I think the patch makes multiprocessing.util._exit_function() run twice in non-main processes because it is registered with atexit, and is also called in Process._bootstrap().

_exit_function() does the following:

 * terminate active daemon processes;

 * join active non-daemon processes;

 * run finalizers with non-None exit priority and clear finalizer registry.

So calling _exit_function() twice is probably harmless but should perhaps be fixed.

P.S. It also appears that _exit_function() should set the global _exiting to True, since it declares the variable as a global but does not use it.  As a result util.is_exiting() always returns False.