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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(self):
 """Stops the adb logcat service."""

        if not self._adb_logcat_process:
            return
        try:
            utils.stop_standing_subprocess(self._adb_logcat_process)
        except:
            self._ad.log.exception('Failed to stop adb logcat.')
        self._adb_logcat_process = None