How to cancel an observable sequence

问题

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

var pulses = Observable.GenerateWithTime(0, i => true, i => i + 1, i => i,
                                         i => TimeSpan.FromMilliseconds(500))

And I have a CancellationTokenSource (that is used to cancel other work that is going on simultaneously).

How can I use the cancellation token source to cancel my observable sequence?

回答1:

If you're using the GenerateWithTime (replaced now with Generate passing in a timespan func overload), you can replace the second parameter to evaulate the state of the cancellation token as follows:

var pulses = Observable.Generate(0,
    i => !ts.IsCancellationRequested,
    i => i + 1,
    i => i,
    i => TimeSpan.FromMilliseconds(500));

Alternatively, if your event which causes the cancellation token to be set can be converted to an observable itself, you could use something like the following:

pulses.TakeUntil(CancelRequested);

I posted a more detailed explanation at http://www.thinqlinq.com/Post.aspx/Title/Cancelling-a-Reactive-Extensions-Observable as well.

回答2:

It is an old thread, but just for future reference, here is a simpler way to do it.

If you have a CancellationToken, you are probably already working with tasks. So, just convert it to a Task and let the framework do the binding:

using System.Reactive.Threading.Tasks;
...
var task = myObservable.ToTask(cancellationToken);

This will create an internal subscriber that will be disposed when the task is cancelled. This will do the trick in most cases because most observables only produce values if there are subscribers.

Now, if you have an actual observable that needs to be disposed for some reason (maybe a hot observable that is not important anymore if a parent task is cancelled), this can be achieved with a continuation:

disposableObservable.ToTask(cancellationToken).ContinueWith(t => {
    if (t.Status == TaskStatus.Canceled)
        disposableObservable.Dispose();
});

回答3:

You can connect your IObservable subscription with CancellationTokenSource with the following snippet

var pulses = Observable.GenerateWithTime(0,
    i => true, i => i + 1, i => i,
    i => TimeSpan.FromMilliseconds(500));

// Get your CancellationTokenSource
CancellationTokenSource ts = ...

// Subscribe
ts.Token.Register(pulses.Subscribe(...).Dispose);

回答4:

You get an IDisposable instance back from subscribing. Call Dispose() on that.

来源：https://stackoverflow.com/questions/6759833/how-to-cancel-an-observable-sequence

标签

system.reactive

cancellation