rotating_file_handler.go
func (handler *RotatingFileHandler) Close() (err error) {
	handler.lock.Lock()
	err = handler.close()
	handler.lock.Unlock()
	return
}
func (handler *RotatingFileHandler) Close() (err error) {
	handler.lock.Lock()
	err = handler.close()
	handler.lock.Unlock()
	return
}
// Close releases resources used by this handler (file that log messages
// were written into).