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// 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 exemplar // import "go.opentelemetry.io/otel/sdk/metric/internal/exemplar"
import (
"context"
"time"
"go.opentelemetry.io/otel/attribute"
"go.opentelemetry.io/otel/sdk/metric/metricdata"
"go.opentelemetry.io/otel/trace"
)
// storage is an exemplar storage for [Reservoir] implementations.
type storage[N int64 | float64] struct {
// store are the measurements sampled.
//
// This does not use []metricdata.Exemplar because it potentially would
// require an allocation for trace and span IDs in the hot path of Offer.
store []measurement[N]
}
func newStorage[N int64 | float64](n int) *storage[N] {
return &storage[N]{store: make([]measurement[N], n)}
}
// Collect returns all the held exemplars.
//
// The Reservoir state is preserved after this call.
func (r *storage[N]) Collect(dest *[]metricdata.Exemplar[N]) {
*dest = reset(*dest, len(r.store), len(r.store))
var n int
for _, m := range r.store {
if !m.valid {
continue
}
m.Exemplar(&(*dest)[n])
n++
}
*dest = (*dest)[:n]
}
// measurement is a measurement made by a telemetry system.
type measurement[N int64 | float64] struct {
// FilteredAttributes are the attributes dropped during the measurement.
FilteredAttributes []attribute.KeyValue
// Time is the time when the measurement was made.
Time time.Time
// Value is the value of the measurement.
Value N
// SpanContext is the SpanContext active when a measurement was made.
SpanContext trace.SpanContext
valid bool
}
// newMeasurement returns a new non-empty Measurement.
func newMeasurement[N int64 | float64](ctx context.Context, ts time.Time, v N, droppedAttr []attribute.KeyValue) measurement[N] {
return measurement[N]{
FilteredAttributes: droppedAttr,
Time: ts,
Value: v,
SpanContext: trace.SpanContextFromContext(ctx),
valid: true,
}
}
// Exemplar returns m as a [metricdata.Exemplar].
func (m measurement[N]) Exemplar(dest *metricdata.Exemplar[N]) {
dest.FilteredAttributes = m.FilteredAttributes
dest.Time = m.Time
dest.Value = m.Value
if m.SpanContext.HasTraceID() {
traceID := m.SpanContext.TraceID()
dest.TraceID = traceID[:]
} else {
dest.TraceID = dest.TraceID[:0]
}
if m.SpanContext.HasSpanID() {
spanID := m.SpanContext.SpanID()
dest.SpanID = spanID[:]
} else {
dest.SpanID = dest.SpanID[:0]
}
}
func reset[T any](s []T, length, capacity int) []T {
if cap(s) < capacity {
return make([]T, length, capacity)
}
return s[:length]
}
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