Tweaks.

src/OpenTelemetry/Metrics/Exemplar/Exemplar.cs

@@ -1,13 +1,15 @@
 // Copyright The OpenTelemetry Authors
 // SPDX-License-Identifier: Apache-2.0
 
+using System.Diagnostics;
 #if EXPOSE_EXPERIMENTAL_FEATURES && NET8_0_OR_GREATER
 using System.Diagnostics.CodeAnalysis;
+#endif
+using System.Runtime.CompilerServices;
+#if EXPOSE_EXPERIMENTAL_FEATURES && NET8_0_OR_GREATER
 using OpenTelemetry.Internal;
 #endif
 
-using System.Diagnostics;
-
 namespace OpenTelemetry.Metrics;
 
 #if EXPOSE_EXPERIMENTAL_FEATURES
@@ -32,7 +34,7 @@ struct Exemplar
     private int tagCount;
     private KeyValuePair<string, object?>[]? tagStorage;
     private MetricPointValueStorage valueStorage;
-    private volatile int isCriticalSectionOccupied;
+    private int isCriticalSectionOccupied;
 
     /// <summary>
     /// Gets the timestamp.
@@ -76,7 +78,7 @@ public readonly ReadOnlyFilteredTagCollection FilteredTags
     internal void Update<T>(in ExemplarMeasurement<T> measurement)
         where T : struct
     {
-        if (Interlocked.CompareExchange(ref this.isCriticalSectionOccupied, 1, 0) != 0)
+        if (Interlocked.Exchange(ref this.isCriticalSectionOccupied, 1) != 0)
         {
             // Some other thread is already writing, abort.
             return;
@@ -112,7 +114,7 @@ internal void Update<T>(in ExemplarMeasurement<T> measurement)
 
         this.StoreRawTags(measurement.Tags);
 
-        this.isCriticalSectionOccupied = 0;
+        Volatile.Write(ref this.isCriticalSectionOccupied, 0);
     }
 
     internal void Reset()
@@ -122,7 +124,7 @@ internal void Reset()
 
     internal readonly bool IsUpdated()
     {
-        if (this.isCriticalSectionOccupied != 0)
+        if (Volatile.Read(ref Unsafe.AsRef(in this.isCriticalSectionOccupied)) != 0)
         {
             this.WaitForUpdateToCompleteRare();
             return true;
@@ -171,6 +173,6 @@ private readonly void WaitForUpdateToCompleteRare()
         {
             spinWait.SpinOnce();
         }
-        while (this.isCriticalSectionOccupied != 0);
+        while (Volatile.Read(ref Unsafe.AsRef(in this.isCriticalSectionOccupied)) != 0);
     }
 }

src/OpenTelemetry/Metrics/Exemplar/FixedSizeExemplarReservoir.cs

@@ -14,7 +14,7 @@ internal abstract class FixedSizeExemplarReservoir : ExemplarReservoir
 {
     private readonly Exemplar[] bufferA;
     private readonly Exemplar[] bufferB;
-    private volatile Exemplar[]? activeBuffer;
+    private Exemplar[]? activeBuffer;
 
     protected FixedSizeExemplarReservoir(int capacity)
     {
@@ -34,11 +34,11 @@ protected FixedSizeExemplarReservoir(int capacity)
     /// <returns><see cref="ReadOnlyExemplarCollection"/>.</returns>
     public sealed override ReadOnlyExemplarCollection Collect()
     {
-        var currentBuffer = this.activeBuffer;
+        var currentBuffer = Volatile.Read(ref this.activeBuffer);
 
         Debug.Assert(currentBuffer != null, "currentBuffer was null");
 
-        this.activeBuffer = null;
+        Volatile.Write(ref this.activeBuffer, null);
 
         var inactiveBuffer = currentBuffer == this.bufferA
             ? this.bufferB
@@ -54,7 +54,7 @@ public sealed override ReadOnlyExemplarCollection Collect()
 
         this.OnCollectionCompleted();
 
-        this.activeBuffer = inactiveBuffer;
+        Volatile.Write(ref this.activeBuffer, inactiveBuffer);
 
         return new(currentBuffer!);
     }
@@ -95,7 +95,7 @@ protected virtual void OnCollectionCompleted()
     protected void UpdateExemplar<T>(int exemplarIndex, in ExemplarMeasurement<T> measurement)
         where T : struct
     {
-        var activeBuffer = this.activeBuffer;
+        var activeBuffer = Volatile.Read(ref this.activeBuffer);
         if (activeBuffer == null)
         {
             // Note: This is expected to happen when we race with a collection.

src/OpenTelemetry/Metrics/Exemplar/SimpleFixedSizeExemplarReservoir.cs

@@ -14,7 +14,7 @@ namespace OpenTelemetry.Metrics;
 /// </remarks>
 internal sealed class SimpleFixedSizeExemplarReservoir : FixedSizeExemplarReservoir
 {
-    private volatile int measurementsSeen;
+    private int measurementsSeen;
 
     public SimpleFixedSizeExemplarReservoir()
         : this(Environment.ProcessorCount)
@@ -41,7 +41,7 @@ protected override void OnCollectionCompleted()
         // Reset internal state irrespective of temporality.
         // This ensures incoming measurements have fair chance
         // of making it to the reservoir.
-        this.measurementsSeen = 0;
+        Volatile.Write(ref this.measurementsSeen, 0);
     }
 
     private void Offer<T>(in ExemplarMeasurement<T> measurement)