Implement IAsyncDisposable and use FlushAsync on TelemetryClient

src/Serilog.Sinks.ApplicationInsights/Sinks/ApplicationInsights/ApplicationInsightsSink.cs

@@ -16,6 +16,7 @@
 using System.Reflection;
 using System.Runtime.ExceptionServices;
 using System.Threading;
+using System.Threading.Tasks;
 using Microsoft.ApplicationInsights;
 using Microsoft.ApplicationInsights.Channel;
 using Serilog.Core;
@@ -29,6 +30,9 @@ namespace Serilog.Sinks.ApplicationInsights;
 ///     Inspired by their NLog Appender implementation.
 /// </summary>
 public class ApplicationInsightsSink : ILogEventSink, IDisposable
+#if NET6_0_OR_GREATER
+, IAsyncDisposable
+#endif
 {
     readonly IFormatProvider _formatProvider;
 
@@ -191,6 +195,29 @@ protected virtual void Dispose(bool disposeManagedResources)
             IsDisposing = false;
         }
     }
+
+#if NET6_0_OR_GREATER
+    /// <summary>
+    /// Disposes the sink and flushes telemetry to App Insights.
+    /// </summary>
+    public async ValueTask DisposeAsync()
+    {
+        if (IsDisposing || IsDisposed)
+            return;
+
+        try
+        {
+            IsDisposing = true;
+            if (_telemetryClient is not null) await _telemetryClient.FlushAsync(CancellationToken.None);
+        }
+        finally
+        {
+            _telemetryClient = null;
+            IsDisposed = true;
+            IsDisposing = false;
+        }
+    }
+#endif
 
     #endregion Implementation of IDisposable
 }

test/Serilog.Sinks.ApplicationInsights.Tests/ApplicationInsightsTest.cs

@@ -23,6 +23,7 @@ protected ApplicationInsightsTest(ITelemetryConverter converter = null)
     }
 
     protected ILogger Logger { get; }
+    protected UnitTestTelemetryChannel Channel => _channel;
 
     protected List<ITelemetry> SubmittedTelemetry => _channel.SubmittedTelemetry;
 

test/Serilog.Sinks.ApplicationInsights.Tests/DisposableTest.cs

@@ -0,0 +1,24 @@
+using System;
+using System.Threading.Tasks;
+using Xunit;
+
+namespace Serilog.Sinks.ApplicationInsights.Tests;
+
+public class DisposableTest : ApplicationInsightsTest
+{
+    [Fact]
+    public void Flush_is_called_on_channel_when_logger_is_disposed()
+    {
+        ((IDisposable)Logger).Dispose();
+        Assert.True(Channel.FlushCalled, "Channel.Flush was not called");
+    }
+
+#if NET6_0_OR_GREATER
+    [Fact]
+    public async Task FlushAsync_is_called_on_channel_when_logger_is_disposed_asynchronously()
+    {
+        await ((IAsyncDisposable)Logger).DisposeAsync();
+        Assert.True(Channel.FlushAsyncCalled, "Channel.FlushAsync was not called");
+    }
+#endif
+}

test/Serilog.Sinks.ApplicationInsights.Tests/UnitTestTelemetryChannel.cs

@@ -1,11 +1,15 @@
 using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
 using Microsoft.ApplicationInsights.Channel;
 
 namespace Serilog.Sinks.ApplicationInsights.Tests;
 
-class UnitTestTelemetryChannel : ITelemetryChannel
+public class UnitTestTelemetryChannel : ITelemetryChannel, IAsyncFlushable
 {
     public List<ITelemetry> SubmittedTelemetry { get; } = new();
+    public bool FlushCalled { get; private set; }
+    public bool FlushAsyncCalled { get; private set; }
 
     public bool? DeveloperMode
     {
@@ -25,6 +29,13 @@ public void Dispose()
 
     public void Flush()
     {
+        FlushCalled = true;
+    }
+
+    public Task<bool> FlushAsync(CancellationToken cancellationToken)
+    {
+        FlushAsyncCalled = true;
+        return Task.FromResult(true);
     }
 
     public void Send(ITelemetry item)