def collect(self):
        """
        Override collect to copy files concurrently. The tasks are populated by
        Command.copy_file() which is called by super().collect().
        """
        ret = super(Command, self).collect()
        if settings.threads:
            Pool(settings.threads).map(self.do_copy_file, self.tasks)
        return ret
Override collect to copy files concurrently. The tasks are populated by
        Command.copy_file() which is called by super().collect().