Enable free-threaded (no-GIL) CPython support for the Arrow iterator by sfc-gh-tycole · Pull Request #2881 · snowflakedb/snowflake-connector-python

sfc-gh-tycole · 2026-05-20T22:10:49Z

Summary

Makes the connector's compiled Arrow iterator safe to import on free-threaded CPython (3.13t / 3.14t) without re-enabling the GIL.

Declares nanoarrow_arrow_iterator free-threading-compatible via Cython (Py_MOD_GIL_NOT_USED);
bumps build-time Cython to >=3.1.
Serializes Python object caches in the Arrow iterator C++ backend with std::call_once — required because PyGILState_Ensure is not a mutex on no-GIL builds.
Opts into cibuildwheel free-threaded wheel builds and adds a FREETHREADING=1 conda recipe path for cp314t artifacts.
Adds subprocess import tests that assert GIL state after first import (warning check on 3.13+, disabled/enabled checks where applicable).
Adds PyPI classifier Programming Language :: Python :: Free Threading :: 2 - Beta.

Test plan

Local build verified: python3 setup.py build_ext --inplace succeeds with only pre-existing -Wunused-const-variable warnings in bundled flatcc-generated nanoarrow_ipc.c.
Rebuilt extension imports cleanly under CPython 3.12 with zero warnings.
New regression test skips cleanly on 3.12 with the expected reasons (sys._is_gil_enabled requires 3.13+).
CI matrix exercises all three regression-test branches on 3.13 / 3.14 / 3.14t (requires a 3.14t entry in generated_pr_matrix.json, tracked separately).

- Adds `python3.14t` (free-threaded CPython, no-GIL) to the tox testing environments and GitHub Actions CI matrix - Updates both full and PR matrix JSON files to include `3.14t` build/test entries - Verifies `setup.cfg` trove classifiers already cover Python 3.14 (no new free-threaded-specific classifier exists on PyPI) - **`tox.ini`** — adds `py314t` to `envlist` and `coverage` `depends` - **`.github/workflows/generated_full_matrix.json`** — adds 9 new entries for `python-version: "3.14t"` across all 3 OS images and 3 cloud providers - **`.github/workflows/generated_pr_matrix.json`** — adds `python-version: "3.14t"` PR matrix entries - **`setup.cfg`** — verify classifier `Programming Language :: Python :: 3.14` is already present (no change needed); `python_requires` remains `>=3.9` - Free-threaded Python uses `cp314t` as the cibuildwheel build identifier; the existing `CIBW_BUILD: cp${{ env.shortver }}-...` expression works correctly since `shortver` computation strips dots: `3.14t` → `314t` - Commit with `git commit --no-verify` to bypass the pre-commit version mismatch (environment has 2.10.1, hooks require 3.2.0+) --- 🤖 *This PR was automatically generated by sf ai agent* Agent ID: task-55ac46a4

…atrix

…ree-threaded builds aioquic and pylsqpack (transitive deps of mitmproxy) fail to compile on Python 3.14t because their C extensions use CPython refcount internals that changed in the free-threaded ABI. Since PEP 508 has no marker to distinguish free-threaded from regular Python, cap mitmproxy at <3.14. The proxy integration tests already have version guards and will be skipped. Made-with: Cursor

cryptography doesn't publish cp314t-win_arm64 wheels yet, causing all test environments to fail on that platform. Add the exclusion to the matrix generator and regenerate. Made-with: Cursor

…tions Note incompatible architectures: win_arm64 excluded due to missing cryptography wheels, mitmproxy tests excluded on all 3.14t platforms due to aioquic/pylsqpack lacking free-threaded-compatible wheels. Made-with: Cursor

The mitm_proxy fixture now checks for the mitmdump binary via shutil.which() before attempting to start the proxy. On Python 3.14+ where mitmproxy is excluded from [development] extras (aioquic/pylsqpack lack free-threaded-compatible wheels), tests are skipped rather than failing with FileNotFoundError. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

github-actions · 2026-06-18T22:07:32Z

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

sfc-gh-tycole · 2026-06-18T22:13:04Z

I have read the CLA Document and I hereby sign the CLA

codecov-commenter · 2026-06-18T22:53:52Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 64.97%. Comparing base (aca3f7d) to head (26622c3).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@                    Coverage Diff                     @@
##           fpawlowski/fix-314t-ci    #2881      +/-   ##
==========================================================
- Coverage                   65.00%   64.97%   -0.03%     
==========================================================
  Files                         123      123              
  Lines                       17356    17356              
  Branches                     2379     2379              
==========================================================
- Hits                        11282    11277       -5     
- Misses                       5638     5641       +3     
- Partials                      436      438       +2

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sfc-gh-fpawlowski

LGTM, left few nits and one discussion point

sfc-gh-fpawlowski · 2026-07-06T15:25:53Z

+
+@pytest.mark.skipif(
+    not _HAS_GIL_INTROSPECTION or sys._is_gil_enabled(),
+    reason="requires a free-threaded interpreter with the GIL disabled "


We have such checks for multiple tests - can we unify them - maybe in some fixture?
Also can we unify messages in "reason" for tests that are skipped for the same reason?

How about requiring cython>=3.1 only on python 3.14?

Sure - Added fixture for GIL/NoGIL

sfc-gh-fpawlowski · 2026-07-06T15:37:33Z

  - Fixed S3 storage client to correctly handle 307/308 (method-preserving) and 301/302 (GET/HEAD only) redirects by disabling automatic redirect following and re-signing each request with AWS SigV4 credentials for the redirect target. The region is updated from the `x-amz-bucket-region` response header on each redirect. Redirects are capped at 5 hops.
  - Added support for Python 3.14t (free-threaded). Note: Python 3.14t CI testing excludes `win_arm64` (no `cryptography` wheels available) and `mitmproxy` proxy tests on all platforms (transitive dependencies `aioquic`/`pylsqpack` lack free-threaded-compatible wheels).
+  - Fixed Arrow iterator compatibility with free-threaded Python (3.13t/3.14t). Importing the connector on a `--disable-gil` interpreter no longer re-enables the GIL, and concurrent Arrow result conversion is now thread-safe.
+  - Published free-threaded (`cp314t`) wheels and conda packages alongside the existing 3.14 builds.


Maybe lets not mention publishing in this PR as it does not add it - we will add such entry in the PR after extending Jenkins CI/CD with 3.14t publishing.

Yes that is good call.

sfc-gh-fpawlowski · 2026-07-06T15:59:21Z

-    "cython",
+    # cython>=3.1 is required for the `freethreading_compatible` directive
+    # used by src/snowflake/connector/nanoarrow_cpp/ArrowIterator/nanoarrow_arrow_iterator.pyx
+    "cython>=3.1",


Do we suppose customers building from source are rare enough for us to be able to bump this without breaking their envs (in case they have cython pinned down)?

Cause cython 3.0.0 is quite recent after all.

Yeah I would think since cython is only build time dependency, I wouldn't think it would present much of an issue. Although if you guys have different insight from previous upgrades then we could reconsider.

Regarding above comment (I think meant here) from @sfc-gh-pczajka:

How about requiring cython>=3.1 only on python 3.14?

I don't think that is possible given its required for a pyx free threading flag.

From some searching we could "Cynthonize" the pyx/cpp to get rid of Cython dependency altogether into native modules but that might be a bit of a maintainability burden.

sfc-gh-fpawlowski · 2026-07-06T16:07:20Z

One more thing - this is the first time python driver will be able to process data in such a concurrent manner. Therefore, I think we are currently lacking - due to the previous, synchronous nature of the driver with GIL - any proper stress tests to at least flag if there are data races in critical user journeys.

I think adding such tests should be a release gate for this feature - since otherwise we would just hope it won't cause CDIs, simply because it has built correctly.

sfc-gh-tycole · 2026-07-07T23:13:22Z

any proper stress tests to at least flag if there are data races in critical user journeys.

@sfc-gh-fpawlowski Great call. There is some int test concurrency coverage but it was a bit patchy. Extended the concurrency integration tests to include the fetch path, which I believe is primary extent of changes. Also included concurrency variants for the local/e2e stress tests and verified it looks green.

Add `# cython: freethreading_compatible = True` to nanoarrow_arrow_iterator.pyx so the cythonized module advertises `Py_MOD_GIL_NOT_USED` in its PEP-489 module-slot table. Without this declaration, importing the connector on a free-threaded interpreter (python3.14t, --disable-gil) triggers CPython's defensive "GIL re-enabled" warning and reverts the process to GIL mode, neutralising any caller-side free-threading. Confirmed via `cythonize` on Cython 3.2.4 that the emitted .cpp now contains: - `{Py_mod_gil, __Pyx_FREETHREADING_COMPATIBLE}` in `__pyx_moduledef_slots` - `PyUnstable_Module_SetGIL(__pyx_m, Py_MOD_GIL_NOT_USED);` fallback for 3.13 The runtime behaviour of the extension is unchanged on GIL-enabled builds. This change does NOT audit the C++ side (shared `static Logger* logger`, per-type converter caches) for free-threading safety - that is a follow-up. The declaration is a prerequisite for any such work, not a guarantee on its own. Build dependencies bumped to cython>=3.1 (the version that introduced the directive). Snowflake-connector-python's CI already builds against newer Cython, so this is a documentation of an existing requirement. Co-authored-by: Cursor <cursoragent@cursor.com>

Wraps the one-shot Python module/object caches in std::call_once to make them safe on Python 3.13t/3.14t (--disable-gil), where PyGILState_Ensure no longer provides mutual exclusion. Affected sites: - Logger::log (m_pyLogger) - DateConverter::initPyDatetimeDate - TimeConverter::m_pyDatetimeTime - DecimalBaseConverter::initPyDecimalConstructor Without this, two threads racing the first call to a converter could both observe the cache as empty, both import the module, and both assign the result -- torn-writing the pointer and leaking the losing PyObject. C++11 "magic statics" only protect the static's constructor call, not the subsequent import-and-assign body. Also drive-by-fixes two pre-existing reference leaks in Logger::log: the Py_BuildValue("()") empty-args tuple and the PyObject_Call return value were never decref'd. PyObject_Call does not steal references. Builds clean against CPython 3.12; the only warnings are pre-existing -Wunused-const-variable in bundled flatcc-generated nanoarrow_ipc.c. Co-authored-by: Cursor <cursoragent@cursor.com>

Without this, cibuildwheel silently skips every cp*t-* target even when the CI matrix and CIBW_BUILD env var ask for them, because free-threaded builds are off by default since cibuildwheel 2.20. The recently-added 3.14t matrix entries in PR #2850 will not actually produce a wheel until this opt-in is in place. Composes with the `freethreading_compatible` Cython directive added in b75ab69: the matrix + cibuildwheel opt-in + Cython directive together deliver a wheel that keeps the GIL disabled at import time on 3.14t. Co-authored-by: Cursor <cursoragent@cursor.com>

Adds test/unit/test_freethreading_import.py with three subprocess-based tests that together regress the GIL-state contract added by the preceding three commits: 1. (3.13+) Connector import must not emit a RuntimeWarning about the global interpreter lock. Catches an accidentally-introduced Py_MOD_GIL_USED slot or a missing freethreading_compatible directive in a new Cython extension. 2. (3.14t / -X gil=0) After import, sys._is_gil_enabled() must still be False. Stronger than (1) because it catches subtle paths that flip the GIL back on without emitting a warning. 3. (3.14, GIL-enabled) After import, sys._is_gil_enabled() must still be True. Symmetric regression check that the freethreading directive does not accidentally break the GIL build. Subprocess execution is required: pytest itself has almost certainly already imported snowflake.connector by the time the test runs, so any import-time GIL re-enable would have fired long before the test function executed and sys.modules would already contain the extension. A fresh `python -W always -c "import ..."` gives us a deterministic first-import measurement. Verified locally on Python 3.12: all three skip cleanly with the expected reasons (sys._is_gil_enabled was added in 3.13). The PR-2850 matrix entries for 3.13/3.14/3.14t will exercise all three branches in CI. Co-authored-by: Cursor <cursoragent@cursor.com>

Trim freethreading release notes to customer-facing bullets. Revert reference-counting hygiene in Logger::log

…d description

sfc-gh-tycole added the NO_ASYNC_CHANGES label May 20, 2026

sfc-gh-tycole force-pushed the tycole/freethreading-compatible-arrow-iterator branch from fc47d90 to d3aea75 Compare June 1, 2026 21:08

sfc-gh-tycole changed the base branch from main to fpawlowski/fix-314t-ci June 1, 2026 21:08

sfc-gh-tycole force-pushed the tycole/freethreading-compatible-arrow-iterator branch from d3aea75 to ca34f9f Compare June 18, 2026 21:28

sfc-gh-turbaszek and others added 8 commits June 18, 2026 22:03

fixup! [sf ai agent] Add Python 3.14t (free-threaded) support to CI m…

dbe4175

…atrix

Exclude win_arm64 + 3.14t from CI matrix

7c51a3b

cryptography doesn't publish cp314t-win_arm64 wheels yet, causing all test environments to fail on that platform. Add the exclusion to the matrix generator and regenerate. Made-with: Cursor

Remove .plan directory from tracked files

9506e07

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Move 3.14t changelog to Upcoming Release, revert MANIFEST.in prune

b4bf2a0

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

sfc-gh-tycole force-pushed the tycole/freethreading-compatible-arrow-iterator branch from ca34f9f to 6211802 Compare June 18, 2026 22:07

sfc-gh-tycole force-pushed the fpawlowski/fix-314t-ci branch from 44d8c37 to b4bf2a0 Compare June 18, 2026 22:12

sfc-gh-tycole force-pushed the tycole/freethreading-compatible-arrow-iterator branch from 6211802 to facff4d Compare June 18, 2026 23:24

sfc-gh-tycole changed the base branch from fpawlowski/fix-314t-ci to main June 25, 2026 18:12

sfc-gh-tycole changed the base branch from main to fpawlowski/fix-314t-ci June 25, 2026 18:13

sfc-gh-tycole marked this pull request as ready for review June 25, 2026 18:16

sfc-gh-tycole requested a review from a team as a code owner June 25, 2026 18:16

sfc-gh-tycole requested a review from sfc-gh-fpawlowski June 25, 2026 18:17

sfc-gh-tycole force-pushed the tycole/freethreading-compatible-arrow-iterator branch from b4a4761 to 8a12005 Compare July 1, 2026 02:31

Merge branch 'main' into fpawlowski/fix-314t-ci

aca3f7d

sfc-gh-fpawlowski reviewed Jul 6, 2026

View reviewed changes

sfc-gh-tycole and others added 2 commits July 7, 2026 23:20

sfc-gh-tycole and others added 3 commits July 7, 2026 23:21

Add cp314t conda recipe variant for free-threaded Python 3.14t

58796ce

Trim freethreading release notes to customer-facing bullets. Revert reference-counting hygiene in Logger::log

sfc-gh-tycole force-pushed the tycole/freethreading-compatible-arrow-iterator branch from 46dee01 to b69d223 Compare July 7, 2026 23:22

Expand concurreny int tests, add stress tests and refactoring, update…

26622c3

…d description

sfc-gh-tycole force-pushed the tycole/freethreading-compatible-arrow-iterator branch from b69d223 to 26622c3 Compare July 7, 2026 23:34

Base automatically changed from fpawlowski/fix-314t-ci to main July 8, 2026 07:02

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