providing .sample() the same observable it samples produces stale output

[nabati]

Thanks for the skeleton @jayphelps

RxJS version:
5.0.0.beta-12

Code to reproduce:
http://jsbin.com/sapuju/4/edit?js,console,output

Expected behavior:
Open the console. 3

Actual behavior:
2

Additional information:

[jayphelps]

@Blesh Is this possibly related to our change in default schedulers? That was my initial hunch, but then I thought that the order should still be the same, even if it's no longer scheduled on the microtask. My latest guess is that this is primary due to the .sample() and the observable provided to .sample() (sampleObservable) both subscribing to the same subject, and in v4 perhaps it has a subtle difference in subscription order compared to v5? i.e. the sampleObservable item$.filter(item => item === 3) is subscribed to before the .sample() operator subscribes to the subject, so when it receives values, .sample() has not yet received that value yet, hence why it outputs 2 instead of 3.

If that's the case, which order is correct is prolly debatable but I think it will only have a practical difference in cases like these so we should prolly reverse the subscription order. ...first glance suggests doing so would be pretty internally awkward though..

---

For other's reference:

RxJS v4 defaulted to micro-task scheduling (was called AyncScheduler but in v5 this is called AsapScheduler and AsyncScheduler in v5 is different!). In v5, for performance reasons, we default to having no scheduler, doing things now, synchronously. (that was called ImmediateScheduler in v4). This is all confusing, we realize, but the changes were thoroughly bikeshed and made for good reasons.

More info on v5 schedulers

[jayphelps]

I think it's more clear to reproduce this without the filter. http://jsbin.com/coreni/edit?js,output

const item$ = new Subject();

item$
  .sample(item$)
  .subscribe(value => {
    console.log(value);
  });

item$.next(1);
item$.next(2);
item$.next(3);

v4: 1 2 3
v5: 1 2

[benlesh]

I'll take a look at this

[lock]

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