https://github.com/python/cpython/commit/d0212f6946dc6bbf82363bff0c93f6708abe76a7
commit: d0212f6946dc6bbf82363bff0c93f6708abe76a7
branch: main
author: Bénédikt Tran <[email protected]>
committer: picnixz <[email protected]>
date: 2026-10-22T10:30:15-07:00
summary:
gh-149527: fix creation of temporary socket files post GH-148578 (#149597)
files:
A Misc/NEWS.d/next/Library/2026-05-09-12-58-04.gh-issue-149527.hX36Yh.rst
M Lib/multiprocessing/connection.py
M Lib/multiprocessing/util.py
M Lib/test/test_multiprocessing_forkserver/test_misc.py
diff --git a/Lib/multiprocessing/connection.py
b/Lib/multiprocessing/connection.py
index be2fc3edf5dce66..e33d1ed800f319f 100644
--- a/Lib/multiprocessing/connection.py
+++ b/Lib/multiprocessing/connection.py
@@ -76,11 +76,12 @@ def arbitrary_address(family):
if family == 'AF_INET':
return ('localhost', 0)
elif family == 'AF_UNIX':
- # NOTE: util.get_temp_dir() is a 0o700 per-process directory. A
- # mktemp-style ToC vs ToU concern is not important; bind() surfaces
- # the extremely unlikely collision as EADDRINUSE.
+ # NOTE: util.get_temp_dir() is a 0o700 per-process directory.
+ # A mktemp-style ToC vs ToU concern is not important as bind()
+ # surfaces the extremely unlikely collision as EADDRINUSE.
+ suffix = os.urandom(util._TMPSOCK_SUFFIXLEN // 2).hex()
return os.path.join(util.get_temp_dir(),
- f'sock-{os.urandom(6).hex()}')
+ f"{util._TMPSOCK_PREFIX}{suffix}")
elif family == 'AF_PIPE':
return (r'\\.\pipe\pyc-%d-%d-%s' %
(os.getpid(), next(_mmap_counter), os.urandom(8).hex()))
diff --git a/Lib/multiprocessing/util.py b/Lib/multiprocessing/util.py
index a84546bbb8fe1e3..28d5d30f7ac89fa 100644
--- a/Lib/multiprocessing/util.py
+++ b/Lib/multiprocessing/util.py
@@ -143,6 +143,41 @@ def is_abstract_socket_namespace(address):
# On Windows platforms, we do not create AF_UNIX sockets.
_SUN_PATH_MAX = None if os.name == 'nt' else 92
+# The temporary socket file path (without NULL terminator) is
+#
+# TEMPDIR/{_TMPPYMP_PREFIX}{S1}/{_TMPSOCK_PREFIX}{S2}
+#
+# where
+#
+# - S1 is a random suffix of length 8 generated by get_temp_dir().
+# This is used to generate the temporary sub-directory that will
+# contains the socket file. Update _TMPPYMP_SUFFIXLEN accordingly
+# if the random suffix length chosen by tempfile.mkdtemp() changes.
+#
+# - S2 is a random suffix of length 2N generated by os.urandom(N).hex()
+# in multiprocessing.connection.arbitrary_address(). The value of N
+# is not fixed and may vary across Python versions as to minimize
+# collisions and path lengths.
+#
+_TMPPYMP_PREFIX = "pymp-"
+_TMPPYMP_PREFIXLEN = len(_TMPPYMP_PREFIX)
+_TMPPYMP_SUFFIXLEN = 8
+_TMPSOCK_PREFIX = "sock-"
+_TMPSOCK_PREFIXLEN = len(_TMPSOCK_PREFIX)
+_TMPSOCK_SUFFIXLEN = 12
+
+# Length of the socket filepath from the chosen temporary directory,
+# including a leading path separator and the path separator between
+# the temporary subdirectory and the socket filename.
+_SUN_PATH_LEN_RESERVED = (
+ len(os.path.sep) + _TMPPYMP_PREFIXLEN + _TMPPYMP_SUFFIXLEN +
+ len(os.path.sep) + _TMPSOCK_PREFIXLEN + _TMPSOCK_SUFFIXLEN
+)
+assert (
+ _SUN_PATH_MAX is None
+ or _SUN_PATH_LEN_RESERVED < _SUN_PATH_MAX
+)
+
def _remove_temp_dir(rmtree, tempdir):
rmtree(tempdir)
@@ -161,9 +196,8 @@ def _get_base_temp_dir(tempfile):
"""
if os.name == 'nt':
return None
- # Most of the time, the default temporary directory is /tmp. Thus,
- # listener sockets files "$TMPDIR/pymp-XXXXXXXX/sock-XXXXXXXX" do
- # not have a path length exceeding SUN_PATH_MAX.
+ # Most of the time, the default temporary directory is /tmp. As such,
+ # the path length of listener sockets files does not exceed SUN_PATH_MAX.
#
# If users specify their own temporary directory, we may be unable
# to create those files. Therefore, we fall back to the system-wide
@@ -171,14 +205,7 @@ def _get_base_temp_dir(tempfile):
#
# See https://github.com/python/cpython/issues/132124.
base_tempdir = tempfile.gettempdir()
- # Files created in a temporary directory are suffixed by a string
- # generated by tempfile._RandomNameSequence, which, by design,
- # is 8 characters long.
- #
- # Thus, the socket file path length (without NULL terminator) will be:
- #
- # len(base_tempdir + '/pymp-XXXXXXXX' + '/sock-XXXXXXXX')
- sun_path_len = len(base_tempdir) + 14 + 14
+ sun_path_len = len(base_tempdir) + _SUN_PATH_LEN_RESERVED
# Strict inequality to account for the NULL terminator.
# See https://github.com/python/cpython/issues/140734.
if sun_path_len < _SUN_PATH_MAX:
@@ -206,8 +233,8 @@ def _get_base_temp_dir(tempfile):
# not be able to write socket files out there.
return base_tempdir
warn("Ignoring user-defined temporary directory: %s", base_tempdir)
- # at most max(map(len, dirlist)) + 14 + 14 = 36 characters
- assert len(base_system_tempdir) + 14 + 14 < _SUN_PATH_MAX
+ # The following assertion must be satisfied with the chosen constants.
+ assert len(base_system_tempdir) + _SUN_PATH_LEN_RESERVED < _SUN_PATH_MAX
return base_system_tempdir
@@ -218,7 +245,7 @@ def get_temp_dir():
# Deferred until first use to keep importing this module cheap.
import shutil, tempfile
base_tempdir = _get_base_temp_dir(tempfile)
- tempdir = tempfile.mkdtemp(prefix='pymp-', dir=base_tempdir)
+ tempdir = tempfile.mkdtemp(prefix=_TMPPYMP_PREFIX, dir=base_tempdir)
info('created temp directory %s', tempdir)
# keep a strong reference to shutil.rmtree(), since the finalizer
# can be called late during Python shutdown
diff --git a/Lib/test/test_multiprocessing_forkserver/test_misc.py
b/Lib/test/test_multiprocessing_forkserver/test_misc.py
index 9cae1b50f71e00b..a3ee2e2b73c3e19 100644
--- a/Lib/test/test_multiprocessing_forkserver/test_misc.py
+++ b/Lib/test/test_multiprocessing_forkserver/test_misc.py
@@ -1,7 +1,47 @@
+import os
+import re
import unittest
+from multiprocessing.util import _SUN_PATH_MAX
from test._test_multiprocessing import install_tests_in_module_dict
+from test.support import os_helper, script_helper
install_tests_in_module_dict(globals(), 'forkserver', exclude_types=True)
+
+class TestForkServerConfiguration(unittest.TestCase):
+ def test_respect_sun_path_max(self):
+ # Ensure that the calculation for temporary filepath lengths is
correct.
+ # See https://github.com/python/cpython/issues/149527.
+
+ cmd = '''if 1:
+ from multiprocessing.connection import arbitrary_address
+ from multiprocessing.util import get_temp_dir
+ if __name__ == "__main__":
+ print(get_temp_dir())
+ print(arbitrary_address("AF_UNIX"))
+ '''
+ with os_helper.temp_dir() as root:
+ self.assertLess(len(root), _SUN_PATH_MAX)
+ _, out, _ = script_helper.assert_python_ok('-c', cmd, TMPDIR=root)
+ res = out.decode().strip().splitlines()
+ self.assertEqual(len(res), 2)
+
+ # get_temp_dir() with a TMPDIR that has a too large length ends up
+ # NOT being used as it is not possible to use it. In particular,
+ # the corresponding path will fallback to one of the "built-in"
+ # ones such as '/tmp', '/var/tmp', or '/usr/tmp'.
+ root_regex = "|".join(map(re.escape, [root, "/tmp", "/var/tmp",
"/usr/tmp"]))
+
+ temp_pymp = res[0]
+ self.assertLess(len(temp_pymp), _SUN_PATH_MAX)
+ temp_pymp_regex = os.path.join(root_regex, r"pymp-\w{8}")
+ self.assertRegex(temp_pymp, temp_pymp_regex)
+
+ temp_sock = res[1]
+ self.assertLess(len(temp_sock), _SUN_PATH_MAX)
+ temp_sock_regex = os.path.join(temp_pymp_regex,
r"sock-[0-9a-fA-F]{12}")
+ self.assertRegex(temp_sock, temp_sock_regex)
+
+
if __name__ == '__main__':
unittest.main()
diff --git
a/Misc/NEWS.d/next/Library/2026-05-09-12-58-04.gh-issue-149527.hX36Yh.rst
b/Misc/NEWS.d/next/Library/2026-05-09-12-58-04.gh-issue-149527.hX36Yh.rst
new file mode 100644
index 000000000000000..d75b285554c0fa8
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-05-09-12-58-04.gh-issue-149527.hX36Yh.rst
@@ -0,0 +1,3 @@
+:mod:`multiprocessing`: fix creation of temporary socket files following
+:gh:`137335` (`PR#148578 <https://github.com/python/cpython/pull/148578>`__
+and corresponding backports). Patch by Bénédikt Tran.
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