Function that wraps the main function in a multiprocessing-friendly way.

This function additionally accepts an extra_state_savers kwarg; users can provide a list of tf_agents.multiprocessing.StateSaver instances, where a StateSaver tells multiprocessing how to store some global state and how to restore it in the subprocess.

parent_main_fn A callable.
*args rgs for parent_main_fn.
**kwargs kwargs for parent_main_fn. This may also include extra_state_savers kwarg.

Output of parent_main_fn.