double measurableValue(long timeMs) {
        synchronized (this.lock) {
            if (isMeasurable())
                return ((Measurable) metricValueProvider).measure(config, timeMs);
            else
                return 0;
        }
    }
Take the metric and return the value, where the underlying metric provider should be a {@link Measurable}
@param timeMs The time that this metric is taken
@return Return the metric value if it's measurable, otherwise 0
clients/src/main/java/org/apache/kafka/common/metrics/KafkaMetric.java