[stdlib-sig] futures - PEP and API

[Antoine Pitrou]

> The executor needs to know when no more futures will be scheduled so  
> it can shutdown its thread/process pool after it has finished the  
> current work items.

Ah, I see and it's useful indeed.
I think it makes things a bit counter-intuitive however. People are used
to "with" releasing things right at the end of the block, not scheduling
them for later release at an unknown point in time.

Regards

Antoine.