Improve registry startup and lookup performance (#674)

* Optimize search for Effect resolution name
Avoid multiple collection of assemblies during startup
Cache handler lookups

* Handle s_initialized check inside of Initialize method

Xamarin.Forms.Core/DependencyService.cs

@@ -14,8 +14,7 @@ public static class DependencyService
 
 		public static T Get<T>(DependencyFetchTarget fetchTarget = DependencyFetchTarget.GlobalInstance) where T : class
 		{
-			if (!s_initialized)
-				Initialize();
+			Initialize();
 
 			Type targetType = typeof(T);
 
@@ -64,12 +63,27 @@ static Type FindImplementor(Type target)
 
 		static void Initialize()
 		{
+			if (s_initialized)
+			{
+				return;
+			}
+
 			Assembly[] assemblies = Device.GetAssemblies();
 			if (Registrar.ExtraAssemblies != null)
 			{
 				assemblies = assemblies.Union(Registrar.ExtraAssemblies).ToArray();
 			}
 
+			Initialize(assemblies);
+		}
+
+		internal static void Initialize(Assembly[] assemblies)
+		{
+			if (s_initialized)
+			{
+				return;
+			}
+
 			Type targetAttrType = typeof(DependencyAttribute);
 
 			// Don't use LINQ for performance reasons

Xamarin.Forms.Core/Registrar.cs

@@ -31,15 +31,18 @@ internal TOut GetHandler<TOut>(Type type) where TOut : TRegistrable
 
 		internal Type GetHandlerType(Type viewType)
 		{
-			Type type = LookupHandlerType(viewType);
-			if (type != null)
+			Type type;
+			if(LookupHandlerType(viewType, out type))
 				return type;
 
 			// lazy load render-view association with RenderWithAttribute (as opposed to using ExportRenderer)
-			// TODO: change Registrar to a LazyImmutableDictionary and pass this logic to ctor as a delegate.
 			var attribute = viewType.GetTypeInfo().GetCustomAttribute<RenderWithAttribute>();
 			if (attribute == null)
+			{
+				Register(viewType, null); // Cache this result so we don't have to do GetCustomAttribute again
 				return null;
+			}
+
 			type = attribute.Type;
 
 			if (type.Name.StartsWith("_"))
@@ -51,30 +54,33 @@ internal Type GetHandlerType(Type viewType)
 
 				if (type.Name.StartsWith("_"))
 				{
-					//var attrs = type.GetTypeInfo ().GetCustomAttributes ().ToArray ();
+					Register(viewType, null); // Cache this result so we don't work through this chain again
 					return null;
 				}
 			}
 
-			Register(viewType, type);
-			return LookupHandlerType(viewType);
+			Register(viewType, type); // Register this so we don't have to look for the RenderWith Attibute again in the future
+
+			return type;
 		}
 
-		Type LookupHandlerType(Type viewType)
+		bool LookupHandlerType(Type viewType, out Type handlerType)
 		{
 			Type type = viewType;
 
-			while (true)
+			while (type != null)
 			{
 				if (_handlers.ContainsKey(type))
-					return _handlers[type];
+				{
+					handlerType = _handlers[type];
+					return true;
+				}
 
 				type = type.GetTypeInfo().BaseType;
-				if (type == null)
-					break;
 			}
 
-			return null;
+			handlerType = null;
+			return false;
 		}
 	}
 
@@ -126,22 +132,25 @@ internal static void RegisterAll(Type[] attrTypes)
 				}
 
 				string resolutionName = assembly.FullName;
-				var resolutionNameAttribute = (ResolutionGroupNameAttribute)assembly.GetCustomAttribute(typeof(ResolutionGroupNameAttribute));
-				if (resolutionNameAttribute != null)
-				{
-					resolutionName = resolutionNameAttribute.ShortName;
-				}
 
 				Attribute[] effectAttributes = assembly.GetCustomAttributes(typeof(ExportEffectAttribute)).ToArray();
 				if (effectAttributes.Length > 0)
 				{
+					var resolutionNameAttribute = (ResolutionGroupNameAttribute)assembly.GetCustomAttribute(typeof(ResolutionGroupNameAttribute));
+					if (resolutionNameAttribute != null)
+					{
+						resolutionName = resolutionNameAttribute.ShortName;
+					}
+
 					foreach (Attribute attribute in effectAttributes)
 					{
 						var effect = (ExportEffectAttribute)attribute;
 						Effects [resolutionName + "." + effect.Id] = effect.Type;
 					}
 				}
 			}
+
+			DependencyService.Initialize(assemblies);
 		}
 	}
 }