How to create a cancellable task loop?

Question

Is it possible to use System.Threading.Task.Task to create a loop of task that can be cancelled?

The flow should start with a Task.Delay(x ms) then continue with userdefined task, then another Task.Delay(y ms) and repeat from the user defined task.

var result = Task.Delay(initialDelay)
              .ContinueWith(t => dostuff..)
              .ContinueWith what goes here?

Is it even doable using tasks?

I could spin up a timer and be done with it, but using task seems to be the right way to go if I need cancellation, no?

Answer 1

await makes this super easy:

public async Task TimedLoop(Action action, 
    CancellationToken token, TimeSpan delay)
{
    while (true)
    {
        token.ThrowIfCancellationRequested();
        action();
        await Task.Delay(delay, token);
    }
}

Without async (but still just using the TPL) it's a bit messier. I generally solve this problem by having a continuation that attaches itself to a variable of type Task. This works fine, but it can take a second to wrap your head around it. Without await it may be easier to just use a Timer instead.

public Task TimedLoop(Action action,
    CancellationToken token, TimeSpan delay)
{
    //You can omit these two lines if you want the method to be void.
    var tcs = new TaskCompletionSource<bool>();
    token.Register(() => tcs.SetCanceled());

    Task previous = Task.FromResult(true);
    Action<Task> continuation = null;
    continuation = t =>
    {
        previous = previous.ContinueWith(t2 => action(), token)
            .ContinueWith(t2 => Task.Delay(delay, token), token)
            .Unwrap()
            .ContinueWith(t2 => previous.ContinueWith(continuation, token));
    };
    previous.ContinueWith(continuation, token);
    return tcs.Task;
}