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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _stop_lock_renewer(self):
 """ Stop the lock renewer. This signals the renewal thread and waits for its exit. """

        if self._lock_renewal_thread is None or not self._lock_renewal_thread.is_alive():
            return
        logger.debug("Signalling the lock refresher to stop")
        self._lock_renewal_stop.set()
        self._lock_renewal_thread.join()
        self._lock_renewal_thread = None
        logger.debug("Lock refresher has stopped")