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[CI/Build]: make it possible to build with a free-threaded interpreter #29241

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Merged
vllm-bot merged 2 commits into from
Nov 28, 2025
Merged

[CI/Build]: make it possible to build with a free-threaded interpreter #29241

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[CI/Build]: make it possible to build with a free-threaded interpreter
rgommers Nov 20, 2025
6db4f98
Merge branch 'main' into bld-freethreading
DarkLight1337 Nov 28, 2025
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8 changes: 7 additions & 1 deletion cmake/utils.cmake
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Original file line number Diff line number Diff line change
Expand Up @@ -495,7 +495,13 @@ function (define_extension_target MOD_NAME)
set(SOABI_KEYWORD "")
endif()

if (ARG_USE_SABI)
run_python(IS_FREETHREADED_PYTHON
"import sysconfig; print(1 if sysconfig.get_config_var(\"Py_GIL_DISABLED\") else 0)"
"Failed to determine whether interpreter is free-threaded")
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rgommers marked this conversation as resolved.

# Free-threaded Python doesn't yet support the stable ABI (see PEP 803/809),
# so avoid using the stable ABI under free-threading only.
if (ARG_USE_SABI AND NOT IS_FREETHREADED_PYTHON)
Python_add_library(${MOD_NAME} MODULE USE_SABI ${ARG_USE_SABI} ${SOABI_KEYWORD} "${ARG_SOURCES}")
else()
Python_add_library(${MOD_NAME} MODULE ${SOABI_KEYWORD} "${ARG_SOURCES}")
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7 changes: 6 additions & 1 deletion setup.py
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Expand Up @@ -10,6 +10,7 @@
import shutil
import subprocess
import sys
import sysconfig
from pathlib import Path
from shutil import which

Expand Down Expand Up @@ -74,9 +75,13 @@ def is_ninja_available() -> bool:
return which("ninja") is not None


def is_freethreaded():
return bool(sysconfig.get_config_var("Py_GIL_DISABLED"))


class CMakeExtension(Extension):
def __init__(self, name: str, cmake_lists_dir: str = ".", **kwa) -> None:
super().__init__(name, sources=[], py_limited_api=True, **kwa)
super().__init__(name, sources=[], py_limited_api=not is_freethreaded(), **kwa)
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@ApostaC ApostaC Nov 24, 2025

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dumb question: is py_limited_api=False required when using the free-threaded python ?

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@rgommers rgommers Nov 24, 2025

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Thanks for the review @ApostaC. Yes, it should be set to False, otherwise setuptools raises an exception. The limited API is not supported yet with free-threading. There is very active work on adding that support for 3.15 (either PEP 803 or PEP 809 will add it, and both require PEP 793), but that's a new ABI which will be compatible with both free-threaded and with-GIL interpreters. Using that in the future will require both a new setuptools version and some source-level changes in vLLM to use PyModExport (PEP 793). So until that's all done, the limited API has to be avoided here.

self.cmake_lists_dir = os.path.abspath(cmake_lists_dir)


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