Use seperate cache field for the type definition

There is a risk of activator cache and generic type definition cache colliding
dotnet · jkotas · Nov 22, 2022 · Nov 13, 2022 · Nov 17, 2022 · Nov 19, 2022
commit 05afc329b61ce517d263997a77a36a579a194eaa
diff --git a/src/coreclr/System.Private.CoreLib/src/System/RuntimeHandles.cs b/src/coreclr/System.Private.CoreLib/src/System/RuntimeHandles.cs
@@ -682,24 +682,7 @@ internal RuntimeType MakePointer()
         internal static partial Interop.BOOL IsCollectible(QCallTypeHandle handle);
 
         [LibraryImport(RuntimeHelpers.QCall, EntryPoint = "RuntimeTypeHandle_GetGenericTypeDefinition")]
-        private static partial void GetGenericTypeDefinition(QCallTypeHandle type, ObjectHandleOnStack retType);
-
-        internal static RuntimeType GetGenericTypeDefinition(RuntimeType type)
-        {
-            Debug.Assert(type.IsGenericType);
-
-            return type.IsGenericTypeDefinition ? type :
-                type.GenericCache is RuntimeType genericDefinition ? genericDefinition : CacheGenericDefinition(type);
-
-            [MethodImpl(MethodImplOptions.NoInlining)]
-            static RuntimeType CacheGenericDefinition(RuntimeType type)
-            {
-                RuntimeType genericDefinition = null!;
-                GetGenericTypeDefinition(new QCallTypeHandle(ref type), ObjectHandleOnStack.Create(ref genericDefinition));
-                type.GenericCache = genericDefinition;
-                return genericDefinition;
-            }
-        }
+        internal static partial void GetGenericTypeDefinition(QCallTypeHandle type, ObjectHandleOnStack retType);
 
         [MethodImpl(MethodImplOptions.InternalCall)]
         internal static extern bool IsGenericVariable(RuntimeType type);

diff --git a/src/coreclr/System.Private.CoreLib/src/System/RuntimeType.CoreCLR.cs b/src/coreclr/System.Private.CoreLib/src/System/RuntimeType.CoreCLR.cs
@@ -1492,9 +1492,9 @@ internal T[] GetMemberList(MemberListType listType, string? name, CacheType cach
             // - Enum names and values (EnumInfo)
             // - Activator.CreateInstance (ActivatorCache)
             // - Array.Initialize (ArrayInitializeCache)
-            // - RuntimeType.GetGenericTypeDefinition (RuntimeType)
             private object? m_genericCache;
             private object[]? _emptyArray; // Object array cache for Attribute.GetCustomAttributes() pathological no-result case.
+            private RuntimeType? _genericTypeDefinition;
             #endregion
 
             #region Constructor
@@ -1648,6 +1648,29 @@ internal TypeCode TypeCode
             }
 
             internal object[] GetEmptyArray() => _emptyArray ??= (object[])Array.CreateInstance(m_runtimeType, 0);
+
+            internal RuntimeType GetGenericTypeDefinition()
+            {
+                Debug.Assert(m_runtimeType.IsGenericType);
+
+                return _genericTypeDefinition ?? CacheGenericDefinition();
+
+                [MethodImpl(MethodImplOptions.NoInlining)]
+                RuntimeType CacheGenericDefinition()
+                {
+                    RuntimeType genericDefinition = null!;
+                    if (m_runtimeType.IsGenericTypeDefinition)
+                    {
+                        genericDefinition = m_runtimeType;
+                    }
+                    else
+                    {
+                        RuntimeType type = m_runtimeType;
+                        RuntimeTypeHandle.GetGenericTypeDefinition(new QCallTypeHandle(ref type), ObjectHandleOnStack.Create(ref genericDefinition));
+                    }
+                    return _genericTypeDefinition = genericDefinition;
+                }
+            }
             #endregion
 
             #region Caches Accessors
@@ -3454,6 +3477,14 @@ public override unsafe bool IsGenericTypeDefinition
             }
         }
 
+        public override Type GetGenericTypeDefinition()
+        {
+            if (!IsGenericType)
+                throw new InvalidOperationException(SR.InvalidOperation_NotGenericType);
+
+            return Cache.GetGenericTypeDefinition();
+        }
+
         public override GenericParameterAttributes GenericParameterAttributes
         {
             get

diff --git a/src/libraries/System.Private.CoreLib/src/System/RuntimeType.cs b/src/libraries/System.Private.CoreLib/src/System/RuntimeType.cs
@@ -245,14 +245,6 @@ public override Type GetEnumUnderlyingType()
             return Enum.InternalGetUnderlyingType(this);
         }
 
-        public override Type GetGenericTypeDefinition()
-        {
-            if (!IsGenericType)
-                throw new InvalidOperationException(SR.InvalidOperation_NotGenericType);
-
-            return RuntimeTypeHandle.GetGenericTypeDefinition(this);
-        }
-
         public override int GetHashCode() => RuntimeHelpers.GetHashCode(this);
 
         internal RuntimeModule GetRuntimeModule() => RuntimeTypeHandle.GetModule(this);

@@ -1283,6 +1283,14 @@ protected override bool IsValueTypeImpl()
         public override bool IsGenericType => RuntimeTypeHandle.HasInstantiation(this);
         public override bool IsGenericTypeDefinition => RuntimeTypeHandle.IsGenericTypeDefinition(this);
 
+        public override Type GetGenericTypeDefinition()
+        {
+            if (!IsGenericType)
+                throw new InvalidOperationException(SR.InvalidOperation_NotGenericType);
+
+            return RuntimeTypeHandle.GetGenericTypeDefinition(this);
+        }
+
         public override GenericParameterAttributes GenericParameterAttributes
         {
             get