PERF: Monitor modules files asynchronously

Monitoring virtual dependency files for modules takes requires a lot
of file I/O, and can be a significant bottleneck on heavily loaded
disk sub-system (5-10 secs). Making this process asynchronous during
startup decreases startup time by almost that amount of time.

--HG--
branch : 1.x

src/Orchard/Environment/DefaultOrchardHost.cs

@@ -19,6 +19,7 @@ namespace Orchard.Environment {
         private readonly IRunningShellTable _runningShellTable;
         private readonly IProcessingEngine _processingEngine;
         private readonly IExtensionLoaderCoordinator _extensionLoaderCoordinator;
+        private readonly IExtensionMonitoringCoordinator _extensionMonitoringCoordinator;
         private readonly ICacheManager _cacheManager;
         private readonly object _syncLock = new object();
 
@@ -30,6 +31,7 @@ namespace Orchard.Environment {
             IRunningShellTable runningShellTable,
             IProcessingEngine processingEngine,
             IExtensionLoaderCoordinator extensionLoaderCoordinator,
+            IExtensionMonitoringCoordinator extensionMonitoringCoordinator,
             ICacheManager cacheManager,
             IHostLocalRestart hostLocalRestart ) {
             _shellSettingsManager = shellSettingsManager;
@@ -37,6 +39,7 @@ namespace Orchard.Environment {
             _runningShellTable = runningShellTable;
             _processingEngine = processingEngine;
             _extensionLoaderCoordinator = extensionLoaderCoordinator;
+            _extensionMonitoringCoordinator = extensionMonitoringCoordinator;
             _cacheManager = cacheManager;
             _hostLocalRestart = hostLocalRestart;
 
@@ -151,7 +154,7 @@ namespace Orchard.Environment {
             // on disk, and we need to reload new/updated extensions.
             _cacheManager.Get("OrchardHost_Extensions",
                               ctx => {
-                                  _extensionLoaderCoordinator.MonitorExtensions(ctx.Monitor);
+                                  _extensionMonitoringCoordinator.MonitorExtensions(ctx.Monitor);
                                   _hostLocalRestart.Monitor(ctx.Monitor);
                                   DisposeShellContext();
                                   return "";

src/Orchard/Environment/Extensions/ExtensionLoaderCoordinator.cs

@@ -165,7 +165,7 @@ namespace Orchard.Environment.Extensions {
             if (duplicates.Count() > 0) {
                 var sb = new StringBuilder();
                 sb.Append(T("There are multiple extensions with the same name installed in this instance of Orchard.\r\n"));
-                foreach(var dup in duplicates) {
+                foreach (var dup in duplicates) {
                     sb.Append(T("Extension '{0}' has been found from the following locations: {1}.\r\n", dup.Key, string.Join(", ", dup.Select(e => e.Location + "/" + e.Id))));
                 }
                 sb.Append(T("This issue can be usually solved by removing or renaming the conflicting extension."));
@@ -300,21 +300,5 @@ namespace Orchard.Environment.Extensions {
                 action();
             }
         }
-
-        public void MonitorExtensions(Action<IVolatileToken> monitor) {
-            Logger.Information("Start monitoring extension files...");
-            // Monitor add/remove of any module/theme
-            monitor(_virtualPathMonitor.WhenPathChanges("~/Modules"));
-            monitor(_virtualPathMonitor.WhenPathChanges("~/Themes"));
-
-            // Give loaders a chance to monitor any additional changes
-            var extensions = _extensionManager.AvailableExtensions().Where(d => DefaultExtensionTypes.IsModule(d.ExtensionType) || DefaultExtensionTypes.IsTheme(d.ExtensionType)).ToList();
-            foreach (var extension in extensions) {
-                foreach (var loader in _loaders) {
-                    loader.Monitor(extension, monitor);
-                }
-            }
-            Logger.Information("Done monitoring extension files...");
-        }
     }
 }

src/Orchard/Environment/Extensions/ExtensionMonitoringCoordinator.cs

@@ -0,0 +1,102 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
+using Orchard.Caching;
+using Orchard.Environment.Extensions.Loaders;
+using Orchard.Environment.Extensions.Models;
+using Orchard.FileSystems.VirtualPath;
+using Orchard.Logging;
+
+namespace Orchard.Environment.Extensions {
+    public class ExtensionMonitoringCoordinator : IExtensionMonitoringCoordinator {
+        private readonly IVirtualPathMonitor _virtualPathMonitor;
+        private readonly IExtensionManager _extensionManager;
+        private readonly IEnumerable<IExtensionLoader> _loaders;
+
+        public ExtensionMonitoringCoordinator(IVirtualPathMonitor virtualPathMonitor,
+            IExtensionManager extensionManager,
+            IEnumerable<IExtensionLoader> loaders) {
+
+            _virtualPathMonitor = virtualPathMonitor;
+            _extensionManager = extensionManager;
+            _loaders = loaders;
+
+            Logger = NullLogger.Instance;
+        }
+
+        public ILogger Logger { get; set; }
+        public bool Disabled { get; set; }
+
+        public void MonitorExtensions(Action<IVolatileToken> monitor) {
+            // We may be disabled by custom host configuration for performance reasons
+            if (Disabled)
+                return;
+
+            //PREF: Monitor extensions asynchronously. IsCurrent will be 'true'
+            //      until all tokens are collected by the work function.
+            var token = new AsyncVolativeToken(MonitorExtensionsWork, Logger);
+            monitor(token);
+            token.QueueWorkItem();
+        }
+
+        public void MonitorExtensionsWork(Action<IVolatileToken> monitor) {
+            Logger.Information("Start monitoring extension files...");
+            // Monitor add/remove of any module/theme
+            monitor(_virtualPathMonitor.WhenPathChanges("~/Modules"));
+            monitor(_virtualPathMonitor.WhenPathChanges("~/Themes"));
+
+            // Give loaders a chance to monitor any additional changes
+            var extensions = _extensionManager.AvailableExtensions().Where(d => DefaultExtensionTypes.IsModule(d.ExtensionType) || DefaultExtensionTypes.IsTheme(d.ExtensionType)).ToList();
+            foreach (var extension in extensions) {
+                foreach (var loader in _loaders) {
+                    loader.Monitor(extension, monitor);
+                }
+            }
+            Logger.Information("Done monitoring extension files...");
+        }
+
+        public class AsyncVolativeToken : IVolatileToken {
+            private readonly Action<Action<IVolatileToken>> _task;
+            private readonly List<IVolatileToken> _taskTokens = new List<IVolatileToken>();
+            private volatile Exception _taskException;
+            private volatile bool _isTaskFinished;
+
+            public AsyncVolativeToken(Action<Action<IVolatileToken>> task, ILogger logger) {
+                _task = task;
+                Logger = logger;
+            }
+
+            public ILogger Logger { get; set; }
+
+            public void QueueWorkItem() {
+                // Start a work item to collect tokens in our internal array
+                ThreadPool.QueueUserWorkItem((state) => {
+                    try {
+                        _task(token => _taskTokens.Add(token));
+                    }
+                    catch (Exception e) {
+                        Logger.Error(e, "Error while monitoring extension files. Assuming extensions are not current.");
+                        _taskException = e;
+                    }
+                    finally {
+                        _isTaskFinished = true;
+                    }
+                });
+            }
+
+            public bool IsCurrent {
+                get {
+                    // We are current until the task has finished
+                    if (_taskException != null) {
+                        return false;
+                    }
+                    if (_isTaskFinished) {
+                        return _taskTokens.All(t => t.IsCurrent);
+                    }
+                    return true;
+                }
+            }
+        }
+    }
+}

src/Orchard/Environment/Extensions/IExtensionLoaderCoordinator.cs

@@ -1,9 +1,5 @@
-using System;
-using Orchard.Caching;
-
-namespace Orchard.Environment.Extensions {
+namespace Orchard.Environment.Extensions {
     public interface IExtensionLoaderCoordinator {
         void SetupExtensions();
-        void MonitorExtensions(Action<IVolatileToken> monitor);
     }
 }

src/Orchard/Environment/Extensions/IExtensionMonitoringCoordinator.cs

@@ -0,0 +1,8 @@
+using System;
+using Orchard.Caching;
+
+namespace Orchard.Environment.Extensions {
+    public interface IExtensionMonitoringCoordinator {
+        void MonitorExtensions(Action<IVolatileToken> monitor);
+    }
+}

src/Orchard/Environment/OrchardStarter.cs

@@ -77,6 +77,7 @@ namespace Orchard.Environment {
                     {
                         builder.RegisterType<ShellContainerRegistrations>().As<IShellContainerRegistrations>().SingleInstance();
                         builder.RegisterType<ExtensionLoaderCoordinator>().As<IExtensionLoaderCoordinator>().SingleInstance();
+                        builder.RegisterType<ExtensionMonitoringCoordinator>().As<IExtensionMonitoringCoordinator>().SingleInstance();
                         builder.RegisterType<ExtensionManager>().As<IExtensionManager>().SingleInstance();
                         {
                             builder.RegisterType<ModuleFolders>().As<IExtensionFolders>().SingleInstance()

src/Orchard/Orchard.Framework.csproj

@@ -175,6 +175,8 @@
     <Compile Include="DisplayManagement\Shapes\ShapeDebugView.cs" />
     <Compile Include="DisplayManagement\Shapes\ITagBuilderFactory.cs" />
     <Compile Include="Environment\CollectionOrderModule.cs" />
+    <Compile Include="Environment\Extensions\ExtensionMonitoringCoordinator.cs" />
+    <Compile Include="Environment\Extensions\IExtensionMonitoringCoordinator.cs" />
     <Compile Include="Environment\Extensions\OrchardSuppressDependencyAttribute.cs" />
     <Compile Include="Environment\Features\IFeatureManager.cs" />
     <Compile Include="Environment\IAssemblyNameResolver.cs" />