chapter22 轻松搞定重复提交（分布式锁） 中的BUG

[yxxcoder]

你好，非常喜欢您的分享，在运行chapter22一章的demo时发现了两个问题，不知道是不是遗留的bug，如理解有问题，请指正😄

1. LockMethodInterceptor.java

   @Around("execution(public * *(..)) && @annotation(com.battcn.annotation.CacheLock)")
   public Object interceptor(ProceedingJoinPoint pjp) {
       MethodSignature signature = (MethodSignature) pjp.getSignature();
       Method method = signature.getMethod();
       CacheLock lock = method.getAnnotation(CacheLock.class);
       if (StringUtils.isEmpty(lock.prefix())) {
           throw new RuntimeException("lock key don't null...");
       }
       final String lockKey = cacheKeyGenerator.getLockKey(pjp);
       String value = UUID.randomUUID().toString();
       try {
           // 假设上锁成功，但是设置过期时间失效，以后拿到的都是 false
           final boolean success = redisLockHelper.lock(lockKey, value, lock.expire(), lock.timeUnit());
           if (!success) {
               throw new RuntimeException("重复提交");
           }
           try {
               return pjp.proceed();
           } catch (Throwable throwable) {
               throw new RuntimeException("系统异常");
           }
       } finally {
           // TODO 如果演示的话需要注释该代码;实际应该放开
           redisLockHelper.unlock(lockKey, value);
       }
   }

   这里的String value = UUID.randomUUID().toString();是不是有多线程问题，当第一个线程未处理完，第二个线程运行到这里是会刷新value，导致第一个线程unlock时会使用第二个线程的value

2. RedisLockHelper.java

   public boolean lock(String lockKey, final String uuid, long timeout, final TimeUnit unit) {
       final long milliseconds = Expiration.from(timeout, unit).getExpirationTimeInMilliseconds();
       boolean success = stringRedisTemplate.opsForValue().setIfAbsent(lockKey, (System.currentTimeMillis() + milliseconds) + DELIMITER + uuid);
       if (success) {
           stringRedisTemplate.expire(lockKey, timeout, TimeUnit.SECONDS);
       } else {
          // 这里直接更新这个值是不是有点问题，应该判断时间，超时再更新
           String oldVal = stringRedisTemplate.opsForValue().getAndSet(lockKey, (System.currentTimeMillis() + milliseconds) + DELIMITER + uuid);
           final String[] oldValues = oldVal.split(Pattern.quote(DELIMITER));
           if (Long.parseLong(oldValues[0]) + 1 <= System.currentTimeMillis()) {
               return true;
           }
       }
       return success;
   }

   我认为这里应该这样写

   public boolean lock(String lockKey, final String uuid, long timeout, final TimeUnit unit) {
       final long milliseconds = Expiration.from(timeout, unit).getExpirationTimeInMilliseconds();
       boolean success = stringRedisTemplate.opsForValue().setIfAbsent(lockKey, (System.currentTimeMillis() + milliseconds) + DELIMITER + uuid);
       if (success) {
           stringRedisTemplate.expire(lockKey, timeout, TimeUnit.SECONDS);
       } else {
           String oldVal = stringRedisTemplate.opsForValue().get(lockKey);
           final String[] oldValues = oldVal.split(Pattern.quote(DELIMITER));
           if (Long.parseLong(oldValues[0]) + 1 <= System.currentTimeMillis()) {
               stringRedisTemplate.opsForValue().set(lockKey, (System.currentTimeMillis() + milliseconds) + DELIMITER + uuid);
               return true;
           }
       }
       return success;
   }

如理解有问题请指正😄

[levin950825]

恩，不过现在有更简单的方案了，springboot2.1.x 支持setex 直接的写法了，不用这么麻烦了

    /**
     * 获取锁
     *
     * @param lockKey lockKey
     * @param uuid    UUID
     * @param timeout 超时时间
     * @param unit    过期单位
     * @return true or false
     */
    public boolean lock(String lockKey, final String uuid, long timeout, final TimeUnit unit) {
        // 新版本 API 中已经直接支持 set nx 方式
        Boolean success = stringRedisTemplate.opsForValue().setIfAbsent(lockKey, uuid, timeout, unit);
        return success == null ? false : success;
    }