Process all pending tasks at the end of the request

Instead of processing tasks asynchronously at the end of a request,
we process them synchronously, so that the behavior is more
deterministic.

--HG--
branch : dev

src/Orchard/Environment/DefaultOrchardHost.cs

@@ -147,6 +147,8 @@ namespace Orchard.Environment {
         }
 
         private void DisposeShellContext() {
+            Logger.Information("Disposing active shell contexts");
+
             if (_current != null) {
                 foreach (var shellContext in _current) {
                     shellContext.Shell.Terminate();
@@ -160,25 +162,14 @@ namespace Orchard.Environment {
             BuildCurrent();
         }
 
-
-        // the exit gate is temporary, until better control strategy is in place
-        private readonly ManualResetEvent _exitGate = new ManualResetEvent(true);
-
         protected virtual void EndRequest() {
-            if (_processingEngine.AreTasksPending()) {
-                _exitGate.Reset();
-                ThreadPool.QueueUserWorkItem(state => {
+            // Synchronously process all pending tasks. It's safe to do this at this point
+            // of the pipeline, as the request transaction has been closed, so creating a new
+            // environment and transaction for these tasks will behave as expected.
             while (_processingEngine.AreTasksPending()) {
                 _processingEngine.ExecuteNextTask();
-                        if (!_processingEngine.AreTasksPending()) {
-                            _exitGate.Set();
             }
         }
-                });
-            }
-
-            _exitGate.WaitOne(250);
-        }
 
         void IShellSettingsManagerEventHandler.Saved(ShellSettings settings) {
             DisposeShellContext();

src/Orchard/Environment/State/DefaultProcessingEngine.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using Orchard.Data;
 using Orchard.Environment.Configuration;
 using Orchard.Environment.ShellBuilders;
 using Orchard.Environment.Descriptor.Models;
@@ -69,13 +70,25 @@ namespace Orchard.Environment.State {
             var shellContext = _shellContextFactory.CreateDescribedContext(entry.ShellSettings, entry.ShellDescriptor);
             using (shellContext.LifetimeScope) {
                 using (var standaloneEnvironment = shellContext.LifetimeScope.CreateWorkContextScope()) {
-                    var eventBus = standaloneEnvironment.Resolve<IEventBus>();
 
+                    ITransactionManager transactionManager;
+                    if (!standaloneEnvironment.TryResolve(out transactionManager))
+                        transactionManager = null;
+
+                    try {
+                        var eventBus = standaloneEnvironment.Resolve<IEventBus>();
                         Logger.Information("Executing event {0} in process {1} for shell {2}",
                                            entry.MessageName,
                                            entry.ProcessId,
                                            entry.ShellSettings.Name);
-                    eventBus.NotifyFailFast(entry.MessageName, entry.EventData);
+                        eventBus.Notify(entry.MessageName, entry.EventData);
+                    }
+                    catch {
+                        // any database changes in this using(env) scope are invalidated
+                        if (transactionManager != null)
+                            transactionManager.Cancel();
+                        throw;
+                    }
                 }
             }
         }