Changes startup logic, no more "Boot" method, the component just handles events

src/Umbraco.Core/Sync/DatabaseServerMessenger.cs

@@ -111,17 +111,11 @@ namespace Umbraco.Core.Sync
 
         #region Sync
 
-        /// <summary>
-        /// Boots the messenger.
-        /// </summary>
-        /// <remarks>
-        /// Thread safety: this is NOT thread safe. Because it is NOT meant to run multi-threaded.
-        /// Callers MUST ensure thread-safety.
-        /// </remarks>
+        [Obsolete("This is no longer used and will be removed in future versions")]
         protected void Boot()
         {
-            var bootState = GetSyncBootState();
-            Booting?.Invoke(this, bootState);
+            // if called, just forces the boot logic
+            _ = GetSyncBootState();
         }
 
         private SyncBootState BootInternal()
@@ -545,8 +539,6 @@ namespace Umbraco.Core.Sync
             + "/D" + AppDomain.CurrentDomain.Id // eg 22
             + "] " + Guid.NewGuid().ToString("N").ToUpper(); // make it truly unique
 
-        public event EventHandler<SyncBootState> Booting;
-
         private string GetDistCacheFilePath(IGlobalSettings globalSettings)
         {
             var fileName = HttpRuntime.AppDomainAppId.ReplaceNonAlphanumericChars(string.Empty) + "-lastsynced.txt";
@@ -565,7 +557,7 @@ namespace Umbraco.Core.Sync
 
         #endregion
 
-        public SyncBootState GetSyncBootState() => _getSyncBootState.Value;
+        public virtual SyncBootState GetSyncBootState() => _getSyncBootState.Value;
 
         #region Notify refreshers
 

src/Umbraco.Web/BatchedDatabaseServerMessenger.cs

@@ -26,6 +26,7 @@ namespace Umbraco.Web
     public class BatchedDatabaseServerMessenger : DatabaseServerMessenger
     {
         private readonly IUmbracoDatabaseFactory _databaseFactory;
+        private readonly Lazy<SyncBootState> _syncBootState;
 
         [Obsolete("This overload should not be used, enableDistCalls has no effect")]
         [EditorBrowsable(EditorBrowsableState.Never)]
@@ -39,28 +40,22 @@ namespace Umbraco.Web
             : base(runtime, scopeProvider, sqlContext, proflog, globalSettings, true, options)
         {
             _databaseFactory = databaseFactory;
-        }
-
-        // invoked by DatabaseServerRegistrarAndMessengerComponent
-        internal void Startup()
-        {
-            UmbracoModule.EndRequest += UmbracoModule_EndRequest;
-
-            if (_databaseFactory.CanConnect == false)
+            _syncBootState = new Lazy<SyncBootState>(() =>
             {
-                Logger.Warn<BatchedDatabaseServerMessenger>("Cannot connect to the database, distributed calls will not be enabled for this server.");
-            }
-            else
-            {
-                Boot();
-            }
+                if (_databaseFactory.CanConnect == false)
+                {
+                    Logger.Warn<BatchedDatabaseServerMessenger>("Cannot connect to the database, distributed calls will not be enabled for this server.");
+                    return SyncBootState.Unknown;
+                }
+                else
+                {
+                    return base.GetSyncBootState();
+                }
+            });
         }
 
-        private void UmbracoModule_EndRequest(object sender, UmbracoRequestEventArgs e)
-        {
-            // will clear the batch - will remain in HttpContext though - that's ok
-            FlushBatch();
-        }
+        // override to deal with database connectivity
+        public override SyncBootState GetSyncBootState() => _syncBootState.Value;
 
         protected override void DeliverRemote(ICacheRefresher refresher, MessageType messageType, IEnumerable<object> ids = null, string json = null)
         {

src/Umbraco.Web/Compose/DatabaseServerRegistrarAndMessengerComponent.cs

@@ -59,15 +59,19 @@ namespace Umbraco.Web.Compose
             if (_registrar != null || _messenger != null)
             {
                 UmbracoModule.RouteAttempt += RegisterBackgroundTasksOnce;
-            }   
-
-            // must come last, as it references some _variables
-            _messenger?.Startup();
+                UmbracoModule.EndRequest += UmbracoModule_EndRequest;
+            }
         }
 
         public void Terminate()
         { }
 
+        private void UmbracoModule_EndRequest(object sender, UmbracoRequestEventArgs e)
+        {
+            // will clear the batch - will remain in HttpContext though - that's ok
+            _messenger?.FlushBatch();
+        }
+
         /// <summary>
         /// Handle when a request is made
         /// </summary>