JSPI - Fix idbstore with jspi.

[brendandahl]

Return the promise from handleSleep so wasm is suspended until each idb operation is done.

Fixes #19989

[sbc100]

I guess this only really matters with ASYNCIFY=2?

[brendandahl]

I guess this only really matters with ASYNCIFY=2?

Yeah, asyncify=1 has its own mechanism in handleSleep to start things back up again. I've contemplated unifying asyncify 1 and 2, where we wouldn't use handleSleep or handleAsync in js library functions, but we would instead always expect a promise back from an async function and resume on that promise. Currently, asyncify=1 supports doing either sync or async from an import and if we went to the promise approach, a function would no longer be able to do the sync resume. I suppose if the user really wanted sync they could import a sync only version though. Maybe, @kripken has thoughts on this?

[kripken]

Unifying 1 and 2 sounds good in general. I don't have a feeling for how limiting it would be to not allow sync imports, though. Do we have examples of that in the test suite or elsewhere?

[brendandahl]

I don't think it will really be limiting, more that it could affect performance. Currently with asyncify=1, a JS function that is calling handleSleep can synchronously call the wakeUp callback so that asyncify=1 won't unwind. If we go the promise route, asyncify=1 will always unwind during a js async import.

[brendandahl]

So far I've been unable to reproduce the test failing locally. I'm going to try with a different version of chrome...

[kripken]

I don't think it will really be limiting, more that it could affect performance. Currently with asyncify=1, a JS function that is calling handleSleep can synchronously call the wakeUp callback so that asyncify=1 won't unwind. If we go the promise route, asyncify=1 will always unwind during a js async import.

Could we not return a resolved promise and not unwind, something like that? (I admit I don't totally follow this, though, so I'm probably missing something... is there an example of a particular import that could get slower due to this?)