Operator: Interval

[benjchristensen]

http://msdn.microsoft.com/en-us/library/hh229027(v=vs.103).aspx
http://msdn.microsoft.com/en-us/library/hh228911(v=vs.103).aspx

[mairbek]

It seems like Interval shares logic with the Timer from issue #92.

Interval could be implemented as a Timer call with dueTime == 0.

[jmhofer]

Sure, as soon as Timer is implemented or schedulers can do periodic scheduling, the implementation of Interval will get a lot simpler.

[samuelgruetter]

Is the interval operator intended to work if there are several subscribers? It looks as if this was simply forgotten...

[jmhofer]

Actually, I'm not sure whether interval itself should or shouldn't support this. - However, you should always be able to use publish/connect. If that doesn't work, then there's definitely something wrong. I can go check that later. I probably didn't think of that when implementing it...

[samuelgruetter]

I just tried it out in C#. This code:

static void Main() {
    var oneNumberPerSecond = Observable.Interval(TimeSpan.FromSeconds(1)).Take(5);
    oneNumberPerSecond.Subscribe(
    x => Console.WriteLine("subscriber 1 got " + x)
    );
    oneNumberPerSecond.Subscribe(
    x => Console.WriteLine("subscriber 2 got " + x)
    );
    Console.ReadLine();
}

produces this output:

subscriber 2 got 0
subscriber 1 got 0
subscriber 2 got 1
subscriber 1 got 1
subscriber 2 got 2
subscriber 1 got 2
subscriber 2 got 3
subscriber 1 got 3
subscriber 2 got 4
subscriber 1 got 4

So I think we should update the RxJava version to support multiple subscribers.

[samuelgruetter]

Compare to Java. Code:

public static void main(String[] args) {
    Observable<Long> oneNumberPerSecond = Observable.interval(1, TimeUnit.SECONDS).take(5);
    oneNumberPerSecond.subscribe(new Action1<Long>() {
        public void call(Long x) {
            System.out.println("subscriber 1 got " + x);
        }           
    });
    oneNumberPerSecond.subscribe(new Action1<Long>() {
        public void call(Long x) {
            System.out.println("subscriber 2 got " + x);
        }           
    });     
}

Output:

subscriber 1 got 0
subscriber 2 got 1
subscriber 1 got 2
subscriber 2 got 3
subscriber 1 got 4
subscriber 2 got 5
subscriber 1 got 6
subscriber 2 got 7
subscriber 1 got 8
subscriber 2 got 9

I think this will be used a lot for small examples and so it should be fixed soon. @benjchristensen could you please reopen this issue?

[jmhofer]

What does Rx.NET do when you wait a bit before subscribing the second time?

Will it do this?

subscriber 1 got 0
subscriber 1 got 1
subscriber 1 got 2
subscriber 2 got 2
subscriber 1 got 3
subscriber 2 got 3
subscriber 1 got 4
subscriber 2 got 4

Or will it still start at 0 with subscriber 2?

[jmhofer]

I added a first test for that use case here: jmhofer@2fe6da7

It fails, as expected from your comment above.

[jmhofer]

The Rx Design Guidelines (5.10) say:

As many observable sequences are cold (see cold vs. hot on Channel 9), each subscription will have a separate set of side-effects. Certain situations require that these side-effects occur only once. The Publish operator provides a mechanism to share subscriptions by broadcasting a single subscription to multiple subscribers.

So I guess it would be okay for the second subscriber to always start at 0 too when subscribing to the same observable later (and not using publish/connect)?