code: def _close_comm(ref):
      """Callback to close Dask Comm when UCX Endpoint closes or errors
  
      Parameters
      ----------
          ref: weak reference to a Dask UCX comm
      """
      comm = ref()
      if comm is not None:
          comm._closed = True
  
imports: from __future__ import annotations
  import functools
  import logging
  import os
  import struct
  import weakref
  from collections.abc import Awaitable, Callable, Collection
  from typing import TYPE_CHECKING, Any
  from unittest.mock import patch
  import dask
  from dask.utils import parse_bytes
  from distributed.comm.addressing import parse_host_port, unparse_host_port
  from distributed.comm.core import BaseListener, Comm, CommClosedError, Connector
  from distributed.comm.registry import Backend, backends
  from distributed.comm.utils import ensure_concrete_host, from_frames, to_frames
  from distributed.diagnostics.nvml import CudaDeviceInfo, get_device_index_and_uuid, has_cuda_context
  from distributed.protocol.utils import host_array
  from distributed.utils import ensure_ip, get_ip, get_ipv6, log_errors, nbytes
label_desc: Use image node_id 6 for calling a global function with example usage: _close_comm(ref) without return types