4.x: Inline disposability into ScheduledItem

[akarnokd]

This PR turns the abstract ScheduledItem into an IDisposable which allows direct cancellation when returned from a Schedule() method. The CurrentThreadScheduler had to wrap it before but I don't see any reason to not have it support dispose directly.

Also since this is a public API change, the API approval check required the expansion of the txt file with the altered signature.

[danielcweber]

Thought about this before, Even if this is not breaking, I don't know if we are going for public surface changes right now per roadmap.

@onovotny @ghuntley Could you please weigh in?

[danielcweber]

I'm thinking of merging this. First, there already were API surface changes from 4.0, second, we can't progress without touching the API and we're not retiring anything. However, could you please implement IDisposable explicitly to avoid confusion about Cancel/Dispose, I think this is good then.

[akarnokd]

However, could you please implement IDisposable explicitly to avoid confusion about Cancel/Dispose, I think this is good then.

I don't follow. I've added IDisposable and public void Dispose() but can't remove Cancel as it is the part of the API surface.

[danielcweber]

No, don't remove Cancel, just have Dispose as explicit interface implementation. Instead

public void Dispose()

you write

void IDisposable.Dispose()

That hides Dispose on ScheduledItem. It will only be accessible if you explicitly cast it to IDisposable. Just to make sure there are no 2 confusing APIs doing the same. System.IO.Stream has it that way with Close and Dispose.