Question

What is a good case/example for using the ScheduledDisposable in Reactive Rx

I like the using the CompositeDisposable and SerialDisposable, but would you need the ScheduledDisposable.

Answer 1

The logic of using the Rx disposables is that code that performs some sort of set up operation can return an IDisposable that anonymously contains the code that will do the associated clean up at a later stage. If this pattern is used consistently then you can compose together many disposables to perform a single clean up operation without any specific knowledge of what is being cleaned up.

The problem is that if that clean up code needs to run on a certain thread then you need some way for Dispose called on one thread to be marshalled to required thread – and that’s where ScheduledDisposable comes in.

The primary example is the SubscribeOn extension method which uses ScheduledDisposable to ensure that the “unsubscribe” (i.e. the Dispose) is run on the same IScheduler that the Subscribe was run on.

This is important for the FromEventPattern extension method, for example, that attaches to and detaches from event handlers which must happen on the UI thread.

Here’s an example of where you might use ScheduledDisposable directly:

var frm = new SomeForm();

frm.Text = "Operation Started.";

var sd = new ScheduledDisposable(
    new ControlScheduler(frm),
    Disposable.Create(() =>
        frm.Text = "Operation Completed."));

Scheduler.ThreadPool.Schedule(() =>
{
    // Long-running task
    Thread.Sleep(2000);
    sd.Dispose();
});

A little contrived, but it should show a reasonable example of how you’d use ScheduledDisposable.