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GeezerVison is showing github.com — bpo-46006: Fix _PyUnicode_EqualToASCIIId() for interned strings by vstinner · Pull Request #30123 · python/cpython

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@vstinner

@vstinner vstinner commented Dec 15, 2021 •
edited by bedevere-bot
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Fix string comparisons for subinterpreters: no longer make the assumption
that two interned strings are not equal if they have different different
memory addresses. This assumption is no longer true since interned
strings have been made per interpreter in Python 3.10.

Fix _PyUnicode_EqualToASCIIId() and type update_slot() functions.

The change makes update_slot() a little bit less efficient:
update_slot() now compares the strings contents, rather than
comparing strings memory addresses.

https://bugs.python.org/issue46006

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@vstinner
bpo-46006: Fix _PyUnicode_EqualToASCIIId() for interned strings
41c1f59 
Fix string comparisons for subinterpreters: no longer make the assumption
that two interned strings are not equal if they have different different
memory addresses. This assumption is no longer true since interned
strings have been made per interpreter in Python 3.10.

Fix _PyUnicode_EqualToASCIIId() and type update_slot() functions.

The change makes update_slot() a little bit less efficient:
update_slot() now compares the strings contents, rather than
comparing strings memory addresses.
@vstinner vstinner added the needs backport to 3.10 label Dec 15, 2021
@vstinner
vstinner requested a review from markshannon as a code owner December 15, 2021 14:44
@the-knights-who-say-ni the-knights-who-say-ni added the CLA signed label Dec 15, 2021
@bedevere-bot bedevere-bot added the awaiting core review label Dec 15, 2021
@vstinner

vstinner commented Dec 15, 2021

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cc @methane @serhiy-storchaka @corona10

We will be able to add again this micro-optimization once Python C extensions and third-party C extensions will no longer define and use static types and will stop sharing objects between two interpreters. Sadly, this long term goal may take a few years...
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@markshannon

markshannon commented Dec 15, 2021

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It is meaningless to compare strings from one fully isolated interpreter with those in another.
So the assumption that id(o1) != id(o2) implies o1 != o2 is still true for a valid comparison of interned strings.

Feel free to add an assert, but please avoid this sort of pessimization for a hypothetical future which may well not happen.
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@hroncok

hroncok commented Dec 15, 2021

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Suggestion: add the reproducer from https://bugs.python.org/issue46034 as a test?
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@vstinner

vstinner commented Dec 15, 2021

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Feel free to add an assert, but please avoid this sort of pessimization for a hypothetical future which may well not happen.

@markshannon: I'm not sure what you are talking about. https://bugs.python.org/issue46006 is affecting multiple Python 3.10 users right now. It's not an hypothetical bug. At least, jep and mod_wsgi projects are known to be affected by the bug:

  • SubIntepreters don't work with DontWriteBytecodeFlag in Python 3.10 ninia/jep#358
  • Decorators on classes ignored GrahamDumpleton/mod_wsgi#729
  • (Py3.10) Error on loading: TypeError: TypeChecker() takes no arguments  poljar/weechat-matrix#293
  • https://bugzilla.redhat.com/show_bug.cgi?id=2030621
  • etc.

The bug may also explain https://bugs.python.org/issue46070 which affects more projects.
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@vstinner

vstinner commented Dec 15, 2021

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It is meaningless to compare strings from one fully isolated interpreter with those in another.

@markshannon: I added long comments as part of the change to explain the issue. Did you see my comments? It's about interned strings of static types which are shared by all interpreters.
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@markshannon

markshannon commented Dec 15, 2021

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I'll comment on the issue.
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@markshannon

markshannon commented Dec 15, 2021

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I agree that a fix is needed. But this is not the needed fix.
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@vstinner

vstinner commented Jan 6, 2022

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I merged GH-20085 instead.
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@vstinner vstinner closed this Jan 6, 2022
@vstinner
vstinner deleted the interned branch January 6, 2022 08:00
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@vstinner @markshannon @hroncok @the-knights-who-say-ni @bedevere-bot
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