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Fix NullReferenceException caught by SDK when metric has a tag with a null value #3325

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merged 8 commits into from
Jun 3, 2022
Merged

Fix NullReferenceException caught by SDK when metric has a tag with a null value #3325

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fafaeed
Add test recording a metric with a null-valued dimension
alanwest Jun 1, 2022
da6b615
Fix null-valued tags
alanwest Jun 2, 2022
4a421ec
Assert.Null instead of Assert.Equal
alanwest Jun 2, 2022
bfe2c3e
Compute hash code in constructor
alanwest Jun 2, 2022
3c38408
Update changelog
alanwest Jun 2, 2022
82f20af
Merge branch 'main' into alanwest/null-valued-dimensions
alanwest Jun 2, 2022
3d57791
Merge branch 'main' into alanwest/null-valued-dimensions
alanwest Jun 3, 2022
a155e08
Merge branch 'main' into alanwest/null-valued-dimensions
cijothomas Jun 3, 2022
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4 changes: 4 additions & 0 deletions src/OpenTelemetry/CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,10 @@

## Unreleased

* Fix issue where a measurement would be dropped when recording it with a
null-valued tag.
([#3325](https://github.com/open-telemetry/opentelemetry-dotnet/pull/3325))

## 1.3.0

Released 2022-Jun-03
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28 changes: 14 additions & 14 deletions src/OpenTelemetry/Metrics/Tags.cs
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Expand Up @@ -20,10 +20,23 @@ namespace OpenTelemetry.Metrics
{
internal readonly struct Tags : IEquatable<Tags>
{
private readonly int hashCode;

public Tags(string[] keys, object[] values)
{
this.Keys = keys;
this.Values = values;

unchecked
{
var hash = 17;
for (int i = 0; i < this.Keys.Length; i++)
{
hash = (hash * 31) + this.Keys[i].GetHashCode() + this.Values[i]?.GetHashCode() ?? 0;
}

this.hashCode = hash;
}
Comment on lines +30 to +39
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Is there any concern that the underlying values of Keys or Values will get changed since the array indexes can still be written to but the hash won't be updated?

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@tgrieger-sf No because the the keys and values never do change. This struct is internal and instances of it are only used within our AggregatorStore for looking up metric points

opentelemetry-dotnet/src/OpenTelemetry/Metrics/AggregatorStore.cs

Line 33 in a19d106

private readonly ConcurrentDictionary<Tags, int> tagsToMetricPointIndexDictionary =
.

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If that's the case, is there any benefit in using ReadOnlySpan<string/object> for Keys and Values to make it explicit?

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ReadOnlySpan is a ref struct and cannot be used a valid type for a dictionary as it has to live on stack.

}

public readonly string[] Keys { get; }
Expand Down Expand Up @@ -78,19 +91,6 @@ public Tags(string[] keys, object[] values)
return true;
}

public override readonly int GetHashCode()
{
int hash = 17;

unchecked
{
for (int i = 0; i < this.Keys.Length; i++)
{
hash = (hash * 31) + this.Keys[i].GetHashCode() + this.Values[i].GetHashCode();
}
}

return hash;
}
public override readonly int GetHashCode() => this.hashCode;
}
}
33 changes: 33 additions & 0 deletions test/OpenTelemetry.Tests/Metrics/MetricAPITest.cs
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Expand Up @@ -42,6 +42,39 @@ public MetricApiTest(ITestOutputHelper output)
this.output = output;
}

[Fact]
public void MeasurementWithNullValuedTag()
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💯

{
using var meter = new Meter(Utils.GetCurrentMethodName());
var exportedItems = new List<Metric>();
using var meterProvider = Sdk.CreateMeterProviderBuilder()
.AddMeter(meter.Name)
.AddInMemoryExporter(exportedItems)
.Build();

var counter = meter.CreateCounter<long>("myCounter");
counter.Add(100, new KeyValuePair<string, object>("tagWithNullValue", null));

meterProvider.ForceFlush(MaxTimeToAllowForFlush);
Assert.Single(exportedItems);
var metric = exportedItems[0];
Assert.Equal("myCounter", metric.Name);
List<MetricPoint> metricPoints = new List<MetricPoint>();
foreach (ref readonly var mp in metric.GetMetricPoints())
{
metricPoints.Add(mp);
}

Assert.Single(metricPoints);
var metricPoint = metricPoints[0];
Assert.Equal(100, metricPoint.GetSumLong());
Assert.Equal(1, metricPoint.Tags.Count);
var tagEnumerator = metricPoint.Tags.GetEnumerator();
tagEnumerator.MoveNext();
Assert.Equal("tagWithNullValue", tagEnumerator.Current.Key);
Assert.Null(tagEnumerator.Current.Value);
}

[Fact]
public void ObserverCallbackTest()
{
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