Add freethreading build and tests

.github/workflows/buildwheel.yml

@@ -86,17 +86,36 @@ jobs:
         os: [ubuntu-24.04, ubuntu-24.04-arm, windows-2019, macos-13, macos-14]
         # This list to be kept in sync with cibuildwheel config
         # and python-requires in pyproject.toml.
-        python-version: ['3.11', '3.12', '3.13'] # , 'pypy3.10']
+        python-version: ['3.11', '3.12', '3.13', '3.13t'] # , 'pypy3.10']
+
+        # XXX: Maybe this exclude can be removed when changing from
+        # Quansight-Labs/setup-python...
+        exclude:
+          - os: ubuntu-24.04-arm
+            python-version: '3.13t'
 
     steps:
-      - uses: actions/setup-python@v5
+      # Quansight-labs/setup-python is needed for 3.13t until a new version of
+      # actions/setup-python (>5.4.0) is released.
+      #
+      # https://github.com/actions/setup-python/pull/973
+      - uses: Quansight-Labs/setup-python@v5
         with:
           python-version: ${{ matrix.python-version }}
       - uses: actions/download-artifact@v4
         with:
           name: wheels-${{ matrix.os }}
           path: wheelhouse
       - run: pip install --no-index --find-links wheelhouse python_flint
+
+      # Check if the GIL is disabled in the free-threading build after import.
+      - run: |
+          python --version --version
+          which python
+          python -c "import sysconfig; print(sysconfig.get_config_var('Py_GIL_DISABLED'))"
+          python -c "import sys; print(getattr(sys, '_is_gil_enabled', lambda: True)())"
+          python -c "import sys; import flint; print(getattr(sys, '_is_gil_enabled', lambda: True)())"
+
       - run: python -m flint.test --verbose
 
   # On new enough Ubuntu we can build against the system deb.
@@ -227,37 +246,6 @@ jobs:
       - run: pip install -r requirements-dev.txt
       - run: bin/coverage.sh
 
-  # On new enough Ubuntu we can build against the system deb.
-  test_freethreaded:
-    name: Free-threaded ${{ matrix.python-version }} on ${{ matrix.os }}
-    runs-on: ${{ matrix.os }}
-    strategy:
-      fail-fast: false
-      matrix:
-        os: [ubuntu-24.04]
-        python-version: ['3.13', '3.14-dev']
-    steps:
-      - uses: actions/checkout@v4
-      # Can't use actions/setup-python
-      # https://github.com/actions/setup-python/issues/771
-      # deadsnakes only works for Ubuntu...
-      - uses: deadsnakes/[email protected]
-        with:
-          python-version: ${{ matrix.python-version }}
-          nogil: true
-      - run: |
-          python --version --version
-          which python
-          python -c "import sysconfig; print(sysconfig.get_config_var('Py_GIL_DISABLED'))"
-          python -c "import sys; print(sys._is_gil_enabled())"
-      - run: sudo apt-get update
-      - run: sudo apt-get install libflint-dev
-      # Need Cython master until 3.1 is released
-      - run: pip install git+https://github.com/cython/cython.git@master
-      - run: pip install -r requirements-dev.txt
-      - run: pip install --no-build-isolation .
-      - run: python -m flint.test --verbose
-
   # Run SymPy test suite against python-flint master
   test_sympy:
     name: Test SymPy ${{ matrix.sympy-version }}

meson.build

@@ -83,6 +83,17 @@ add_project_arguments(
     language : 'cython'
 )
 
+# Enable free-threading if Cython is new enough. The check should be
+# >= 3.1.0a1 but meson gets confused by the a1 alpha release suffix.
+# so we go with >= 3.1 (which will be correct once 3.1 is released).
+cy = meson.get_compiler('cython')
+if cy.version().version_compare('>=3.1')
+  message('Enabling freethreading')
+  add_project_arguments('-Xfreethreading_compatible=true', language : 'cython')
+else
+  message('Disabling freethreading')
+endif
+
 if get_option('coverage')
    add_project_arguments('-X', 'linetrace=True', language : 'cython')
    add_project_arguments('-DCYTHON_TRACE=1', language : 'c')

pyproject.toml

@@ -6,6 +6,7 @@ version = "0.7.0"
 requires-python = ">= 3.11"
 authors = [
     {name = "Fredrik Johansson", email = "[email protected]"},
+    {name = "Oscar Benjamin", email = "[email protected]"},
 ]
 license = {text = "MIT"}
 classifiers = [
@@ -27,16 +28,16 @@ content-type = "text/markdown"
 # Minimum build requirements tested in CI need to be kept in sync with the
 # versions in requires below so that they are tested.
 #
-# The upper cap on Cython is speculative but we may as well cap it given that
-# it is only a build requirement and that it is not uncommon for newer Cython
-# versions to break the build. For example Cython 3.0 broke the build and then
-# Cython 3.1 broke the build again so python-flint 0.6.0 did not have any upper
-# cap but it should have had cython>=3.0,<3.1 i.e. precisely one minor release
-# of Cython works. In future we could contemplate not having an upper cap but
-# until we have actually witnessed a Cython 3.x release that does not break the
-# build we should keep the upper cap.
+# To support the freethreaded build (CPython 3.13t) the alpha release 3.1.0a1
+# of Cython is needed as a minimum requirement. It is possible that future
+# versions of Cython might still work but typically a Cython release breaks
+# something in the build of python-flint so we pin the exact version here.
 #
-requires = ["meson-python>=0.13", "cython>=3.0.11,<=3.1.0a1"]
+# Apart from the freethreading build any Cython version from 3.0.11 onwards is
+# fine. It is not possible to have a separate version constraint here for the
+# freethreading build only though.
+#
+requires = ["meson-python>=0.13", "cython==3.1.0a1"]
 build-backend = "mesonpy"
 
 [tool.cython-lint]
@@ -81,12 +82,10 @@ package = "flint"
 [tool.cibuildwheel]
 # requires-python needs to keep in sync with this and also the list of Python
 # versions the wheels are tested against in CI.
-build = "cp311-* cp312-* cp313-*" # pp311-*"
+build = "cp311-* cp312-* cp313-* cp313t-*" # pp311-*"
 skip = "*-win32 *-manylinux_i686 *-musllinux_*"
 
-# This is needed for free-threaded wheels:
-# build = "cp313t-*"
-# free-threaded-support = true
+free-threaded-support = true
 
 manylinux-x86_64-image = "manylinux2014"
 manylinux-aarch64-image = "manylinux_2_28"

src/flint/test/test_all.py

@@ -1612,10 +1612,12 @@ def set_bad2():
     M6 = M6_copy
     assert M6.nullspace() == (M([[1,15,1],[0,0,0],[0,0,0]],17).transpose(), 1)
 
+
 def test_nmod_series():
     # XXX: currently no code in nmod_series.pyx
     pass
 
+
 def test_arb():
     A = flint.arb
     assert A(3) > A(2.5)
@@ -1626,6 +1628,7 @@ def test_arb():
     assert A(3) != A(2)
     assert not (A("1.1") == A("1.1"))
 
+
 def test_pickling():
     objects = [
         flint.fmpz(1),
@@ -4735,6 +4738,54 @@ def test_fq_default_poly():
         assert raises(lambda: f.pow_trunc(-1, 5), ValueError)
 
 
+def test_python_threads():
+    #
+    # https://github.com/flintlib/python-flint/issues/224
+    #
+    # XXX: This test crashes under the free-threading mode because of memory
+    # corruption.
+    #
+    # It is not clear if this should be fixed or if mutating
+    # matrices/polynomials that are shared between multiple threads should just
+    # be disallowed.
+    #
+
+    # Skip the test on the free-threaded build...
+    import sys
+    if sys.version_info[:2] >= (3, 13) and not sys._is_gil_enabled():
+        return
+
+    from threading import Thread
+
+    iterations = 10**5
+    threads = 3 + 1
+    size = 3
+    M = flint.fmpz_mat([[0]*size for _ in range(size)])
+
+    def set_values():
+        for i in range(iterations // 5):
+            i = random.randrange(M.nrows())
+            j = random.randrange(M.ncols())
+            if random.uniform(0, 1) > 0.5:
+                # Bigger than 2**62:
+                M[i,j] = 10**128
+            else:
+                # Smaller than 2**62:
+                M[i,j] = 0
+
+    def get_dets():
+        for i in range(iterations):
+            M.det()
+
+    threads = [Thread(target=set_values) for _ in range(threads-1)]
+    threads.append(Thread(target=get_dets))
+
+    for t in threads:
+        t.start()
+    for t in threads:
+        t.join()
+
+
 def test_all_tests():
     test_funcs = {f for name, f in globals().items() if name.startswith("test_")}
     untested = test_funcs - set(all_tests)
@@ -4813,5 +4864,7 @@ def test_all_tests():
 
     test_pickling,
 
+    test_python_threads,
+
     test_all_tests,
 ]