Description

colesbury

opened on Feb 14, 2024

Issue body actions

Feature or enhancement

The free-threaded implementation of dict and list try avoid acquiring locks during read operations. To support this, we need to be able to access the reference count fields of Python objects after they are deallocated (and possibly reallocated). Some of this support is provided by #115103. Additionally, we need to ensure that the debug allocators do not overwrite these fields with "dead" bytes 0xDD, which might make the object look "alive" by having a non-zero reference count.

We still would like to overwrite the rest of the allocation (i.e., from ob_type onwards) to detect use-after-frees in debug builds.

See also: https://peps.python.org/pep-0703/#optimistically-avoiding-locking

Linked PRs

• gh-115491: Keep some fields valid across allocations (free-threading) #115573
• gh-115491: Keep some fields valid across allocations in obmalloc (free-threading) #115745
• gh-115491: Fix Clang compiler warning #116153

Activity

1. colesbury

   added

   type-featureA feature request or enhancementA feature request or enhancement

   topic-free-threading

   on Feb 14, 2024
2. colesbury

   self-assigned this

   on Feb 15, 2024
3. colesbury

   added 4 commits that reference this issue on Feb 16, 2024

   pythongh-115491: Keep some fields valid across allocations (free-thre…

   58a2d1f

   pythongh-115491: Keep some fields valid across allocations in obmallo…

   20c0c81

   gh-115491: Keep some fields valid across allocations (free-threading) (…

   cc82e33

   pythongh-115491: Keep some fields valid across allocations in obmallo…

   85b3647
4. DinoV

   added a commit that references this issue on Feb 21, 2024

   gh-115491: Keep some fields valid across allocations in obmalloc (fre…

   347acde
5. colesbury commented on Feb 21, 2024

   

   colesbury

   on Feb 21, 2024

   ContributorAuthor

   More actions

   This still needs the mimalloc support in #115103 to fully preserve the fields, but the changes to filling debug bytes is done now.
6. colesbury

   closed this as completedon Feb 21, 2024
7. colesbury

   added a commit that references this issue on Feb 29, 2024

   pythongh-115491: Fix compiler warning on macOS

   36a959e
8. DinoV

   added a commit that references this issue on Mar 1, 2024

   gh-115491: Fix Clang compiler warning (#116153)

   d7ddd90
9. woodruffw

   added 3 commits that reference this issue on Mar 4, 2024

   pythongh-115491: Keep some fields valid across allocations (free-thre…

   be2dcd0

   pythongh-115491: Keep some fields valid across allocations in obmallo…

   041aa45

   pythongh-115491: Fix Clang compiler warning (python#116153)

   625d530
10. adorilson

    added a commit that references this issue on Mar 25, 2024

    pythongh-115491: Fix Clang compiler warning (python#116153)

    18be625
11. diegorusso

    added 3 commits that reference this issue on Apr 17, 2024

    pythongh-115491: Keep some fields valid across allocations (free-thre…

    de74b97

    pythongh-115491: Keep some fields valid across allocations in obmallo…

    6e942bd

    pythongh-115491: Fix Clang compiler warning (python#116153)

    b1dd0bb
12. LukasWoodtli

    added 2 commits that reference this issue on Jan 22, 2025

    pythongh-115491: Keep some fields valid across allocations (free-thre…

    0bb51fd

    pythongh-115491: Keep some fields valid across allocations in obmallo…

    9720a85
13. corona10

    added 2 commits that reference this issue on Oct 10, 2026

    Re-apply CPython-specific changes to mimalloc v2.5.2

    fa3a143

    Re-apply CPython-specific changes to mimalloc v2.5.2

    836dced
14. corona10

    added 2 commits that reference this issue on Oct 22, 2026

    gh-159111: Update vendored mimalloc to v2.5.2 (gh-159112)

    aff7a2e

    [3.15] pythongh-159111: Update vendored mimalloc to v2.5.2 (pythongh-…

    265f0fb

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