gh-140260: Fix data race in _struct module initialization with subinterpreters#140909

ashm-dev

Issue: ThreadSanitizer: data race in _struct module initialization with InterpreterPoolExecutor (free-threading build) #140260

ZeroIntensity

Please add a test stressing this.

ZeroIntensity

I think the failing job will be solved by a rebase.

ZeroIntensity

LGTM

ZeroIntensity

Hm, that failure looks unrelated. @encukou, is it possible that #138190 broke something?

encukou

It did (now fixed thanks to Victor), but I don't think it broke mobile. Maybe it's sequential tests, or cross-compilation?

kumaraditya303

Seems like Android and iOS do not support subinterpreters so the test should be skipped on those platforms.

ZeroIntensity

Good catch, I disabled auto-merge for the time being.

miss-islington-app

Thanks @ashm-dev for the PR, and @kumaraditya303 for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖

…h subinterpreters (pythonGH-140909) (cherry picked from commit 63548b3) Co-authored-by: Shamil <ashm.tech@proton.me>

bedevere-app

GH-141501 is a backport of this pull request to the 3.14 branch.

bedevere-bot

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 Debian root 3.x (tier-1) has failed when building commit 63548b3.

What do you need to do:

Don't panic.
Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/345/builds/12669) and take a look at the build logs.
Check if the failure is related to this commit (63548b3) or if it is a false positive.
If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/345/builds/12669

Failed tests:

test.test_os.test_os

Failed subtests:

test_timerfd_interval - test.test_os.test_os.TimerfdTests.test_timerfd_interval

Summary of the results of the build (if available):

==

Click to see traceback logs

Traceback (most recent call last):
  File "/root/buildarea/3.x.angelico-debian-amd64/build/Lib/test/test_os/test_os.py", line 4017, in test_timerfd_interval
    self.assertEqual(self.read_count_signaled(fd), count)
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: 4 != 3

…th subinterpreters (GH-140909) (#141501) gh-140260: fix data race in `_struct` module initialization with subinterpreters (GH-140909) (cherry picked from commit 63548b3) Co-authored-by: Shamil <ashm.tech@proton.me>

* main: (463 commits) pythongh-140601: Add ResourceWarning to iterparse when not closed (pythonGH-140603) pythongh-137969: Fix double evaluation of `ForwardRef`s which rely on globals (python#140974) pythongh-139109: A new tracing JIT compiler frontend for CPython (pythonGH-140310) pythongh-141004: Document `PyErr_RangedSyntaxLocationObject` (python#141521) pythongh-140873: Add support of non-descriptor callables in functools.singledispatchmethod() (pythonGH-140884) pythongh-139653: Add PyUnstable_ThreadState_SetStackProtection() (python#139668) pythongh-141004: Document `PyCode_Optimize` (pythonGH-141378) pythongh-141004: Document C APIs for dictionary keys, values, and items (pythonGH-141009) pythongh-137959: Fix `TIER1_TO_TIER2` macro name in JIT InternalDocs (pythonGH-141496) pythongh-139871: Add `bytearray.take_bytes([n])` to efficiently extract `bytes` (pythonGH-140128) pythongh-140601: Refactor ElementTree.iterparse() tests (pythonGH-141499) pythongh-135801: Add the module parameter to compile() etc (pythonGH-139652) pythongh-140260: fix data race in `_struct` module initialization with subinterpreters (python#140909) pythongh-137109: refactor warning about threads when forking (python#141438) pythongh-141004: Document `PyRun_InteractiveOneObject` (pythonGH-141405) pythongh-124111: Fix TCL 9 thread detection (pythonGH-128103) pythongh-141442: Add escaping to iOS testbed arguments (python#141443) pythongh-140936: Fix JIT assertion crash at finalization if some generator is alive (pythonGH-140969) Add details about JIT build infrastructure and updating dependencies to `Tools/jit` (python#141167) pythongh-141412: Use reliable target URL for urllib example (pythonGH-141428) ...

* 'main' of github.com:python/cpython: (464 commits) pythongh-140601: Add ResourceWarning to iterparse when not closed (pythonGH-140603) pythongh-137969: Fix double evaluation of `ForwardRef`s which rely on globals (python#140974) pythongh-139109: A new tracing JIT compiler frontend for CPython (pythonGH-140310) pythongh-141004: Document `PyErr_RangedSyntaxLocationObject` (python#141521) pythongh-140873: Add support of non-descriptor callables in functools.singledispatchmethod() (pythonGH-140884) pythongh-139653: Add PyUnstable_ThreadState_SetStackProtection() (python#139668) pythongh-141004: Document `PyCode_Optimize` (pythonGH-141378) pythongh-141004: Document C APIs for dictionary keys, values, and items (pythonGH-141009) pythongh-137959: Fix `TIER1_TO_TIER2` macro name in JIT InternalDocs (pythonGH-141496) pythongh-139871: Add `bytearray.take_bytes([n])` to efficiently extract `bytes` (pythonGH-140128) pythongh-140601: Refactor ElementTree.iterparse() tests (pythonGH-141499) pythongh-135801: Add the module parameter to compile() etc (pythonGH-139652) pythongh-140260: fix data race in `_struct` module initialization with subinterpreters (python#140909) pythongh-137109: refactor warning about threads when forking (python#141438) pythongh-141004: Document `PyRun_InteractiveOneObject` (pythonGH-141405) pythongh-124111: Fix TCL 9 thread detection (pythonGH-128103) pythongh-141442: Add escaping to iOS testbed arguments (python#141443) pythongh-140936: Fix JIT assertion crash at finalization if some generator is alive (pythonGH-140969) Add details about JIT build infrastructure and updating dependencies to `Tools/jit` (python#141167) pythongh-141412: Use reliable target URL for urllib example (pythonGH-141428) ...

mhsmith

Seems like Android and iOS do not support subinterpreters so the test should be skipped on those platforms.

Based on discussions on Discord, it looks like this failure would happen on any platform if you run the tests with --single-process. So Android and iOS actually do support subintepreters, it's just that they're the only platforms that use --single-process in GitHub Actions.

…h subinterpreters (python#140909)

Fix data race in _struct module endian table initialization

243b5f0

bedevere-app Bot added the awaiting review label Nov 2, 2025

bedevere-app Bot mentioned this pull request Nov 2, 2025

ThreadSanitizer: data race in _struct module initialization with InterpreterPoolExecutor (free-threading build) #140260

Closed

fix doc

4c9892e

ashm-dev requested a review from ericsnowcurrently as a code owner November 2, 2025 12:58

refactor(c-analyzer): add endian_tables_init_once to globals-to-fix list

95958e8

ashm-dev force-pushed the tsan branch from 64f49c0 to 95958e8 Compare November 2, 2025 13:10

ZeroIntensity reviewed Nov 2, 2025

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ZeroIntensity added needs backport to 3.14 bugs and security fixes topic-subinterpreters labels Nov 2, 2025

ZeroIntensity reviewed Nov 2, 2025

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Use Py_UNUSED for unused arg in init_endian_tables

3130512

ashm-dev force-pushed the tsan branch from 68ffe6d to 3130512 Compare November 2, 2025 16:28

ashm-dev requested a review from ZeroIntensity November 2, 2025 16:47

ZeroIntensity reviewed Nov 2, 2025

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picnixz reviewed Nov 2, 2025

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fix: remove duplicate include of pycore_lock.h in _struct.c

d33514b

ashm-dev requested a review from ZeroIntensity November 3, 2025 14:31

ZeroIntensity reviewed Nov 3, 2025

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add test

c4f577f

ashm-dev force-pushed the tsan branch from 219b7df to c4f577f Compare November 3, 2025 16:13

ashm-dev requested a review from ZeroIntensity November 3, 2025 16:22

ZeroIntensity reviewed Nov 3, 2025

View reviewed changes

Remove return check for endian table init

238c40e

ashm-dev force-pushed the tsan branch from e21838a to 238c40e Compare November 3, 2025 16:39

Use InterpreterPoolExecutor in struct tests

f4d24ff

ashm-dev requested review from ZeroIntensity and picnixz November 3, 2025 16:52

ZeroIntensity reviewed Nov 3, 2025

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ZeroIntensity approved these changes Nov 5, 2025

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bedevere-app Bot added awaiting merge and removed awaiting review labels Nov 5, 2025

Merge branch 'main' into tsan

434dbab

kumaraditya303 approved these changes Nov 6, 2025

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kumaraditya303 enabled auto-merge (squash) November 6, 2025 05:54

ZeroIntensity disabled auto-merge November 11, 2025 20:31

fix: tests

3844826

ashm-dev requested review from ZeroIntensity and kumaraditya303 November 13, 2025 09:29

Merge branch 'main' into tsan

b825107

bedevere-app Bot removed the awaiting merge label Nov 13, 2025

bedevere-app Bot removed the needs backport to 3.14 bugs and security fixes label Nov 13, 2025

ashm-dev deleted the tsan branch November 13, 2025 11:03

StanFromIreland pushed a commit to StanFromIreland/cpython that referenced this pull request Dec 6, 2025

pythongh-140260: fix data race in _struct module initialization wit… …

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…h subinterpreters (python#140909)

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gh-140260: Fix data race in _struct module initialization with subinterpreters#140909

gh-140260: Fix data race in _struct module initialization with subinterpreters#140909
kumaraditya303 merged 20 commits into
python:mainfrom
ashm-dev:tsan

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