Issue #8184: multiprocessing: On Windows, don't set SO_REUSEADDR on Connection

sockets, and set FILE_FLAG_FIRST_PIPE_INSTANCE on named pipes, to make sure two
listeners can't bind to the same socket/pipe (or any existing socket/pipe).

Lib/multiprocessing/connection.py

@@ -544,7 +544,8 @@ else:
             obsize, ibsize = 0, BUFSIZE
 
         h1 = win32.CreateNamedPipe(
-            address, openmode | win32.FILE_FLAG_OVERLAPPED,
+            address, openmode | win32.FILE_FLAG_OVERLAPPED |
+            win32.FILE_FLAG_FIRST_PIPE_INSTANCE,
             win32.PIPE_TYPE_MESSAGE | win32.PIPE_READMODE_MESSAGE |
             win32.PIPE_WAIT,
             1, obsize, ibsize, win32.NMPWAIT_WAIT_FOREVER, win32.NULL
@@ -576,7 +577,10 @@ class SocketListener(object):
     def __init__(self, address, family, backlog=1):
         self._socket = socket.socket(getattr(socket, family))
         try:
-            self._socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+            # SO_REUSEADDR has different semantics on Windows (issue #2550).
+            if os.name == 'posix':
+                self._socket.setsockopt(socket.SOL_SOCKET,
+                                        socket.SO_REUSEADDR, 1)
             self._socket.bind(address)
             self._socket.listen(backlog)
             self._address = self._socket.getsockname()
@@ -630,7 +634,8 @@ if sys.platform == 'win32':
         def __init__(self, address, backlog=None):
             self._address = address
             handle = win32.CreateNamedPipe(
-                address, win32.PIPE_ACCESS_DUPLEX,
+                address, win32.PIPE_ACCESS_DUPLEX |
+                win32.FILE_FLAG_FIRST_PIPE_INSTANCE,
                 win32.PIPE_TYPE_MESSAGE | win32.PIPE_READMODE_MESSAGE |
                 win32.PIPE_WAIT,
                 win32.PIPE_UNLIMITED_INSTANCES, BUFSIZE, BUFSIZE,

Lib/test/test_multiprocessing.py

@@ -1779,6 +1779,17 @@ class _TestConnection(BaseTestCase):
         self.assertRaises(RuntimeError, reduction.recv_handle, conn)
         p.join()
 
+class _TestListener(BaseTestCase):
+
+    ALLOWED_TYPES = ('processes')
+
+    def test_multiple_bind(self):
+        for family in self.connection.families:
+            l = self.connection.Listener(family=family)
+            self.addCleanup(l.close)
+            self.assertRaises(OSError, self.connection.Listener,
+                              l.address, family)
+
 class _TestListenerClient(BaseTestCase):
 
     ALLOWED_TYPES = ('processes', 'threads')
@@ -1799,6 +1810,7 @@ class _TestListenerClient(BaseTestCase):
             self.assertEqual(conn.recv(), 'hello')
             p.join()
             l.close()
+
 #
 # Test of sending connection and socket objects between processes
 #

Misc/NEWS

@@ -472,6 +472,11 @@ Library
 
 - Issue #13846: Add time.monotonic(), monotonic clock.
 
+- Issue #8184: multiprocessing: On Windows, don't set SO_REUSEADDR on
+  Connection sockets, and set FILE_FLAG_FIRST_PIPE_INSTANCE on named pipes, to
+  make sure two listeners can't bind to the same socket/pipe (or any existing
+  socket/pipe).
+
 - Issue #10811: Fix recursive usage of cursors. Instead of crashing,
   raise a ProgrammingError now.
 

Modules/_multiprocessing/win32_functions.c

@@ -784,6 +784,7 @@ create_win32_namespace(void)
     WIN32_CONSTANT(F_DWORD, ERROR_PIPE_BUSY);
     WIN32_CONSTANT(F_DWORD, ERROR_PIPE_CONNECTED);
     WIN32_CONSTANT(F_DWORD, ERROR_SEM_TIMEOUT);
+    WIN32_CONSTANT(F_DWORD, FILE_FLAG_FIRST_PIPE_INSTANCE);
     WIN32_CONSTANT(F_DWORD, FILE_FLAG_OVERLAPPED);
     WIN32_CONSTANT(F_DWORD, GENERIC_READ);
     WIN32_CONSTANT(F_DWORD, GENERIC_WRITE);