OperationContext.Current is null after first await when using async/await in WCF service

Question

I am using async/await pattern in .NET 4.5 to implement some service methods in WCF. Example service:

Contract:

[ServiceContract(Namespace = "http://async.test/")]
public interface IAsyncTest
{
    Task DoSomethingAsync();
}

Implementation:

MyAsyncService : IAsyncTest
{
    public async Task DoSomethingAsync()
    {
        var context = OperationContext.Current; // context is present

        await Task.Delay(10);

        context = OperationContext.Current; // context is null
    }
}

The problem I am having is that after first await OperationContext.Current returns null and I can't access OperationContext.Current.IncomingMessageHeaders.

In this simple example this is not a problem since I can capture the context before the await. But in the real world case OperationContext.Current is being accessed from deep inside the call stack and I really don't want to change lots of code just to pass the context further.

Is there a way to get operation context after await point without passing it down the stack manually?

Answer 1

It is unfortunate that this doesn't work and we will see about getting a fix out in a future release.

In the mean time, there is a way to reapply the context to the current thread so that you don't have to pass the object around:

    public async Task<double> Add(double n1, double n2)
    {

        OperationContext ctx = OperationContext.Current;

        await Task.Delay(100);

        using (new OperationContextScope(ctx))
        {
            DoSomethingElse();
        }
        return n1 + n2;
    }  

In the above example, the DoSomethingElse() method will have access to OperationContext.Current as expected.

Answer 2

I think your best option is to actually capture it and pass it manually. You may find this improves the testability of your code.

That said, there are a couple of other options:

1. Add it to the LogicalCallContext.
2. Install your own SynchronizationContext which will set OperationContext.Current when it does a Post; this is how ASP.NET preserves its HttpContext.Current.
3. Install your own TaskScheduler which sets OperationContext.Current.

You may also want to raise this issue on Microsoft Connect.

Answer 3

It seems to be fixed in .Net 4.6.2. See the announcement