code: def flush(self):
      with self._lock:
          if self._closed:
              raise IOError("Writer is closed.")
          # Waiting all data to flush of writer.
          self._bytes_queue.join()
          self._record_writer.flush()
  
imports: from visualdl.io import bfile
  from visualdl.utils.crc32 import masked_crc32c
  from visualdl.proto import record_pb2
  import struct
  import time
  import queue
  import threading
  import os
label_desc: Use image node_id 3 for calling the _AsyncWriter obj's underlying member method code with example usage: obj.flush() without return types