rebuilds empty indexes on startup on managed background thread

src/Umbraco.Web/Search/ExamineComponent.cs

@@ -27,6 +27,8 @@ using Umbraco.Web.Composing;
 using Umbraco.Web.PropertyEditors;
 using Umbraco.Examine;
 using Umbraco.Core.Persistence.DatabaseModelDefinitions;
+using Umbraco.Web.Scheduling;
+using System.Threading.Tasks;
 
 namespace Umbraco.Web.Search
 {
@@ -43,6 +45,7 @@ namespace Umbraco.Web.Search
         private IScopeProvider _scopeProvider;
         private UrlSegmentProviderCollection _urlSegmentProviders;
         private ServiceContext _services;
+        private BackgroundTaskRunner<IBackgroundTask> _rebuildOnStartupRunner;
 
         // the default enlist priority is 100
         // enlist with a lower priority to ensure that anything "default" runs after us
@@ -55,6 +58,11 @@ namespace Umbraco.Web.Search
             _urlSegmentProviders = urlSegmentProviderCollection;
             _scopeProvider = scopeProvider;
             _examineManager = examineManager;
+            _rebuildOnStartupRunner = new BackgroundTaskRunner<IBackgroundTask>(
+                "RebuildIndexesOnStartup",
+                profilingLogger.Logger,
+                //hook into MainDom so that no index building occurs unless on MainDom
+                BackgroundTaskRunner<IBackgroundTask>.MainDomHook.Create(null, null));
 
             //We want to manage Examine's appdomain shutdown sequence ourselves so first we'll disable Examine's default behavior
             //and then we'll use MainDom to control Examine's shutdown
@@ -121,22 +129,9 @@ namespace Umbraco.Web.Search
             //TODO: need a way to disable rebuilding on startup
 
             logger.Info<ExamineComponent>("Starting initialize async background thread.");
-
-            // make it async in order not to slow down the boot
-            // fixme - should be a proper background task else we cannot stop it!
-            var bg = new Thread(() =>
-            {
-                try
-                {
-                    // rebuilds any empty indexes
-                    RebuildIndexes(true, _examineManager, logger);
-                }
-                catch (Exception ex)
-                {
-                    logger.Error<ExamineComponent>(ex, "Failed to rebuild empty indexes.");
-                }
-            });
-            bg.Start();
+            //do the rebuild on a managed background thread
+            var task = new RebuildOnStartupTask(_examineManager, logger);
+            _rebuildOnStartupRunner.TryAdd(task);
         }
 
         /// <summary>
@@ -223,6 +218,7 @@ namespace Umbraco.Web.Search
             }
         }
 
+        #region Cache refresher updated event handlers
         private void MemberCacheRefresherUpdated(MemberCacheRefresher sender, CacheRefresherEventArgs args)
         {
             if (Suspendable.ExamineEvents.CanIndex == false)
@@ -578,7 +574,9 @@ namespace Umbraco.Web.Search
                 // BUT ... pretty sure it is! see test "Index_Delete_Index_Item_Ensure_Heirarchy_Removed"
             }
         }
+        #endregion
 
+        #region ReIndex/Delete for entity
         private void ReIndexForContent(IContent content, IContent published)
         {
             if (published != null && content.VersionId == published.VersionId)
@@ -644,7 +642,9 @@ namespace Umbraco.Web.Search
             else
                 DeferedDeleteIndex.Execute(this, entityId, keepIfUnpublished);
         }
+        #endregion
 
+        #region Defered Actions
         private class DeferedActions
         {
             private readonly List<DeferedAction> _actions = new List<DeferedAction>();
@@ -799,6 +799,46 @@ namespace Umbraco.Web.Search
                         .Where(x => x.EnableDefaultEventHandler));
             }
         }
+        #endregion
 
+        /// <summary>
+        /// Background task used to rebuild empty indexes on startup
+        /// </summary>
+        private class RebuildOnStartupTask : IBackgroundTask
+        {
+            private readonly IExamineManager _examineManager;
+            private readonly ILogger _logger;
+
+            public RebuildOnStartupTask(IExamineManager examineManager, ILogger logger)
+            {
+                _examineManager = examineManager;
+                _logger = logger;
+            }
+
+            public bool IsAsync => false;
+
+            public void Dispose()
+            {
+                throw new NotImplementedException();
+            }
+
+            public void Run()
+            {
+                try
+                {
+                    // rebuilds any empty indexes
+                    RebuildIndexes(true, _examineManager, _logger);
+                }
+                catch (Exception ex)
+                {
+                    _logger.Error<ExamineComponent>(ex, "Failed to rebuild empty indexes.");
+                }
+            }
+
+            public Task RunAsync(CancellationToken token)
+            {
+                throw new NotImplementedException();
+            }
+        }
     }
 }