Implement support for the free-threaded build of CPython 3.13 (#618)

* Implement support for the free-threaded build of CPython 3.13

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Add towncrier blurbs

* Fix thread safety issues with critical sections

- This requires Cython nightly, so build configs have been changed
  to accomodate that.
- Reverted some of the changes that weren't related to free-threading

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Fix linting

* Use C++ atomics for frozen instead of critical sections

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Revert to using actions/setup-python

* Update packaging/pep517_backend/_backend.py

Co-authored-by: 🇺🇦 Sviatoslav Sydorenko (Святослав Сидоренко) <[email protected]>

* Revert changes to codecov flags now that actions/setup-python is used

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: J. Nick Koston <[email protected]>
Co-authored-by: 🇺🇦 Sviatoslav Sydorenko (Святослав Сидоренко) <[email protected]>

Author: 4 people

.github/workflows/ci-cd.yml

@@ -174,6 +174,7 @@ jobs:
     strategy:
       matrix:
         pyver:
+        - 3.13t
         - 3.13
         - 3.12
         - 3.11
@@ -238,7 +239,8 @@ jobs:
     - name: Install dependencies
       uses: py-actions/py-dependency-install@v4
       with:
-        path: requirements/test.txt
+        path: requirements/test${{
+          matrix.pyver == '3.13t' && '-freethreading' || '' }}.txt
     - name: Determine pre-compiled compatible wheel
       env:
         # NOTE: When `pip` is forced to colorize output piped into `jq`,

CHANGES/618.feature.rst

@@ -0,0 +1 @@
+Implemented support for the free-threaded build of CPython 3.13 -- by :user:`lysnikolaou`.

CHANGES/618.packaging.rst

@@ -0,0 +1 @@
+Started building wheels for the free-threaded build of CPython 3.13 -- by :user:`lysnikolaou`.

frozenlist/_frozenlist.pyx

@@ -1,30 +1,40 @@
+# cython: freethreading_compatible = True
+# distutils: language = c++
+
+from cpython.bool import PyBool_FromLong
+from libcpp.atomic cimport atomic
+
 import types
 from collections.abc import MutableSequence
 
 
 cdef class FrozenList:
     __class_getitem__ = classmethod(types.GenericAlias)
 
-    cdef readonly bint frozen
+    cdef atomic[bint] _frozen
     cdef list _items
 
     def __init__(self, items=None):
-        self.frozen = False
+        self._frozen.store(False)
         if items is not None:
             items = list(items)
         else:
             items = []
         self._items = items
 
+    @property
+    def frozen(self):
+        return PyBool_FromLong(self._frozen.load())
+
     cdef object _check_frozen(self):
-        if self.frozen:
+        if self._frozen.load():
             raise RuntimeError("Cannot modify frozen list.")
 
     cdef inline object _fast_len(self):
         return len(self._items)
 
     def freeze(self):
-        self.frozen = True
+        self._frozen.store(True)
 
     def __getitem__(self, index):
         return self._items[index]
@@ -103,11 +113,11 @@ cdef class FrozenList:
         return self._items.count(item)
 
     def __repr__(self):
-        return '<FrozenList(frozen={}, {!r})>'.format(self.frozen,
+        return '<FrozenList(frozen={}, {!r})>'.format(self._frozen.load(),
                                                       self._items)
 
     def __hash__(self):
-        if self.frozen:
+        if self._frozen.load():
             return hash(tuple(self._items))
         else:
             raise RuntimeError("Cannot hash unfrozen list.")

packaging/pep517_backend/_backend.py

@@ -4,6 +4,7 @@
 from __future__ import annotations
 
 import os
+import sysconfig
 from contextlib import contextmanager, nullcontext, suppress
 from functools import partial
 from pathlib import Path
@@ -372,10 +373,12 @@ def get_requires_for_build_wheel(
             stacklevel=999,
         )
 
-    c_ext_build_deps = [] if is_pure_python_build else [
-        'Cython ~= 3.0.0; python_version >= "3.12"',
-        'Cython; python_version < "3.12"',
-    ]
+    if is_pure_python_build:
+        c_ext_build_deps = []
+    elif sysconfig.get_config_var('Py_GIL_DISABLED'):
+        c_ext_build_deps = ['Cython ~= 3.1.0a1']
+    else:
+        c_ext_build_deps = ['Cython >= 3.0.12']
 
     return _setuptools_get_requires_for_build_wheel(
         config_settings=config_settings,

pyproject.toml

@@ -63,6 +63,7 @@ linetrace = "True"  # Implies `profile=True`
 #error_on_uninitialized = "True"
 
 [tool.cibuildwheel]
+enable = ["cpython-freethreading"]
 build-frontend = "build"
 before-test = [
   # NOTE: Attempt to have pip pre-compile PyYAML wheel with our build

requirements/cython-freethreading.txt

@@ -0,0 +1 @@
+cython==3.1.0a1

requirements/test-freethreading.txt

@@ -0,0 +1,2 @@
+-r cython-freethreading.txt
+-r test-pure.txt

requirements/test-pure.txt

@@ -0,0 +1,3 @@
+coverage==7.6.1
+pytest==7.4.3
+pytest-cov==4.1.0

requirements/test.txt

@@ -1,4 +1,2 @@
 -r cython.txt
-coverage==7.6.1
-pytest==7.4.3
-pytest-cov==4.1.0
+-r test-pure.txt