[Python-Dev] Timeout for PEP 550 (original) (raw)

[Python-Dev] Timeout for PEP 550 / Execution Context discussion

Ethan Furman ethan at stoneleaf.us
Wed Oct 18 02:25:15 EDT 2017

On 10/17/2017 09:40 PM, Nick Coghlan wrote:

On 18 October 2017 at 05:55, Yury Selivanov wrote:

I actually like what you did in https://github.com/gvanrossum/pep550/blob/master/simpler.py <https://github.com/gvanrossum/pep550/blob/master/simpler.py>, it seems reasonable. The only thing that I'd change is to remove "setctx" from the public API and add "Context.run(callable)". This makes the API more flexible to potential future changes and amendments. Yep, with that tweak, I like Guido's suggested API as well.

Attempting to explain why I think we want "Context.run(callable)" rather "contextvars.setctx()" by drawing an analogy to thread local storage: 1. In C, the compiler & CPU work together to ensure you can't access another thread's thread locals. 2. In Python's thread locals API, we do the same thing: you can only get access to the running thread's thread locals, not anyone else's At the Python API layer, we don't expose the ability to switch explicitly to another thread state while remaining within the current function. Instead, we only offer two options: starting a new thread, and waiting for a thread to finish execution. The lifecycle of the thread local storage is then intrinsically linked to the lifecycle of the thread it belongs to.

I seem to remember mention about frameworks being able to modify contexts for various tasks/coroutines; if the framework cannot create and switch to a new context how will it set them up? Or did I misunderstand?

-- Ethan

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