Remove :class:`Actor` which are not alive from the
        :class:`PoolMixin.managed_actors` and return the number of actors
        still alive.

        :parameter stop: if ``True`` stops all alive actor.

def manage_actors(self, monitor, stop=False):
        '''Remove :class:`Actor` which are not alive from the
        :class:`PoolMixin.managed_actors` and return the number of actors
        still alive.

        :parameter stop: if ``True`` stops all alive actor.
        '''
        alive = 0
        if self.managed_actors:
            for aid, actor in list(self.managed_actors.items()):
                alive += self.manage_actor(monitor, actor, stop)
        return alive