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gh-144503: Pass sys.argv as separate command line arguments. #144508

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gh-144503: Pass sys.argv as separate command line arguments. #144508

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gh-144503: Pass `sys.argv` as separate command line arguments.
sjoerdjob Feb 5, 2026
5b8ff7b
gh-144503: Add news entry
sjoerdjob Feb 5, 2026
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gh-144503: Accept non-importable resource
sjoerdjob Feb 5, 2026
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11 changes: 8 additions & 3 deletions Lib/multiprocessing/forkserver.py
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Original file line number Diff line number Diff line change
Expand Up @@ -172,8 +172,6 @@ def ensure_running(self):
main_kws['sys_path'] = data['sys_path']
if 'init_main_from_path' in data:
main_kws['main_path'] = data['init_main_from_path']
if 'sys_argv' in data:
main_kws['sys_argv'] = data['sys_argv']
if self._preload_on_error != 'ignore':
main_kws['on_error'] = self._preload_on_error

Expand All @@ -197,6 +195,8 @@ def ensure_running(self):
exe = spawn.get_executable()
args = [exe] + util._args_from_interpreter_flags()
args += ['-c', cmd]
if self._preload_modules:
args += data["sys_argv"]
pid = util.spawnv_passfds(exe, args, fds_to_pass)
except:
os.close(alive_w)
Expand Down Expand Up @@ -282,7 +282,7 @@ def _handle_preload(preload, main_path=None, sys_path=None, sys_argv=None,


def main(listener_fd, alive_r, preload, main_path=None, sys_path=None,
*, sys_argv=None, authkey_r=None, on_error='ignore'):
*, authkey_r=None, on_error='ignore'):
"""Run forkserver."""
if authkey_r is not None:
try:
Expand All @@ -293,6 +293,11 @@ def main(listener_fd, alive_r, preload, main_path=None, sys_path=None,
else:
authkey = b''

if preload:
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@sjoerdjob sjoerdjob Feb 5, 2026

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I'm kind-of inclined to think that this logic should be in _handle_preload, but I'm not sure how to combine that with the tests that were introduced in gh-141859.

sys_argv = sys.argv[1:]
else:
sys_argv = None

_handle_preload(preload, main_path, sys_path, sys_argv, on_error)

util._close_stdin()
Expand Down
27 changes: 27 additions & 0 deletions Lib/test/_test_multiprocessing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -81,6 +81,11 @@
except ImportError:
msvcrt = None

try:
import resource
except ImportError:
resource = None


if support.HAVE_ASAN_FORK_BUG:
# gh-89363: Skip multiprocessing tests if Python is built with ASAN to
Expand Down Expand Up @@ -7106,6 +7111,28 @@ def test_preload_main_sys_argv(self):
'',
])

def test_preload_main_sys_argv_limits(self):
# gh-144503: Check that sys.argv is set before __main__ is pre-loaded
if multiprocessing.get_start_method() != "forkserver":
self.skipTest("forkserver specific test")

max_str_arglen = 32 * resource.getpagesize()
argv = ["a" * (max_str_arglen - 1), "b"]
name = os.path.join(os.path.dirname(__file__), 'mp_preload_sysargv.py')
_, out, err = test.support.script_helper.assert_python_ok(
name, *argv)
self.assertEqual(err, b'')

out = out.decode().split("\n")
expected_argv = str(argv)
self.assertEqual(out, [
f"module:{expected_argv}",
f"fun:{expected_argv}",
f"module:{expected_argv}",
f"fun:{expected_argv}",
'',
])

#
# Mixins
#
Expand Down
3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2026-02-05-16-29-45.gh-issue-144503.f9sl_I.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Fix :mod:`multiprocessing` ``forkserver`` bug which prevented starting of
the forkserver if the total length of command line arguments in ``sys.argv``
exceeded the maximum length of a single command line argument.
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