Description

sergey-miryanov

opened on Oct 13, 2025

Issue body actions

Feature or enhancement

Proposal:

There are a lot of places where Py_REFCNT(..)==1 used. IIUC it is not correct for no-gil version.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Linked PRs

• GH-140061: Use _PyObject_IsUniquelyReferenced to check if object is uniquely referenced #140062
• [3.14] gh-140061: Use _PyObject_IsUniquelyReferenced() to check if objects are uniquely referenced (gh-140062) #140157

Activity

1. sergey-miryanov

   added

   type-featureA feature request or enhancementA feature request or enhancement

   on Oct 13, 2025
2. picnixz

   added

   interpreter-core(Objects, Python, Grammar, and Parser dirs)(Objects, Python, Grammar, and Parser dirs)

   extension-modulesC modules in the Modules dirC modules in the Modules dir

   type-refactorCode refactoring (with no changes in behavior)Code refactoring (with no changes in behavior)

   topic-free-threading

   and removed

   type-featureA feature request or enhancementA feature request or enhancement

   on Oct 13, 2025
3. picnixz

   changed the title [-]Widely use _PyObject_IsUniquelyReferenced to check if object is uniquely referenced[/-] [+]Use _PyObject_IsUniquelyReferenced instead of `Py_REFCNT(x) == 1` for free-threaded compatibility[/+] on Oct 13, 2025
4. colesbury

   added a commit that references this issue on Oct 15, 2025

   gh-140061: Use `_PyObject_IsUniquelyReferenced()` to check if objects…

   32c2649
5. miss-islington

   added a commit that references this issue on Oct 15, 2025

   pythongh-140061: Use `_PyObject_IsUniquelyReferenced()` to check if o…

   2b285c1
6. colesbury

   added a commit that references this issue on Oct 15, 2025

   [3.14] gh-140061: Use `_PyObject_IsUniquelyReferenced()` to check if …

   045e349
7. sergey-miryanov

   closed this as completedon Oct 15, 2025
8. StanFromIreland

   added a commit that references this issue on Dec 6, 2025

   pythongh-140061: Use `_PyObject_IsUniquelyReferenced()` to check if o…

   f4baa5c
9. cmaloney commented on Sep 14, 2026

   

   cmaloney

   on Sep 14, 2026

   Contributor

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   As a heads up this migration led to a subtle free-threading only bug in _PyBytes_Resize (GH-157373). _IsUniquelyReferenced returns false when a reference crosses a thread boundary while Py_REFCNT(x) == 1 returns true. That resulted in an immortal constant object being returned because resize thought the bytes was shared (and thus immutable) in a case where code could still modify the bytes.

   I used AI to spot-check the rest of the migrations here (Claude Fable 5.1) and it found one other behavior change worth noting: PySet_Add on a single reference frozenset which crosses thread boundaries now raises SystemError rather than passing.
10. vstinner commented on Sep 15, 2026

    

    vstinner

    on Sep 15, 2026

    Member

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    I used AI to spot-check the rest of the migrations here (Claude Fable 5.1) and it found one other behavior change worth noting: PySet_Add on a single reference frozenset which crosses thread boundaries now raises SystemError rather than passing.

    IMO PySet_Add(frozenset, key) works as expected here: you must not modify a frozenset from a thread different than the one which created it. If you think that the documentation isn't explicit about this point, maybe you can suggest a change for PySet_Add() documentation.

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