[feature request] support ContextVars

It seem that setting context variables in on_startup is not supported.

My naïve understanding is that there needs to be a new (copied) context in which all of on_startup, asgi request and then on_shutdown are ran.

Otherwise, the value that’s been set is not accessible in the request handlers and/or the context var cannot be reset in the shutdown function using the token that was generated in the startup function.

[dimaqq]

@florimondmanca I think you may be right, I’m using fastapi/starlette/uvicorn and andeed my context var setup needs tricky context saving/switching because lifespan is a separate call (from middleware’s point of view).

[florimondmanca]

A few questions to get the investigation going…

• Is there an even simpler example to allow us to reproduce this? Does it reproduce without Starlette? (Manual ASGI lifespan app with this async context manager lifespan handler)
• Does it reproduce on other ASGI servers? Hypercorn?

If we know in what happens in these situations then we may be able to pinpoint where the problem might be.

Now that I think about it, I said at the beginning of this thread that lifespan is a long running task, but more precisely I believe that’s how Uvicorn does it. Still, this « token was created in a different Context » error seems different, even odd. I looked up Starlette code, and the lifespan_context there runs as a single async with call, no strange task stuff going on. Which strengthens my belief that we might want to look at how Uvicorn runs lifespan…