code: def should_fork(self):
          
          return (
              super(NewStylePlanner, self).should_fork() or
              (self._inv.task_vars.get('mitogen_task_isolation') == 'fork') or
              (self._inv.module_name in self.ALWAYS_FORK_MODULES) or
              (len(self.get_module_map()['custom']) > 0)
          )
docs: In addition to asynchronous tasks, new-style modules should be forked
          if:
  
          * the user specifies mitogen_task_isolation=fork, or
          * the new-style module has a custom module search path, or
          * the module is known to leak like a sieve.