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[subinterpreters] Don't share Python objects between interpreters #84713Description
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assignee = None
closed_at = None
created_at = <Date 2020-05-06.15:11:35.602>
labels = ['expert-subinterpreters', '3.9']
title = "[subinterpreters] Don't share Python objects between interpreters"
updated_at = <Date 2022-01-13.17:32:56.034>
user = 'https://github.com/vstinner' bugs.python.org fields:
activity = <Date 2022-01-13.17:32:56.034>
actor = 'vstinner'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Subinterpreters']
creation = <Date 2020-05-06.15:11:35.602>
creator = 'vstinner'
dependencies = []
files = []
hgrepos = []
issue_num = 40533
keywords = ['patch']
message_count = 8.0
messages = ['368262', '368274', '368276', '368279', '380105', '388966', '408606', '410499']
nosy_count = 3.0
nosy_names = ['vstinner', 'eric.snow', 'shihai1991']
pr_nums = ['19958', '19961']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue40533'
versions = ['Python 3.9'] Activityvstinner commented on May 6, 2020 To get one GIL per interpreter (bpo-40512), either PyObject.ob_refcnt member must become an atomic variable, or subinterpreters must not share any object.
Right now, subinterpreters share Python objects. For example, PyModule_Type is declared statically and so shared by all interpreters and so PyModule_Type.tp_mro tuple is accessed in parallel by multiple interpreters. If PyObject.ob_refcnt is not atomic, Py_INCREF() and Py_DECREF() are unsafe and tp_mro tuple can be destroyed whereas it is still used.
I propose to make PyObject.ob_refcnt atomic for now, when Python is built with EXPERIMENTAL_ISOLATED_SUBINTERPRETERS macro defined. It's a temporary workaround until subinterpreters stop sharing objects. ericsnowcurrently commented on May 6, 2020 Yep, before per-interpreter GIL is official we must get to the point where *no* PyObject objects are shared.
Making PyObject.ob_refcnt atomic until then (only as part of the experiment) should be fine. vstinner commented on May 6, 2020
Yep, before per-interpreter GIL is official we must get to the point where *no* PyObject objects are shared.
I would like to add: "no PyObject objects are shared in the stdlib" ;-) vstinner commented on May 6, 2020 changed the title [-]Subinterpreters: don't share Python objects between interpreters[/-] [+][subinterpreters] Don't share Python objects between interpreters[/+] on May 15, 2020changed the title [-]Subinterpreters: don't share Python objects between interpreters[/-] [+][subinterpreters] Don't share Python objects between interpreters[/+] on May 15, 2020vstinner commented on Oct 31, 2020
For example, PyModule_Type is declared statically and so shared by all interpreters and so PyModule_Type.tp_mro tuple is accessed in parallel by multiple interpreters.
Another example of this issue are parallel Py_INCREF/Py_DECREF calls on the tp_bases member of a type. vstinner commented on Mar 17, 2021
To get one GIL per interpreter (bpo-40512), either PyObject.ob_refcnt member must become an atomic variable, or subinterpreters must not share any object.
The current plan is to not share any object between two interpreters, so this PR is not needed. I close my PR 19958 which marked PyObject.ob_refcnt as atomic. vstinner commented on Dec 15, 2021 Until all Python stdlib C extensions and all third-party C extensions will be modified to no longer use and define static types and will stop shared Python objects between two interpreters, we can no longer micro-optimize the comparison of two interned strings by only comparing their memory addresse. See bpo-46006. vstinner commented on Jan 13, 2022 vstinner commented on Nov 3, 2022 I don't have the bandwidth to work on this issue, so I just close it.
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