[shortfin] Fix issues with free threaded Python builds. (#226)

* Fixes a method signature issue that manifested on 3.13 generally (not
FT related).
* Bumps nanobind to a recent HEAD commit to pick up free threaded
support.
* Adds nanobind option to enable free threading if building for a
CPython with it enabled.
* Adds a README stanza advising on how to acquire a free threaded
CPython.
* Makes fastapi tests skip if deps not met (not yet available / hard to
install).
* Adds an LSAN exclusion for something unrelated that has snuck in.
* Sets FT CMAKE_BUILD_TYPE=Debug in the CI.

Note that on the large NUMA system I was testing on, the CPU test which
creates an executor on each NUMA node for all processes exceeded the
default file handle ulimit, requiring it to be increased. I assume that
the FT CPython internally uses more synchronization handles and it just
happened to go over budget. This resulted in fixing
iree-org/iree#18609, which was causing an assert
to be hit in this specific RESOURCE_EXHAUSTED scenario.

.github/workflows/ci_linux_x64_nogil-libshortfin.yml

@@ -79,6 +79,7 @@ jobs:
         mkdir ${{ env.LIBSHORTFIN_DIR }}/build
         cd ${{ env.LIBSHORTFIN_DIR }}/build
         cmake -GNinja \
+          -DCMAKE_BUILD_TYPE=Debug \
           -DCMAKE_C_COMPILER=clang-18 \
           -DCMAKE_CXX_COMPILER=clang++-18 \
           -DCMAKE_LINKER_TYPE=LLD \

libshortfin/README.md

@@ -101,3 +101,23 @@ recommended:
 * Compile dependencies with `-fvisibility=hidden`
 * Enable LTO builds of libshortfin
 * Set flags to enable symbol versioning
+
+# Miscellaneous Build Topics
+
+## Free threaded Python
+
+Support for free threaded Python builds (aka. "nogil") is in progress. It
+is currently being tested via dev builds of CPython 3.13 with the
+`--disable-gil` option set. There are multiple ways to acquire such an
+environment. If using `pyenv`, here is a way:
+
+```
+# Build a 3.13-dev-nogil version.
+PYTHON_CONFIGURE_OPTS='--disable-gil' \
+$(pyenv root)/plugins/python-build/bin/python-build 3.13-dev \
+  $(pyenv root)/versions/3.13-dev-nogil
+
+# Test (should print "1").
+pyenv shell 3.13-dev-nogil
+python -c 'import sysconfig; print(sysconfig.get_config_var("Py_GIL_DISABLED"))'
+```

libshortfin/build_tools/python_lsan_suppressions.txt

@@ -7,3 +7,4 @@ leak:google/_upb
 leak:import_find_and_load
 leak:pyo3::pyclass::create_type_object
 leak:ufunc
+leak:pydantic_core

libshortfin/python/CMakeLists.txt

@@ -11,14 +11,17 @@
 # Others.
 
 # nanobind
+# Pinned to a pre 2.2.0 commit hash which includes free threaded support.
+# TODO: Bump to 2.2.0 when available.
 FetchContent_Declare(
   nanobind
   GIT_REPOSITORY https://github.com/wjakob/nanobind.git
-  GIT_TAG        9641bb7151f04120013b812789b3ebdfa7e7324f # 2.1.0
+  GIT_TAG        8ce0dee7f62add575f85c0de386a9c819e4d50af # HEAD > 2.1.0
 )
 FetchContent_MakeAvailable(nanobind)
 
-nanobind_add_module(shortfin_python_extension NB_STATIC LTO
+nanobind_add_module(shortfin_python_extension
+  NB_STATIC LTO FREE_THREADED
   array_binding.cc
   array_host_ops.cc
   lib_ext.cc

libshortfin/python/_shortfin/asyncio_bridge.py

@@ -17,8 +17,8 @@ def get_debug(self):
         # Requirement of asyncio.
         return False
 
-    def create_task(self, coro):
-        return asyncio.Task(coro, loop=self)
+    def create_task(self, coro, *, name=None, context=None):
+        return asyncio.Task(coro, loop=self, name=name, context=context)
 
     def create_future(self):
         return asyncio.Future(loop=self)

libshortfin/tests/examples/fastapi_test.py

@@ -20,6 +20,10 @@
 
 @pytest.fixture(scope="session")
 def server():
+    try:
+        import fastapi
+    except ModuleNotFoundError as e:
+        pytest.skip(f"Required dep not available: {e}")
     runner = ServerRunner([])
     yield runner
     print("Sending kill signal")