Race condition in multiple instance in kubernates

Hi i have a race condition in given method i have 2 instances in kubernates and checking in redis

public void method(GuestDTO guestDTO) {    String executeName = "addingGuestToCache" + guestDTO.getUser();    if (!redisService.checkExecute(executeName)) {        redisService.startExecute(executeName);        OpenGuestDTO openGuestDTO = new OpenGuestDTO();        RMap<String, List<OpenGuestDTO>> openGuestDTOList = redisService.getOpenGuestDTOList();        List<OpenGuestDTO> userGuestList = openGuestDTOList.get(guestDTO.getUser());        if (userGuestList == null) {            userGuestList = Collections.synchronizedList(new ArrayList<OpenGuestDTO>());        }        for (OpenGuestDTO guestDTO1 : userGuestList) {            if (guestDTO1.getGuestName().equalsIgnoreCase(guestDTO.getGuestName())) {                redisService.deleteExecute(executeName);                return;            }        }        openGuestDTOList.add(openGuestDTO);        openGuestDTOList.fastPut(guestDTO.getUser(), userGuestList);        redisService.deleteExecute(executeName);    }else{        method(guestDTO);    }}