Refining the heat beat timeout

I've been playing around with different ways of expressing the timeout described in my last post. To refresh your memory, I originally defined it like this;

// Once we've told the consumer that we are connected, we will start a timer that will yield false if it ever expires.
Observable.Timer(TimeSpan.FromSeconds(2).Select(_ => false)

There are lots of way you can define this behaviour in Rx, for example;

Observable.Never<bool>().Timeout(TimeSpan.FromSeconds(2), Observable.Return(false))

Observable.Return(false).Delay(TimeSpan.FromSeconds(2))

I'm settling on the latter in this case. Less characters is better :)

To recap, I've now generalized the solution described in the last post into the following method.

private IObservable<bool> IsConnected<T>(IObservable<T> heartbeats, TimeSpan timeout)
{
    var connected = Observable.Return(true);
    var disconnected = Observable.Return(false).Delay(timeout);

    return Observable.Switch
        (
            from hb in heartbeats
            select connected.Concat(disconnected)
        ).DistinctUntilChanged();
}

It takes a stream of heartbeats for a session & introduces a true/false switch, telling you if the session is active or not.

This will be useful in my next post, "Monitoring cluster nodes using Rx".