How to transform task.Wait(CancellationToken) to an await statement?

Question

So, task.Wait() can be transformed to await task. The semantics are different, of course, but this is roughly how I would go about transforming a blocking code with Waits to an asynchronous code with awaits.

My question is how to transform task.Wait(CancellationToken) to the respective await statement?

Answer 1

await is used for asynchronous methods/delegates, which either accept a CancellationToken and so you should pass one when you call it (i.e. await Task.Delay(1000, cancellationToken)), or they don't and they can't really be canceled (e.g. waiting for an I/O result).

What you can do however, is abandon* these kinds of tasks with this extension method:

public static Task<T> WithCancellation<T>(this Task<T> task, CancellationToken cancellationToken)
{
    return task.IsCompleted // fast-path optimization
        ? task
        : task.ContinueWith(
            completedTask => completedTask.GetAwaiter().GetResult(),
            cancellationToken,
            TaskContinuationOptions.ExecuteSynchronously,
            TaskScheduler.Default);
}

Usage:

await task.WithCancellation(cancellationToken);

---

^{* The abandoned task doesn't get cancelled, but your code behaves as though it has. It either ends with a result/exception or it will stay alive forever.}