Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Web.DynamicData/DynamicData/Util/FileChangeNotifier.cs

@@ -0,0 +1,75 @@
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+using System.Linq.Expressions;
+using System.Text;
+using System.Web.UI;
+using System.Web.UI.WebControls;
+using System.Collections.Specialized;
+using System.Diagnostics;
+using System.Web.Resources;
+using System.Globalization;
+using System.Web.Caching;
+using System.Web.Hosting;
+
+namespace System.Web.DynamicData {
+    delegate void FileChangedCallback(string path);
+
+    class FileChangeNotifier {
+        private static VirtualPathProvider _vpp;
+
+        internal static VirtualPathProvider VirtualPathProvider {
+            private get {
+                if (_vpp == null) {
+                    _vpp = HostingEnvironment.VirtualPathProvider;
+                }
+                return _vpp;
+            }
+            // For unit test purpose
+            set {
+                _vpp = value;
+            }
+        }
+
+        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA1806:DoNotIgnoreMethodResults",
+            MessageId = "System.Web.DynamicData.FileChangeNotifier",
+            Justification="The object deals with file change notifications and we don't need to hold on to it")]
+        internal static void Register(string virtualPath, FileChangedCallback onFileChanged) {
+            new FileChangeNotifier(virtualPath, onFileChanged);
+        }
+
+        private FileChangedCallback _onFileChanged;
+
+        private FileChangeNotifier(string virtualPath, FileChangedCallback onFileChanged) {
+            _onFileChanged = onFileChanged;
+            RegisterForNextNotification(virtualPath);
+        }
+
+        private void RegisterForNextNotification(string virtualPath) {
+            // Get a CacheDependency from the BuildProvider, so that we know anytime something changes
+            var virtualPathDependencies = new List<string>();
+            virtualPathDependencies.Add(virtualPath);
+            CacheDependency cacheDependency = VirtualPathProvider.GetCacheDependency(
+                virtualPath, virtualPathDependencies, DateTime.UtcNow);
+
+            // Rely on the ASP.NET cache for file change notifications, since FileSystemWatcher
+            // doesn't work in medium trust
+            HttpRuntime.Cache.Insert(virtualPath /*key*/, virtualPath /*value*/, cacheDependency,
+                Cache.NoAbsoluteExpiration, Cache.NoSlidingExpiration,
+                CacheItemPriority.NotRemovable, new CacheItemRemovedCallback(OnCacheItemRemoved));
+        }
+
+        private void OnCacheItemRemoved(string key, object value, CacheItemRemovedReason reason) {
+
+            // We only care about dependency changes
+            if (reason != CacheItemRemovedReason.DependencyChanged)
+                return;
+
+            _onFileChanged(key);
+
+            // We need to register again to get the next notification
+            RegisterForNextNotification(key);
+        }
+    }
+}
+