IObserver -- what should the observer do when IObserver.OnError is called

Question

I'm using the IObserver/IObservable interfaces in a project of mine.

The CommandReader is an IObservable which continuously reads data from a stream and then passes it to its CommandHandler IObserver(s).

When the underlying stream is closed (e.g. connection dies) then I will notify the observers with the IObserver.OnError(exception) method

What should the observer do when it receives this notification? Should it release itself from the observable? Or is that the parent class' responsibility?

Answer 1

For starters you generally should not implement your own IObservable and IObserver objects. Your question kind of hints at why. It is very difficult to get the underlying behaviour correct.

Now each call to IObservable.Subscribe returns an IDisposable. This is used if the caller of Subscribe wishes to unsubscribe from an observable before an OnCompleted or OnError is called. However, if an OnCompleted or OnError is called then the IDisposable is automatically disposed of. So effectively Rx automatically cleans up after itself when an observable collection complete.

Each individual observer does not need to manage it's own subscription lifetime. The observer only needs to respond to the OnCompleted/OnError message.

In your code I would suggest that you think about changing your code slightly. I would expect a CommandReaderPublisher class with a Subscribe method might be more appropriate than a CommandReader class. Once an Rx stream completes it cannot continue to be used.

Also I wonder if calling OnCompleted would be better than OnError(exception) when the underlying stream closes. If an error occurs then that's fine, but if it closes then ONCompleted might be better.