Reactive extensions - how to do variable rate polling? - reactive-programming

Question

I am wondering how can I poll/invoke a method at a set interval. I would like to be able to vary this regular interval also. So something like this.
[Reactive]
public TimeSpan Rate { get; set; }
IObservable<TimeSpan> rate = this.WhenAnyValue(vm => vm.Rate);
// poll should emit at the current rate set in `rate observable`
rate.Poll().InvokeCommand(cmd);
In marble diagram
rate ---4----------2--------∞----------4----------------
Poll ---X---X---X--X-X-X-X-XX----------X---X---X---X---X
X - the time when method is executed
Point to note, a new value in rate should force Poll to emit immediately and cancel any previous value that was supposed to be emitted.
I attempted to write a Poll Operator. However, it complains when I try to pass a large TimeSpan.
public static IObservable<TimeSpan> Poll(this IObservable<TimeSpan> sourceObservable, IScheduler scheduler = null)
{
scheduler = scheduler ?? NewThreadScheduler.Default;
return Observable.Create<TimeSpan>(observer =>
{
return scheduler.ScheduleAsync(async (s, ct) =>
{
var timerTokenSource = new CancellationTokenSource();
var compositeTokenSource = CancellationTokenSource.CreateLinkedTokenSource(timerTokenSource.Token, ct);
TimeSpan interval = TimeSpan.MaxValue;
sourceObservable.Subscribe(t =>
{
interval = t;
timerTokenSource.Cancel();
timerTokenSource = new CancellationTokenSource();
compositeTokenSource = CancellationTokenSource.CreateLinkedTokenSource(timerTokenSource.Token, ct);
},
ct);
while (!ct.IsCancellationRequested)
{
await s.Sleep(interval, compositeTokenSource.Token);
observer.OnNext(interval);
}
});
});
}

Answer 1

I think this is what you want:
public static IObservable<TimeSpan> Poll(this IObservable<TimeSpan> sourceObservable, IScheduler scheduler = null)
{
scheduler = scheduler ?? NewThreadScheduler.Default;
return
sourceObservable
.Select(ts => Observable.Timer(TimeSpan.Zero, ts).Select(x => ts))
.ObserveOn(scheduler)
.Switch();
}
I don't know why you're returning a TimeSpan. Why is that?