
catch (CommunicationException /* communicationException */)
{
// Handle the communication exception
Factory.Abort();
}
}
}
4) WCF will fault the channel not the factory. You can implement a re-connect logic but that would require that you create and derive your clients from some custom ProxyBase e.g.
protected I Channel
{
get
{
lock (_channelLock)
{
if (! object.Equals(innerChannel, default(I)))
{
ICommunicationObject channelObject = innerChannel as ICommunicationObject;
if ((channelObject.State == CommunicationState.Faulted) || (channelObject.State == CommunicationState.Closed))
{
// Channel is faulted or closing for some reason, attempt to recreate channel
innerChannel = default(I);
}
}
if (object.Equals(innerChannel, default(I)))
{
Debug.Assert(Factory != null);
innerChannel = Factory.CreateChannel();
((ICommunicationObject)innerChannel).Faulted += new EventHandler(Channel_Faulted);
}
}
return innerChannel;
}
}
5) Do not re-use channels. Open, do something, close is the normal usage pattern.
6) Create common proxy base class and derive all your clients from it. This can be helpful, like re-connecting, using pre-invoke/post invoke logic, consuming events from factory (e.g. Faulted, Opening)
7) Create your own CustomChannelFactory this gives you further control how factory behaves e.g. Set default timeouts, enforce various binding settings (MaxMessageSizes) etc.
public static void SetTimeouts(Binding binding, TimeSpan? timeout = null, TimeSpan? debugTimeout = null)
{
if (timeout == null)
{
timeout = new TimeSpan(0, 0, 1, 0);
}
if (debugTimeout == null)
{
debugTimeout = new TimeSpan(0, 0, 10, 0);
}
if (Debugger.IsAttached)
{
binding.ReceiveTimeout = debugTimeout.Value;
binding.SendTimeout = debugTimeout.Value;
}
else
{
binding.ReceiveTimeout = timeout.Value;
binding.SendTimeout = timeout.Value;
}
}

WCF: How to handle errors when calling another WCF service?

I have a project where I should write WCF service that calls another WCF service. It looks as following:
[ServiceContract]
public interface IAsurService
{
[OperationContract(ReplyAction = AsurService.ReplyAction_GetCatalogList)]
Message GetCatalogList();
public Message GetCatalogList()
{
// The external client service
GetNsiClient client = new GetNsiClient();
authContext auth = new authContext
{
company = "asur_nsi",
password = "lapshovva",
user = "dogm_LapshovVA"
};
catalogs catalogs = client.getCatalogList(auth);
How can I handle errors in this case? Can I use standard fault contract approach like this:
[DataContract]
public class AsurDataFaultException
{
private string reason;
[DataMember]
public string Reason
{
get { return reason; }
set { reason = value; }
}
}
public Message GetCatalogList()
{
// The external client service
GetNsiClient client = new GetNsiClient();
authContext auth = new authContext
{
company = "asur_nsi",
password = "lapshovva",
user = "dogm_LapshovVA"
};
catalogs catalogs = null;
try
{
catalogs = client.getCatalogList(auth);
}
catch (Exception exception)
{
AsurDataFaultException fault = new AsurDataFaultException();
fault.Reason = "The error: " + exception.Message.ToString();
throw new FaultException<AsurDataFaultException>(fault);
}
Or something else?
Thank you in advance.
Goran
If the remote WCF service's failure causes a failure of your code, then obviously you should throw a fault but that fault should not expose the inner details of the remote WCF service or its exception, like so:
catch (Exception exception)
{
// Indicate all that you may expose -- that the data is unavailable.
DataUnavailableFault fault = new DataUnavailableFault();
throw new FaultException<DataUnavailableFault>(fault);
}
You may of course also use a retry mechanism, but obviously if what you end up with is a failure in the remote service, you should indicate that to your caller by throwing an appropriate fault.

Maximum threads issue

To begin with, I checked the discussions regarding this issue and couldn't find an answer to my problem and that's why I'm opening this question.
I've set up a web service using restlet 2.0.15.The implementation is only for the server. The connections to the server are made through a webpage, and therefore I didn't use ClientResource.
Most of the answers to the exhaustion of the thread pool problem suggested the inclusion of
#exhaust + #release
The process of web service can be described as a single function.Receive GET requests from the webpage, query the database, frame the results in XML and return the final representation. I used a Filter to override the beforeHandle and afterHandle.
The code for component creation code:
Component component = new Component();
component.getServers().add(Protocol.HTTP, 8188);
component.getContext().getParameters().add("maxThreads", "512");
component.getContext().getParameters().add("minThreads", "100");
component.getContext().getParameters().add("lowThreads", "145");
component.getContext().getParameters().add("maxQueued", "100");
component.getContext().getParameters().add("maxTotalConnections", "100");
component.getContext().getParameters().add("maxIoIdleTimeMs", "100");
component.getDefaultHost().attach("/orcamento2013", new ServerApp());
component.start();
The parameters are the result of a discussion present in this forum and modification by my part in an attempt to maximize efficiency.
Coming to the Application, the code is as follows:
#Override
public synchronized Restlet createInboundRoot() {
// Create a router Restlet that routes each call to a
// new instance of HelloWorldResource.
Router router = new Router(getContext());
// Defines only one route
router.attach("/{taxes}", ServerImpl.class);
//router.attach("/acores/{taxes}", ServerImplAcores.class);
System.out.println(router.getRoutes().size());
OriginFilter originFilter = new OriginFilter(getContext());
originFilter.setNext(router);
return originFilter;
}
I used an example Filter found in a discussion here, too. The implementation is as follows:
public OriginFilter(Context context) {
super(context);
}
#Override
protected int beforeHandle(Request request, Response response) {
if (Method.OPTIONS.equals(request.getMethod())) {
Form requestHeaders = (Form) request.getAttributes().get("org.restlet.http.headers");
String origin = requestHeaders.getFirstValue("Origin", true);
Form responseHeaders = (Form) response.getAttributes().get("org.restlet.http.headers");
if (responseHeaders == null) {
responseHeaders = new Form();
response.getAttributes().put("org.restlet.http.headers", responseHeaders);
responseHeaders.add("Access-Control-Allow-Origin", origin);
responseHeaders.add("Access-Control-Allow-Methods", "GET,POST,DELETE");
responseHeaders.add("Access-Control-Allow-Headers", "Content-Type");
responseHeaders.add("Access-Control-Allow-Credentials", "true");
response.setEntity(new EmptyRepresentation());
return SKIP;
}
}
return super.beforeHandle(request, response);
}
#Override
protected void afterHandle(Request request, Response response) {
if (!Method.OPTIONS.equals(request.getMethod())) {
Form requestHeaders = (Form) request.getAttributes().get("org.restlet.http.headers");
String origin = requestHeaders.getFirstValue("Origin", true);
Form responseHeaders = (Form) response.getAttributes().get("org.restlet.http.headers");
if (responseHeaders == null) {
responseHeaders = new Form();
response.getAttributes().put("org.restlet.http.headers", responseHeaders);
responseHeaders.add("Access-Control-Allow-Origin", origin);
responseHeaders.add("Access-Control-Allow-Methods", "GET,POST,DELETE"); //
responseHeaders.add("Access-Control-Allow-Headers", "Content-Type");
responseHeaders.add("Access-Control-Allow-Credentials", "true");
}
}
super.afterHandle(request, response);
Representation requestRepresentation = request.getEntity();
if (requestRepresentation != null) {
try {
requestRepresentation.exhaust();
} catch (IOException e) {
// handle exception
}
requestRepresentation.release();
}
Representation responseRepresentation = response.getEntity();
if(responseRepresentation != null) {
try {
responseRepresentation.exhaust();
} catch (IOException ex) {
Logger.getLogger(OriginFilter.class.getName()).log(Level.SEVERE, null, ex);
} finally {
}
}
}
The responseRepresentation does not have a #release method because it crashes the processes giving the warning WARNING: A response with a 200 (Ok) status should have an entity (...)
The code of the ServerResource implementation is the following:
public class ServerImpl extends ServerResource {
String itemName;
#Override
protected void doInit() throws ResourceException {
this.itemName = (String) getRequest().getAttributes().get("taxes");
}
#Get("xml")
public Representation makeItWork() throws SAXException, IOException {
DomRepresentation representation = new DomRepresentation(MediaType.TEXT_XML);
DAL dal = new DAL();
String ip = getRequest().getCurrent().getClientInfo().getAddress();
System.out.println(itemName);
double tax = Double.parseDouble(itemName);
Document myXML = Auxiliar.getMyXML(tax, dal, ip);
myXML.normalizeDocument();
representation.setDocument(myXML);
return representation;
}
#Override
protected void doRelease() throws ResourceException {
super.doRelease();
}
}
I've tried the solutions provided in other threads but none of them seem to work. Firstly, it does not seem that the thread pool is augmented with the parameters set as the warnings state that the thread pool available is 10. As mentioned before, the increase of the maxThreads value only seems to postpone the result.
Example: INFO: Worker service tasks: 0 queued, 10 active, 17 completed, 27 scheduled.
There could be some error concerning the Restlet version, but I downloaded the stable version to verify this was not the issue.The Web Service is having around 5000 requests per day, which is not much.Note: the insertion of the #release method either in the ServerResource or OriginFilter returns error and the referred warning ("WARNING: A response with a 200 (Ok) status should have an entity (...)")
Please guide.
Thanks!
By reading this site the problem residing in the server-side that I described was resolved by upgrading the Restlet distribution to the 2.1 version.
You will need to alter some code. You should consult the respective migration guide.