Redisson 分布式限流器 RRateLimiter 的使用及原理

本文主要是介绍Redisson 分布式限流器 RRateLimiter 的使用及原理，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

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

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
@SpringBootTest
class RateLimiterTest {@Autowiredprivate RedissonClient redissonClient;private static final int threadCount = 10;@Testvoid 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 < threadCount; i++) {new Thread(() -> {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 9
2024-01-16 20:14:27 INFO  [Thread-3] atreus.ink.rate.RateLimiterTest : latch count 8
2024-01-16 20:14:28 INFO  [Thread-1] atreus.ink.rate.RateLimiterTest : latch count 7
2024-01-16 20:14:29 INFO  [Thread-10] atreus.ink.rate.RateLimiterTest : latch count 6
2024-01-16 20:14:29 INFO  [Thread-8] atreus.ink.rate.RateLimiterTest : latch count 5
2024-01-16 20:14:30 INFO  [Thread-5] atreus.ink.rate.RateLimiterTest : latch count 4
2024-01-16 20:14:30 INFO  [Thread-4] atreus.ink.rate.RateLimiterTest : latch count 3
2024-01-16 20:14:30 INFO  [Thread-6] atreus.ink.rate.RateLimiterTest : latch count 2
2024-01-16 20:14:30 INFO  [Thread-7] atreus.ink.rate.RateLimiterTest : latch count 1
2024-01-16 20:14:30 INFO  [Thread-9] atreus.ink.rate.RateLimiterTest : latch count 0

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 key
local 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' thenvalueName = 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 10redis.call('set', valueName, rate);-- zadd {my_limiter}:permits 1705396021850 6966135962453115904_1redis.call('zadd', permitsName, ARGV[2], struct.pack('fI', ARGV[3], ARGV[1]));-- decrby {my_limiter}:permits 3redis.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 1705396020850local 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) dolocal random, permits = struct.unpack('fI', v);-- released = released + 2-- released = released + 5released = 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_5redis.call('zrem', permitsName, unpack(expiredValues));currentValue = tonumber(currentValue) + released;-- incrby {my_limiter}:value 7redis.call('set', valueName, currentValue);end;if tonumber(currentValue) < tonumber(ARGV[1]) then-- 如果回收后可用令牌数仍然不足 返回需要等待的时间-- zrangebyscore {my_limiter}:permits (1705396020850 1705396021850 withscores limit 0 1local nearest = redis.call('zrangebyscore', permitsName, '(' .. (tonumber(ARGV[2]) - interval), tonumber(ARGV[2]), 'withscores', 'limit', 0, 1);local random, permits = struct.unpack('fI', nearest[1]);-- 1705396021650 - 1705396021850 + 1000 = 800return tonumber(nearest[2]) - (tonumber(ARGV[2]) - interval);elseredis.call('zadd', permitsName, ARGV[2], struct.pack('fI', ARGV[3], ARGV[1]));redis.call('decrby', valueName, ARGV[1]);return nil;end;
end;