Add EventSource for ApplicationInsightsMetricExporter

Author: jviau

src/WebJobs.Script/Diagnostics/ApplicationInsightsMetricExporter.EventSource.cs

@@ -0,0 +1,58 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the MIT License. See License.txt in the project root for license information.
+
+using System;
+using System.Diagnostics.Metrics;
+using System.Diagnostics.Tracing;
+
+namespace Microsoft.Azure.WebJobs.Script.Diagnostics
+{
+    public sealed partial class ApplicationInsightsMetricExporter
+    {
+        [EventSource(Name = "Azure-Functions-Application-Insights-Metric-Exporter")]
+        private sealed class Events : EventSource
+        {
+            public static readonly Events Log = new();
+
+            private Events()
+            {
+            }
+
+            [Event(1, Message ="Failed to collect observable instruments: {0}", Level = EventLevel.Error)]
+            public void FailedToCollectInstruments(Exception error)
+            {
+                WriteEvent(1, $"{error.GetType().FullName}: {error.Message}");
+            }
+
+            [Event(2, Message = "Begin collecting observable instruments.")]
+            public void BeginCollectObservables()
+            {
+                WriteEvent(2);
+            }
+
+            [Event(3, Message = "End collecting observable instruments.")]
+            public void EndCollectObservables()
+            {
+                WriteEvent(2);
+            }
+
+            [Event(4, Message = "Meter listening started.")]
+            public void MeterListeningStarted()
+            {
+                WriteEvent(4);
+            }
+
+            [Event(5, Message = "Meter listening stopped.")]
+            public void MeterListeningStopped()
+            {
+                WriteEvent(5);
+            }
+
+            [Event(6, Message = "Subscribed to instrument {0} on meter {1}.")]
+            public void SubscribedToInstrument(Instrument instrument)
+            {
+                WriteEvent(6, instrument.Name, instrument.Meter.Name);
+            }
+        }
+    }
+}

src/WebJobs.Script/Diagnostics/ApplicationInsightsMetricExporter.cs

@@ -18,7 +18,7 @@ namespace Microsoft.Azure.WebJobs.Script.Diagnostics
     /// <summary>
     /// A meter listener which exports metrics to Application Insights.
     /// </summary>
-    public sealed class ApplicationInsightsMetricExporter : ITelemetryModule, IAsyncDisposable
+    public sealed partial class ApplicationInsightsMetricExporter : ITelemetryModule, IAsyncDisposable
     {
         private readonly MeterListener _listener;
         private readonly ApplicationInsightsMetricExporterOptions _options;
@@ -42,6 +42,7 @@ public ApplicationInsightsMetricExporter(IOptions<ApplicationInsightsMetricExpor
                 {
                     if (_options.ShouldListenTo(instrument))
                     {
+                        Events.Log.SubscribedToInstrument(instrument);
                         listener.EnableMeasurementEvents(instrument, this);
                     }
                 },
@@ -65,6 +66,8 @@ public void Initialize(TelemetryConfiguration configuration)
         {
             ArgumentNullException.ThrowIfNull(configuration);
             ObjectDisposedException.ThrowIf(_shutdown.IsCancellationRequested, this);
+
+            Events.Log.MeterListeningStarted();
             _client = new TelemetryClient(configuration);
             _listener.Start();
             _exportTask = CollectAsync(_shutdown.Token);
@@ -73,6 +76,7 @@ public void Initialize(TelemetryConfiguration configuration)
         /// <inheritdoc />
         public async ValueTask DisposeAsync()
         {
+            Events.Log.MeterListeningStopped();
             _listener.Dispose();
 
             await _shutdown.CancelNoThrowAsync();
@@ -114,12 +118,14 @@ private async Task CollectAsync(CancellationToken cancellation)
             {
                 try
                 {
+                    Events.Log.BeginCollectObservables();
                     _listener.RecordObservableInstruments();
+                    Events.Log.EndCollectObservables();
                     await Task.Delay(_options.CollectInterval, cancellation);
                 }
                 catch (Exception ex) when (!ex.IsFatal())
                 {
-                    // swallow exceptions
+                    Events.Log.FailedToCollectInstruments(ex);
                 }
             }
         }