[AzureMonitorDistro] Fix livemetrics reporting incorrect values (Azure#46429)

* removing buffer capacity

* remove counter

* remove DocumentBuffer class

* changelog

Author: Timothy Mothra

sdk/monitor/Azure.Monitor.OpenTelemetry.AspNetCore/CHANGELOG.md

@@ -21,6 +21,9 @@
 * Fixed a bug in LiveMetrics that counted all manually created Dependencies as failures.
   ([#45103](https://github.com/Azure/azure-sdk-for-net/pull/45103))
 
+* Fixed a bug in LiveMetrics that caused incorrect counts for telemetry.
+  ([#46429](https://github.com/Azure/azure-sdk-for-net/pull/46429))
+
 ### Other Changes
 
 * Updated the code of vendored resource detector library `OpenTelemetry.Resources.Azure` from the OpenTelemetry .NET contrib repository.

sdk/monitor/Azure.Monitor.OpenTelemetry.AspNetCore/src/LiveMetrics/DataCollection/DocumentBuffer.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT License.
 
+using System.Collections.Concurrent;
 using Azure.Monitor.OpenTelemetry.AspNetCore.Models;
 
 namespace Azure.Monitor.OpenTelemetry.AspNetCore.LiveMetrics.DataCollection
@@ -14,17 +15,17 @@ namespace Azure.Monitor.OpenTelemetry.AspNetCore.LiveMetrics.DataCollection
     /// </summary>
     internal class DoubleBuffer
     {
-        private DocumentBuffer _currentBuffer = new();
+        private ConcurrentQueue<DocumentIngress> _currentBuffer = new();
 
         public void WriteDocument(DocumentIngress document)
         {
-            _currentBuffer.Add(document);
+            _currentBuffer.Enqueue(document);
         }
 
-        public DocumentBuffer FlipDocumentBuffers()
+        public ConcurrentQueue<DocumentIngress> FlipDocumentBuffers()
         {
             // Atomically exchange the current buffer with a new empty buffer and return the old buffer
-            return Interlocked.Exchange(ref _currentBuffer, new DocumentBuffer());
+            return Interlocked.Exchange(ref _currentBuffer, new ConcurrentQueue<DocumentIngress>());
         }
     }
 }

sdk/monitor/Azure.Monitor.OpenTelemetry.AspNetCore/src/LiveMetrics/DataCollection/DoubleBuffer.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT License.
 
+using System.Collections.Concurrent;
 using Azure.Monitor.OpenTelemetry.AspNetCore.LiveMetrics;
 using Azure.Monitor.OpenTelemetry.AspNetCore.LiveMetrics.DataCollection;
 using Azure.Monitor.OpenTelemetry.AspNetCore.LiveMetrics.Filtering;
@@ -45,9 +46,10 @@ public MonitoringDataPoint GetDataPoint()
             string projectionError = string.Empty;
             Dictionary<string, AccumulatedValues> metricAccumulators = CreateMetricAccumulators(_collectionConfiguration);
             LiveMetricsBuffer liveMetricsBuffer = new();
-            DocumentBuffer filledBuffer = _documentBuffer.FlipDocumentBuffers();
             IEnumerable<DocumentStream> documentStreams = _collectionConfiguration.DocumentStreams;
-            foreach (var item in filledBuffer.ReadAllAndClear())
+
+            ConcurrentQueue<DocumentIngress> filledBuffer = _documentBuffer.FlipDocumentBuffers();
+            while (filledBuffer.TryDequeue(out DocumentIngress? item))
             {
                 bool matchesDocumentStreamFilter = false;