fix: support persistent lifespans in asgi

[dom96]

Ensures that mutable lifespans are persisted across requests. Adds fastapi and asgi-specific tests.

[ask-bonk]

I'm Bonk, and I've done a quick review of your PR.

Makes ASGI entrypoint lifespan state persist across requests.

1. High: Posted 1 actionable inline suggestion.

github run

[hoodmane]

Generally looks reasonable, though I'd set _start_future on the AsgiWorkerEntrypoint instance rather than the class and initialize _start_future to None in AsgiWorkerEntrypoint.__init__(). Could adjust it in a followup if you like though.

[dom96]

So we do actually want it set on the class because the instance is re-created on every worker invocation. The lifespan is supposed to stay alive for the duration of the lifetime of the isolate. I added a comment to explain this.

[hoodmane]

the instance is re-created on every worker invocation

That is really weird, can we migrate away from that?

[hoodmane]

In JavaScript is the WorkerEntrypoint instantiated on every request?

[dom96]

Yes, according to https://developers.cloudflare.com/workers/runtime-apis/bindings/service-bindings/rpc/#the-workerentrypoint-class

A new instance of the class is created every time the Worker is called.

[hoodmane]

Right it also says:

Note that even though the Worker is implemented as a class, it is still stateless — the class instance only lasts for the duration of the invocation. If you need to persist or coordinate state in Workers, you should use Durable Objects.

What is this persistent lifespan state being used for? Is it volatile cache kind of stuff? Would be interested if you could post the use case.

[dom96]

As far as I understand it's for reconstructible event-loop-local resources like HTTP clients, database pools, etc. Perhaps it isn't all that useful for Workers, but existing FastAPI apps that wish to run on Workers may find it useful. It's just about keeping things that are reused by each requested handled inside a single isolate.

If you don't think it's worth the complexity that's fine too. We can close :)

[ryanking13]

Approving to unblock, but probably we need to consider refactoring asgi.py as it is getting more complicated.

[ryanking13]

I think lifespan state would be more useful for Durable Objects, which has a longer lifecycle.

Currently, DurableObject class do not inherit AsgiWorkerEntrypoint so it cannot benefit from this change, so we could possibly refactor this in the future to better handle botgh regular workers and DO