class_docstr: Internal implementation of TimerService for ProcessFunction and CoProcessFunction.
code: def current_watermark(self):
      return self._current_watermark
  
imports: import collections
  import time
  from enum import Enum
  from io import BytesIO
  from pyflink.common import Row
  from pyflink.datastream import TimerService
  from pyflink.fn_execution.datastream.timerservice import InternalTimer, K, N, InternalTimerService
label_desc: Use image node_id 3 for calling the NonKeyedTimerServiceImpl obj's underlying member method code with example usage: obj.current_watermark() and returns: self