Add `getData` method for GeoJSON sources. about maplibre-gl-js HOT 5 OPEN

Looking at the PR I'm guessing that you figured out the answer to your questions, if there's anything that still needs my help let me know. We can continue the discussion in the PR or here, which ever works better for you.
I rewrote the entire actor communication layer, so it should be fairly easy to use it to send a message and get the response back with data.

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The only issue I can think of is the requirement to move the update process into the tile generation in the worker.
i.e. in theory, in the future we want all the manipulation logic of the tiles to happen in the worker and all the data to be stored in something that might not be easy to extract the information from.
Currently the data is duplicated: one copy in the worker is in the tiles and the other copy in an in-memory variable.
Having said that, there's no real progress to move all the logic of update into the tile generation as it requires changes to the geojson-vt package, which chances of seeing this happen are low right now.
To be on the safe side I would recommend getting the data from the worker so that we consider the worker data as the source of truth, and in the future see if we can facilitate getting the data on one hand while keeping on a single copy on the other.
I hope that make sense, if not, let me know.
Otherwise, I don't see any issues with this proposal.

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The only issue I can think of is the requirement to move the update process into the tile generation in the worker.

Sounds to me like a separate task.

Currently the data is duplicated: one copy in the worker is in the tiles and the other copy in an in-memory variable.

I guess it's the _data field I talk about in the OP. And yes, there's a line which updates it in setData, but there's no such line in updateData, which is expected since in the case with updateData the diff is sent to the worker, not the real "parsed" data. So it seems to me that

1. this _data field is redundant (I don't really see any usages of it in the main thread code)
2. even if it's not redundant, it's not updated in updateData, so the code shouldn't rely on it anyway.

Given all that, there currently is a single source of truth: data inside the worker.

To be on the safe side I would recommend getting the data from the worker so that we consider the worker data as the source of truth

Exactly. I think there's no other option anyway.

The question, however, is how. Trying to dive deeper into the source code, but I'm getting confused with between-threads communication.

I can see that the main thread sends requests to the worker thread using the sendAsync method of actor. But how should I send the data back? Should it also be the same (or a similar one) call? Or maybe there's some events-based mechanism?

Namely, what I'm talking about, is the following:

here's the _updateWorkerData method (which is called from either setData and updateData):

then it calls (

My question is, whether there's an example somewhere of a vice-versa process? Where a worker needs to send data back to the main thread?

Another thing. There are events like sourcedata which happen after the source data gets updated. Should I do anything about them? Like listening to that event to be fired before responding to the main thread with GeoJSON?

And is it OK for the getData method to be async? As I understnand, it must be, since there is communication in-between threads going on. It's also the case with setData and updateData, but those are not async because 1) interaction is events-based and 2) it doesn't really matter when the data gets set/updated, as we don't really want to do anything with it.

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Another question that came to my mind is what happens if the data is big? So the worker message have a size limit? Is paging needed in that case?

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Another question that came to my mind is what happens if the data is big? So the worker message have a size limit? Is paging needed in that case?

That's a good question. Didn't think of it as I didn't even know there are limitations regarding the message size. I'll try to check what happens in such cases. Thanks for pointing that out.

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