1 files changed, 96 insertions, 0 deletions
diff --git a/vendor/go.opentelemetry.io/otel/sdk/metric/exemplar.go b/vendor/go.opentelemetry.io/otel/sdk/metric/exemplar.go
new file mode 100644
index 000000000..3f1ce9f1d
--- /dev/null
+++ b/vendor/go.opentelemetry.io/otel/sdk/metric/exemplar.go
@@ -0,0 +1,96 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package metric // import "go.opentelemetry.io/otel/sdk/metric"
+
+import (
+	"os"
+	"runtime"
+
+	"go.opentelemetry.io/otel/sdk/metric/internal/exemplar"
+	"go.opentelemetry.io/otel/sdk/metric/internal/x"
+)
+
+// reservoirFunc returns the appropriately configured exemplar reservoir
+// creation func based on the passed InstrumentKind and user defined
+// environment variables.
+//
+// Note: This will only return non-nil values when the experimental exemplar
+// feature is enabled and the OTEL_METRICS_EXEMPLAR_FILTER environment variable
+// is not set to always_off.
+func reservoirFunc[N int64 | float64](agg Aggregation) func() exemplar.Reservoir[N] {
+	if !x.Exemplars.Enabled() {
+		return nil
+	}
+
+	// https://github.com/open-telemetry/opentelemetry-specification/blob/d4b241f451674e8f611bb589477680341006ad2b/specification/metrics/sdk.md#exemplar-defaults
+	resF := func() func() exemplar.Reservoir[N] {
+		// Explicit bucket histogram aggregation with more than 1 bucket will
+		// use AlignedHistogramBucketExemplarReservoir.
+		a, ok := agg.(AggregationExplicitBucketHistogram)
+		if ok && len(a.Boundaries) > 0 {
+			cp := make([]float64, len(a.Boundaries))
+			copy(cp, a.Boundaries)
+			return func() exemplar.Reservoir[N] {
+				bounds := cp
+				return exemplar.Histogram[N](bounds)
+			}
+		}
+
+		var n int
+		if a, ok := agg.(AggregationBase2ExponentialHistogram); ok {
+			// Base2 Exponential Histogram Aggregation SHOULD use a
+			// SimpleFixedSizeExemplarReservoir with a reservoir equal to the
+			// smaller of the maximum number of buckets configured on the
+			// aggregation or twenty (e.g. min(20, max_buckets)).
+			n = int(a.MaxSize)
+			if n > 20 {
+				n = 20
+			}
+		} else {
+			// https://github.com/open-telemetry/opentelemetry-specification/blob/e94af89e3d0c01de30127a0f423e912f6cda7bed/specification/metrics/sdk.md#simplefixedsizeexemplarreservoir
+			//   This Exemplar reservoir MAY take a configuration parameter for
+			//   the size of the reservoir. If no size configuration is
+			//   provided, the default size MAY be the number of possible
+			//   concurrent threads (e.g. number of CPUs) to help reduce
+			//   contention. Otherwise, a default size of 1 SHOULD be used.
+			n = runtime.NumCPU()
+			if n < 1 {
+				// Should never be the case, but be defensive.
+				n = 1
+			}
+		}
+
+		return func() exemplar.Reservoir[N] {
+			return exemplar.FixedSize[N](n)
+		}
+	}
+
+	// https://github.com/open-telemetry/opentelemetry-specification/blob/d4b241f451674e8f611bb589477680341006ad2b/specification/configuration/sdk-environment-variables.md#exemplar
+	const filterEnvKey = "OTEL_METRICS_EXEMPLAR_FILTER"
+
+	switch os.Getenv(filterEnvKey) {
+	case "always_on":
+		return resF()
+	case "always_off":
+		return exemplar.Drop[N]
+	case "trace_based":
+		fallthrough
+	default:
+		newR := resF()
+		return func() exemplar.Reservoir[N] {
+			return exemplar.SampledFilter(newR())
+		}
+	}
+}