<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def emit(self, signal, message='__nomessagetoken__'):
 """Emit a signal to the frontend. :param str signal: name of the signal :param message: message to send :returns: return value from frontend emit function :rtype: tornado.concurrent.Future """

        # call pre-emit hooks
        if signal == 'log':
            self.log_backend.info(message)
        elif signal == 'warn':
            self.log_backend.warn(message)
        elif signal == 'error':
            self.log_backend.error(message)

        return self.emit_to_frontend(signal, message)