Direct state in context

[dai-shi]

As it went well in https://github.com/dai-shi/react-tracked, I'm trying the same technique in reactive-react-redux too.

We put redux state in context and set observedBits = 0.
This should hopefully resolve the concurrent mode issue (but who knows what is concurrent mode...)
Closes #15, unless we further see other concurrent mode issues (in this case file a new issue).

[dai-shi]

So, it slightly decreases performance especially in "select row".

I'll take a deeper look later. Maybe, it can't be helped.

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edit1: 168.2 (+/-) 157.1 seems weird.

edit2: I re-run it. Now, it's moderate. 88.7 (+/-) 7.0 Probably, my computer wasn't stable then.

[dai-shi]

@markerikson You might have some technical interests in this. I'm not sure how react-redux v6 is implemented at code level, but what I'm trying here is to put state in context and still using subscription model. It doesn't seem to gain performance, but hopefully it's concurrent mode friendly.

[markerikson]

I would generally expect that propagating state via context is going to be a noticeable drop in performance. because that's what we saw with v6.

[dai-shi]

@markerikson It's not that bad. I think it's different from rr v6, in which context propagate all components and HoCs stop updating. Whereas, this one, context doesn't propagate, but calls listeners in batchedUpdates. Probably, the batchedUpdates is important for performance.

[dai-shi]

Probably, the batchedUpdates is important for performance.

This is not correct in this case, because it is in useEffect.

[dai-shi]

Run js-framework-benchmark again. This time, the control is react-redux v7.1.0.

I'm pretty confident that performances are fine.

Only the comparison is:

• reactive-react-redux v3.0.0 uses store context with unstable_batchedUpdates for correctness and performance
• reactive-react-redux v4.0.0-alpha.2 uses more or less state context with unstable_calculateChangedBits to avoid context propagation, and it should be concurrent mode friendly

Which is better? A hard question. Anyone have comments? Our hero @gaearon

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[dai-shi]

My intuition is go for it.

I would expect when React would drop the observedBits feature, it should provide other method to bail out useContext.

I would appreciate for any comments even after this PR is merged. Thanks.