dubbo服務端限流

在服務端調用鏈條裏，會有一個TpsLimitFilter類，用來對服務端限流

public boolean isAllowable(URL url, Invocation invocation) {
        int rate = url.getParameter(Constants.TPS_LIMIT_RATE_KEY, -1);
        long interval = url.getParameter(Constants.TPS_LIMIT_INTERVAL_KEY,
                                         Constants.DEFAULT_TPS_LIMIT_INTERVAL);
        String serviceKey = url.getServiceKey();
        if (rate > 0) {
            StatItem statItem = stats.get(serviceKey);
            if (statItem == null) {
                stats.putIfAbsent(serviceKey,
                                  new StatItem(serviceKey, rate, interval));
                statItem = stats.get(serviceKey);
            }
            return statItem.isAllowable(url, invocation);
        } else {
            StatItem statItem = stats.get(serviceKey);
            if (statItem != null) {
                stats.remove(serviceKey);
            }
        }

        return true;
    }

public boolean isAllowable(URL url, Invocation invocation) {
        long now = System.currentTimeMillis();
        if (now > lastResetTime + interval) {
            token.set(rate);
            lastResetTime = now;
        }

        int value = token.get();
        boolean flag = false;
        while (value > 0 && !flag) {
            flag = token.compareAndSet(value, value - 1);
            value = token.get();
        }

        return flag;
    }

interval是計算的時間默認爲1分鐘
rate是interval時間裏面的請求數