Review feedback for IApplicationLifetimeEvents

- Renamed the type to IHostedService and added Start and Stop.
- Split up the IHostedService execution and IApplicationLifetime to avoid
circular references
- Trigger IHostedService.Start after starting the server
- Trigger IHostedService.Stop before disposing the service provider

#895 #894

src/Microsoft.AspNetCore.Hosting.Abstractions/IApplicationLifetimeEvents.cs → src/Microsoft.AspNetCore.Hosting.Abstractions/IHostedService.cs

@@ -4,28 +4,20 @@
 namespace Microsoft.AspNetCore.Hosting
 {
     /// <summary>
-    /// Allows consumers to perform cleanup during a graceful shutdown.
+    /// Defines methods for objects that are managed by the host.
     /// </summary>
-    public interface IApplicationLifetimeEvents
+    public interface IHostedService
     {
         /// <summary>
-        /// Triggered when the application host has fully started and is about to wait
-        /// for a graceful shutdown.
+        /// Triggered when the application host has fully started and the server is waiting
+        /// for requests.
         /// </summary>
-        void OnApplicationStarted();
+        void Start();
 
         /// <summary>
         /// Triggered when the application host is performing a graceful shutdown.
         /// Requests may still be in flight. Shutdown will block until this event completes.
         /// </summary>
-        void OnApplicationStopping();
-
-        /// <summary>
-        /// Triggered when the application host is performing a graceful shutdown.
-        /// All requests should be complete at this point. Shutdown will block
-        /// until this event completes.
-        /// </summary>
-        void OnApplicationStopped();
-
+        void Stop();
     }
 }

src/Microsoft.AspNetCore.Hosting/Internal/ApplicationLifetime.cs

@@ -17,13 +17,11 @@ public class ApplicationLifetime : IApplicationLifetime
         private readonly CancellationTokenSource _startedSource = new CancellationTokenSource();
         private readonly CancellationTokenSource _stoppingSource = new CancellationTokenSource();
         private readonly CancellationTokenSource _stoppedSource = new CancellationTokenSource();
-        private readonly IEnumerable<IApplicationLifetimeEvents> _handlers = Enumerable.Empty<IApplicationLifetimeEvents>();
         private readonly ILogger<ApplicationLifetime> _logger;
 
-        public ApplicationLifetime(ILogger<ApplicationLifetime> logger, IEnumerable<IApplicationLifetimeEvents> handlers)
+        public ApplicationLifetime(ILogger<ApplicationLifetime> logger)
         {
             _logger = logger;
-            _handlers = handlers;
         }
 
         /// <summary>
@@ -57,7 +55,7 @@ public void StopApplication()
             {
                 try
                 {
-                    ExecuteHandlers(_stoppingSource, handler => handler.OnApplicationStopping());
+                    ExecuteHandlers(_stoppingSource);
                 }
                 catch (Exception ex)
                 {
@@ -75,7 +73,7 @@ public void NotifyStarted()
         {
             try
             {
-                ExecuteHandlers(_startedSource, handler => handler.OnApplicationStarted());
+                ExecuteHandlers(_startedSource);
             }
             catch (Exception ex)
             {
@@ -92,7 +90,7 @@ public void NotifyStopped()
         {
             try
             {
-                ExecuteHandlers(_stoppedSource, handler => handler.OnApplicationStopped());
+                ExecuteHandlers(_stoppedSource);
             }
             catch (Exception ex)
             {
@@ -102,7 +100,7 @@ public void NotifyStopped()
             }
         }
 
-        private void ExecuteHandlers(CancellationTokenSource cancel, Action<IApplicationLifetimeEvents> callback)
+        private void ExecuteHandlers(CancellationTokenSource cancel)
         {
             // Noop if this is already cancelled
             if (cancel.IsCancellationRequested)
@@ -127,24 +125,6 @@ private void ExecuteHandlers(CancellationTokenSource cancel, Action<IApplication
                 exceptions.Add(ex);
             }
 
-            // Run the handlers
-            foreach (var handler in _handlers)
-            {
-                try
-                {
-                    callback(handler);
-                }
-                catch (Exception ex)
-                {
-                    if (exceptions == null)
-                    {
-                        exceptions = new List<Exception>();
-                    }
-
-                    exceptions.Add(ex);
-                }
-            }
-
             // Throw an aggregate exception if there were any exceptions
             if (exceptions != null)
             {

src/Microsoft.AspNetCore.Hosting/Internal/HostedServiceExecutor.cs

@@ -0,0 +1,70 @@
+using System;
+using System.Collections.Generic;
+using Microsoft.Extensions.Logging;
+
+namespace Microsoft.AspNetCore.Hosting.Internal
+{
+    public class HostedServiceExecutor
+    {
+        private readonly IEnumerable<IHostedService> _services;
+        private readonly ILogger<HostedServiceExecutor> _logger;
+
+        public HostedServiceExecutor(ILogger<HostedServiceExecutor> logger, IEnumerable<IHostedService> services)
+        {
+            _logger = logger;
+            _services = services;
+        }
+
+        public void Start()
+        {
+            try
+            {
+                Execute(service => service.Start());
+            }
+            catch (Exception ex)
+            {
+                _logger.ApplicationError(LoggerEventIds.HostedServiceStartException, "An error occurred starting the application", ex);
+            }
+        }
+
+        public void Stop()
+        {
+            try
+            {
+                Execute(service => service.Stop());
+            }
+            catch (Exception ex)
+            {
+                _logger.ApplicationError(LoggerEventIds.HostedServiceStopException, "An error occurred stopping the application", ex);
+            }
+        }
+
+        private void Execute(Action<IHostedService> callback)
+        {
+            List<Exception> exceptions = null;
+
+            foreach (var service in _services)
+            {
+                try
+                {
+                    callback(service);
+                }
+                catch (Exception ex)
+                {
+                    if (exceptions == null)
+                    {
+                        exceptions = new List<Exception>();
+                    }
+
+                    exceptions.Add(ex);
+                }
+            }
+
+            // Throw an aggregate exception if there were any exceptions
+            if (exceptions != null)
+            {
+                throw new AggregateException(exceptions);
+            }
+        }
+    }
+}

src/Microsoft.AspNetCore.Hosting/Internal/LoggerEventIds.cs

@@ -13,5 +13,7 @@ internal static class LoggerEventIds
         public const int ApplicationStartupException = 6;
         public const int ApplicationStoppingException = 7;
         public const int ApplicationStoppedException = 8;
+        public const int HostedServiceStartException = 9;
+        public const int HostedServiceStopException = 10;
     }
 }

src/Microsoft.AspNetCore.Hosting/Internal/WebHost.cs

@@ -28,6 +28,7 @@ public class WebHost : IWebHost
         private readonly IServiceCollection _applicationServiceCollection;
         private IStartup _startup;
         private ApplicationLifetime _applicationLifetime;
+        private HostedServiceExecutor _hostedServiceExecutor;
 
         private readonly IServiceProvider _hostingServiceProvider;
         private readonly WebHostOptions _options;
@@ -68,6 +69,7 @@ public WebHost(
             _applicationServiceCollection = appServices;
             _hostingServiceProvider = hostingServiceProvider;
             _applicationServiceCollection.AddSingleton<IApplicationLifetime, ApplicationLifetime>();
+            _applicationServiceCollection.AddSingleton<HostedServiceExecutor>();
         }
 
         public IServiceProvider Services
@@ -104,11 +106,17 @@ public virtual void Start()
             Initialize();
 
             _applicationLifetime = _applicationServices.GetRequiredService<IApplicationLifetime>() as ApplicationLifetime;
+            _hostedServiceExecutor = _applicationServices.GetRequiredService<HostedServiceExecutor>();
             var diagnosticSource = _applicationServices.GetRequiredService<DiagnosticSource>();
             var httpContextFactory = _applicationServices.GetRequiredService<IHttpContextFactory>();
             Server.Start(new HostingApplication(_application, _logger, diagnosticSource, httpContextFactory));
 
+            // Fire IApplicationLifetime.Started
             _applicationLifetime?.NotifyStarted();
+
+            // Fire IHostedService.Start
+            _hostedServiceExecutor.Start();
+
             _logger.Started();
         }
 
@@ -243,9 +251,17 @@ private void EnsureServer()
         public void Dispose()
         {
             _logger?.Shutdown();
+
+            // Fire IApplicationLifetime.Stopping
             _applicationLifetime?.StopApplication();
+
+            // Fire the IHostedService.Stop
+            _hostedServiceExecutor?.Stop();
+
             (_hostingServiceProvider as IDisposable)?.Dispose();
             (_applicationServices as IDisposable)?.Dispose();
+
+            // Fire IApplicationLifetime.Stopped
             _applicationLifetime?.NotifyStopped();
 
             HostingEventSource.Log.HostStop();