def _ensure_worker(self):
        """Ensure there are enough workers available"""
        while len(self._workers) < self._min_workers or len(self._workers) < self._queue.qsize() < self._max_workers:
            worker = threading.Thread(
                target=self._execute_futures,
                name=self.identifier + '_%d' % time.time(),
            )
            worker.daemon = True
            self._workers.add(worker)
            worker.start()
Ensure there are enough workers available