Remove macros Py_ALLOW_RECURSION/Py_END_ALLOW_RECURSION

[serhiy-storchaka]

BPO	41936
Nosy	@gvanrossum, @vstinner, @serhiy-storchaka
PRs	bpo-41936. Remove macros Py_ALLOW_RECURSION/Py_END_ALLOW_RECURSION #22552

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2020-10-05.09:32:22.618>
created_at = <Date 2020-10-04.22:20:31.657>
labels = ['expert-C-API', 'type-feature', '3.10']
title = 'Remove macros Py_ALLOW_RECURSION/Py_END_ALLOW_RECURSION'
updated_at = <Date 2020-10-05.09:32:22.618>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2020-10-05.09:32:22.618>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2020-10-05.09:32:22.618>
closer = 'serhiy.storchaka'
components = ['C API']
creation = <Date 2020-10-04.22:20:31.657>
creator = 'serhiy.storchaka'
dependencies = []
files = []
hgrepos = []
issue_num = 41936
keywords = ['patch']
message_count = 3.0
messages = ['377978', '378002', '378010']
nosy_count = 3.0
nosy_names = ['gvanrossum', 'vstinner', 'serhiy.storchaka']
pr_nums = ['22552']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue41936'
versions = ['Python 3.10']

[serhiy-storchaka]

Macros Py_ALLOW_RECURSION and Py_END_ALLOW_RECURSION together with field recursion_critical of the PyInterpreterState structure were added in 5b22213 but were never documented. It seems that the reason of adding them was to work around the fact that PyDict_GetItem() can silence any exception including recursion error. But PyDict_GetItem() no longer used in that code and the macros are also no longer used (see bpo-41909).

GvR proposed to remove these macros. I think that recursion_critical can be removed too.

[vstinner]

I failed to find users of these macros outside the CPython code base, so it sounds safe to remove it, especially if it's documented in What's New in Python 3.10.

If someone reports the removal as a regression and describes a legit use case, we can reconsider to revert the removal. Until that, I'm fine with removing them.

--

I ran grep on Cython and numpy code base: I cannot find "Py_ALLOW_RECURSION", "Py_END_ALLOW_RECURSION" or "recursion_critical".

On GitHub, I only found copies of Include/ceval.h (I looked at the first 5 pages of result):
https://github.com/search?l=C&q=Py_ALLOW_RECURSION&type=Code

[serhiy-storchaka]

New changeset dcc5421 by Serhiy Storchaka in branch 'master':
bpo-41936. Remove macros Py_ALLOW_RECURSION/Py_END_ALLOW_RECURSION (GH-22552)
dcc5421