Fixes issue #3826 and #4791:

Have SocketIO objects update their reference count in the underlying
socket object on close() so that the underlying socket object is
closed immediately when the last user is done rather than at an
unknown later time when garbage collection can do it.

Lib/socket.py

@@ -225,11 +225,12 @@ class SocketIO(io.RawIOBase):
         return self._writing and not self.closed
 
     def fileno(self):
+        self._checkClosed()
         return self._sock.fileno()
 
     @property
     def name(self):
-        return self._sock.fileno()
+        return self.fileno()
 
     @property
     def mode(self):
@@ -239,9 +240,12 @@ class SocketIO(io.RawIOBase):
         if self.closed:
             return
         io.RawIOBase.close(self)
+        self._sock._decref_socketios()
+        self._sock = None
 
     def __del__(self):
-        self._sock._decref_socketios()
+        if not self.closed:
+            self._sock._decref_socketios()
 
 
 def getfqdn(name=''):

Lib/test/test_socket.py

@@ -856,6 +856,16 @@ class FileObjectClassTestCase(SocketConnectedTest):
         self.assertEqual(self.cli_file.mode, 'wb')
         self.assertEqual(self.cli_file.name, self.serv_conn.fileno())
 
+    def testRealClose(self):
+        self.serv_file.close()
+        self.assertRaises(ValueError, self.serv_file.fileno)
+        self.cli_conn.close()
+        self.assertRaises(socket.error, self.cli_conn.getsockname)
+
+    def _testRealClose(self):
+        pass
+
+
 class UnbufferedFileObjectClassTestCase(FileObjectClassTestCase):
 
     """Repeat the tests from FileObjectClassTestCase with bufsize==0.
@@ -881,6 +891,29 @@ class UnbufferedFileObjectClassTestCase(FileObjectClassTestCase):
         self.cli_file.write(b"B. " + MSG)
         self.cli_file.flush()
 
+    def testMakefileClose(self):
+        # The file returned by makefile should keep the socket open...
+        self.cli_conn.close()
+        msg = self.cli_conn.recv(1024)
+        self.assertEqual(msg, MSG)
+        # ...until the file is itself closed
+        self.serv_file.close()
+        self.assertRaises(socket.error, self.cli_conn.recv, 1024)
+
+    def _testMakefileClose(self):
+        self.cli_file.write(MSG)
+        self.cli_file.flush()
+
+    def testMakefileCloseSocketDestroy(self):
+        refcount_before = sys.getrefcount(self.cli_conn)
+        self.serv_file.close()
+        refcount_after = sys.getrefcount(self.cli_conn)
+        self.assertEqual(refcount_before - 1, refcount_after)
+
+    def _testMakefileCloseSocketDestroy(self):
+        pass
+
+
 class LineBufferedFileObjectClassTestCase(FileObjectClassTestCase):
 
     bufsize = 1 # Default-buffered for reading; line-buffered for writing

Misc/NEWS

@@ -111,6 +111,10 @@ Core and Builtins
 Library
 -------
 
+- Issue #3826 and #4791: The socket module now closes the underlying socket
+  appropriately when it is being used via socket.makefile() objects
+  rather than delaying the close by waiting for garbage collection to do it.
+
 - Issue #3860: GzipFile and BZ2File now support the context manager protocol.
 
 - Issue #4867: Fixed a crash in ctypes when passing a string to a