class_docstr: Base class to inherit for concrete executors such as Celery, Kubernetes, Local, Sequential, etc.
  
  :param parallelism: how many jobs should run at one time. Set to ``0`` for infinity.
class_docstr_tok: ["Base","class","to","inherit","for","concrete","executors","such","as","Celery",",","Kubernetes",",","Local",",","Sequential",",","etc",".",":","param","parallelism",":","how","many","jobs","should","run","at","one","time",".","Set","to","``","0","``","for","infinity","."]
docstr: Send callback for execution.
  
  Provides a default implementation which sends the callback to the `callback_sink` object.
  
  :param request: Callback request to be executed.
docstr_tok: ["Send","callback","for","execution",".","Provides","a","default","implementation","which","sends","the","callback","to","the","`","callback_sink","`","object",".",":","param","request",":","Callback","request","to","be","executed","."]
code: def send_callback(self, request: CallbackRequest) -> None:
      """Send callback for execution.
  
      Provides a default implementation which sends the callback to the `callback_sink` object.
  
      :param request: Callback request to be executed.
      """
      if not self.callback_sink:
          raise ValueError("Callback sink is not ready.")
      self.callback_sink.send(request)
  
imports: from __future__ import annotations
  import logging
  import sys
  import warnings
  from collections import defaultdict
  from dataclasses import dataclass, field
  from typing import TYPE_CHECKING, Any, List, Optional, Sequence, Tuple
  import pendulum
  from airflow.cli.cli_config import DefaultHelpParser
  from airflow.configuration import conf
  from airflow.exceptions import RemovedInAirflow3Warning
  from airflow.stats import Stats
  from airflow.utils.log.logging_mixin import LoggingMixin
  from airflow.utils.state import TaskInstanceState
label_desc: Use image node_id 26 for calling the BaseExecutor obj's underlying member method code with example usage: obj.send_callback(request) without return types