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Reduce flakyness of testExemplarsClassicHistogram #1842

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Merged
zeitlinger merged 4 commits into from
Feb 4, 2026
+44 −5
Merged

Reduce flakyness of testExemplarsClassicHistogram #1842

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db6cd4f
use awaitility to avoid flakyness
jaydeluca Feb 2, 2026
55d7520
Apply suggestions from code review
jaydeluca Feb 2, 2026
0430478
add version back in
jaydeluca Feb 2, 2026
5ff610e
remove dependency
jaydeluca Feb 3, 2026
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6 changes: 6 additions & 0 deletions prometheus-metrics-core/pom.xml
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Original file line number Diff line number Diff line change
Expand Up @@ -51,5 +51,11 @@
<version>3.6.1</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.awaitility</groupId>
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<artifactId>awaitility</artifactId>
<version>4.3.0</version>
<scope>test</scope>
</dependency>
</dependencies>
</project>
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51 changes: 46 additions & 5 deletions prometheus-metrics-core/src/test/java/io/prometheus/metrics/core/metrics/HistogramTest.java
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Original file line number Diff line number Diff line change
@@ -1,9 +1,11 @@
package io.prometheus.metrics.core.metrics;

import static io.prometheus.metrics.core.metrics.TestUtil.assertExemplarEquals;
import static java.util.concurrent.TimeUnit.SECONDS;
import static org.assertj.core.api.Assertions.assertThat;
import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
import static org.assertj.core.data.Offset.offset;
import static org.awaitility.Awaitility.await;

import io.prometheus.metrics.config.EscapingScheme;
import io.prometheus.metrics.config.MetricsProperties;
Expand Down Expand Up @@ -1020,10 +1022,17 @@ public void markCurrentSpanAsExemplar() {}
assertThat(getExemplar(snapshot, Double.POSITIVE_INFINITY, "path", "/hello")).isNull();
assertThat(getExemplar(snapshot, Double.POSITIVE_INFINITY, "path", "/world")).isNull();

Thread.sleep(sampleIntervalMillis + 1);
waitForSampleInterval(sampleIntervalMillis);
histogram.labelValues("/hello").observe(4.5);
histogram.labelValues("/world").observe(4.5);

await()
.atMost(2, SECONDS)
.until(
() ->
getExemplar(histogram.collect(), Double.POSITIVE_INFINITY, "path", "/hello") != null
&& getExemplar(histogram.collect(), Double.POSITIVE_INFINITY, "path", "/world")
!= null);
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snapshot = histogram.collect();
assertExemplarEquals(ex1a, getExemplar(snapshot, 1.0, "path", "/hello"));
assertExemplarEquals(ex1b, getExemplar(snapshot, 1.0, "path", "/world"));
Expand All @@ -1036,16 +1045,28 @@ public void markCurrentSpanAsExemplar() {}
assertExemplarEquals(ex2a, getExemplar(snapshot, Double.POSITIVE_INFINITY, "path", "/hello"));
assertExemplarEquals(ex2b, getExemplar(snapshot, Double.POSITIVE_INFINITY, "path", "/world"));

Thread.sleep(sampleIntervalMillis + 1);
waitForSampleInterval(sampleIntervalMillis);
histogram.labelValues("/hello").observe(1.5);
histogram.labelValues("/world").observe(1.5);
Thread.sleep(sampleIntervalMillis + 1);
waitForSampleInterval(sampleIntervalMillis);
histogram.labelValues("/hello").observe(2.5);
histogram.labelValues("/world").observe(2.5);
Thread.sleep(sampleIntervalMillis + 1);
waitForSampleInterval(sampleIntervalMillis);
histogram.labelValues("/hello").observe(3.5);
histogram.labelValues("/world").observe(3.5);

await()
.atMost(2, SECONDS)
.until(
() -> {
HistogramSnapshot s = histogram.collect();
return getExemplar(s, 2.0, "path", "/hello") != null
&& getExemplar(s, 2.0, "path", "/world") != null
&& getExemplar(s, 3.0, "path", "/hello") != null
&& getExemplar(s, 3.0, "path", "/world") != null
&& getExemplar(s, 4.0, "path", "/hello") != null
&& getExemplar(s, 4.0, "path", "/world") != null;
});
snapshot = histogram.collect();
assertExemplarEquals(ex1a, getExemplar(snapshot, 1.0, "path", "/hello"));
assertExemplarEquals(ex1b, getExemplar(snapshot, 1.0, "path", "/world"));
Expand All @@ -1072,15 +1093,35 @@ public void markCurrentSpanAsExemplar() {}
"span_id",
"spanId-11"))
.build();
Thread.sleep(sampleIntervalMillis + 1);
waitForSampleInterval(sampleIntervalMillis);
histogram
.labelValues("/hello")
.observeWithExemplar(3.4, Labels.of("key1", "value1", "key2", "value2"));
await()
.atMost(2, SECONDS)
.until(
() -> {
Exemplar actual = getExemplar(histogram.collect(), 4.0, "path", "/hello");
return actual != null && Math.abs(actual.getValue() - 3.4) < 0.0001;
});
snapshot = histogram.collect();
// custom exemplars have preference, so the automatic exemplar is replaced
assertExemplarEquals(custom, getExemplar(snapshot, 4.0, "path", "/hello"));
}

/**
* Waits for the exemplar sampler's rate limit window so the next observation is accepted. Uses a
* deterministic delay (2x sample interval) so the scheduler is ready.
*/
private static void waitForSampleInterval(long sampleIntervalMillis) {
try {
Thread.sleep(2 * sampleIntervalMillis);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
throw new AssertionError("Interrupted while waiting for sample interval", e);
}
}

private Exemplar getExemplar(HistogramSnapshot snapshot, double le, String... labels) {
HistogramSnapshot.HistogramDataPointSnapshot data =
snapshot.getDataPoints().stream()
Expand Down
3 changes: 3 additions & 0 deletions prometheus-metrics-core/src/test/java/io/prometheus/metrics/core/metrics/TestUtil.java
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,9 @@
public class TestUtil {

public static void assertExemplarEquals(Exemplar expected, Exemplar actual) {
assertThat(actual)
.as("Expected exemplar to be present (rate-limited sampler may not have accepted yet)")
.isNotNull();
// ignore timestamp
assertThat(actual.getValue()).isCloseTo(expected.getValue(), offset(0.00001));
assertThat((Iterable<? extends Label>) actual.getLabels()).isEqualTo(expected.getLabels());
Expand Down
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