public boolean isExpired() {
            if (this.values != null) {
                for (Map<String, Metrics> value : this.values) {
                    if (value != null) {
                        return false;
                    }
                }
            }
            return true;
        }
A metrics window, based on AlarmRule#period. This window slides with time, just keeps the recent N(period)
buckets.
oap-server/server-alarm-plugin/src/main/java/org/apache/skywalking/oap/server/core/alarm/provider/RunningRule.java