code: def stop(self):
          
          stopped = []
          for host, _ in self.host_cores:
              if self.status(host)[0][1] == 'not-running':
                  print('%s not running' % host)
                  continue
              ctrl_url = 'tcp://%s:%s' % (host, self.ctrl_port)
              with z.Socket(ctrl_url, z.zmq.REQ, 'connect') as sock:
                  sock.send('stop')
                  stopped.append(host)
          if hasattr(self, 'streamer'):
              self.streamer.terminate()
          return 'stopped %s' % stopped
docs: Send a "stop" command to all worker pools