public Measurable measurable() {
        if (isMeasurable())
            return (Measurable) metricValueProvider;
        else
            throw new IllegalStateException("Not a measurable: " + this.metricValueProvider.getClass());
    }
Get the underlying metric provider, which should be a {@link Measurable}
@return Return the metric provider
@throws IllegalStateException if the underlying metric is not a {@link Measurable}.
clients/src/main/java/org/apache/kafka/common/metrics/KafkaMetric.java