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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
Merged

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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Limit the number of attempts.
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@serhiy-storchaka
serhiy-storchaka committed Feb 10, 2026
commit cae80b95be20edaf386c942390b97d6caae2fb36
5 changes: 4 additions & 1 deletion Lib/asyncio/windows_utils.py
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Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,7 @@
PIPE = subprocess.PIPE
STDOUT = subprocess.STDOUT
_mmap_counter = itertools.count()
_MAX_PIPE_ATTEMPTS = 100
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# Replacement for os.pipe() using handles instead of fds
Expand Down Expand Up @@ -51,7 +52,7 @@ def pipe(*, duplex=False, overlapped=(True, True), bufsize=BUFSIZE):

h1 = h2 = None
try:
while True:
for attempts in itertools.count():
address = r'\\.\pipe\python-pipe-{:d}-{:d}-{}'.format(
os.getpid(), next(_mmap_counter), os.urandom(8).hex())
try:
Expand All @@ -60,6 +61,8 @@ def pipe(*, duplex=False, overlapped=(True, True), bufsize=BUFSIZE):
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):
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@gpshead gpshead Feb 10, 2026

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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)

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@serhiy-storchaka serhiy-storchaka Feb 10, 2026

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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
Expand Down
9 changes: 7 additions & 2 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 @@ -480,12 +481,14 @@ def __init__(self, address=None, family=None, backlog=1, authkey=None):
if address:
self._listener = PipeListener(address, backlog)
else:
while True:
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
Expand Down Expand Up @@ -589,7 +592,7 @@ def Pipe(duplex=True):
access = _winapi.GENERIC_WRITE
obsize, ibsize = 0, BUFSIZE

while True:
for attempts in itertools.count():
address = arbitrary_address('AF_PIPE')
try:
h1 = _winapi.CreateNamedPipe(
Expand All @@ -603,6 +606,8 @@ def Pipe(duplex=True):
)
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
Expand Down
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