[New-bugs-announce] [issue34075] We should prohibit setting a ProcessPoolExecutor in with set_default_executor

[Yury Selivanov]

New submission from Yury Selivanov <yselivanov at gmail.com>:

I've had a few conversations with people who were confused that asyncio starts to behave weirdly when a ProcessPoolExecutor is set as the default one.  We don't really test that asyncio's built-in functionality (like DNS resolving) works well with a process-pool, which leads to bug reports like [1].  Third-party libraries also always assume that the loop is always configured to use the ThreadPoolExecutor (as it is by default), and also don't even test against ProcessPool.

My idea here would be to deprecate setting ProcessPoolExecutor as a default one in 3.8 and prohibit that in 3.9.

Guido, Andrew, what do you think?

[1] https://bugs.python.org/issue34073

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components: asyncio
messages: 321324
nosy: asvetlov, gvanrossum, yselivanov
priority: normal
severity: normal
status: open
title: We should prohibit setting a ProcessPoolExecutor in with set_default_executor
type: behavior
versions: Python 3.8

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue34075>
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