kevin-wu24 commented on code in PR #18304:
URL: https://github.com/apache/kafka/pull/18304#discussion_r1935864197
##########
raft/src/main/java/org/apache/kafka/raft/internals/KafkaRaftMetrics.java:
##########
@@ -137,6 +99,14 @@ public KafkaRaftMetrics(Metrics metrics, String
metricGrpPrefix, QuorumState sta
"Number of unknown voters whose connection information is not
cached; would never be larger than quorum-size.");
metrics.addMetric(this.numUnknownVoterConnectionsMetricName, (mConfig,
currentTimeMs) -> numUnknownVoterConnections);
+ this.numVotersMetricName = metrics.metricName("number-of-voters",
metricGroupName, "Number of voters for a KRaft topic partition.");
+ metrics.addMetric(this.numVotersMetricName, (Gauge<Integer>) (mConfig,
currentTimestamp) -> numVoters);
Review Comment:
I believe we are exposing doubles unintentionally. When we take the metric
and return the value in `KafkaMetric.metricValue()`:
```
@Override
public Object metricValue() {
long now = time.milliseconds();
synchronized (this.lock) {
if (isMeasurable())
return ((Measurable) metricValueProvider).measure(config,
now);
else if (this.metricValueProvider instanceof Gauge)
return ((Gauge<?>) metricValueProvider).value(config, now);
else
throw new IllegalStateException("Not a valid metric: " +
this.metricValueProvider.getClass());
}
}
```
We would be calling `Measurable.measure()` and returning a double.
I don't think I've ever seen this kind of case before where we overload a
method signature in this fashion (the first signature takes in `Measurable`, an
interface that extends MetricValueProvider<Double>, while the second signature
takes a generic of the `MetricValueProvider<T>` parent interface).
Unless I perform an explicit cast/declaration of a
Gauge<Integer/Boolean/etc.> object to pass in as the second parameter of
`addMetric`, the compiler always assigns the method to call as
`addMetric(MetricName, Measurable)`. I think this is because the second method
signature is taking in the super-interface `MetricValueProvider` as a
parameter, which is not a functional interface and cannot be implemented with a
lambda like `Measurable`, rather than its child `Gauge<T>`.
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