Halt a sampling running in another thread.

def halt(self):
        """Halt a sampling running in another thread."""
        self.status = 'halt'
        # The _halt method is called by _loop.
        if hasattr(
                self, '_sampling_thread') and self._sampling_thread.isAlive():
            print_('Waiting for current iteration to finish...')
            while self._sampling_thread.isAlive():
                sleep(.1)