Fixes issue with scopes being disposed or referenced incorrectly

src/Umbraco.Examine.Lucene/UmbracoContentIndex.cs

@@ -86,7 +86,7 @@ namespace Umbraco.Examine
                         || !validator.ValidateProtectedContent(path, v.Category))
                     ? 0
                     : 1;
-            });
+            }).ToList();
 
             var hasDeletes = false;
             var hasUpdates = false;
@@ -105,7 +105,7 @@ namespace Umbraco.Examine
                 {
                     hasUpdates = true;
                     //these are the valid ones, so just index them all at once
-                    base.PerformIndexItems(group, onComplete);
+                    base.PerformIndexItems(group.ToList(), onComplete);
                 }
             }
 

src/Umbraco.Infrastructure/Search/ExamineComponent.cs

@@ -583,6 +583,26 @@ namespace Umbraco.Web.Search
 
             public static void Execute(ExamineComponent examineComponent, IContent content, bool isPublished)
             {
+                // TODO: This is ugly, it is going to build the value set 3x and for 2 of those times it will be the same value
+                // set. We can do better.
+
+                // TODO: We are .ToList() ing each of the calls to GetValueSets here. This is currently required but isn't the way
+                // that this was intended to work. Ideally, the IEnumerable package gets passed to Examine and it is only iterated/executed
+                // when the indexing takes place which would occur on a background thread. This is problematic with how the ContentValueSetBuilder
+                // in combination with UmbracoContentIndex.PerformIndexItems works because (at least what I've come to believe) we are using yield
+                // return in the GetValueSets call in combination with trying to lazily resolve the enumerable but because we GroupBy in
+                // UmbracoContentIndex.PerformIndexItems it's eagerly executed but then lazily executed again on the background thread and I believe
+                // that in doing this when the call is made to _userService.GetProfilesById it's trying to resolve a scope from an AsyncLocal instance
+                // that has already been disposed higher up it's chain. I 'think' to how the eager/lazy enumeration happens with yield return that it's
+                // capturing a scope/AsyncLocal instance that it shouldn't really be using.
+
+                // TODO: We don't want these value sets to be eagerly built in this thread since this is most likely going to be a request thread.
+                // This is why the lazy execution of the Enumerable had the intended affect of executing only when requested on the background thread.
+                // This could still be acheived: Either we have a custom Enumerable/Enumerator to do this, or we simply call the below code
+                // on a background thread... which would be much easier!
+
+                // TODO: I think this is an issue in v8 too!
+
                 foreach (var index in examineComponent._examineManager.Indexes.OfType<IUmbracoIndex>()
                     //filter the indexers
                     .Where(x => isPublished || !x.PublishedValuesOnly)
@@ -593,7 +613,7 @@ namespace Umbraco.Web.Search
                         ? examineComponent._publishedContentValueSetBuilder
                         : (IValueSetBuilder<IContent>)examineComponent._contentValueSetBuilder;
 
-                    index.IndexItems(builder.GetValueSets(content));
+                    index.IndexItems(builder.GetValueSets(content).ToList());
                 }
             }
         }

src/Umbraco.Infrastructure/Sync/DatabaseServerMessenger.cs

@@ -63,6 +63,13 @@ namespace Umbraco.Core.Sync
             _lastPruned = _lastSync = DateTime.UtcNow;
             _syncIdle = new ManualResetEvent(true);
             _distCacheFilePath = new Lazy<string>(() => GetDistCacheFilePath(hostingEnvironment));
+
+            // See notes on LocalIdentity
+            LocalIdentity = NetworkHelper.MachineName // eg DOMAIN\SERVER
+                + "/" + _hostingEnvironment.ApplicationId // eg /LM/S3SVC/11/ROOT
+                + " [P" + Process.GetCurrentProcess().Id // eg 1234
+                + "/D" + AppDomain.CurrentDomain.Id // eg 22
+                + "] " + Guid.NewGuid().ToString("N").ToUpper(); // make it truly unique
         }
 
         protected ILogger Logger { get; }
@@ -526,11 +533,7 @@ namespace Umbraco.Core.Sync
         /// <para>Practically, all we really need is the guid, the other infos are here for information
         /// and debugging purposes.</para>
         /// </remarks>
-        protected string LocalIdentity => NetworkHelper.MachineName // eg DOMAIN\SERVER
-            + "/" + _hostingEnvironment.ApplicationId // eg /LM/S3SVC/11/ROOT
-            + " [P" + Process.GetCurrentProcess().Id // eg 1234
-            + "/D" + AppDomain.CurrentDomain.Id // eg 22
-            + "] " + Guid.NewGuid().ToString("N").ToUpper(); // make it truly unique
+        protected string LocalIdentity { get; }
 
         private string GetDistCacheFilePath(IHostingEnvironment hostingEnvironment)
         {