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/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