class_docstr: Metaclass that allows to implement singleton pattern.
class_docstr_tok: ["Metaclass","that","allows","to","implement","singleton","pattern","."]
code: def __call__(cls: Singleton[T], *args, **kwargs) -> T:
      if cls not in cls._instances:
          cls._instances[cls] = super().__call__(*args, **kwargs)
      return cls._instances[cls]
  
imports: from __future__ import annotations
  import contextlib
  import json
  import multiprocessing
  import time
  from queue import Empty, Queue
  from typing import TYPE_CHECKING, Any, Generic, TypeVar
  from kubernetes import client, watch
  from kubernetes.client.rest import ApiException
  from urllib3.exceptions import ReadTimeoutError
  from airflow.exceptions import AirflowException
  from airflow.providers.cncf.kubernetes.kube_client import get_kube_client
  from airflow.providers.cncf.kubernetes.kubernetes_helper_functions import annotations_for_logging_task_metadata, annotations_to_key, create_pod_id
  from airflow.providers.cncf.kubernetes.pod_generator import PodGenerator
  from airflow.utils.log.logging_mixin import LoggingMixin
  from airflow.utils.state import TaskInstanceState
label_desc: Use image node_id 1 for calling the Singleton obj's underlying member method code with example usage: obj.__call__(cls) and returns: cls