Description

eendebakpt

opened on Feb 23, 2026

Issue body actions

Crash report

What happened?

A reproducer (in the format of Lib/tests/test_free_threading/xxx.py):

import unittest
from test.support import threading_helper

threading_helper.requires_working_threading(module=True)


class ItertoolsThreading(unittest.TestCase):

    @threading_helper.reap_threads
    def test_maketrans(self):
        number_of_iterations = 10
        number_of_attempts=100
        for _ in range(number_of_iterations):
            print(f'iteration {_}')
            d = {2000: 'a'}
            def work_iterator(dct):
                for idx in range(number_of_attempts):
                    str.maketrans(dct)
                    idx = 2000 + idx # outside range of small ints
                    dct[idx] = chr(idx%16)
                    dct.pop(idx, None)
            threading_helper.run_concurrently(work_iterator, nthreads=10, args=[d])

if __name__ == "__main__":
    unittest.main()
    print('done')

At first glance it seems that the iteration using PyDict_Next is not safe (but maybe there are more unsafe parts):

cpython/Objects/unicodeobject.c

Line 13158 in 24cc998

while (PyDict_Next(x, &i, &key, &value)) {

(found when reviewing #145129)

CPython versions tested on:

CPython main branch

Operating systems tested on:

Windows

Output from running 'python -VV' on the command line:

No response

Linked PRs

• gh-145142: Make str.maketrans safe under free-threading #145157
• [3.14] gh-145142: Make str.maketrans safe under free-threading (gh-145157) #145320

Activity

1. eendebakpt

   added

   type-crashA hard crash of the interpreter, possibly with a core dumpA hard crash of the interpreter, possibly with a core dump

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

   topic-free-threading

   on Feb 23, 2026
2. colesbury commented on Feb 23, 2026

   

   colesbury

   on Feb 23, 2026

   Contributor

   More actions

   Yes, PyDict_Next isn't thread-safe if there are concurrent modifications of the dict. We should wrap the loop with a critical section on x here.

   Do you want to make the change?
3. eendebakpt commented on Feb 23, 2026

   

   eendebakpt

   on Feb 23, 2026

   ContributorAuthor

   More actions

   Do you want to make the change?

   I am adding the easy label for newcomers. If not picked up, I will make the change.

   Reacted by Sam Gross
4. eendebakpt

   added

   easy

   on Feb 23, 2026
5. VanshAgarwal24036 commented on Feb 23, 2026

   

   VanshAgarwal24036

   on Feb 23, 2026

   Contributor

   More actions

   I am working on this issue.
6. VanshAgarwal24036

   added 5 commits that reference this issue on Feb 23, 2026

   pythongh-145142: Make str.maketrans safe under free-threading

   3bedfff

   Merge branch 'main' into pythongh-145142-dict-next-critical-section

   d487864

   Merge remote-tracking branch 'upstream/main' into pythongh-145142-dic…

   ca3b943

   Merge branch 'main' into pythongh-145142-dict-next-critical-section

   206f6b2

   pythongh-145142: Make str.maketrans safe under free-threading

   0745e41
7. colesbury

   added 2 commits that reference this issue on Feb 27, 2026

   Merge branch 'main' into pythongh-145142-dict-next-critical-section

   4994663

   gh-145142: Make str.maketrans safe under free-threading (gh-145157)

   a249795
8. miss-islington

   added a commit that references this issue on Feb 27, 2026

   pythongh-145142: Make str.maketrans safe under free-threading (python…

   0efb6a2
9. colesbury

   added a commit that references this issue on Feb 27, 2026

   [3.14] gh-145142: Make str.maketrans safe under free-threading (gh-14…

   d76c56e
10. colesbury

    closed this as completedon Feb 27, 2026
11. brijkapadia

    added a commit that references this issue on Feb 28, 2026

    pythongh-145142: Make str.maketrans safe under free-threading (python…

    bbcb932
12. ljfp

    added a commit that references this issue on Apr 25, 2026

    pythongh-145142: Make str.maketrans safe under free-threading (python…

    1f6c471

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