gh-137335: Fix unlikely name conflicts for named pipes in multiprocessing and asyncio...

Since os.stat() raises an OSError for existing named pipe "\\.\pipe\...",
os.path.exists() always returns False for it, and tempfile.mktemp() can
return a name that matches an existing named pipe.

So, tempfile.mktemp() cannot be used to generate unique names for named
pipes. Instead, CreateNamedPipe() should be called in a loop with
different names until it completes successfully.

diff --git a/Lib/asyncio/windows_utils.py b/Lib/asyncio/windows_utils.py
index ef277fac3e291c307d5e26ada8ef5e28c47434f1..acd49441131b04252b31c8dbef846fac35800d95 100644 (file)
--- a/Lib/asyncio/windows_utils.py
+++ b/Lib/asyncio/windows_utils.py
@@ -10,7 +10,6 @@ import itertools
 import msvcrt
 import os
 import subprocess
-import tempfile
 import warnings
 
 
@@ -24,6 +23,7 @@ BUFSIZE = 8192
 PIPE = subprocess.PIPE
 STDOUT = subprocess.STDOUT
 _mmap_counter = itertools.count()
+_MAX_PIPE_ATTEMPTS = 20
 
 
 # Replacement for os.pipe() using handles instead of fds
@@ -31,10 +31,6 @@ _mmap_counter = itertools.count()
 
 def pipe(*, duplex=False, overlapped=(True, True), bufsize=BUFSIZE):
     """Like os.pipe() but with overlapped support and using handles not fds."""
-    address = tempfile.mktemp(
-        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
@@ -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):
+                    raise
 
         h2 = _winapi.CreateFile(
             address, access, 0, _winapi.NULL, _winapi.OPEN_EXISTING,

diff --git a/Lib/multiprocessing/connection.py b/Lib/multiprocessing/connection.py
index 64ec53884aeb5d67b733d120ca79b75dca67e46b..41b36066c62fcbf1d112fc3e30a0816ff92b0a96 100644 (file)
--- a/Lib/multiprocessing/connection.py
+++ b/Lib/multiprocessing/connection.py
@@ -46,6 +46,7 @@ BUFSIZE = 64 * 1024
 CONNECTION_TIMEOUT = 20.
 
 _mmap_counter = itertools.count()
+_MAX_PIPE_ATTEMPTS = 100
 
 default_family = 'AF_INET'
 families = ['AF_INET']
@@ -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')
 
@@ -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):
@@ -570,7 +583,6 @@ else:
         '''
         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
@@ -580,15 +592,25 @@ else:
             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

diff --git a/Misc/NEWS.d/next/Library/2025-08-04-23-20-43.gh-issue-137335.IIjDJN.rst b/Misc/NEWS.d/next/Library/2025-08-04-23-20-43.gh-issue-137335.IIjDJN.rst
new file mode 100644 (file)
index 0000000..2311ace
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-08-04-23-20-43.gh-issue-137335.IIjDJN.rst
@@ -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.