def _processing_controller_status(self):
        """Report on the status of the Processing Block queue(s)."""
        LOG.info('Starting Processing Block queue reporter.')
        while True:
            LOG.info('PB queue length = %d', len(self._queue))
            time.sleep(self._report_interval)
            if active_count() != 5:
                LOG.critical('Processing Controller not running '
                             'correctly! (%d/%d threads active)',
                             active_count(), 5)