Make Cecil property getters thread-safe.

Mono.Cecil/Mono.Cecil/AssemblyDefinition.cs

@@ -62,7 +62,7 @@ namespace Mono.Cecil {
 					return modules;
 
 				if (main_module.HasImage)
-					return modules = main_module.Read (this, (_, reader) => reader.ReadModules ());
+					return main_module.Read (ref modules, this, (_, reader) => reader.ReadModules ());
 
 				return modules = new Collection<ModuleDefinition> { main_module };
 			}
@@ -87,7 +87,7 @@ namespace Mono.Cecil {
 		}
 
 		public Collection<CustomAttribute> CustomAttributes {
-			get { return custom_attributes ?? (custom_attributes = this.GetCustomAttributes (main_module)); }
+			get { return custom_attributes ?? (this.GetCustomAttributes (ref custom_attributes, main_module)); }
 		}
 
 		public bool HasSecurityDeclarations {
@@ -100,7 +100,7 @@ namespace Mono.Cecil {
 		}
 
 		public Collection<SecurityDeclaration> SecurityDeclarations {
-			get { return security_declarations ?? (security_declarations = this.GetSecurityDeclarations (main_module)); }
+			get { return security_declarations ?? (this.GetSecurityDeclarations (ref security_declarations, main_module)); }
 		}
 
 		internal AssemblyDefinition ()

Mono.Cecil/Mono.Cecil/AssemblyNameReference.cs

@@ -107,9 +107,10 @@ namespace Mono.Cecil {
 				if (public_key_token.IsNullOrEmpty () && !public_key.IsNullOrEmpty ()) {
 					var hash = HashPublicKey ();
 					// we need the last 8 bytes in reverse order
-					public_key_token = new byte [8];
-					Array.Copy (hash, (hash.Length - 8), public_key_token, 0, 8);
-					Array.Reverse (public_key_token, 0, 8);
+					byte[] local_public_key_token = new byte [8];
+					Array.Copy (hash, (hash.Length - 8), local_public_key_token, 0, 8);
+					Array.Reverse (local_public_key_token, 0, 8);
+					public_key_token = local_public_key_token; // publish only once finished (required for thread-safety)
 				}
 				return public_key_token;
 			}

Mono.Cecil/Mono.Cecil/AssemblyReader.cs

@@ -1558,10 +1558,11 @@ namespace Mono.Cecil {
 			var methods = type.Methods;
 			for (int i = 0; i < methods.Count; i++) {
 				var method = methods [i];
-				if (method.sem_attrs.HasValue)
+				if (method.sem_attrs_ready)
 					continue;
 
 				method.sem_attrs = ReadMethodSemantics (method);
+				method.sem_attrs_ready = true;
 			}
 		}
 

Mono.Cecil/Mono.Cecil/CustomAttribute.cs

@@ -191,7 +191,7 @@ namespace Mono.Cecil {
 			if (!HasImage || signature == 0)
 				throw new NotSupportedException ();
 
-			return blob = Module.Read (this, (attribute, reader) => reader.ReadCustomAttributeBlob (attribute.signature));
+			return Module.Read (ref blob, this, (attribute, reader) => reader.ReadCustomAttributeBlob (attribute.signature));
 		}
 
 		void Resolve ()
@@ -199,23 +199,22 @@ namespace Mono.Cecil {
 			if (resolved || !HasImage)
 				return;
 
-			try {
-				Module.Read (this, (attribute, reader) => {
+			Module.Read (this, (attribute, reader) => {
+				try {
 					reader.ReadCustomAttributeSignature (attribute);
-					return this;
-				});
-
-				resolved = true;
-			} catch (ResolutionException) {
-				if (arguments != null)
-					arguments.Clear ();
-				if (fields != null)
-					fields.Clear ();
-				if (properties != null)
-					properties.Clear ();
-
-				resolved = false;
-			}
+					resolved = true;
+				} catch (ResolutionException) {
+					if (arguments != null)
+						arguments.Clear ();
+					if (fields != null)
+						fields.Clear ();
+					if (properties != null)
+						properties.Clear ();
+					
+					resolved = false;
+				}
+				return this;
+			});
 		}
 	}
 

Mono.Cecil/Mono.Cecil/EventDefinition.cs

@@ -113,7 +113,7 @@ namespace Mono.Cecil {
 		}
 
 		public Collection<CustomAttribute> CustomAttributes {
-			get { return custom_attributes ?? (custom_attributes = this.GetCustomAttributes (Module)); }
+			get { return custom_attributes ?? (this.GetCustomAttributes (ref custom_attributes, Module)); }
 		}
 
 		#region EventAttributes
@@ -148,16 +148,18 @@ namespace Mono.Cecil {
 
 		void InitializeMethods ()
 		{
-			if (add_method != null
-				|| invoke_method != null
-				|| remove_method != null)
-				return;
-
 			var module = this.Module;
-			if (!module.HasImage ())
-				return;
+			lock (module.SyncRoot) {
+				if (add_method != null
+					|| invoke_method != null
+					|| remove_method != null)
+					return;
+
+				if (!module.HasImage ())
+					return;
 
-			module.Read (this, (@event, reader) => reader.ReadMethods (@event));
+				module.Read (this, (@event, reader) => reader.ReadMethods (@event));
+			}
 		}
 
 		public override EventDefinition Resolve ()

Mono.Cecil/Mono.Cecil/FieldDefinition.cs

@@ -154,7 +154,7 @@ namespace Mono.Cecil {
 		}
 
 		public Collection<CustomAttribute> CustomAttributes {
-			get { return custom_attributes ?? (custom_attributes = this.GetCustomAttributes (Module)); }
+			get { return custom_attributes ?? (this.GetCustomAttributes (ref custom_attributes, Module)); }
 		}
 
 		public bool HasMarshalInfo {
@@ -167,7 +167,7 @@ namespace Mono.Cecil {
 		}
 
 		public MarshalInfo MarshalInfo {
-			get { return marshal_info ?? (marshal_info = this.GetMarshalInfo (Module)); }
+			get { return marshal_info ?? (this.GetMarshalInfo (ref marshal_info, Module)); }
 			set { marshal_info = value; }
 		}
 

Mono.Cecil/Mono.Cecil/GenericParameter.cs

@@ -78,7 +78,7 @@ namespace Mono.Cecil {
 					return constraints;
 
 				if (HasImage)
-					return constraints = Module.Read (this, (generic_parameter, reader) => reader.ReadGenericConstraints (generic_parameter));
+					return Module.Read (ref constraints, this, (generic_parameter, reader) => reader.ReadGenericConstraints (generic_parameter));
 
 				return constraints = new Collection<TypeReference> ();
 			}
@@ -94,7 +94,7 @@ namespace Mono.Cecil {
 		}
 
 		public Collection<CustomAttribute> CustomAttributes {
-			get { return custom_attributes ?? (custom_attributes = this.GetCustomAttributes (Module)); }
+			get { return custom_attributes ?? (this.GetCustomAttributes (ref custom_attributes, Module)); }
 		}
 
 		internal new bool HasImage {

Mono.Cecil/Mono.Cecil/IConstantProvider.cs

@@ -44,9 +44,10 @@ namespace Mono.Cecil {
 			ref object constant,
 			ModuleDefinition module)
 		{
-			constant = module.HasImage ()
-				? module.Read (self, (provider, reader) => reader.ReadConstant (provider))
-				: Mixin.NoValue;
+			if (module.HasImage ())
+				module.Read (ref constant, self, (provider, reader) => reader.ReadConstant (provider));
+			else
+				constant = Mixin.NoValue;
 		}
 	}
 }

Mono.Cecil/Mono.Cecil/ICustomAttributeProvider.cs

@@ -27,7 +27,6 @@
 //
 
 using System;
-
 using Mono.Collections.Generic;
 
 namespace Mono.Cecil {
@@ -52,11 +51,12 @@ namespace Mono.Cecil {
 
 		public static Collection<CustomAttribute> GetCustomAttributes (
 			this ICustomAttributeProvider self,
+			ref Collection<CustomAttribute> variable,
 			ModuleDefinition module)
 		{
 			return module.HasImage ()
-				? module.Read (self, (provider, reader) => reader.ReadCustomAttributes (provider))
-				: new Collection<CustomAttribute> ();
+				? module.Read (ref variable, self, (provider, reader) => reader.ReadCustomAttributes (provider))
+				: variable = new Collection<CustomAttribute>();
 		}
 	}
 }

Mono.Cecil/Mono.Cecil/IGenericParameterProvider.cs

@@ -65,11 +65,12 @@ namespace Mono.Cecil {
 
 		public static Collection<GenericParameter> GetGenericParameters (
 			this IGenericParameterProvider self,
+			ref Collection<GenericParameter> collection,
 			ModuleDefinition module)
 		{
 			return module.HasImage ()
-				? module.Read (self, (provider, reader) => reader.ReadGenericParameters (provider))
-				: new Collection<GenericParameter> ();
+				? module.Read (ref collection, self, (provider, reader) => reader.ReadGenericParameters (provider))
+				: collection = new Collection<GenericParameter> ();
 		}
 	}
 }

Mono.Cecil/Mono.Cecil/IMarshalInfoProvider.cs

@@ -47,10 +47,11 @@ namespace Mono.Cecil {
 
 		public static MarshalInfo GetMarshalInfo (
 			this IMarshalInfoProvider self,
+			ref MarshalInfo variable,
 			ModuleDefinition module)
 		{
 			return module.HasImage ()
-				? module.Read (self, (provider, reader) => reader.ReadMarshalInfo (provider))
+				? module.Read (ref variable, self, (provider, reader) => reader.ReadMarshalInfo (provider))
 				: null;
 		}
 	}

Mono.Cecil/Mono.Cecil/MethodDefinition.cs

@@ -37,7 +37,8 @@ namespace Mono.Cecil {
 
 		ushort attributes;
 		ushort impl_attributes;
-		internal MethodSemanticsAttributes? sem_attrs;
+		internal volatile bool sem_attrs_ready;
+		internal MethodSemanticsAttributes sem_attrs;
 		Collection<CustomAttribute> custom_attributes;
 		Collection<SecurityDeclaration> security_declarations;
 
@@ -59,23 +60,24 @@ namespace Mono.Cecil {
 
 		public MethodSemanticsAttributes SemanticsAttributes {
 			get {
-				if (sem_attrs.HasValue)
-					return sem_attrs.Value;
+				if (sem_attrs_ready)
+					return sem_attrs;
 
 				if (HasImage) {
 					ReadSemantics ();
-					return sem_attrs.Value;
+					return sem_attrs;
 				}
 
 				sem_attrs = MethodSemanticsAttributes.None;
-				return sem_attrs.Value;
+				sem_attrs_ready = true;
+				return sem_attrs;
 			}
 			set { sem_attrs = value; }
 		}
 
 		internal void ReadSemantics ()
 		{
-			if (sem_attrs.HasValue)
+			if (sem_attrs_ready)
 				return;
 
 			var module = this.Module;
@@ -98,7 +100,7 @@ namespace Mono.Cecil {
 		}
 
 		public Collection<SecurityDeclaration> SecurityDeclarations {
-			get { return security_declarations ?? (security_declarations = this.GetSecurityDeclarations (Module)); }
+			get { return security_declarations ?? (this.GetSecurityDeclarations (ref security_declarations, Module)); }
 		}
 
 		public bool HasCustomAttributes {
@@ -111,7 +113,7 @@ namespace Mono.Cecil {
 		}
 
 		public Collection<CustomAttribute> CustomAttributes {
-			get { return custom_attributes ?? (custom_attributes = this.GetCustomAttributes (Module)); }
+			get { return custom_attributes ?? (this.GetCustomAttributes (ref custom_attributes, Module)); }
 		}
 
 		public int RVA {
@@ -138,7 +140,7 @@ namespace Mono.Cecil {
 					return null;
 
 				if (HasImage && rva != 0)
-					return body = Module.Read (this, (method, reader) => reader.ReadMethodBody (method));
+					return Module.Read (ref body, this, (method, reader) => reader.ReadMethodBody (method));
 
 				return body = new MethodBody (this);
 			}
@@ -160,7 +162,7 @@ namespace Mono.Cecil {
 					return pinvoke;
 
 				if (HasImage && IsPInvokeImpl)
-					return pinvoke = Module.Read (this, (method, reader) => reader.ReadPInvokeInfo (method));
+					return Module.Read (ref pinvoke, this, (method, reader) => reader.ReadPInvokeInfo (method));
 
 				return null;
 			}
@@ -188,7 +190,7 @@ namespace Mono.Cecil {
 					return overrides;
 
 				if (HasImage)
-					return overrides = Module.Read (this, (method, reader) => reader.ReadOverrides (method));
+					return Module.Read (ref overrides, this, (method, reader) => reader.ReadOverrides (method));
 
 				return overrides = new Collection<MethodReference> ();
 			}
@@ -204,7 +206,7 @@ namespace Mono.Cecil {
 		}
 
 		public override Collection<GenericParameter> GenericParameters {
-			get { return generic_parameters ?? (generic_parameters = this.GetGenericParameters (Module)); }
+			get { return generic_parameters ?? (this.GetGenericParameters (ref generic_parameters, Module)); }
 		}
 
 		#region MethodAttributes

Mono.Cecil/Mono.Cecil/ModuleDefinition.cs

@@ -29,8 +29,8 @@
 using System;
 using System.Collections.Generic;
 using System.IO;
+using System.Threading;
 using SR = System.Reflection;
-
 using Mono.Cecil.Cil;
 using Mono.Cecil.Metadata;
 using Mono.Cecil.PE;
@@ -261,7 +261,11 @@ namespace Mono.Cecil {
 
 #if !READ_ONLY
 		internal MetadataImporter MetadataImporter {
-			get { return importer ?? (importer = new MetadataImporter (this)); }
+			get {
+				if (importer == null)
+					Interlocked.CompareExchange(ref importer, new MetadataImporter(this), null);
+				return importer;
+			}
 		}
 #endif
 
@@ -270,7 +274,11 @@ namespace Mono.Cecil {
 		}
 
 		public TypeSystem TypeSystem {
-			get { return type_system ?? (type_system = TypeSystem.CreateTypeSystem (this)); }
+			get {
+				if (type_system == null)
+					Interlocked.CompareExchange(ref type_system, TypeSystem.CreateTypeSystem (this), null);
+				return type_system;
+			}
 		}
 
 		public bool HasAssemblyReferences {
@@ -288,7 +296,7 @@ namespace Mono.Cecil {
 					return references;
 
 				if (HasImage)
-					return references = Read (this, (_, reader) => reader.ReadAssemblyReferences ());
+					return Read (ref references, this, (_, reader) => reader.ReadAssemblyReferences ());
 
 				return references = new Collection<AssemblyNameReference> ();
 			}
@@ -309,7 +317,7 @@ namespace Mono.Cecil {
 					return modules;
 
 				if (HasImage)
-					return modules = Read (this, (_, reader) => reader.ReadModuleReferences ());
+					return Read (ref modules, this, (_, reader) => reader.ReadModuleReferences ());
 
 				return modules = new Collection<ModuleReference> ();
 			}
@@ -333,7 +341,7 @@ namespace Mono.Cecil {
 					return resources;
 
 				if (HasImage)
-					return resources = Read (this, (_, reader) => reader.ReadResources ());
+					return Read (ref resources, this, (_, reader) => reader.ReadResources ());
 
 				return resources = new Collection<Resource> ();
 			}
@@ -349,7 +357,7 @@ namespace Mono.Cecil {
 		}
 
 		public Collection<CustomAttribute> CustomAttributes {
-			get { return custom_attributes ?? (custom_attributes = this.GetCustomAttributes (this)); }
+			get { return custom_attributes ?? (this.GetCustomAttributes (ref custom_attributes, this)); }
 		}
 
 		public bool HasTypes {
@@ -367,7 +375,7 @@ namespace Mono.Cecil {
 					return types;
 
 				if (HasImage)
-					return types = Read (this, (_, reader) => reader.ReadTypes ());
+					return Read (ref types, this, (_, reader) => reader.ReadTypes ());
 
 				return types = new TypeDefinitionCollection (this);
 			}
@@ -388,7 +396,7 @@ namespace Mono.Cecil {
 					return exported_types;
 
 				if (HasImage)
-					return exported_types = Read (this, (_, reader) => reader.ReadExportedTypes ());
+					return Read (ref exported_types, this, (_, reader) => reader.ReadExportedTypes ());
 
 				return exported_types = new Collection<ExportedType> ();
 			}
@@ -400,7 +408,7 @@ namespace Mono.Cecil {
 					return entry_point;
 
 				if (HasImage)
-					return entry_point = Read (this, (_, reader) => reader.ReadEntryPoint ());
+					return Read (ref entry_point, this, (_, reader) => reader.ReadEntryPoint ());
 
 				return entry_point = null;
 			}
@@ -760,6 +768,10 @@ namespace Mono.Cecil {
 		
 		readonly object module_lock = new object();
 
+		internal object SyncRoot {
+			get { return module_lock; }
+		}
+
 		internal TRet Read<TItem, TRet> (TItem item, Func<TItem, MetadataReader, TRet> read)
 		{
 			lock (module_lock) {
@@ -774,6 +786,24 @@ namespace Mono.Cecil {
 				return ret;
 			}
 		}
+		
+		internal TRet Read<TItem, TRet> (ref TRet variable, TItem item, Func<TItem, MetadataReader, TRet> read) where TRet : class
+		{
+			lock (module_lock) {
+				if (variable != null)
+					return variable;
+				
+				var position = reader.position;
+				var context = reader.context;
+
+				var ret = read (item, reader);
+
+				reader.position = position;
+				reader.context = context;
+
+				return variable = ret;
+			}
+		}
 
 		void ProcessDebugHeader ()
 		{

Mono.Cecil/Mono.Cecil/ParameterDefinition.cs

@@ -81,7 +81,7 @@ namespace Mono.Cecil {
 		}
 
 		public Collection<CustomAttribute> CustomAttributes {
-			get { return custom_attributes ?? (custom_attributes = this.GetCustomAttributes (parameter_type.Module)); }
+			get { return custom_attributes ?? (this.GetCustomAttributes (ref custom_attributes, parameter_type.Module)); }
 		}
 
 		public bool HasMarshalInfo {
@@ -94,7 +94,7 @@ namespace Mono.Cecil {
 		}
 
 		public MarshalInfo MarshalInfo {
-			get { return marshal_info ?? (marshal_info = this.GetMarshalInfo (parameter_type.Module)); }
+			get { return marshal_info ?? (this.GetMarshalInfo (ref marshal_info, parameter_type.Module)); }
 			set { marshal_info = value; }
 		}
 

Mono.Cecil/Mono.Cecil/PropertyDefinition.cs

@@ -76,7 +76,7 @@ namespace Mono.Cecil {
 		}
 
 		public Collection<CustomAttribute> CustomAttributes {
-			get { return custom_attributes ?? (custom_attributes = this.GetCustomAttributes (Module)); }
+			get { return custom_attributes ?? (this.GetCustomAttributes (ref custom_attributes, Module)); }
 		}
 
 		public MethodDefinition GetMethod {
@@ -245,14 +245,16 @@ namespace Mono.Cecil {
 
 		void InitializeMethods ()
 		{
-			if (get_method != null || set_method != null)
-				return;
-
 			var module = this.Module;
-			if (!module.HasImage ())
-				return;
+			lock (module.SyncRoot) {
+				if (get_method != null || set_method != null)
+					return;
 
-			module.Read (this, (property, reader) => reader.ReadMethods (property));
+				if (!module.HasImage ())
+					return;
+
+				module.Read (this, (property, reader) => reader.ReadMethods (property));
+			}
 		}
 
 		public override PropertyDefinition Resolve ()

Mono.Cecil/Mono.Cecil/SecurityDeclaration.cs

@@ -27,7 +27,7 @@
 //
 
 using System;
-
+using System.Threading;
 using Mono.Collections.Generic;
 
 namespace Mono.Cecil {
@@ -172,11 +172,12 @@ namespace Mono.Cecil {
 
 		public static Collection<SecurityDeclaration> GetSecurityDeclarations (
 			this ISecurityDeclarationProvider self,
+			ref Collection<SecurityDeclaration> variable,
 			ModuleDefinition module)
 		{
 			return module.HasImage ()
-				? module.Read (self, (provider, reader) => reader.ReadSecurityDeclarations (provider))
-				: new Collection<SecurityDeclaration> ();
+				? module.Read (ref variable, self, (provider, reader) => reader.ReadSecurityDeclarations (provider))
+				: LazyInitializer.EnsureInitialized(ref variable);
 		}
 	}
 }

Mono.Cecil/Mono.Cecil/TypeDefinition.cs

@@ -131,7 +131,7 @@ namespace Mono.Cecil {
 					return interfaces;
 
 				if (HasImage)
-					return interfaces = Module.Read (this, (type, reader) => reader.ReadInterfaces (type));
+					return Module.Read (ref interfaces, this, (type, reader) => reader.ReadInterfaces (type));
 
 				return interfaces = new Collection<TypeReference> ();
 			}
@@ -155,7 +155,7 @@ namespace Mono.Cecil {
 					return nested_types;
 
 				if (HasImage)
-					return nested_types = Module.Read (this, (type, reader) => reader.ReadNestedTypes (type));
+					return Module.Read (ref nested_types, this, (type, reader) => reader.ReadNestedTypes (type));
 
 				return nested_types = new MemberDefinitionCollection<TypeDefinition> (this);
 			}
@@ -183,7 +183,7 @@ namespace Mono.Cecil {
 					return methods;
 
 				if (HasImage)
-					return methods = Module.Read (this, (type, reader) => reader.ReadMethods (type));
+					return Module.Read (ref methods, this, (type, reader) => reader.ReadMethods (type));
 
 				return methods = new MemberDefinitionCollection<MethodDefinition> (this);
 			}
@@ -207,7 +207,7 @@ namespace Mono.Cecil {
 					return fields;
 
 				if (HasImage)
-					return fields = Module.Read (this, (type, reader) => reader.ReadFields (type));
+					return Module.Read (ref fields, this, (type, reader) => reader.ReadFields (type));
 
 				return fields = new MemberDefinitionCollection<FieldDefinition> (this);
 			}
@@ -231,7 +231,7 @@ namespace Mono.Cecil {
 					return events;
 
 				if (HasImage)
-					return events = Module.Read (this, (type, reader) => reader.ReadEvents (type));
+					return Module.Read (ref events, this, (type, reader) => reader.ReadEvents (type));
 
 				return events = new MemberDefinitionCollection<EventDefinition> (this);
 			}
@@ -255,7 +255,7 @@ namespace Mono.Cecil {
 					return properties;
 
 				if (HasImage)
-					return properties = Module.Read (this, (type, reader) => reader.ReadProperties (type));
+					return Module.Read (ref properties, this, (type, reader) => reader.ReadProperties (type));
 
 				return properties = new MemberDefinitionCollection<PropertyDefinition> (this);
 			}
@@ -271,7 +271,7 @@ namespace Mono.Cecil {
 		}
 
 		public Collection<SecurityDeclaration> SecurityDeclarations {
-			get { return security_declarations ?? (security_declarations = this.GetSecurityDeclarations (Module)); }
+			get { return security_declarations ?? (this.GetSecurityDeclarations (ref security_declarations, Module)); }
 		}
 
 		public bool HasCustomAttributes {
@@ -284,7 +284,7 @@ namespace Mono.Cecil {
 		}
 
 		public Collection<CustomAttribute> CustomAttributes {
-			get { return custom_attributes ?? (custom_attributes = this.GetCustomAttributes (Module)); }
+			get { return custom_attributes ?? (this.GetCustomAttributes (ref custom_attributes, Module)); }
 		}
 
 		public override bool HasGenericParameters {
@@ -297,7 +297,7 @@ namespace Mono.Cecil {
 		}
 
 		public override Collection<GenericParameter> GenericParameters {
-			get { return generic_parameters ?? (generic_parameters = this.GetGenericParameters (Module)); }
+			get { return generic_parameters ?? (this.GetGenericParameters (ref generic_parameters, Module)); }
 		}
 
 		#region TypeAttributes

Mono.Cecil/Mono.Cecil/TypeSystem.cs

@@ -174,18 +174,27 @@ namespace Mono.Cecil {
 
 		internal abstract TypeReference LookupType (string @namespace, string name);
 
-		TypeReference LookupSystemType (string name, ElementType element_type)
+		TypeReference LookupSystemType (ref TypeReference typeRef, string name, ElementType element_type)
 		{
-			var type = LookupType ("System", name);
-			type.etype = element_type;
-			return type;
+			lock (module.SyncRoot) {
+				if (typeRef != null)
+					return typeRef;
+				var type = LookupType ("System", name);
+				type.etype = element_type;
+				return typeRef = type;
+			}
 		}
 
-		TypeReference LookupSystemValueType (string name, ElementType element_type)
+		TypeReference LookupSystemValueType (ref TypeReference typeRef, string name, ElementType element_type)
 		{
-			var type = LookupSystemType (name, element_type);
-			type.IsValueType = true;
-			return type;
+			lock (module.SyncRoot) {
+				if (typeRef != null)
+					return typeRef;
+				var type = LookupType ("System", name);
+				type.etype = element_type;
+				type.IsValueType = true;
+				return typeRef = type;
+			}
 		}
 
 		public IMetadataScope Corlib {
@@ -199,75 +208,75 @@ namespace Mono.Cecil {
 		}
 
 		public TypeReference Object {
-			get { return type_object ?? (type_object = LookupSystemType ("Object", ElementType.Object)); }
+			get { return type_object ?? (LookupSystemType (ref type_object, "Object", ElementType.Object)); }
 		}
 
 		public TypeReference Void {
-			get { return type_void ?? (type_void = LookupSystemType ("Void", ElementType.Void)); }
+			get { return type_void ?? (LookupSystemType (ref type_void, "Void", ElementType.Void)); }
 		}
 
 		public TypeReference Boolean {
-			get { return type_bool ?? (type_bool = LookupSystemValueType ("Boolean", ElementType.Boolean)); }
+			get { return type_bool ?? (LookupSystemValueType (ref type_bool, "Boolean", ElementType.Boolean)); }
 		}
 
 		public TypeReference Char {
-			get { return type_char ?? (type_char = LookupSystemValueType ("Char", ElementType.Char)); }
+			get { return type_char ?? (LookupSystemValueType (ref type_char, "Char", ElementType.Char)); }
 		}
 
 		public TypeReference SByte {
-			get { return type_sbyte ?? (type_sbyte = LookupSystemValueType ("SByte", ElementType.I1)); }
+			get { return type_sbyte ?? (LookupSystemValueType (ref type_sbyte, "SByte", ElementType.I1)); }
 		}
 
 		public TypeReference Byte {
-			get { return type_byte ?? (type_byte = LookupSystemValueType ("Byte", ElementType.U1)); }
+			get { return type_byte ?? (LookupSystemValueType (ref type_byte, "Byte", ElementType.U1)); }
 		}
 
 		public TypeReference Int16 {
-			get { return type_int16 ?? (type_int16 = LookupSystemValueType ("Int16", ElementType.I2)); }
+			get { return type_int16 ?? (LookupSystemValueType (ref type_int16, "Int16", ElementType.I2)); }
 		}
 
 		public TypeReference UInt16 {
-			get { return type_uint16 ?? (type_uint16 = LookupSystemValueType ("UInt16", ElementType.U2)); }
+			get { return type_uint16 ?? (LookupSystemValueType (ref type_uint16, "UInt16", ElementType.U2)); }
 		}
 
 		public TypeReference Int32 {
-			get { return type_int32 ?? (type_int32 = LookupSystemValueType ("Int32", ElementType.I4)); }
+			get { return type_int32 ?? (LookupSystemValueType (ref type_int32, "Int32", ElementType.I4)); }
 		}
 
 		public TypeReference UInt32 {
-			get { return type_uint32 ?? (type_uint32 = LookupSystemValueType ("UInt32", ElementType.U4)); }
+			get { return type_uint32 ?? (LookupSystemValueType (ref type_uint32, "UInt32", ElementType.U4)); }
 		}
 
 		public TypeReference Int64 {
-			get { return type_int64 ?? (type_int64 = LookupSystemValueType ("Int64", ElementType.I8)); }
+			get { return type_int64 ?? (LookupSystemValueType (ref type_int64, "Int64", ElementType.I8)); }
 		}
 
 		public TypeReference UInt64 {
-			get { return type_uint64 ?? (type_uint64 = LookupSystemValueType ("UInt64", ElementType.U8)); }
+			get { return type_uint64 ?? (LookupSystemValueType (ref type_uint64, "UInt64", ElementType.U8)); }
 		}
 
 		public TypeReference Single {
-			get { return type_single ?? (type_single = LookupSystemValueType ("Single", ElementType.R4)); }
+			get { return type_single ?? (LookupSystemValueType (ref type_single, "Single", ElementType.R4)); }
 		}
 
 		public TypeReference Double {
-			get { return type_double ?? (type_double = LookupSystemValueType ("Double", ElementType.R8)); }
+			get { return type_double ?? (LookupSystemValueType (ref type_double, "Double", ElementType.R8)); }
 		}
 
 		public TypeReference IntPtr {
-			get { return type_intptr ?? (type_intptr = LookupSystemValueType ("IntPtr", ElementType.I)); }
+			get { return type_intptr ?? (LookupSystemValueType (ref type_intptr, "IntPtr", ElementType.I)); }
 		}
 
 		public TypeReference UIntPtr {
-			get { return type_uintptr ?? (type_uintptr = LookupSystemValueType ("UIntPtr", ElementType.U)); }
+			get { return type_uintptr ?? (LookupSystemValueType (ref type_uintptr, "UIntPtr", ElementType.U)); }
 		}
 
 		public TypeReference String {
-			get { return type_string ?? (type_string = LookupSystemType ("String", ElementType.String)); }
+			get { return type_string ?? (LookupSystemType (ref type_string, "String", ElementType.String)); }
 		}
 
 		public TypeReference TypedReference {
-			get { return type_typedref ?? (type_typedref = LookupSystemValueType ("TypedReference", ElementType.TypedByRef)); }
+			get { return type_typedref ?? (LookupSystemValueType (ref type_typedref, "TypedReference", ElementType.TypedByRef)); }
 		}
 	}
 }