Redisson分散式限流的實現原理解析

RedissonClient redissonClient = Redisson.create();
RRateLimiter rateLimiter = redissonClient.getRateLimiter("xindoo.limiter");
rateLimiter.trySetRate(RateType.OVERALL, 100, 1, RateIntervalUnit.HOURS); 

rateLimiter.acquire(1); // 申請1份許可，直到成功
boolean res = rateLimiter.tryAcquire(1, 5, TimeUnit.SECONDS); // 申請1份許可，如果5s內未申請到就放棄

    private <T> RFuture<T> tryAcquireAsync(RedisCommand<T> command, Long value) {
        byte[] random = new byte[8];
        ThreadLocalRandom.current().nextBytes(random);
        return commandExecutor.evalWriteAsync(getRawName(), LongCodec.INSTANCE, command,
                "——————————————————————————————————————"
                + "這裡是一大段lua程式碼"
                + "____________________________________",
                Arrays.asList(getRawName(), getValueName(), getClientValueName(), getPermitsName(), getClientPermitsName()),
                value, System.currentTimeMillis(), random);
    }

local rate = redis.call("hget", KEYS[1], "rate")  # 100 
local interval = redis.call("hget", KEYS[1], "interval")  # 3600000
local type = redis.call("hget", KEYS[1], "type")  # 0
assert(rate ~= false and interval ~= false and type ~= false, "RateLimiter is not initialized")
local valueName = KEYS[2]      # {xindoo.limiter}:value 用來儲存剩餘許可數量
local permitsName = KEYS[4]    # {xindoo.limiter}:permits 記錄了所有許可發出的時間戳  
# 如果是單範例模式，name資訊後面就需要拼接上clientId來區分出來了
if type == "1" then
    valueName = KEYS[3]        # {xindoo.limiter}:value:b474c7d5-862c-4be2-9656-f4011c269d54
    permitsName = KEYS[5]      # {xindoo.limiter}:permits:b474c7d5-862c-4be2-9656-f4011c269d54
end
# 對引數校驗 
assert(tonumber(rate) >= tonumber(ARGV[1]), "Requested permits amount could not exceed defined rate")
# 獲取當前還有多少許可 
local currentValue = redis.call("get", valueName)   
local res
# 如果有記錄當前還剩餘多少許可 
if currentValue ~= false then
    # 回收已過期的許可數量
    local expiredValues = redis.call("zrangebyscore", permitsName, 0, tonumber(ARGV[2]) - interval)
    local released = 0
    for i, v in ipairs(expiredValues) do
        local random, permits = struct.unpack("Bc0I", v)
        released = released + permits
    end
    # 清理已過期的許可記錄
    if released > 0 then
        redis.call("zremrangebyscore", permitsName, 0, tonumber(ARGV[2]) - interval)
        if tonumber(currentValue) + released > tonumber(rate) then
            currentValue = tonumber(rate) - redis.call("zcard", permitsName)
        else
            currentValue = tonumber(currentValue) + released
        end
        redis.call("set", valueName, currentValue)
    end
    # ARGV  permit  timestamp  random， random是一個隨機的8位元組
    # 如果剩餘許可不夠，需要在res中返回下個許可需要等待多長時間 
    if tonumber(currentValue) < tonumber(ARGV[1]) then
        local firstValue = redis.call("zrange", permitsName, 0, 0, "withscores")
        res = 3 + interval - (tonumber(ARGV[2]) - tonumber(firstValue[2]))
    else
        redis.call("zadd", permitsName, ARGV[2], struct.pack("Bc0I", string.len(ARGV[3]), ARGV[3], ARGV[1]))
        # 減小可用許可量 
        redis.call("decrby", valueName, ARGV[1])
        res = nil
    end
else # 反之，記錄到還有多少許可，說明是初次使用或者之前已記錄的資訊已經過期了，就將設定rate寫進去，並減少許可數 
    redis.call("set", valueName, rate)
    redis.call("zadd", permitsName, ARGV[2], struct.pack("Bc0I", string.len(ARGV[3]), ARGV[3], ARGV[1]))
    redis.call("decrby", valueName, ARGV[1])
    res = nil
end
local ttl = redis.call("pttl", KEYS[1])
# 重置
if ttl > 0 then
    redis.call("pexpire", valueName, ttl)
    redis.call("pexpire", permitsName, ttl)
end
return res