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Fix issue where histogram snapshot mutates its state #126

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Merged
merged 1 commit into from
Jun 27, 2024
Merged

Fix issue where histogram snapshot mutates its state #126

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8 changes: 4 additions & 4 deletions core/src/main/java/com/uber/m3/tally/HistogramImpl.java
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Original file line number Diff line number Diff line change
Expand Up @@ -145,8 +145,8 @@ private double getLowerBoundValueForBucket(int bucketIndex) {
return bucketIndex == 0 ? Double.MIN_VALUE : specification.getValueUpperBounds().get(bucketIndex - 1);
}

private long getCounterValue(int index) {
return bucketCounters[index] != null ? bucketCounters[index].value() : 0;
private long snapshotCounterValue(int index) {
return bucketCounters[index] != null ? bucketCounters[index].snapshot() : 0;
}

// NOTE: Only used in testing
Expand All @@ -158,7 +158,7 @@ Map<Double, Long> snapshotValues() {
Map<Double, Long> values = new HashMap<>(bucketCounters.length, 1);

for (int i = 0; i < bucketCounters.length; ++i) {
values.put(getUpperBoundValueForBucket(i), getCounterValue(i));
values.put(getUpperBoundValueForBucket(i), snapshotCounterValue(i));
}

return values;
Expand All @@ -172,7 +172,7 @@ Map<Duration, Long> snapshotDurations() {
Map<Duration, Long> durations = new HashMap<>(bucketCounters.length, 1);

for (int i = 0; i < bucketCounters.length; ++i) {
durations.put(getUpperBoundDurationForBucket(i), getCounterValue(i));
durations.put(getUpperBoundDurationForBucket(i), snapshotCounterValue(i));
}

return durations;
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44 changes: 44 additions & 0 deletions core/src/test/java/com/uber/m3/tally/HistogramImplTest.java
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Expand Up @@ -217,6 +217,28 @@ public void snapshotValues() {
assertEquals(expectedMap, histogram.snapshotValues());
}

@Test
public void snapshotValuesIsIdempotent() {
ValueBuckets buckets = ValueBuckets.custom(0, 10);

histogram =
new HistogramImpl(
scope,
"",
null,
buckets
);

histogram.recordValue(5);

Map<Double, Long> snapshot = histogram.snapshotValues();
assertEquals(1, snapshot.get(10D).longValue());

// snapshot again to ensure the first snapshot didn't mutate internal state
snapshot = histogram.snapshotValues();
assertEquals(1, snapshot.get(10D).longValue());
}

@Test
public void snapshotDurations() {
Buckets buckets = DurationBuckets.linear(Duration.ZERO, Duration.ofMillis(10), 5);
Expand Down Expand Up @@ -247,4 +269,26 @@ public void snapshotDurations() {

assertEquals(expectedMap, histogram.snapshotDurations());
}

@Test
public void snapshotDurationsIsIdempotent() {
DurationBuckets buckets = DurationBuckets.custom(Duration.ofMillis(0), Duration.ofMillis(10));

histogram =
new HistogramImpl(
scope,
"",
null,
buckets
);

histogram.recordDuration(Duration.ofMillis(5));

Map<Duration, Long> snapshot = histogram.snapshotDurations();
assertEquals(1, snapshot.get(Duration.ofMillis(10)).longValue());

// snapshot again to ensure the first snapshot didn't mutate internal state
snapshot = histogram.snapshotDurations();
assertEquals(1, snapshot.get(Duration.ofMillis(10)).longValue());
}
}