code: def _readexactly(self, n: int):
      # asyncio StreamReader may not guarantee to read n bytes
      # for it we need to call `readexactly` instead
      read = (
          self._file.readexactly
          if hasattr(self._file, "readexactly")
          else self._file.read
      )
      return read(n)
  
file_path: mars/mars/serialization/aio.py
imports: import asyncio
  import struct
  from io import BytesIO
  from typing import Any
  import cloudpickle
  import numpy
  from ..utils import lazy_import
  from .core import serialize_with_spawn, deserialize
label_desc: Use image node_id 2 for calling the AioDeserializer obj's underlying member method code with example usage: obj._readexactly(n) and returns: read