[Async-sig] Inadvertent layering of synchronous code as frameworks adopt asyncio

[Ben Darnell]

On Mon, Mar 25, 2019 at 8:02 PM Guido van Rossum <guido at python.org> wrote:

>
> Given PBP, I wonder if we should just relent and have a configurable flag
> (off by default) to allow nested loop invocations (both the same loop and a
> different loop).
>
>
Allowing reentrant calls to the same loop is not a good idea IMO. At best,
you'll need to carefully ensure that the event loop and task
implementations are themselves reentrancy-safe (including the C
accelerators and third parties like uvloop?), and then it just invites
subtle issues in the applications built on top of it. I don't think there's
a good reason to allow or support this (and nest_asyncio should be heavily
discouraged). I do, however, think that PBP is a good enough reason to
allow opt-in use of multiple event loops nested inside each other (maybe
something on the EventLoopPolicy for configuration?).

-Ben
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