Deferring Taxonomies term count calculation to a processing engine task, lowering the chance of DB deadlocks

src/Orchard.Web/Modules/Orchard.Taxonomies/Handlers/TermsPartHandler.cs

@@ -9,6 +9,9 @@ using Orchard.ContentManagement.Handlers;
 using Orchard.ContentManagement.MetaData;
 using Orchard.Core.Title.Models;
 using Orchard.Data;
+using Orchard.Environment.State;
+using Orchard.Environment.Configuration;
+using Orchard.Environment.Descriptor;
 
 namespace Orchard.Taxonomies.Handlers {
     public class TermsPartHandler : ContentHandler {
@@ -19,14 +22,17 @@ namespace Orchard.Taxonomies.Handlers {
             IContentDefinitionManager contentDefinitionManager,
             IRepository<TermsPartRecord> repository,
             ITaxonomyService taxonomyService,
-            IContentManager contentManager) {
+            IContentManager contentManager,
+            IProcessingEngine processingEngine,
+            ShellSettings shellSettings,
+            IShellDescriptorManager shellDescriptorManager) {
             _contentDefinitionManager = contentDefinitionManager;
             _contentManager = contentManager;
 
             Filters.Add(StorageFilter.For(repository));
-            OnPublished<TermsPart>((context, part) => RecalculateCount(taxonomyService, part));
+            OnPublished<TermsPart>((context, part) => RecalculateCount(processingEngine, shellSettings, shellDescriptorManager, part));
-            OnUnpublished<TermsPart>((context, part) => RecalculateCount(taxonomyService, part));
+            OnUnpublished<TermsPart>((context, part) => RecalculateCount(processingEngine, shellSettings, shellDescriptorManager, part));
-            OnRemoved<TermsPart>((context, part) => RecalculateCount(taxonomyService, part));
+            OnRemoved<TermsPart>((context, part) => RecalculateCount(processingEngine, shellSettings, shellDescriptorManager, part));
 
             // Tells how to load the field terms on demand, when a content item it loaded or when it has been created
             OnInitialized<TermsPart>((context, part) => InitializerTermsLoader(part));
@@ -82,20 +88,11 @@ namespace Orchard.Taxonomies.Handlers {
             });
         }
 
-        // Retrieve the number of associated content items, for the whole hierarchy
+        
-        private static void RecalculateCount(ITaxonomyService taxonomyService, TermsPart part) {
+        // Fires off a processing engine task to run the count processing after the request so it's non-blocking.
-            foreach (var term in part.Terms) {
+        private void RecalculateCount(IProcessingEngine processingEngine, ShellSettings shellSettings, IShellDescriptorManager shellDescriptorManager, TermsPart part) {
-                var termPart = taxonomyService.GetTerm(term.TermRecord.Id);
+            processingEngine.AddTask(shellSettings, shellDescriptorManager.GetShellDescriptor(), "ITermCountProcessor.Process", new Dictionary<string, object> { { "termsPartId", part.ContentItem.Id } });
-                while (termPart != null) {
-                    termPart.Count = (int)taxonomyService.GetContentItemsCount(termPart);
 
-                    // compute count for the hierarchy too
-                    if (termPart.Container != null) {
-                        var parentTerm = termPart.Container.As<TermPart>();
-                        termPart = parentTerm;
-                    }
-                }
-            }
         }
 
         protected override void Activating(ActivatingContentContext context) {

src/Orchard.Web/Modules/Orchard.Taxonomies/Orchard.Taxonomies.csproj

@@ -99,7 +99,9 @@
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="Fields\TaxonomyField.cs" />
     <Compile Include="Services\ITaxonomyService.cs" />
+    <Compile Include="Services\ITermCountProcessor.cs" />
     <Compile Include="Services\TaxonomyService.cs" />
+    <Compile Include="Services\TermCountProcessor.cs" />
     <Compile Include="Settings\TermPartEditorEvents.cs" />
     <Compile Include="Settings\TaxonomyFieldEditorEvents.cs" />
     <Compile Include="Settings\TermPartSettings.cs" />

src/Orchard.Web/Modules/Orchard.Taxonomies/Services/ITermCountProcessor.cs

@@ -0,0 +1,12 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Orchard.Events;
+
+namespace Orchard.Taxonomies.Services {
+    public interface ITermCountProcessor : IEventHandler {
+        void Process(int termsPartId);
+    }
+}

src/Orchard.Web/Modules/Orchard.Taxonomies/Services/TermCountProcessor.cs

@@ -0,0 +1,40 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Web;
+using Orchard.ContentManagement;
+using Orchard.Taxonomies.Models;
+
+namespace Orchard.Taxonomies.Services {
+    public class TermCountProcessor : ITermCountProcessor {
+        private readonly IContentManager _contentManager;
+        private readonly ITaxonomyService _taxonomyService;
+
+        public TermCountProcessor(IContentManager contentManager, ITaxonomyService taxonomyService) {
+            _contentManager = contentManager;
+            _taxonomyService = taxonomyService;
+        }
+        
+        public void Process(int termsPartId) {
+            var termsPart = _contentManager.Get<TermsPart>(termsPartId);
+
+            if (termsPart == null) {
+                return;
+            }
+
+            // Retrieve the number of associated content items, for the whole hierarchy
+            foreach (var term in termsPart.Terms) {
+                var termPart = _taxonomyService.GetTerm(term.TermRecord.Id);
+                while (termPart != null) {
+                    termPart.Count = (int)_taxonomyService.GetContentItemsCount(termPart);
+
+                    // compute count for the hierarchy too
+                    if (termPart.Container != null) {
+                        var parentTerm = termPart.Container.As<TermPart>();
+                        termPart = parentTerm;
+                    }
+                }
+            }
+        }
+    }
+}