How to cancel an async WCF call?

Question

I have been trying some time to find out how to implement WCF call cancellation based on the new .NET 4.5 CancellationToken mechanism. All the samples I found are not WCF ba

Answer 1

After the edit of the question I see that it is acceptable to have cancellation of logic level. If so, the following algorithm can be tried.

1) Create a service with InstanceContextMode=InstanceContextMode.PerSession, so that will guarantee you having the same instance of service for serving subsequent requests.

2) to start new sessions use service operations marked with OperationContract(IsInitiating = True)

3) create as service member. not static. it will be service state

CancellationTokenSource ct = new CancellationTokenSource();

4) inside every service method you will have to start new computations inside tasks and put cancellation token as a parameter for this task.

[ServiceContract(SessionMode = SessionMode.Allowed)]
public interface ICalculator
{
   [OperationContract(IsInitiating = True)]
   Bool Begin()

   [OperationContract(IsInitiating = false)]
   double Add(double n1, double n2)
}

[ServiceBehavior(InstanceContextMode=InstanceContextMode.PerSession)]
public class CalculatorService : ICalculator
{
    CancellationTokenSource cts = new CancellationTokenSource();

    public double Add(double n1, double n2)
    {
        var cancellationToken = cts.Token;

        var t = Task.Factory.StartNew(() => { 
           // here you can do something long
           while(true){
           // and periodically check if task should be cancelled or not
           if(cancellationToken.IsCancellationRequested)
             throw new OperationCanceledException();

           // or same in different words
           cancellationToken.ThrowIfCancellationRequested();
           }
           return n1 + n2;
        }, cancellationToken);

        return t.Result;
    }

    public Bool Begin(){}
}

Here is a quick descriptions of WCF sessions.

All the examples are just from my head, haven't tried if it really work. But you can try.