New threads should inherit the contextvars.Context of their creator

[nascheme]

Feature or enhancement

Proposal:

It would be convenient and likely less surprising if threads inherited the context of their creator, rather than starting with an empty context. This would match what asynio.Task does. This has been requested before, as gh-86981.

Has this already been discussed elsewhere?

I have already discussed this feature proposal on Discourse

Links to previous discussion of this feature:

https://discuss.python.org/t/thread-safe-warning-filters/

Linked PRs

• gh-128555: Add 'context' keyword parameter to Thread. #128209

[rhettinger]

It would be convenient and likely less surprising if threads inherited the context of their creator, rather than starting with an empty context.

My mental model for context vars is that they operate similarly to thread.local() and that it would be surprising if they didn't.

[StanSvec]

+1 on this idea. When a parent task needs to split work into concurrent subtasks, having access to the same context just makes sense. I can't see any real downsides to doing this, but I can think of many cases where inherited context would be helpful.