remove subscriptions race

CHANGELOG.md

@@ -1,6 +1,7 @@
 # Changelog
 
 ## Version 2.3.0-beta2
+- [Fixed race condition on dispose to close #651](https://github.com/Microsoft/ApplicationInsights-aspnetcore/pull/652)
 -Removed DomainNameRoleInstanceTelemetryInitializer as it is deprecated.
 -Reuse AzureWebAppRoleEnvironmentTelemetryInitializer from WindowsServer repo instead of outdated implementation in this repo.
 - Updated Web/Base SDK version dependency to 2.6.0-beta4

src/Microsoft.ApplicationInsights.AspNetCore/Implementation/ApplicationInsightsInitializer.cs

@@ -2,18 +2,20 @@ namespace Microsoft.ApplicationInsights.AspNetCore
 {
     using System;
     using System.Collections.Generic;
+    using System.Collections.Concurrent;
     using System.Diagnostics;
     using Extensions;
     using Microsoft.ApplicationInsights.AspNetCore.DiagnosticListeners;
     using Microsoft.Extensions.Logging;
     using Microsoft.Extensions.Options;
+    using System.Threading;
 
     /// <summary>
     /// Class used to initialize Application Insight diagnostic listeners.
     /// </summary>
     internal class ApplicationInsightsInitializer : IObserver<DiagnosticListener>, IDisposable
     {
-        private readonly List<IDisposable> subscriptions;
+        private ConcurrentBag<IDisposable> subscriptions;
         private readonly IEnumerable<IApplicationInsightDiagnosticListener> diagnosticListeners;
 
         /// <summary>
@@ -26,7 +28,7 @@ public ApplicationInsightsInitializer(
             IServiceProvider serviceProvider)
         {
             this.diagnosticListeners = diagnosticListeners;
-            this.subscriptions = new List<IDisposable>();
+            this.subscriptions = new ConcurrentBag<IDisposable>();
 
             // Add default logger factory for debug mode only if enabled and instrumentation key not set
             if (options.Value.EnableDebugLogger && string.IsNullOrEmpty(options.Value.InstrumentationKey))
@@ -48,11 +50,17 @@ public void Start()
         /// <inheritdoc />
         void IObserver<DiagnosticListener>.OnNext(DiagnosticListener value)
         {
+            var subs = Volatile.Read(ref this.subscriptions);
+            if (subs is null)
+            {
+                return;
+            }
+
             foreach (var applicationInsightDiagnosticListener in this.diagnosticListeners)
             {
                 if (applicationInsightDiagnosticListener.ListenerName == value.Name)
                 {
-                    this.subscriptions.Add(value.SubscribeWithAdapter(applicationInsightDiagnosticListener));
+                    subs.Add(value.SubscribeWithAdapter(applicationInsightDiagnosticListener));
                 }
             }
         }
@@ -75,13 +83,21 @@ public void Dispose()
 
         protected virtual void Dispose(bool disposing)
         {
-            if (disposing)
+            if (!disposing)
             {
-                foreach (var subscription in this.subscriptions)
-                {
-                    subscription.Dispose();
-                }
+                return;
+            }
+
+            var subs = Interlocked.Exchange(ref this.subscriptions, null);
+            if (subs is null)
+            {
+                return;
+            }
+
+            foreach (var subscription in subs)
+            {
+                subscription.Dispose();
             }
         }
     }
-}
+}