code: func (l *Log) exit(err error) {
  	fmt.Fprintf(os.Stderr, "log: exiting because of error: %s\n", err)
  	// If logExitFunc is set, we do that instead of exiting.
  	if logExitFunc != nil {
  		logExitFunc(err)
  		return
  	}
  	l.flushAll()
  	os.Exit(2)
  }
docs: // exit is called if there is trouble creating or writing log files.
  // It flushes the logs and exits the program; there's no point in hanging around.
  // l.mu is held.