Question

My original method looks like:

string DoSomeWork();

Method DoSomeWork starts some work on another thread and returns execution ID (just random string). Later on I can query results by the returned execution ID. Main point is to make execution ID available before job will complete.

Now I want to change signature to return Task, so user can wait if he want to.

Task DoSomeWork();

At the same time I still need to return execution ID (for tracing purposes for example) and I see a few options. First, use an out parameter, second, return tuple with both execution ID and task (in C# this looks like not a best option), and third, about which I actually want to ask.

What if I create a class that derives Task:

public class ExtendedTask : Task
{
     public string ExecutionID {get; set;}
}

Does this look ok? Or is it better to decide other options?

P.S. In BCL there are some classes derived from Task.

UPDATE, seems I was not able to define this clear enough. But I need access to ExecutionID before the job completes so I cannot use Task.Result.

Answer 1

I wouldn’t personally extend Task<T>, I’d compose it instead. That way you don’t need to worry about any APIs which only return Task<T> – you can just wrap the task. You can have a property which exposes the underlying task, and for the C# 5 async purposes you can implement the awaiter pattern on your own type – but it feels to me like creating your own derived type is likely to do more harm than good. It’s mostly a gut feeling though.

Another option is to work the other way round: store your extra state in the Task.AsyncState property; that’s what it’s there for, after all. That way you can easily pass the task around without losing the execution context it’s logically part of.