func (l *Log) SetLogDir(logDir string) {
	if logDir != "" {
		l.mu.Lock()
		defer l.mu.Unlock()
		l.logDirs = append([]string{logDir}, l.logDirs...)
	}
}
func (l *Log) SetLogDir(logDir string) {
	if logDir != "" {
		l.mu.Lock()
		defer l.mu.Unlock()
		l.logDirs = append([]string{logDir}, l.logDirs...)
	}
}
func ( l * Log ) SetLogDir ( logDir string ) { if logDir != " " { l . mu . Lock ( ) defer l . mu . Unlock ( ) l . logDirs = append ( [ ] string { logDir } , l . logDirs ... ) } }
// logDir if non-empty, write log files to this directory.
logDir if non - empty write log files to this directory .