This is an implementation pattern, rather than something strictly for the ASGI spec.

Something that cropped up while implementing https://github.com/encode/sentry-asgi is that Python's ThreadPoolExecutor does not default to preserving the contextvars context, which really is what you want.

If you're using something like the Sentry SDK, then you needs contextvars in order to properly tie otherwise unrelated events together into, and you need it to continue working properly when threadpools are used.

Here's my fix in Starlette: Kludex/starlette#192

Other ASGI tools and frameworks will want to use something similar when running sync code in threadpools.

Links to core issue here: Kludex/starlette#191