Update popen_fork.py

Author: geryogam

Lib/multiprocessing/popen_fork.py

@@ -74,10 +74,10 @@ def _launch(self, process_obj):
         else:
             os.close(child_w)
             os.close(child_r)
-            self.finalizer = util.Finalize(self, util.close_fds,
-                                           (parent_r, parent_w,))._key
+            self._finalizer = util.Finalize(self, util.close_fds,
+                                            (parent_r, parent_w,))._key
             self.sentinel = parent_r
 
     def close(self):
         if self.finalizer is not None:
-            util._finalizer_registry[self.finalizer()]()
+            util._finalizer_registry[self._finalizer]()