PE tasks list init and start background timer after PE tasks.

Fixes #6742

src/Orchard.Tests.Modules/Comments/Services/CommentServiceTests.cs

@@ -203,6 +203,8 @@ namespace Orchard.Tests.Modules.Comments.Services {
 
     public class ProcessingEngineStub : IProcessingEngine {
 
+        public void Initialize() { }
+
         public string AddTask(ShellSettings shellSettings, ShellDescriptor shellDescriptor, string messageName, Dictionary<string, object> parameters) {
             return "";
         }

src/Orchard/Environment/DefaultOrchardHost.cs

@@ -147,6 +147,10 @@ namespace Orchard.Environment {
             // Load all tenants, and activate their shell.
             if (allSettings.Any()) {
                 Parallel.ForEach(allSettings, settings => {
+
+                    _processingEngine.Initialize();
+                    ShellContext context = null;
+
                     for (var i = 0; i <= Retries; i++) {
 
                         // Not the first attempt, wait for a while ...
@@ -157,10 +161,10 @@ namespace Orchard.Environment {
                         }
 
                         try {
-                            var context = CreateShellContext(settings);
+                            context = CreateShellContext(settings);
                             ActivateShell(context);
 
-                            // If everything went well, return to stop the retry loop
+                            // If everything went well, break the retry loop
                             break;
                         }
                         catch (Exception ex) {
@@ -172,12 +176,18 @@ namespace Orchard.Environment {
                                 Logger.Error(ex, "A tenant could not be started: " + settings.Name + " Attempt number: " + i);
                             }
                         }
-                        
                     }
 
-                    while (_processingEngine.AreTasksPending()) {
-                        Logger.Debug("Processing pending task after activate Shell");
-                        _processingEngine.ExecuteNextTask();
+                    if (_processingEngine.AreTasksPending()) {
+
+                        context.Shell.Sweep.Terminate();
+
+                        while (_processingEngine.AreTasksPending()) {
+                            Logger.Debug("Processing pending task after activate Shell");
+                            _processingEngine.ExecuteNextTask();
+                        }
+
+                        context.Shell.Sweep.Activate();
                     }
                 });
             }

src/Orchard/Environment/DefaultOrchardShell.cs

@@ -50,6 +50,7 @@ namespace Orchard.Environment {
         }
 
         public ILogger Logger { get; set; }
+        public ISweepGenerator Sweep { get { return _sweepGenerator; } }
 
         public void Activate() {
             var appBuilder = new AppBuilder();

src/Orchard/Environment/IOrchardShell.cs

@@ -1,6 +1,9 @@
+using Orchard.Tasks;
+
 namespace Orchard.Environment {
     public interface IOrchardShell {
         void Activate();
         void Terminate();
+        ISweepGenerator Sweep { get; }
     }
 }

src/Orchard/Environment/State/DefaultProcessingEngine.cs

@@ -22,6 +22,10 @@ namespace Orchard.Environment.State {
             _entries = new ContextState<IList<Entry>>("DefaultProcessingEngine.Entries", () => new List<Entry>());
         }
 
+        public void Initialize() {
+            _entries.SetState(new List<Entry>());
+        }
+
         public string AddTask(ShellSettings shellSettings, ShellDescriptor shellDescriptor, string eventName, Dictionary<string, object> parameters) {
 
             var entry = new Entry {

src/Orchard/Environment/State/IProcessingEngine.cs

@@ -6,6 +6,11 @@ namespace Orchard.Environment.State
 {
     public interface IProcessingEngine
     {
+        /// <summary>
+        /// Init a new tasks list in the http context or in a new logical context.
+        /// </summary>
+        void Initialize();
+
         /// <summary>
         /// Queue an event to fire inside of an explicitly decribed shell context
         /// </summary>