[issue22239] asyncio: nested event loop

[Yury Selivanov]

Yury Selivanov <yselivanov at gmail.com> added the comment:

> Yeah, writing a trivial "event loop" to drive actually-synchronous code is easy. Try it out:

This is exactly the approach I used in edgedb-python.

> I guess there's technically some overhead, but it's tiny.

Correct, the overhead isn't even detectable in microbenchmarks. In most async programs regular function calls dominate awaits by a few factors of magnitude.

> I think dropping 'await' syntax has two major downsides:

For the extra context, in the case of using this approach for something like edgedb-python these downsides don't really apply, because we're adapting async/await implementation to be sync. The async/await code can handle cancellation etc. whereas the sync code only needs to support the general protocol parsing flow. FWIW I don't think it would be possible to apply my approach to SQLA without a very invasive rewrite, which isn't probably worth it.

> tl;dr: I think switching from async/await -> greenlets would make it much easier to write programs that are 90% correct, and much harder to write programs that are 100% correct. That might be a good tradeoff in some situations, but it's a lot more complicated than it seems.

Yeah, this sums up my opinion on this topic.

Also, having spent a couple of years writing and debugging big and small greenlet-heavy code bases I wouldn't want to touch them ever again. Your mileage may vary, Mike.

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<https://bugs.python.org/issue22239>
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