[sdk-metrics] Support .NET 9 Synchronous Gauge

src/OpenTelemetry/CHANGELOG.md

@@ -31,6 +31,11 @@ Notes](../../RELEASENOTES.md).
  See [#5854](https:/open-telemetry/opentelemetry-dotnet/pull/5854)
  for details.
 
+* Add support for collecting metrics from
+ [Gauge](https://learn.microsoft.com/dotnet/api/system.diagnostics.metrics.gauge-1)
+ API
+ ([#5867](https:/open-telemetry/opentelemetry-dotnet/pull/5867))
+
 ## 1.9.0
 
 Released 2024-Jun-14

src/OpenTelemetry/Metrics/Metric.cs

@@ -117,6 +117,12 @@ internal Metric(
  aggType = AggregationType.DoubleGauge;
  this.MetricType = MetricType.DoubleGauge;
  }
+ else if (instrumentIdentity.InstrumentType == typeof(Gauge<double>)
+ || instrumentIdentity.InstrumentType == typeof(Gauge<float>))
+ {
+ aggType = AggregationType.DoubleGauge;
+ this.MetricType = MetricType.DoubleGauge;
+ }
  else if (instrumentIdentity.InstrumentType == typeof(ObservableGauge<long>)
  || instrumentIdentity.InstrumentType == typeof(ObservableGauge<int>)
  || instrumentIdentity.InstrumentType == typeof(ObservableGauge<short>)
@@ -125,6 +131,14 @@ internal Metric(
  aggType = AggregationType.LongGauge;
  this.MetricType = MetricType.LongGauge;
  }
+ else if (instrumentIdentity.InstrumentType == typeof(Gauge<long>)
+ || instrumentIdentity.InstrumentType == typeof(Gauge<int>)
+ || instrumentIdentity.InstrumentType == typeof(Gauge<short>)
+ || instrumentIdentity.InstrumentType == typeof(Gauge<byte>))
+ {
+ aggType = AggregationType.LongGauge;
+ this.MetricType = MetricType.LongGauge;
+ }
  else if (instrumentIdentity.IsHistogram)
  {
  var explicitBucketBounds = instrumentIdentity.HistogramBucketBounds;

src/OpenTelemetry/Metrics/Reader/MetricReader.cs

@@ -27,6 +27,7 @@ public abstract partial class MetricReader : IDisposable
 
  // Temporality is not defined for gauges, so this does not really affect anything.
  var type when type == typeof(ObservableGauge<>) => AggregationTemporality.Delta,
+ var type when type == typeof(Gauge<>) => AggregationTemporality.Delta,
 
  var type when type == typeof(UpDownCounter<>) => AggregationTemporality.Cumulative,
  var type when type == typeof(ObservableUpDownCounter<>) => AggregationTemporality.Cumulative,

test/OpenTelemetry.Tests/Metrics/MetricApiTestsBase.cs

@@ -1613,6 +1613,34 @@ public void UnsupportedMetricInstrument()
  Assert.Empty(exportedItems);
  }
 
+ [Fact]
+ public void GaugeIsExportedCorrectly()
+ {
+ var exportedItems = new List<Metric>();
+
+ using var meter = new Meter($"{Utils.GetCurrentMethodName()}");
+
+ using var container = this.BuildMeterProvider(out var meterProvider, builder => builder
+ .AddMeter(meter.Name)
+ .AddInMemoryExporter(exportedItems));
+
+ var gauge = meter.CreateGauge<long>(name: "NoiseLevel", unit: "dB", description: "Background Noise Level");
+ gauge.Record(10);
+ meterProvider.ForceFlush(MaxTimeToAllowForFlush);
+ Assert.Single(exportedItems);
+ var metric = exportedItems[0];
+ Assert.Equal("Background Noise Level", metric.Description);
+ List<MetricPoint> metricPoints = new List<MetricPoint>();
+ foreach (ref readonly var mp in metric.GetMetricPoints())
+ {
+ metricPoints.Add(mp);
+ }
+
+ var histogramPoint = metricPoints[0];
+ var lastValue = metricPoints[0].GetGaugeLastValueLong();
+ Assert.Equal(10, lastValue);
+ }
+
  internal static IConfiguration BuildConfiguration(bool emitOverflowAttribute, bool shouldReclaimUnusedMetricPoints)
  {
  var configurationData = new Dictionary<string, string>();