code: def send(command, data):
      
      global _lock
      try:
          _lock.acquire()
          data = data.encode('utf8')
          assert len(data) < 1000000, 'Command too long'
          msg = b'%b%06d%b' % (command.value, len(data), data)
          logging.getLogger(__name__).debug('Sending command, data: [%s]' % msg)
          _out_file.write(msg)
          _out_file.flush()
      finally:
          _lock.release()
docs: Send command to Training Service.
      command: CommandType object.
      data: string payload.