class_docstr: Subclass Tornado Future, reinstating cancellation.
code: def cancel(self):
      if self.done():
          return False
      self.set_exception(CancelledError())
      return True
  
imports: import zmq
  from zmq._future import _AsyncPoller, _AsyncSocket
  from tornado.concurrent import Future
  from tornado.ioloop import IOLoop
label_desc: Use image node_id 1 for calling the _TornadoFuture obj's underlying member method code with example usage: obj.cancel() and returns: True, False