关于Sentinel中冷启动限流原理WarmUpController

public class WarmUpController implements TrafficShapingController {
	// FlowRule中设置的阈值
    protected double count;
    // 冷却因子，默认为3，通过SentinelConfig加载，可以修改
    private int coldFactor;
    // 预警token数量
    protected int warningToken = 0;
    // 最大token数量
    private int maxToken;
    // 斜率，用于计算当前生成token的时间间隔，即生成速率
    protected double slope;
	// 令牌桶中剩余令牌数
    protected AtomicLong storedTokens = new AtomicLong(0);
    // 最后一次添加令牌的时间戳
    protected AtomicLong lastFilledTime = new AtomicLong(0);
    public WarmUpController(double count, int warmUpPeriodInSec, int coldFactor) {
        construct(count, warmUpPeriodInSec, coldFactor);
    }
    public WarmUpController(double count, int warmUpPeriodInSec) {
        construct(count, warmUpPeriodInSec, 3);
    }
    private void construct(double count, int warmUpPeriodInSec, int coldFactor) {
        if (coldFactor <= 1) {
            throw new IllegalArgumentException("Cold factor should be larger than 1");
        }
        this.count = count;
		// 默认为3
        this.coldFactor = coldFactor;
        // thresholdPermits = 0.5 * warmupPeriod / stableInterval.
        // warningToken = 100;
        // 计算预警token数量
        // 例如 count=5，warmUpPeriodInSec=10，coldFactor=3，则waringToken=5*10/2=25
        warningToken = (int)(warmUpPeriodInSec * count) / (coldFactor - 1);
        // / maxPermits = thresholdPermits + 2 * warmupPeriod / (stableInterval + coldInterval)
        // maxToken = 200
        // 最大token数量=25+2*10*5/4=50
        maxToken = warningToken + (int)(2 * warmUpPeriodInSec * count / (1.0 + coldFactor));
        // slope
        // slope = (coldIntervalMicros - stableIntervalMicros) / (maxPermits- thresholdPermits);
        // 倾斜度=(3-1)/5/(50-25) = 0.016
        slope = (coldFactor - 1.0) / count / (maxToken - warningToken);
    }
}

stableInterval=1/count=200ms，coldInterval=coldFactor*stableInterval=600ms
warningToken=warmUpPeriodSec/(coldFactor-1)/stableInterval=(warmUpPeriodSec*count)/(coldFactor-1)=25
maxToken=2warmUpPeriodSec/(stableInterval+coldInterval)+warningToken=warningToken+2warmUpPeriodSeccount/(coldFactor+1)=50
slope=(coldInterval-stableInterval)/(maxToken-warningToken)=(coldFactor-1)/count/(maxToken-warningToken)=0.016

public boolean canPass(Node node, int acquireCount, boolean prioritized) {
    // 获取当前1s的QPS
    long passQps = (long) node.passQps();
    // 获取上一窗口通过的qps
    long previousQps = (long) node.previousPassQps();
    // 生成和滑落token
    syncToken(previousQps);
    // 如果进入了警戒线，开始调整他的qps
    long restToken = storedTokens.get();
    // 如果令牌桶中的token数量大于警戒值，说明还未预热结束，需要判断token的生成速度和消费速度
    if (restToken >= warningToken) {
        long aboveToken = restToken - warningToken;
        // 消耗的速度要比warning快，但是要比慢
        // y轴，当前token生成时间 current interval = restToken*slope+stableInterval
        // 计算此时1s内能够生成token的数量
        double warningQps = Math.nextUp(1.0 / (aboveToken * slope + 1.0 / count));
        // 判断token消费速度是否小于生成速度，如果是则正常请求，否则限流
        if (passQps + acquireCount <= warningQps) {
            return true;
        }
    } else {
        // 预热结束，直接判断是否超过设置的阈值
        if (passQps + acquireCount <= count) {
            return true;
        }
    }

    return false;
}

protected void syncToken(long passQps) {
    long currentTime = TimeUtil.currentTimeMillis();
    // 获取整秒数
    currentTime = currentTime - currentTime % 1000;
    // 上一次的操作时间
    long oldLastFillTime = lastFilledTime.get();
    // 判断成立，如果小于，说明可能出现了时钟回拨
    // 如果等于，说明当前请求都处于同一秒内，则不进行token添加和滑落操作，避免的重复扣减
    // 时间窗口的跨度为1s
    if (currentTime <= oldLastFillTime) {
        return;
    }
    // token数量
    long oldValue = storedTokens.get();
    long newValue = coolDownTokens(currentTime, passQps);
    // 重置token数量
    if (storedTokens.compareAndSet(oldValue, newValue)) {
        // token滑落，即token消费
        // 减去上一个时间窗口的通过请求数
        long currentValue = storedTokens.addAndGet(0 - passQps);
        if (currentValue < 0) {
            storedTokens.set(0L);
        }
        // 设置最后添加令牌时间
        lastFilledTime.set(currentTime);
    }

}
private long coolDownTokens(long currentTime, long passQps) {
    long oldValue = storedTokens.get();
    long newValue = oldValue;

    // 添加令牌的判断前提条件:
    // 当令牌的消耗程度远远低于警戒线的时候
    if (oldValue < warningToken) {
        // 计算过去一段时间内，可以通过的QPS总量
        // 初始加载时，令牌数量达到maxToken
        newValue = (long)(oldValue + (currentTime - lastFilledTime.get()) * count / 1000);
    } else if (oldValue > warningToken) {
        // 处于预热过程，且消费速度低于冷却速度，则补充令牌
        if (passQps < (int)count / coldFactor) {
            newValue = (long)(oldValue + (currentTime - lastFilledTime.get()) * count / 1000);
        }
    }
    // 当令牌桶满了之后，抛弃多余的令牌
    return Math.min(newValue, maxToken);
}