code: def is_shared_filesystem(
      strategy: "Strategy",
      path: Optional[_PATH] = None,
      timeout: int = 3,
  ) -> bool:
      """Checks whether the filesystem under the given path is shared across all processes.
  
      This function should only be used in a context where distributed is initialized.
  
      Args:
          strategy: The strategy being used, either from Fabric (``fabric.strategy``) or from Trainer
              (``trainer.strategy``).
          path: The path to check. Defaults to the current working directory. The user must have permissions to write
              to this path or the parent folder, and the filesystem must be writable.
          timeout: If any of the processes can't list the file created by rank 0 within this many seconds, the
              filesystem is determined to be not shared.
  
      """
      # Fast path: Any non-local filesystem is considered shared (e.g., S3)
      if path is not None and not _is_local_file_protocol(path):
          return True
  
      path = Path(Path.cwd() if path is None else path).resolve()
  
      # Fast path: Only distributed strategies can detect shared filesystems
      if (
          not hasattr(strategy, "world_size")
          or strategy.world_size == 1
      ):
          return True
  
      # Fast path: If the path is not the same on all ranks we know it's not a shared filesystem
      rank_zero_path = strategy.broadcast(path)
      if not strategy.reduce_boolean_decision(
          rank_zero_path == path, all=True
      ):
          return False
  
      if not strategy.reduce_boolean_decision(path.exists(), all=True):
          raise FileNotFoundError(
              f"Unable to determine if the path belongs to a shared filesystem. The path does not exist: {path}"
          )
  
      path = path.parent if path.is_file() else path
      check_file = path / ".lightning_shared_fs_check"
      check_file.unlink(missing_ok=True)
  
      strategy.barrier()
      if strategy.is_global_zero:
          # Rank 0 creates the file
          check_file.touch()
          found = True
      else:
          # All other ranks will wait until they find the file or timeout
          start = time.perf_counter()
          found = False
          while not found and (time.perf_counter() - start) < timeout:
              found = check_file.exists()
      strategy.barrier()
  
      all_found = strategy.reduce_boolean_decision(found, all=True)
  
      with contextlib.suppress(
          OSError
      ):  # handle race condition on deletion
          check_file.unlink()
  
      return all_found
  
imports: import contextlib
  import logging
  import os
  import time
  from contextlib import nullcontext
  from pathlib import Path
  from typing import TYPE_CHECKING, Any, Iterable, Iterator, List, Optional, Sized, Union
  import torch
  import torch.nn.functional
  from lightning_utilities.core.imports import package_available
  from torch import Tensor
  from torch.utils.data import Dataset, DistributedSampler, Sampler
  from typing_extensions import override
  from lightning.fabric.utilities.cloud_io import _is_local_file_protocol
  from lightning.fabric.utilities.data import _num_cpus_available
  from lightning.fabric.utilities.rank_zero import rank_zero_info
  from lightning.fabric.utilities.types import _PATH, ReduceOp
label_desc: Use image node_id 1 for calling a global function with example usage: is_shared_filesystem(strategy, path, timeout) and returns: all_found, True, True, False