Redisson 分布式限流器 RRateLimiter 的使用及原理

文章目录

• 一、基本使用
• • 1.1 创建限流器
  • 1.2 获取令牌
  • 1.3 使用示例
  • 二、实现原理

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    一、基本使用

    1.1 创建限流器

    /** * Returns rate limiter instance by name *  * @param name of rate limiter * @return RateLimiter object */RRateLimiter getRateLimiter(String name);

    /** * Initializes RateLimiter's state and stores config to Redis server. *  * @param mode - rate mode * @param rate - rate * @param rateInterval - rate time interval * @param rateIntervalUnit - rate time interval unit * @return true if rate was set and false otherwise */boolean trySetRate(RateType mode, long rate, long rateInterval, RateIntervalUnit rateIntervalUnit);

    trySetRate 用于设置限流参数。其中 RateType 包含 OVERALL 和 PER_CLIENT 两个枚举常量，分别表示全局限流和单机限流。后面三个参数表明了令牌的生成速率，即每 rateInterval 生成 rate 个令牌，rateIntervalUnit 为 rateInterval 的时间单位。

    1.2 获取令牌

    /** * Acquires a specified permits from this RateLimiter,  * blocking until one is available. * * Acquires the given number of permits, if they are available  * and returns immediately, reducing the number of available permits  * by the given amount. *  * @param permits the number of permits to acquire */void acquire(long permits);/** * Acquires the given number of permits only if all are available * within the given waiting time. * * Acquires the given number of permits, if all are available and returns immediately, * with the value true, reducing the number of available permits by one. * * If no permit is available then the current thread becomes * disabled for thread scheduling purposes and lies dormant until * the specified waiting time elapses. * * If a permits is acquired then the value true is returned. * * If the specified waiting time elapses then the value false * is returned.  If the time is less than or equal to zero, the method * will not wait at all. * * @param permits amount * @param timeout the maximum time to wait for a permit * @param unit the time unit of the timeout argument * @return true if a permit was acquired and false *         if the waiting time elapsed before a permit was acquired */boolean tryAcquire(long permits, long timeout, TimeUnit unit);

    acquire 和 tryAcquire 均可用于获取指定数量的令牌，不过 acquire 会阻塞等待，而 tryAcquire 会等待 timeout 时间，如果仍然没有获得指定数量的令牌直接返回 false。

    1.3 使用示例

    @Slf4j@SpringBootTestclass RateLimiterTest {        @Autowired    private RedissonClient redissonClient;        private static final int threadCount = 10;    @Test    void test() throws InterruptedException {        RRateLimiter rateLimiter = redissonClient.getRateLimiter("my_limiter");        rateLimiter.trySetRate(RateType.OVERALL, 10, 1, RateIntervalUnit.SECONDS);        CountDownLatch latch = new CountDownLatch(threadCount);        for (int i = 0; i  {                rateLimiter.tryAcquire(5, 3, TimeUnit.SECONDS);                latch.countDown();                log.info("latch count {}", latch.getCount());            }).start();        }                latch.await();    }}

    2024-01-16 20:14:27 INFO  [Thread-2] atreus.ink.rate.RateLimiterTest : latch count 92024-01-16 20:14:27 INFO  [Thread-3] atreus.ink.rate.RateLimiterTest : latch count 82024-01-16 20:14:28 INFO  [Thread-1] atreus.ink.rate.RateLimiterTest : latch count 72024-01-16 20:14:29 INFO  [Thread-10] atreus.ink.rate.RateLimiterTest : latch count 62024-01-16 20:14:29 INFO  [Thread-8] atreus.ink.rate.RateLimiterTest : latch count 52024-01-16 20:14:30 INFO  [Thread-5] atreus.ink.rate.RateLimiterTest : latch count 42024-01-16 20:14:30 INFO  [Thread-4] atreus.ink.rate.RateLimiterTest : latch count 32024-01-16 20:14:30 INFO  [Thread-6] atreus.ink.rate.RateLimiterTest : latch count 22024-01-16 20:14:30 INFO  [Thread-7] atreus.ink.rate.RateLimiterTest : latch count 12024-01-16 20:14:30 INFO  [Thread-9] atreus.ink.rate.RateLimiterTest : latch count 0

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    二、实现原理

    Redisson 的 RRateLimiter 基于令牌桶实现，令牌桶的主要特点如下：

    • 令牌以固定速率生成。
    • 生成的令牌放入令牌桶中存放，如果令牌桶满了则多余的令牌会直接丢弃，当请求到达时，会尝试从令牌桶中取令牌，取到了令牌的请求可以执行。
    • 如果桶空了，那么尝试取令牌的请求会被直接丢弃。

      RRateLimiter 在创建限流器时通过下面 Lua 脚本设置限流器的相关参数：

      redis.call('hsetnx', KEYS[1], 'rate', ARGV[1]);redis.call('hsetnx', KEYS[1], 'interval', ARGV[2]);return redis.call('hsetnx', KEYS[1], 'type', ARGV[3]);

      而获取令牌则是通过以下的 Lua 脚本实现：

      -- 请求参数示例-- KEYS[1] my_limiter-- KEYS[2] {my_limiter}:value-- KEYS[4] {my_limiter}:permits-- ARGV[1] 3 本次请求的令牌数-- ARGV[2] 1705396021850 System.currentTimeMillis()-- ARGV[3] 6966135962453115904 ThreadLocalRandom.current().nextLong()-- 读取 RRateLimiter.trySetRate 中配置的限流器信息local rate = redis.call('hget', KEYS[1], 'rate');  -- 10 一个时间窗口内产生的令牌数local interval = redis.call('hget', KEYS[1], 'interval');  -- 1000 一个时间窗口对应的毫秒数local type = redis.call('hget', KEYS[1], 'type');  -- 0 全局限流assert(rate ~= false and interval ~= false and type ~= false, 'RateLimiter is not initialized')local valueName = KEYS[2];  -- {my_limiter}:value 当前可用令牌数字符串的 keylocal permitsName = KEYS[4];  -- {my_limiter}:permits 授权记录有序集合的 key-- 单机限流配置 无需考虑if type == '1' then    valueName = KEYS[3];    permitsName = KEYS[5];end;-- 查询当前可用的令牌数 查询失败表明是首次请求令牌local currentValue = redis.call('get', valueName);if currentValue == false then -- 首次请求令牌    -- 单次请求的令牌数不能超过一个时间窗口内产生的令牌数    assert(tonumber(rate) >= tonumber(ARGV[1]), 'Requested permits amount could not exceed defined rate');        -- 更新当前可用令牌数以及令牌授权记录 {my_limiter}:permits    -- set {my_limiter}:permits 10    redis.call('set', valueName, rate);    -- zadd {my_limiter}:permits 1705396021850 6966135962453115904_1    redis.call('zadd', permitsName, ARGV[2], struct.pack('fI', ARGV[3], ARGV[1]));    -- decrby {my_limiter}:permits 3    redis.call('decrby', valueName, ARGV[1]);    return nil;else -- 再次请求令牌    -- 查询可以回收的令牌对应的授权记录 即一个时间窗口前的所有授权记录且包括一个时间窗口前这一时刻    -- 旧令牌回收的本质是新令牌的加入 如果一个令牌是在一个时间窗口前被分配的 那经过一个时间窗口后这个空出的位置应该已经由新令牌填充    -- zrangebyscore {my_limiter}:permits 0 1705396020850    local expiredValues = redis.call('zrangebyscore', permitsName, 0, tonumber(ARGV[2]) - interval); -- [1936135962853113704_2, 536135765023123704_5]        -- 统计可以回收的令牌数    local released = 0;    for i, v in ipairs(expiredValues) do        local random, permits = struct.unpack('fI', v);        -- released = released + 2        -- released = released + 5        released = released + permits;    end;    -- 删除授权记录并回收令牌    if released > 0 then        -- zrem {my_limiter}:permits 1936135962853113704_2 536135765023123704_5        redis.call('zrem', permitsName, unpack(expiredValues));        currentValue = tonumber(currentValue) + released;        -- incrby {my_limiter}:value 7        redis.call('set', valueName, currentValue);    end;    if tonumber(currentValue)  
      参考：
       
      https://github.com/oneone1995/blog/issues/13
      https://www.infoq.cn/article/Qg2tX8fyw5Vt-f3HH673