class_docstr: Schedules the given callback to be called once.
  
  The callback is called once, after callback_time milliseconds.
  
  `start` must be called after the DelayedCallback is created.
  
  The timeout is calculated from when `start` is called.
class_docstr_tok: ["Schedules","the","given","callback","to","be","called","once",".","The","callback","is","called","once",",","after","callback_time","milliseconds",".","`","start","`","must","be","called","after","the","DelayedCallback","is","created",".","The","timeout","is","calculated","from","when","`","start","`","is","called","."]
code: def _run(self):
      if not self._running:
          return
      self._running = False
      try:
          self.callback()
      except Exception:
          gen_log.error("Error in delayed callback", exc_info=True)
  
imports: from __future__ import absolute_import, division, with_statement
  import os
  import time
  import warnings
  from zmq import Poller, POLLIN, POLLOUT, POLLERR, ZMQError, ETERM
  from .minitornado.ioloop import PollIOLoop, PeriodicCallback
  from .minitornado.log import gen_log
label_desc: Use image node_id 3 for calling the DelayedCallback obj's underlying member method code with example usage: obj._run() without return types