class_docstr: A file like object that publishes the stream to a 0MQ PUB socket.
  
  Output is handed off to an IO Thread
class_docstr_tok: ["A","file","like","object","that","publishes","the","stream","to","a","0MQ","PUB","socket",".","Output","is","handed","off","to","an","IO","Thread"]
docstr: trigger actual zmq send
  
  send will happen in the background thread
code: def flush(self):
      """trigger actual zmq send
  
      send will happen in the background thread
      """
      if self.pub_thread.thread.is_alive():
          # request flush on the background thread
          self.pub_thread.schedule(self._flush)
          # wait for flush to actually get through, if we can.
          # waiting across threads during import can cause deadlocks
          # so only wait if import lock is not held
          if not import_lock_held():
              evt = threading.Event()
              self.pub_thread.schedule(evt.set)
              # and give a timeout to avoid
              if not evt.wait(self.flush_timeout):
                  # write directly to __stderr__ instead of warning because
                  # if this is happening sys.stderr may be the problem.
                  print("IOStream.flush timed out", file=sys.__stderr__)
      else:
          self._flush()
  
imports: from __future__ import print_function
  import atexit
  from binascii import b2a_hex
  from collections import deque
  import os
  import sys
  import threading
  import warnings
  from io import StringIO, TextIOBase
  import zmq
  from zmq.eventloop.ioloop import IOLoop
  from zmq.eventloop.zmqstream import ZMQStream
  from jupyter_client.session import extract_header
  from ipython_genutils import py3compat
  from ipython_genutils.py3compat import unicode_type
label_desc: Use image node_id 7 for calling the OutStream obj's underlying member method code with example usage: obj.flush() without return types