Use 'UsingScopeCache' instance for caching the extension methods.

ICSharpCode.NRefactory/CSharp/Refactoring/TypeSystemAstBuilder.cs

@@ -115,7 +115,7 @@ namespace ICSharpCode.NRefactory.CSharp.Refactoring
 			
 			if (resolver != null) {
 				// Look if there's an alias to the target type
-				for (UsingScope usingScope = resolver.UsingScope; usingScope != null; usingScope = usingScope.Parent) {
+				for (UsingScope usingScope = resolver.CurrentUsingScope; usingScope != null; usingScope = usingScope.Parent) {
 					foreach (var pair in usingScope.UsingAliases) {
 						IType type = pair.Value.Resolve(resolver.Context);
 						if (TypeMatches(type, typeDef, typeArguments))
@@ -200,7 +200,7 @@ namespace ICSharpCode.NRefactory.CSharp.Refactoring
 		{
 			if (resolver != null) {
 				// Look if there's an alias to the target namespace
-				for (UsingScope usingScope = resolver.UsingScope; usingScope != null; usingScope = usingScope.Parent) {
+				for (UsingScope usingScope = resolver.CurrentUsingScope; usingScope != null; usingScope = usingScope.Parent) {
 					foreach (var pair in usingScope.UsingAliases) {
 						// maybe add some caching? we're resolving all aliases N times when converting a namespace name with N parts
 						NamespaceResolveResult nrr = pair.Value.ResolveNamespace(resolver.Context);

ICSharpCode.NRefactory/CSharp/Resolver/AliasNamespaceReference.cs

@@ -45,7 +45,7 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver
 		public ResolveResult DoResolve(ITypeResolveContext context)
 		{
 			CSharpResolver r = new CSharpResolver(context);
-			r.UsingScope = parentUsingScope;
+			r.CurrentUsingScope = parentUsingScope;
 			return r.ResolveAlias(identifier);
 		}
 		

ICSharpCode.NRefactory/CSharp/Resolver/CSharpResolver.cs

@@ -17,6 +17,7 @@
 // DEALINGS IN THE SOFTWARE.
 
 using System;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Globalization;
@@ -25,6 +26,7 @@ using System.Text;
 using System.Threading;
 using ICSharpCode.NRefactory.TypeSystem;
 using ICSharpCode.NRefactory.TypeSystem.Implementation;
+using ICSharpCode.NRefactory.Utils;
 
 namespace ICSharpCode.NRefactory.CSharp.Resolver
 {
@@ -82,10 +84,67 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver
 		/// </summary>
 		public ITypeDefinition CurrentTypeDefinition { get; set; }
 		
+		UsingScopeCache currentUsingScope;
+		
 		/// <summary>
 		/// Gets/Sets the current using scope that is used to look up identifiers as class names.
 		/// </summary>
-		public UsingScope UsingScope { get; set; }
+		public UsingScope CurrentUsingScope {
+			get { return currentUsingScope != null ? currentUsingScope.UsingScope : null; }
+			set {
+				if (value == null) {
+					currentUsingScope = null;
+				} else {
+					if (currentUsingScope != null && currentUsingScope.UsingScope == value)
+						return;
+					
+					CacheManager cache = context.CacheManager;
+					if (cache != null) {
+						object obj;
+						if (cache.Dictionary.TryGetValue(value, out obj)) {
+							currentUsingScope = (UsingScopeCache)obj;
+						} else {
+							currentUsingScope = new UsingScopeCache(value);
+							cache.Dictionary.TryAdd(value, currentUsingScope);
+						}
+					} else {
+						currentUsingScope = new UsingScopeCache(value);
+					}
+				}
+			}
+		}
+		
+		/// <summary>
+		/// Gets the current project content.
+		/// Returns <c>CurrentUsingScope.ProjectContent</c>.
+		/// </summary>
+		public IProjectContent ProjectContent {
+			get {
+				if (currentUsingScope != null)
+					return currentUsingScope.UsingScope.ProjectContent;
+				else
+					return null;
+			}
+		}
+		#endregion
+		
+		#region Per-UsingScope Cache
+		/// <summary>
+		/// There is one cache instance per using scope; and it might be shared between multiple resolvers
+		/// that are on different threads, so it must be thread-safe.
+		/// </summary>
+		sealed class UsingScopeCache
+		{
+			public readonly UsingScope UsingScope;
+			
+			public volatile List<List<IMethod>> AllExtensionMethods;
+			
+			
+			public UsingScopeCache(UsingScope usingScope)
+			{
+				this.UsingScope = usingScope;
+			}
+		}
 		#endregion
 		
 		#region Local Variable Management
@@ -1910,6 +1969,7 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver
 			if (parameterizeResultType && typeArguments.All(t => t.Kind == TypeKind.UnboundTypeArgument))
 				parameterizeResultType = false;
 			
+			ResolveResult r;
 			// look in current type definitions
 			for (ITypeDefinition t = this.CurrentTypeDefinition; t != null; t = t.DeclaringTypeDefinition) {
 				if (k == 0) {
@@ -1928,7 +1988,6 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver
 				}
 				
 				MemberLookup lookup = new MemberLookup(context, t, t.ProjectContent);
-				ResolveResult r;
 				if (lookupMode == SimpleNameLookupMode.Expression || lookupMode == SimpleNameLookupMode.InvocationTarget) {
 					r = lookup.Lookup(new TypeResolveResult(t), identifier, typeArguments, lookupMode == SimpleNameLookupMode.InvocationTarget);
 				} else {
@@ -1939,7 +1998,7 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver
 			}
 			
 			// look in current namespace definitions
-			for (UsingScope n = this.UsingScope; n != null; n = n.Parent) {
+			for (UsingScope n = this.CurrentUsingScope; n != null; n = n.Parent) {
 				// first look for a namespace
 				if (k == 0) {
 					string fullName = NamespaceDeclaration.BuildQualifiedName(n.NamespaceName, identifier);
@@ -1966,7 +2025,7 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver
 					if (n.ExternAliases.Contains(identifier)) {
 						return ResolveExternAlias(identifier);
 					}
-					if (lookupMode != SimpleNameLookupMode.TypeInUsingDeclaration || n != this.UsingScope) {
+					if (lookupMode != SimpleNameLookupMode.TypeInUsingDeclaration || n != this.CurrentUsingScope) {
 						foreach (var pair in n.UsingAliases) {
 							if (pair.Key == identifier) {
 								NamespaceResolveResult ns = pair.Value.ResolveNamespace(context);
@@ -1979,7 +2038,7 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver
 					}
 				}
 				// finally, look in the imported namespaces:
-				if (lookupMode != SimpleNameLookupMode.TypeInUsingDeclaration || n != this.UsingScope) {
+				if (lookupMode != SimpleNameLookupMode.TypeInUsingDeclaration || n != this.CurrentUsingScope) {
 					IType firstResult = null;
 					foreach (var u in n.Usings) {
 						NamespaceResolveResult ns = u.ResolveNamespace(context);
@@ -2020,7 +2079,7 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver
 			if (identifier == "global")
 				return new NamespaceResolveResult(string.Empty);
 			
-			for (UsingScope n = this.UsingScope; n != null; n = n.Parent) {
+			for (UsingScope n = this.CurrentUsingScope; n != null; n = n.Parent) {
 				if (n.ExternAliases.Contains(identifier)) {
 					return ResolveExternAlias(identifier);
 				}
@@ -2033,7 +2092,7 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver
 			return ErrorResult;
 		}
 		
-		ResolveResult ResolveExternAlias(string alias)
+		static ResolveResult ResolveExternAlias(string alias)
 		{
 			// TODO: implement extern alias support
 			return new NamespaceResolveResult(string.Empty);
@@ -2069,7 +2128,7 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver
 				if (mgrr != null) {
 					Debug.Assert(mgrr.extensionMethods == null);
 					// set the values that are necessary to make MethodGroupResolveResult.GetExtensionMethods() work
-					mgrr.usingScope = this.UsingScope;
+					mgrr.usingScope = this.CurrentUsingScope;
 					mgrr.resolver = this;
 				}
 			}
@@ -2115,7 +2174,7 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver
 		/// </summary>
 		public MemberLookup CreateMemberLookup()
 		{
-			return new MemberLookup(context, this.CurrentTypeDefinition, this.UsingScope != null ? this.UsingScope.ProjectContent : null);
+			return new MemberLookup(context, this.CurrentTypeDefinition, this.ProjectContent);
 		}
 		#endregion
 		
@@ -2178,17 +2237,16 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver
 		/// Gets all extension methods available in the current using scope.
 		/// This list includes unaccessible
 		/// </summary>
-		List<List<IMethod>> GetAllExtensionMethods()
+		IList<List<IMethod>> GetAllExtensionMethods()
-		{
+		{
-			// TODO: maybe cache the result?
+			if (currentUsingScope == null)
-			// Idea: class ExtensionMethodGroupCache : List<List<IMethod>>
+				return EmptyList<List<IMethod>>.Instance;
-			// a new ExtensionMethodGroupCache instance would be created whenever the UsingScope is changed
+			List<List<IMethod>> extensionMethodGroups = currentUsingScope.AllExtensionMethods;
-			// The list contents would be initialized on-demand.
+			if (extensionMethodGroups != null)
-			// Because cloning the resolver would re-use the cache, it must be thread-safe.
+				return extensionMethodGroups;
-			// The cache could be passed to the MethodGroupResolveResult instead of passing the resolver.
+			extensionMethodGroups = new List<List<IMethod>>();
-			List<List<IMethod>> extensionMethodGroups = new List<List<IMethod>>();
 			List<IMethod> m;
-			for (UsingScope scope = this.UsingScope; scope != null; scope = scope.Parent) {
+			for (UsingScope scope = currentUsingScope.UsingScope; scope != null; scope = scope.Parent) {
 				m = GetExtensionMethods(scope.NamespaceName).ToList();
 				if (m.Count > 0)
 					extensionMethodGroups.Add(m);
@@ -2202,6 +2260,7 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver
 				if (m.Count > 0)
 					extensionMethodGroups.Add(m);
 			}
+			currentUsingScope.AllExtensionMethods = extensionMethodGroups;
 			return extensionMethodGroups;
 		}
 		

ICSharpCode.NRefactory/CSharp/Resolver/ConstantValues.cs

@@ -53,7 +53,7 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver.ConstantValues
 			return new CSharpResolver(context) {
 				CheckForOverflow = false, // TODO: get project-wide overflow setting
 				CurrentTypeDefinition = parentTypeDefinition,
-				UsingScope = parentUsingScope
+				CurrentUsingScope = parentUsingScope
 			};
 		}
 		

ICSharpCode.NRefactory/CSharp/Resolver/MemberTypeOrNamespaceReference.cs

@@ -71,7 +71,7 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver
 				return targetRR;
 			CSharpResolver r = new CSharpResolver(context);
 			r.CurrentTypeDefinition = parentTypeDefinition;
-			r.UsingScope = parentUsingScope;
+			r.CurrentUsingScope = parentUsingScope;
 			IType[] typeArgs = new IType[typeArguments.Count];
 			for (int i = 0; i < typeArgs.Length; i++) {
 				typeArgs[i] = typeArguments[i].Resolve(context);

ICSharpCode.NRefactory/CSharp/Resolver/MethodGroupResolveResult.cs

@@ -138,12 +138,12 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver
 		{
 			if (resolver != null) {
 				Debug.Assert(extensionMethods == null);
-				UsingScope oldUsingScope = resolver.UsingScope;
+				UsingScope oldUsingScope = resolver.CurrentUsingScope;
 				try {
-					resolver.UsingScope = usingScope;
+					resolver.CurrentUsingScope = usingScope;
 					extensionMethods = resolver.GetExtensionMethods(this.TargetType, methodName, typeArguments);
 				} finally {
-					resolver.UsingScope = oldUsingScope;
+					resolver.CurrentUsingScope = oldUsingScope;
 					resolver = null;
 					usingScope = null;
 				}

ICSharpCode.NRefactory/CSharp/Resolver/ResolveVisitor.cs

@@ -357,31 +357,31 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver
 		#region Track UsingScope
 		public override ResolveResult VisitCompilationUnit(CompilationUnit unit, object data)
 		{
-			UsingScope previousUsingScope = resolver.UsingScope;
+			UsingScope previousUsingScope = resolver.CurrentUsingScope;
 			try {
 				if (parsedFile != null)
-					resolver.UsingScope = parsedFile.RootUsingScope;
+					resolver.CurrentUsingScope = parsedFile.RootUsingScope;
 				ScanChildren(unit);
 				return voidResult;
 			} finally {
-				resolver.UsingScope = previousUsingScope;
+				resolver.CurrentUsingScope = previousUsingScope;
 			}
 		}
 		
 		public override ResolveResult VisitNamespaceDeclaration(NamespaceDeclaration namespaceDeclaration, object data)
 		{
-			UsingScope previousUsingScope = resolver.UsingScope;
+			UsingScope previousUsingScope = resolver.CurrentUsingScope;
 			try {
 				if (parsedFile != null) {
-					resolver.UsingScope = parsedFile.GetUsingScope(namespaceDeclaration.StartLocation);
+					resolver.CurrentUsingScope = parsedFile.GetUsingScope(namespaceDeclaration.StartLocation);
 				}
 				ScanChildren(namespaceDeclaration);
-				if (resolver.UsingScope != null)
+				if (resolver.CurrentUsingScope != null)
-					return new NamespaceResolveResult(resolver.UsingScope.NamespaceName);
+					return new NamespaceResolveResult(resolver.CurrentUsingScope.NamespaceName);
 				else
 					return null;
 			} finally {
-				resolver.UsingScope = previousUsingScope;
+				resolver.CurrentUsingScope = previousUsingScope;
 			}
 		}
 		#endregion
@@ -782,11 +782,11 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver
 		public override ResolveResult VisitAnonymousTypeCreateExpression(AnonymousTypeCreateExpression anonymousTypeCreateExpression, object data)
 		{
 			// 7.6.10.6 Anonymous object creation expressions
-			if (resolver.UsingScope == null) {
+			if (resolver.ProjectContent == null) {
 				ScanChildren(anonymousTypeCreateExpression);
 				return errorResult;
 			}
-			var anonymousType = new DefaultTypeDefinition(resolver.UsingScope.ProjectContent, string.Empty, "$Anonymous$");
+			var anonymousType = new DefaultTypeDefinition(resolver.ProjectContent, string.Empty, "$Anonymous$");
 			anonymousType.IsSynthetic = true;
 			resolver.PushInitializerType(anonymousType);
 			foreach (var expr in anonymousTypeCreateExpression.Initializers) {
@@ -2100,7 +2100,7 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver
 					
 					IConstantValue cv = null;
 					if (isConst) {
-						cv = TypeSystemConvertVisitor.ConvertConstantValue(type, vi.Initializer, resolver.CurrentTypeDefinition, resolver.CurrentMember as IMethod, resolver.UsingScope);
+						cv = TypeSystemConvertVisitor.ConvertConstantValue(type, vi.Initializer, resolver.CurrentTypeDefinition, resolver.CurrentMember as IMethod, resolver.CurrentUsingScope);
 					}
 					resolver.AddVariable(type, MakeRegion(vi), vi.Name, cv);
 					
@@ -2299,7 +2299,7 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver
 		
 		ITypeReference MakeTypeReference(AstType type)
 		{
-			return TypeSystemConvertVisitor.ConvertType(type, resolver.CurrentTypeDefinition, resolver.CurrentMember as IMethod, resolver.UsingScope, currentTypeLookupMode);
+			return TypeSystemConvertVisitor.ConvertType(type, resolver.CurrentTypeDefinition, resolver.CurrentMember as IMethod, resolver.CurrentUsingScope, currentTypeLookupMode);
 		}
 		
 		sealed class VarTypeReference : ITypeReference
@@ -2440,7 +2440,7 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver
 		ResolveResult HandleAttributeType(AstType astType)
 		{
 			ScanChildren(astType);
-			IType type = TypeSystemConvertVisitor.ConvertAttributeType(astType, resolver.CurrentTypeDefinition, resolver.CurrentMember as IMethod, resolver.UsingScope).Resolve(resolver.Context);
+			IType type = TypeSystemConvertVisitor.ConvertAttributeType(astType, resolver.CurrentTypeDefinition, resolver.CurrentMember as IMethod, resolver.CurrentUsingScope).Resolve(resolver.Context);
 			if (type.Kind != TypeKind.Unknown)
 				return new TypeResolveResult(type);
 			else

ICSharpCode.NRefactory/CSharp/Resolver/SimpleTypeOrNamespaceReference.cs

@@ -66,7 +66,7 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver
 			
 			CSharpResolver r = new CSharpResolver(context);
 			r.CurrentTypeDefinition = parentTypeDefinition;
-			r.UsingScope = parentUsingScope;
+			r.CurrentUsingScope = parentUsingScope;
 			IType[] typeArgs = new IType[typeArguments.Count];
 			for (int i = 0; i < typeArgs.Length; i++) {
 				typeArgs[i] = typeArguments[i].Resolve(context);