fixes after rebase

Author: dashpole

CHANGELOG.md

@@ -15,7 +15,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - Improve performance of concurrent histogram measurements in `go.opentelemetry.io/otel/sdk/metric`. (#7474)
 - Add experimental observability metrics in `go.opentelemetry.io/otel/exporters/stdout/stdoutmetric`. (#7492)
 - Improve the concurrent performance of `HistogramReservoir` in `go.opentelemetry.io/otel/sdk/metric/exemplar` by 4x. (#7443)
-- Improve the concurrent performance of `FixedSizeReservoir` in `go.opentelemetry.io/otel/sdk/metric/exemplar` by 3x. (#7447)
+- Improve the concurrent performance of `FixedSizeReservoir` in `go.opentelemetry.io/otel/sdk/metric/exemplar` by 4x. (#7447)
 
 <!-- Released section -->
 <!-- Don't change this section unless doing release -->

sdk/metric/exemplar/benchmark_test.go

@@ -22,9 +22,7 @@ func BenchmarkFixedSizeReservoirOffer(b *testing.B) {
 			// reservoirs records exemplars very infrequently after a large
 			// number of collect calls.
 			if i%100 == 99 {
-				reservoir.mu.Lock()
 				reservoir.reset()
-				reservoir.mu.Unlock()
 			}
 			i++
 		}

sdk/metric/exemplar/fixed_size_reservoir.go

@@ -104,11 +104,11 @@ func (r *FixedSizeReservoir) Offer(ctx context.Context, t time.Time, n Value, a
 	count, next := r.incrementCount()
 	intCount := int(count) // nolint:gosec // count is at most 32 bits in length
 	if intCount < r.k {
-		r.store(intCount, newMeasurement(ctx, t, n, a))
+		r.store(ctx, intCount, t, n, a)
 	} else if count == next {
 		// Overwrite a random existing measurement with the one offered.
 		idx := rand.IntN(r.k)
-		r.store(idx, newMeasurement(ctx, t, n, a))
+		r.store(ctx, idx, t, n, a)
 		r.wMu.Lock()
 		defer r.wMu.Unlock()
 		r.advance()

sdk/metric/exemplar/fixed_size_reservoir_test.go

@@ -45,15 +45,8 @@ func TestNewFixedSizeReservoirSamplingCorrectness(t *testing.T) {
 	}
 
 	var sum float64
-	for _, val := range r.measurements {
-		loaded := val.Load()
-		if loaded == nil {
-			continue
-		}
-		m := loaded.(*measurement)
-		if m != nil {
-			sum += m.Value.Float64()
-		}
+	for i := range r.measurements {
+		sum += r.measurements[i].Value.Float64()
 	}
 	mean := sum / float64(sampleSize)