code: def is_checkpointing() -> bool:
      """Whether the current forward propagation is under checkpointing.
  
      Returns:
          bool: :data:`True` if it's under checkpointing.
  
      """
      return thread_local.is_checkpointing
  
imports: from collections import deque
  from contextlib import contextmanager
  import threading
  from typing import TYPE_CHECKING, Deque, Generator, List, Optional, Tuple, Union
  import torch
  from torch import ByteTensor, Tensor
  import torch.autograd
  from .dependency import fork, join
  from .microbatch import Batch
  from .phony import get_phony
label_desc: Use image node_id 3 for calling a global function with example usage: is_checkpointing() and returns: thread_local