Add an ApplicationStarted event

src/Microsoft.AspNet.Hosting.Abstractions/IApplicationLifetime.cs

@@ -10,6 +10,12 @@ namespace Microsoft.AspNet.Hosting
     /// </summary>
     public interface IApplicationLifetime
     {
+        /// <summary>
+        /// Triggered when the application host has fully started and is about to wait
+        /// for a graceful shutdown.
+        /// </summary>
+        CancellationToken ApplicationStarted { get; }
+
         /// <summary>
         /// Triggered when the application host is performing a graceful shutdown.
         /// Request may still be in flight. Shutdown will block until this event completes.

src/Microsoft.AspNet.Hosting/ApplicationLifetime.cs

@@ -11,9 +11,19 @@ namespace Microsoft.AspNet.Hosting
     /// </summary>
     public class ApplicationLifetime : IApplicationLifetime
     {
+        private readonly CancellationTokenSource _startedSource = new CancellationTokenSource();
         private readonly CancellationTokenSource _stoppingSource = new CancellationTokenSource();
         private readonly CancellationTokenSource _stoppedSource = new CancellationTokenSource();
 
+        /// <summary>
+        /// Triggered when the application host has fully started and is about to wait
+        /// for a graceful shutdown.
+        /// </summary>
+        public CancellationToken ApplicationStarted
+        {
+            get { return _startedSource.Token; }
+        }
+
         /// <summary>
         /// Triggered when the application host is performing a graceful shutdown.
         /// Request may still be in flight. Shutdown will block until this event completes.
@@ -35,6 +45,21 @@ namespace Microsoft.AspNet.Hosting
             get { return _stoppedSource.Token; }
         }
 
+        /// <summary>
+        /// Signals the ApplicationStarted event and blocks until it completes.
+        /// </summary>
+        public void NotifyStarted()
+        {
+            try
+            {
+                _startedSource.Cancel(throwOnFirstException: false);
+            }
+            catch (Exception)
+            {
+                // TODO: LOG
+            }
+        }
+
         /// <summary>
         /// Signals the ApplicationStopping event and blocks until it completes.
         /// </summary>

src/Microsoft.AspNet.Hosting/Internal/HostingEngine.cs

@@ -79,6 +79,8 @@ namespace Microsoft.AspNet.Hosting.Internal
                     }
                 });
 
+            _applicationLifetime.NotifyStarted();
+
             return new Disposable(() =>
             {
                 _applicationLifetime.NotifyStopping();

test/Microsoft.AspNet.Hosting.Tests/HostingEngineTests.cs

@@ -90,6 +90,21 @@ namespace Microsoft.AspNet.Hosting
             Assert.Equal(1, _startInstances[0].DisposeCalls);
         }
 
+        [Fact]
+        public void HostingEngineNotifiesApplicationStarted()
+        {
+            var host = CreateBuilder()
+                .UseServer(this)
+                .Build();
+            var applicationLifetime = host.ApplicationServices.GetRequiredService<IApplicationLifetime>();
+
+            Assert.False(applicationLifetime.ApplicationStarted.IsCancellationRequested);
+            using (host.Start())
+            {
+                Assert.True(applicationLifetime.ApplicationStarted.IsCancellationRequested);
+            }
+        }
+
         [Fact]
         public void HostingEngineInjectsHostingEnvironment()
         {