Address PR comments, fix build

Author: jviau

src/WebJobs.Script/Diagnostics/ApplicationInsightsMetricExporter.cs

@@ -30,7 +30,6 @@ public sealed class ApplicationInsightsMetricExporter : ITelemetryModule, IAsync
         /// <summary>
         /// Initializes a new instance of the <see cref="ApplicationInsightsMetricExporter"/> class.
         /// </summary>
-        /// <param name="lifetime">The application lifetime.</param>
         /// <param name="options">The options.</param>
         public ApplicationInsightsMetricExporter(IOptions<ApplicationInsightsMetricExporterOptions> options)
         {
@@ -65,9 +64,10 @@ public ApplicationInsightsMetricExporter(IOptions<ApplicationInsightsMetricExpor
         public void Initialize(TelemetryConfiguration configuration)
         {
             ArgumentNullException.ThrowIfNull(configuration);
+            ObjectDisposedException.ThrowIf(_shutdown.IsCancellationRequested, this);
             _client = new TelemetryClient(configuration);
-            _exportTask = CollectAsync(_shutdown.Token);
             _listener.Start();
+            _exportTask = CollectAsync(_shutdown.Token);
         }
 
         /// <inheritdoc />
@@ -77,7 +77,12 @@ public async ValueTask DisposeAsync()
 
             await _shutdown.CancelNoThrowAsync();
             await _exportTask.ConfigureAwait(false);
-            await _client.FlushAsync(default).ConfigureAwait(false);
+
+            if (_client is { } client)
+            {
+                await client.FlushAsync(default).ConfigureAwait(false);
+            }
+
             _shutdown.Dispose();
         }
 

src/WebJobs.Script/Diagnostics/ApplicationInsightsMetricExporterOptions.cs

@@ -6,6 +6,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics.Metrics;
+using Microsoft.Azure.WebJobs.Script.Metrics;
 
 namespace Microsoft.Azure.WebJobs.Script.Diagnostics
 {
@@ -14,6 +15,13 @@ namespace Microsoft.Azure.WebJobs.Script.Diagnostics
     /// </summary>
     public class ApplicationInsightsMetricExporterOptions
     {
+        // AppInsights has some metrics which are already emitted a different way.
+        // We ignore them here to ensure we don't duplicate the metric.
+        private static readonly HashSet<string> IgnoredInstruments =
+        [
+            HostMetrics.FaasInvokeDuration,
+        ];
+
         /// <summary>
         /// Gets the set of meter names to listen to.
         /// </summary>
@@ -40,7 +48,7 @@ public bool ShouldListenTo(Instrument instrument)
 
             // TODO: consider allowing wildcards or regex
             // For now, just exact match on meter name
-            return Meters.Contains(instrument.Meter.Name);
+            return Meters.Contains(instrument.Meter.Name) && !IgnoredInstruments.Contains(instrument.Name);
         }
     }
 }

test/WebJobs.Script.Tests/Diagnostics/ApplicationInsightsMetricExporterTests.cs

@@ -133,12 +133,10 @@ public void MeterListener_TracksConfiguredInstruments(string test)
                 });
         }
 
-        private static ApplicationInsightsMetricExporter CreateExporter(
-            params ReadOnlySpan<string> meters)
+        private static ApplicationInsightsMetricExporter CreateExporter(params string[] meters)
             => new(CreateOptions(meters));
 
-        private static OptionsWrapper<ApplicationInsightsMetricExporterOptions> CreateOptions(
-            params ReadOnlySpan<string> meters)
+        private static OptionsWrapper<ApplicationInsightsMetricExporterOptions> CreateOptions(params string[] meters)
         {
             ApplicationInsightsMetricExporterOptions options = new();
             foreach (string meter in meters)