From 77ff52d21840627f99dc2312916c6dcf8cceceb8 Mon Sep 17 00:00:00 2001
From: Nikita Tsukanov <keks9n@gmail.com>
Date: Sun, 26 Jun 2022 02:30:56 +0300
Subject: [PATCH] Use a zeroed huge object instead of uninitialized one

---
 .../Composition/Server/ServerObject.cs        | 21 +++++++++++--
 .../CompositionGenerator/Generator.cs         | 31 +++++++------------
 2 files changed, 30 insertions(+), 22 deletions(-)

diff --git a/src/Avalonia.Base/Rendering/Composition/Server/ServerObject.cs b/src/Avalonia.Base/Rendering/Composition/Server/ServerObject.cs
index a2af34c7f0..4c358605fc 100644
--- a/src/Avalonia.Base/Rendering/Composition/Server/ServerObject.cs
+++ b/src/Avalonia.Base/Rendering/Composition/Server/ServerObject.cs
@@ -61,11 +61,28 @@ namespace Avalonia.Rendering.Composition.Server
         {
             
         }
+
+        [StructLayout(LayoutKind.Sequential)]
+        protected class OffsetDummy
+        {
+#pragma warning disable CS0649
+            public FillerStruct Filler;
+#pragma warning restore CS0649
+        }
         
+        [StructLayout(LayoutKind.Sequential)]
+        protected unsafe struct FillerStruct
+        {
+            public fixed byte FillerData[8192];
+        }
+
+        private static readonly object s_OffsetDummy = new OffsetDummy();
+        protected static T GetOffsetDummy<T>() where T : ServerObject => Unsafe.As<T>(s_OffsetDummy);
+
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        protected int GetOffset(ref ServerObjectSubscriptionStore field)
+        protected static int GetOffset(ServerObject obj, ref ServerObjectSubscriptionStore field)
         {
-            return Unsafe.ByteOffset(ref _activationCount,
+            return Unsafe.ByteOffset(ref obj._activationCount,
                     ref Unsafe.As<ServerObjectSubscriptionStore, uint>(ref field))
                 .ToInt32();
         }
diff --git a/src/tools/DevGenerators/CompositionGenerator/Generator.cs b/src/tools/DevGenerators/CompositionGenerator/Generator.cs
index 4df5a91c4b..0bb4e30f75 100644
--- a/src/tools/DevGenerators/CompositionGenerator/Generator.cs
+++ b/src/tools/DevGenerators/CompositionGenerator/Generator.cs
@@ -153,18 +153,10 @@ namespace Avalonia.SourceGenerator.CompositionGenerator
             );
 
             var uninitializedObjectName = "dummy";
-            var serverStaticCtorBody = cl.Abstract
-                ? Block()
-                : Block(
-                    ParseStatement(
-                        $"var dummy = ({serverName})System.Runtime.Serialization.FormatterServices.GetUninitializedObject(typeof({serverName}));"),
-                    ParseStatement($"System.GC.SuppressFinalize(dummy);"),
-                    ParseStatement("InitializeFieldOffsets(dummy);")
-                );
+            var serverStaticCtorBody = Block(
+                ParseStatement($"var dummy = GetOffsetDummy<{serverName}>();")
+            );
 
-            var initializeFieldOffsetsBody = cl.Inherits == null
-                ? Block()
-                : Block(ParseStatement($"Server{cl.Inherits}.InitializeFieldOffsets(dummy);"));
 
             var resetBody = Block();
             var startAnimationBody = Block();
@@ -294,11 +286,15 @@ namespace Avalonia.SourceGenerator.CompositionGenerator
                 serverGetFieldOffsetBody = ApplyGetProperty(serverGetFieldOffsetBody, prop, fieldOffsetName);
 
                 server = server.AddMembers(DeclareField("int", fieldOffsetName, SyntaxKind.StaticKeyword));
-                initializeFieldOffsetsBody = initializeFieldOffsetsBody.AddStatements(ExpressionStatement(
+                serverStaticCtorBody = serverStaticCtorBody.AddStatements(ExpressionStatement(
                     AssignmentExpression(SyntaxKind.SimpleAssignmentExpression, IdentifierName(fieldOffsetName),
-                        InvocationExpression(MemberAccess(IdentifierName(uninitializedObjectName), "GetOffset"),
-                            ArgumentList(SingletonSeparatedList(Argument(
-                                RefExpression(MemberAccess(MemberAccess(IdentifierName(uninitializedObjectName), fieldName), "Subscriptions")))))))));
+                        InvocationExpression(IdentifierName("GetOffset"),
+                            ArgumentList(SeparatedList(new[]
+                            {
+                                Argument(IdentifierName(uninitializedObjectName)),
+                                Argument(RefExpression(MemberAccess(
+                                    MemberAccess(IdentifierName(uninitializedObjectName), fieldName), "Subscriptions")))
+                            }))))));
                 
                 if (prop.DefaultValue != null)
                 {
@@ -312,11 +308,6 @@ namespace Avalonia.SourceGenerator.CompositionGenerator
             server = server.AddMembers(ConstructorDeclaration(serverName)
                 .WithModifiers(TokenList(Token(SyntaxKind.StaticKeyword)))
                 .WithBody(serverStaticCtorBody));
-            
-            server = server.AddMembers(
-                ((MethodDeclarationSyntax)ParseMemberDeclaration(
-                    $"protected static void InitializeFieldOffsets({serverName} dummy){{}}")!)
-                .WithBody(initializeFieldOffsetsBody));
 
             server = server
                 .AddMembers(((MethodDeclarationSyntax)ParseMemberDeclaration(