def is_running(self):
        """Return whether this process is running."""
        if self._gone:
            return False
        try:
            # Checking if pid is alive is not enough as the pid might
            # have been reused by another process.
            # pid + creation time, on the other hand, is supposed to
            # identify a process univocally.
            return self.create_time == \
                   self._platform_impl.get_process_create_time()
        except NoSuchProcess:
            self._gone = True
            return False
Return whether this process is running.