code: def _get_dmatrix_chunks_workers(ctx, dmatrix):
      # dmatrix_chunk.inputs is concat, and concat's input is the coallocated chunks
      metas = ctx.get_chunks_meta(
          [c.inputs[0].inputs[0].key for c in dmatrix.chunks],
          fields=["bands"],
      )
      return [m["bands"][0][0] for m in metas]
  
imports: import itertools
  import logging
  import pickle
  from collections import OrderedDict, defaultdict
  import numpy
  from ....None import opcodes
  from ....core import OutputType
  from ....core.context import get_context
  from ....core.operand import MergeDictOperand
  from ....serialization.serializables import FieldTypes, DictField, KeyField, ListField
  from ....utils import ensure_own_data
  from .dmatrix import ToDMatrix, to_dmatrix
  from .start_tracker import StartTracker
label_desc: Use image node_id 4 for calling the XGBTrain obj's underlying member method code with example usage: obj._get_dmatrix_chunks_workers(ctx, dmatrix) and returns: unknown