With Rx, how do I ignore all-except-the-latest value when my Subscribe method is running

Question

Using Reactive Extensions, I want to ignore messages coming from my event stream that occur while my Subscribe method is running. I.e. it sometimes takes me lon

Answer 1

Here's a Task based implementation, with cancellation semantics, which doesn't use a subject. Calling dispose allows the subscribed action to cancel processing, if so desired.

    public static IDisposable SampleSubscribe(this IObservable observable, Action action)
    {
        var cancellation = new CancellationDisposable();
        var token = cancellation.Token;
        Task task = null;

        return new CompositeDisposable(
            cancellation,
            observable.Subscribe(value =>
            {
                if (task == null || task.IsCompleted)
                    task = Task.Factory.StartNew(() => action(value, token), token);
            })
        );
    }

Here's a simple test:

Observable.Interval(TimeSpan.FromMilliseconds(150))
                      .SampleSubscribe((v, ct) =>
                      {   
                          //cbeck for cancellation, do work
                          for (int i = 0; i < 10 && !ct.IsCancellationRequested; i++)
                              Thread.Sleep(100);

                          Console.WriteLine(v);
                      });

The output:

0
7
14
21
28
35