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gh-137335: Fix unlikely name conflicts for named pipes in multiprocessing and asyncio on Windows by serhiy-storchaka · Pull Request #137389 · python/cpython · GitHub

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gh-137335: Fix unlikely name conflicts for named pipes in multiprocessing and asyncio on Windows #137389

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Merged
serhiy-storchaka merged 9 commits into from
Feb 24, 2026
Conversation 12 Commits 9 Checks 49 Files changed
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gh-137335: Fix unlikely name conflicts for named pipes in multiprocessing and asyncio on Windows #137389

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2a0a5e9
gh-137335: Fix unlikely nmae conflicts for named pipes in multiproces…
serhiy-storchaka Aug 4, 2025
5b91a56
Fix typo
serhiy-storchaka Aug 5, 2025
ed050a0
Do not use os.getpid() and tempfile._get_candidate_names().
serhiy-storchaka Aug 5, 2025
7363c99
Merge branch 'main' into temp-named-pipes
serhiy-storchaka Feb 5, 2026
5243b9e
Use os.urandom().
serhiy-storchaka Feb 5, 2026
81cb66e
Merge branch 'main' into temp-named-pipes
serhiy-storchaka Feb 10, 2026
5207bf6
Restore the PID and sequential number for debugging and reducing chan…
serhiy-storchaka Feb 10, 2026
cae80b9
Limit the number of attempts.
serhiy-storchaka Feb 10, 2026
de04089
Apply suggestion from @serhiy-storchaka
serhiy-storchaka Feb 10, 2026
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23 changes: 15 additions & 8 deletions Lib/asyncio/windows_utils.py
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Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,6 @@
import msvcrt
import os
import subprocess
import tempfile
import warnings


Expand All @@ -24,17 +23,14 @@
PIPE = subprocess.PIPE
STDOUT = subprocess.STDOUT
_mmap_counter = itertools.count()
_MAX_PIPE_ATTEMPTS = 20


# Replacement for os.pipe() using handles instead of fds


def pipe(*, duplex=False, overlapped=(True, True), bufsize=BUFSIZE):
"""Like os.pipe() but with overlapped support and using handles not fds."""
address = tempfile.mktemp(
Comment thread
kumaraditya303 marked this conversation as resolved.
prefix=r'\\.\pipe\python-pipe-{:d}-{:d}-'.format(
os.getpid(), next(_mmap_counter)))

if duplex:
openmode = _winapi.PIPE_ACCESS_DUPLEX
access = _winapi.GENERIC_READ | _winapi.GENERIC_WRITE
Expand All @@ -56,9 +52,20 @@ def pipe(*, duplex=False, overlapped=(True, True), bufsize=BUFSIZE):

h1 = h2 = None
try:
h1 = _winapi.CreateNamedPipe(
address, openmode, _winapi.PIPE_WAIT,
1, obsize, ibsize, _winapi.NMPWAIT_WAIT_FOREVER, _winapi.NULL)
for attempts in itertools.count():
address = r'\\.\pipe\python-pipe-{:d}-{:d}-{}'.format(
os.getpid(), next(_mmap_counter), os.urandom(8).hex())
try:
h1 = _winapi.CreateNamedPipe(
address, openmode, _winapi.PIPE_WAIT,
1, obsize, ibsize, _winapi.NMPWAIT_WAIT_FOREVER, _winapi.NULL)
break
except OSError as e:
if attempts >= _MAX_PIPE_ATTEMPTS:
raise
if e.winerror not in (_winapi.ERROR_PIPE_BUSY,
_winapi.ERROR_ACCESS_DENIED):

gpshead Feb 10, 2026

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

an infinite loop retrying on this error could potentially hide an error if the system simply doesn't allow this process to create a pipe with the given address? (here and below)

serhiy-storchaka Feb 10, 2026

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

I do not know if this is even possible (\\.\pipe\ is not a real directory which you can forbid access to), but it will not harm if limit the number of attempts.
raise

h2 = _winapi.CreateFile(
address, access, 0, _winapi.NULL, _winapi.OPEN_EXISTING,
Expand Down
58 changes: 40 additions & 18 deletions Lib/multiprocessing/connection.py
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Original file line number Diff line number Diff line change
Expand Up @@ -46,6 +46,7 @@
CONNECTION_TIMEOUT = 20.

_mmap_counter = itertools.count()
_MAX_PIPE_ATTEMPTS = 100

default_family = 'AF_INET'
families = ['AF_INET']
Expand Down Expand Up @@ -78,8 +79,8 @@ def arbitrary_address(family):
elif family == 'AF_UNIX':
return tempfile.mktemp(prefix='sock-', dir=util.get_temp_dir())
elif family == 'AF_PIPE':
return tempfile.mktemp(prefix=r'\\.\pipe\pyc-%d-%d-' %
(os.getpid(), next(_mmap_counter)), dir="")
return (r'\\.\pipe\pyc-%d-%d-%s' %
(os.getpid(), next(_mmap_counter), os.urandom(8).hex()))
else:
raise ValueError('unrecognized family')

Expand Down Expand Up @@ -472,17 +473,29 @@ class Listener(object):
def __init__(self, address=None, family=None, backlog=1, authkey=None):
family = family or (address and address_type(address)) \
or default_family
address = address or arbitrary_address(family)

_validate_family(family)
if authkey is not None and not isinstance(authkey, bytes):
raise TypeError('authkey should be a byte string')

if family == 'AF_PIPE':
self._listener = PipeListener(address, backlog)
if address:
self._listener = PipeListener(address, backlog)
else:
for attempts in itertools.count():
address = arbitrary_address(family)
try:
self._listener = PipeListener(address, backlog)
break
except OSError as e:
if attempts >= _MAX_PIPE_ATTEMPTS:
raise
if e.winerror not in (_winapi.ERROR_PIPE_BUSY,
_winapi.ERROR_ACCESS_DENIED):
raise
else:
address = address or arbitrary_address(family)
self._listener = SocketListener(address, family, backlog)

if authkey is not None and not isinstance(authkey, bytes):
raise TypeError('authkey should be a byte string')

self._authkey = authkey

def accept(self):
Expand Down Expand Up @@ -570,7 +583,6 @@ def Pipe(duplex=True):
'''
Returns pair of connection objects at either end of a pipe
'''
address = arbitrary_address('AF_PIPE')
if duplex:
openmode = _winapi.PIPE_ACCESS_DUPLEX
access = _winapi.GENERIC_READ | _winapi.GENERIC_WRITE
Expand All @@ -580,15 +592,25 @@ def Pipe(duplex=True):
access = _winapi.GENERIC_WRITE
obsize, ibsize = 0, BUFSIZE

h1 = _winapi.CreateNamedPipe(
address, openmode | _winapi.FILE_FLAG_OVERLAPPED |
_winapi.FILE_FLAG_FIRST_PIPE_INSTANCE,
_winapi.PIPE_TYPE_MESSAGE | _winapi.PIPE_READMODE_MESSAGE |
_winapi.PIPE_WAIT,
1, obsize, ibsize, _winapi.NMPWAIT_WAIT_FOREVER,
# default security descriptor: the handle cannot be inherited
_winapi.NULL
)
for attempts in itertools.count():
address = arbitrary_address('AF_PIPE')
try:
h1 = _winapi.CreateNamedPipe(
address, openmode | _winapi.FILE_FLAG_OVERLAPPED |
_winapi.FILE_FLAG_FIRST_PIPE_INSTANCE,
_winapi.PIPE_TYPE_MESSAGE | _winapi.PIPE_READMODE_MESSAGE |
_winapi.PIPE_WAIT,
1, obsize, ibsize, _winapi.NMPWAIT_WAIT_FOREVER,
# default security descriptor: the handle cannot be inherited
_winapi.NULL
)
break
except OSError as e:
if attempts >= _MAX_PIPE_ATTEMPTS:
raise
if e.winerror not in (_winapi.ERROR_PIPE_BUSY,
_winapi.ERROR_ACCESS_DENIED):
raise
h2 = _winapi.CreateFile(
address, access, 0, _winapi.NULL, _winapi.OPEN_EXISTING,
_winapi.FILE_FLAG_OVERLAPPED, _winapi.NULL
Expand Down
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2025-08-04-23-20-43.gh-issue-137335.IIjDJN.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Get rid of any possibility of a name conflict for named pipes in
:mod:`multiprocessing` and :mod:`asyncio` on Windows, no matter how small.
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