fix(vanilla): deal with promise resolving race condition

[dmaskasky]

Related Issues or Discussions

#2192

Related Issue

#2191

Summary

Adds tests for the issue linked above.

Description of Issue

A primitive atom (atomP) exists and has a value (valueP)
An async atom (atomA) gets the value (valueAP) from atomP and then has a delay (delayA) before returning the value from atomP.
A derived async atom (atomB) gets the value (valueBP) from atomP and after a microtask or greater delay (delayB) it gets the value (valueBA) from atomA.
The bug requires delayB < delayA.
So,

• atomP is a synchronous dependency of atomA and atomB
• atomA is an asynchronous dependency of atomB

After all atoms mount,
atomP is changed twice with a delay (delayC) less than delayA.
This first multi-change proceeds nominally. ✅

atomP is then changed twice again with a delay (delayD) less than delayA.
This second multi-change does NOT proceed nominally.
The first value of this multi-change is used for ALL subsequent values of this multi-change.
Therefore, subsequent values use a stale value. ❌

Timing

See below for this timing in depth:

init valueP to 0
inside atomB.read: before await valueBA, valueBP is 0
change valueP to 1
inside atomB.read: before await valueBA, valueBP is 1
change valueP to 2
inside atomB.read: before await valueBA, valueBP is 2

inside atomA.read: after delayA, valueAP is 0
inside atomA.read: after delayA, valueAP is 1
inside atomA.read: after delayA, valueAP is 2

inside atomB.read: before await valueBA, valueBP is 2, valueBA is 2
inside atomB.read: before await valueBA, valueBP is 1, valueBA is 2
inside atomB.read: before await valueBA, valueBP is 0, valueBA is 2
===== above is nominal ✅ =====

change valueP to 3
inside atomB.read: before await valueBA, valueBP is 3
change valueP to 4
inside atomB.read: before await valueBA, valueBP is 4
inside atomA.read: after delayA, valueAP is 3
inside atomA.read: after delayA, valueAP is 4
inside atomB.read: before await valueBA, valueBP is 3, valueBA is 3 // Error: should be 4
inside atomB.read: before await valueBA, valueBP is 4, valueBA is 3 // Error: should be 4
===== above is anomalous ❌ =====

Theory

Likely, as a performance optimization there is logic in store.ts to reuse the existing value. The bug is probably due to caching the incorrect value.

The microsecond delay (delayB) in atomB is significant for some reason. Not sure why yet.

The store.sub is also significant for some reason.

Unit Test

I'm having trouble getting a unit test to work with just the store. Subsequent fires of setCount(increment) do not cause asyncAtom.read to refire unless I use a React hook. Not sure why.

It would be preferable to write a unit test and not depend on the React library for testing core Jotai functionality.

Check List

• yarn run prettier for formatting code and docs

https://codesandbox.io/s/jovial-kepler-d9v27h

Screen.Recording.2023-10-17.at.7.46.48.PM.mov

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Name	Status	Preview	Comments	Updated (UTC)
jotai	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Oct 23, 2023 1:10pm

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[dai-shi]

Thanks. It would be really nice to have store api tests.

Also, could you avoid renderHook somehow? All of our tests never depend on it.

[dai-shi]

Sorry for minor requests. I will do the rest afterwards.

[dai-shi]

Thanks so much for your help. This must be a huge bug fix.

[dmaskasky]

Thanks so much for your help. This must be a huge bug fix.

Thanks for your help. Merge is blocked for me, kindly merge at the next opportunity.