How to cancel an observable sequence

Question

I have a very simple IObservable that acts as a pulse generator every 500ms:

var pulses = Observable.GenerateWithTime(0, i => true         


        

Answer 1

Here are two handy operators for canceling observable sequences. The difference between them is on what happens in case of cancellation. The TakeUntil causes a normal completion of the sequence (OnCompleted), while the WithCancellation causes an exceptional termination (OnError).

/// 
Returns the elements from the source observable sequence until the
/// CancellationToken is canceled.
public static IObservable TakeUntil(
    this IObservable source, CancellationToken cancellationToken)
{
    return source
        .TakeUntil(Observable.Create(observer =>
            cancellationToken.Register(() => observer.OnNext(default))));
}

/// 
Ties a CancellationToken to an observable sequence. In case of
/// cancellation propagates an OperationCanceledException to the observer.
public static IObservable WithCancellation(
    this IObservable source, CancellationToken cancellationToken)
{
    return source
        .TakeUntil(Observable.Create(o => cancellationToken.Register(() =>
            o.OnError(new OperationCanceledException(cancellationToken)))));
}

Usage example:

var cts = new CancellationTokenSource(TimeSpan.FromSeconds(30));

var pulses = Observable
    .Generate(0, i => true, i => i + 1, i => i, i => TimeSpan.FromMilliseconds(500))
    .WithCancellation(cts.Token);