in the spring container environment, does it ensure that the program is available by performing time-consuming logic through synchronized (this) locks?
I tested that if there is no return value, the order can be guaranteed, and if there is a return value, there will be a problem.
: the reason for adding synchronized is that it may concurrently access lockUserVouchers to modify the data state, and the status will be returned if the modification succeeds or fails

@Test
public void testLock() throws InterruptedException {
    CountDownLatch latch = new CountDownLatch(3);
    for (int i = 1; i <= 3; iPP) {
        new Thread(new RunnerLock(userVouchersService, latch)).start();
    }
    latch.await();
}

public class RunnerLock implements Runnable {
    UserVouchersService userVouchersService;

    CountDownLatch countDownLatch;

    public RunnerLock(UserVouchersService userVouchersService, CountDownLatch     countDownLatch) {
        this.userVouchersService = userVouchersService;
        this.countDownLatch = countDownLatch;
    }

    @Override
    public void run() {
        CsAuctionUserVouchers csAuctionUserVouchers = new CsAuctionUserVouchers();
        csAuctionUserVouchers.setId(ThreadLocalRandom.current().nextLong(0, 9999));
        long l = userVouchersService.lockUserVouchers(csAuctionUserVouchers);
        log.info("--------------- --- {}---------------------------------", l);
        countDownLatch.countDown();
    }
}

    @Transactional(rollbackFor = Exception.class)
    public long lockUserVouchers(CsAuctionUserVouchers csAuctionUserVouchers) {
        synchronized (this) {
            log.info("-------------------test----------------------");
            try {
                Thread.sleep(1000);
                //
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            log.info("------------------ --test----------------------");
            return csAuctionUserVouchers.getId();
        }
    }