guozhangwang commented on code in PR #12121:
URL: https://github.com/apache/kafka/pull/12121#discussion_r876234679
##########
clients/src/main/java/org/apache/kafka/common/metrics/Metrics.java:
##########
@@ -563,10 +615,15 @@ public synchronized void removeReporter(MetricsReporter
reporter) {
}
}
- synchronized void registerMetric(KafkaMetric metric) {
+ synchronized void registerMetric(KafkaMetric metric, boolean
raiseIfMetricExists) {
Review Comment:
Hey @vamossagar12 @jolshan @dajac , since `registerMetric` is a package
private function I'm thinking about modifying its signature to return the
already existed metric (null if it does not exist, not null means no changes to
the underlying registry since there's already a metric), hence indicating if
the register-metric succeeded or not. And let the caller (`addMetric` or
`metricOrElseCreate`) to react accordingly: e.g. the former would still throw
exception if it gets a non-null return value, while the latter just returns the
metric. WDYT?
##########
clients/src/main/java/org/apache/kafka/common/metrics/Metrics.java:
##########
@@ -524,6 +524,58 @@ public void addMetric(MetricName metricName,
MetricValueProvider<?> metricValueP
addMetric(metricName, null, metricValueProvider);
}
+ /**
+ * Create or get an existing metric to monitor an object that implements
Measurable.
+ * This metric won't be associated with any sensor. This is a way to
expose existing values as metrics.
+ *
+ * This method is kept for binary compatibility purposes, it has the same
behaviour as
+ * {@link #metricOrElseCreate(MetricName, MetricConfig,
MetricValueProvider)}.
+ *
+ * @param metricName The name of the metric
+ * @param config The configuration to use when measuring this measurable
+ * @param measurable The measurable that will be measured by this metric
+ * @return Existing KafkaMetric if already registered or else a newly
created one
+ */
+ public KafkaMetric metricOrElseCreate(MetricName metricName, MetricConfig
config, Measurable measurable) {
+ return metricOrElseCreate(metricName, config, (MetricValueProvider<?>)
measurable);
+ }
+
+ /**
+ * Create or get an existing metric to monitor an object that implements
MetricValueProvider.
+ * This metric won't be associated with any sensor. This is a way to
expose existing values as metrics.
+ * This method takes care of synchronisation while updating/accessing
metrics by concurrent threads.
+ *
+ * @param metricName The name of the metric
+ * @param metricValueProvider The metric value provider associated with
this metric
+ * @return Existing KafkaMetric if already registered or else a newly
created one
+ */
+ public KafkaMetric metricOrElseCreate(MetricName metricName,
MetricValueProvider<?> metricValueProvider) {
+ return metricOrElseCreate(metricName, null, metricValueProvider);
+ }
+
+ /**
+ * Create or get an existing metric to monitor an object that implements
MetricValueProvider.
+ * This metric won't be associated with any sensor. This is a way to
expose existing values as metrics.
+ * This method takes care of synchronisation while updating/accessing
metrics by concurrent threads.
+ *
+ * @param metricName The name of the metric
+ * @param metricValueProvider The metric value provider associated with
this metric
+ * @return Existing KafkaMetric if already registered or else a newly
created one
+ */
+ public KafkaMetric metricOrElseCreate(MetricName metricName, MetricConfig
config, MetricValueProvider<?> metricValueProvider) {
Review Comment:
If we agree on the other comment I had, i.e. letting the `registerMetric` to
return the existing metric, then this function can be a single op: we just
blindly create the metric, and tries to call `registerMetric`, if it returns
non-null value, then just return that one; otherwise return the newly created
metric.
In this case we do not need the `first check, then create` two operations
and worries about its atomicity.
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