class_docstr: A task scheduler for subpipeline.
code: def cancel(self, cancel_task: task_lib.CancelTask) -> None:
      self._cancel.set()
  
imports: import copy
  import threading
  from typing import Callable, Optional
  from absl import flags
  from absl import logging
  from tfx.orchestration import metadata
  from tfx.orchestration.experimental.core import pipeline_ops
  from tfx.orchestration.experimental.core import pipeline_state
  from tfx.orchestration.experimental.core import task
  from tfx.orchestration.experimental.core import task_scheduler
  from tfx.orchestration.portable.mlmd import context_lib
  from tfx.orchestration.portable.mlmd import execution_lib
  from tfx.proto.orchestration import pipeline_pb2
  from tfx.utils import status
  from ml_metadata.proto import metadata_store_pb2
label_desc: Use image node_id 5 for calling the SubPipelineTaskScheduler obj's underlying member method code with example usage: obj.cancel(cancel_task) without return types