为什么调度程序会杀死我的洗牌算法

Question

我想出了这个算法，用于将随机用户洗牌给另一个用户。（对于秘密圣诞老人游戏）但是当我在给定时间启动随机播放的异步过程时，它会在第 5 个用户处停止。知道为什么吗？

我的算法服务并启动它：

public class GitfteeServiceImpl implements GifteeService{
@Autowired
private  UserRepository userRepository;
private final ScheduledExecutorService shufflingScheduler = Executors.newSingleThreadScheduledExecutor();
@Override
public void setGifteeToAll() {
    List<User> users = userRepository.findAll();
    List<User> usersGiftees = userRepository.findAll();
    List<Long> userIds = usersGiftees.stream().map(User::getUserId).collect(Collectors.toList());
    log.info(users.toString());
    for(User u : users){
        User giftee = getGifteeForOne(u, usersGiftees,userIds);
        userIds.remove(giftee.getUserId());
        usersGiftees.remove(giftee);
    }
}
private User getGifteeForOne(User user, List<User> users, List<Long> ids) {
    Long randomId = getRandomId(ids);
    User giftee = userRepository.findByUserId(randomId);
    while (giftee == null || !users.contains(giftee) || Objects.equals(user.getUserId(), randomId)){
        randomId = getRandomId(ids);
        giftee = userRepository.findByUserId(randomId);
    }
    user.setGiftee(giftee);
    userRepository.save(user);
    return giftee;
}
private Long getRandomId(List<Long> ids) {
    Collections.shuffle(ids);
    return ids.get(0);
}
@Override
public void scheduleShuffling(LocalDateTime gameDuration) {
    Runnable scheduleShufflingTask = this::setGifteeToAll;
    Duration duration = Duration.between(LocalDateTime.now(), gameDuration);
    shufflingScheduler.schedule(scheduleShufflingTask, duration.getSeconds(), TimeUnit.SECONDS);
}

}

这是我的控制器：

public class AdminController {
@Autowired
GifteeService gifteeService;
@PostMapping("/start_date")
public void hi(@RequestBody LocalDateTime localDateTime) {
    LocalDateTime aDateTime = LocalDateTime.of(2019, Month.JANUARY, 17, 22, 39, 50);
    gifteeService.scheduleShuffling(aDateTime);
}

Answer 1

所以经过深度调试，我发现其实我的算法是不对的，被调度程序杀死是正常的。 这是我所做的更改：

private User getGifteeForOne(User user, List<User> users, List<Long> ids) {
Long randomId = getRandomId(ids);
User giftee = userRepository.findByUserId(randomId);
//The line that was incorrect
while (giftee == null || users.contains(giftee) || Objects.equals(user.getUserId(), randomId)){
    randomId = getRandomId(ids);
    giftee = userRepository.findByUserId(randomId);
}
user.setGiftee(giftee);
userRepository.save(user);
return giftee;
}