// 三个 Redis 集群
RLock lock1 = redissionInstance1.getLock("lock1");
RLock lock2 = redissionInstance2.getLock("lock2");
RLock lock3 = redissionInstance3.getLock("lock3");

RedissionRedLock lock = new RedissionLock(lock1, lock2, lock2);
lock.lock();
// do something....
lock.unlock();

// SET/ SETEX/ SETTEX/ SETNX 最底层实现
void setGenericCommand(client *c, int flags, robj *key, robj *val, robj *expire, int unit, robj *ok_reply, robj *abort_reply) {
    long long milliseconds = 0; /* initialized to avoid any harmness warning */

    // 如果定义了 key 的过期时间则保存到上面定义的变量中
    // 如果过期时间设置错误则返回错误信息
    if (expire) {
        if (getLongLongFromObjectOrReply(c, expire, &milliseconds, NULL) != C_OK)
            return;
        if (milliseconds <= 0) {
            addReplyErrorFormat(c,"invalid expire time in %s",c->cmd->name);
            return;
        }
        if (unit == UNIT_SECONDS) milliseconds *= 1000;
    }

    // lookupKeyWrite 函数是为执行写操作而取出 key 的值对象
    // 这里的判断条件是：
    // 1.如果设置了 NX(不存在)，并且在数据库中找到了 key 值
    // 2.或者设置了 XX(存在)，并且在数据库中没有找到该 key
    // => 那么回复 abort_reply 给客户端
    if ((flags & OBJ_SET_NX && lookupKeyWrite(c->db,key) != NULL) ||
        (flags & OBJ_SET_XX && lookupKeyWrite(c->db,key) == NULL))
    {
        addReply(c, abort_reply ? abort_reply : shared.null[c->resp]);
        return;
    }
    
    // 在当前的数据库中设置键为 key 值为 value 的数据
    genericSetKey(c->db,key,val,flags & OBJ_SET_KEEPTTL);
    // 服务器每修改一个 key 后都会修改 dirty 值
    server.dirty++;
    if (expire) setExpire(c,c->db,key,mstime()+milliseconds);
    notifyKeyspaceEvent(NOTIFY_STRING,"set",key,c->db->id);
    if (expire) notifyKeyspaceEvent(NOTIFY_GENERIC,
        "expire",key,c->db->id);
    addReply(c, ok_reply ? ok_reply : shared.ok);
}

> SET lock:test true ex 5 nx
OK
... do something critical ...
> del lock:test

private static final String LOCK_SUCCESS = "OK";
private static final Long RELEASE_SUCCESS = 1L;
private static final String SET_IF_NOT_EXIST = "NX";
private static final String SET_WITH_EXPIRE_TIME = "PX";

@Override
public String acquire() {
    try {
        // 获取锁的超时时间，超过这个时间则放弃获取锁
        long end = System.currentTimeMillis() + acquireTimeout;
        // 随机生成一个 value
        String requireToken = UUID.randomUUID().toString();
        while (System.currentTimeMillis() < end) {
            String result = jedis
                .set(lockKey, requireToken, SET_IF_NOT_EXIST, SET_WITH_EXPIRE_TIME, expireTime);
            if (LOCK_SUCCESS.equals(result)) {
                return requireToken;
            }
            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            }
        }
    } catch (Exception e) {
        log.error("acquire lock due to error", e);
    }

    return null;
}

@Override
public boolean release(String identify) {
    if (identify == null) {
        return false;
    }

    String script = "if redis.call('get', KEYS[1]) == ARGV[1] then return redis.call('del', KEYS[1]) else return 0 end";
    Object result = new Object();
    try {
        result = jedis.eval(script, Collections.singletonList(lockKey),
            Collections.singletonList(identify));
        if (RELEASE_SUCCESS.equals(result)) {
            log.info("release lock success, requestToken:{}", identify);
            return true;
        }
    } catch (Exception e) {
        log.error("release lock due to error", e);
    } finally {
        if (jedis != null) {
            jedis.close();
        }
    }

    log.info("release lock failed, requestToken:{}, result:{}", identify, result);
    return false;
}