Merge pull request #391 from nuskey8/codex/memory-safety-fixes

Fix runtime memory lifetimes and validate loaded bytecode

Author: akeit0

README.md

@@ -537,6 +537,8 @@ print(v1 - v2) -- <-1, -1, -1>
 > [!NOTE]  
 > `__index` and `__newindex` cannot be set as they are used internally by the code generated by `[LuaObject]`.
 
+Generated default metatables are immutable and shared by all instances of the same C# type, across Lua states. You can still assign writable C# members from Lua. To customize an individual object's metatable, replace `ILuaUserData.Metatable` in C# or use `debug.setmetatable` in Lua; replacement tables remain mutable. Ordinary Lua tables and metatables remain mutable.
+
 ## Module Loading
 
 In Lua, you can load modules using the `require` function. In regular Lua, modules are managed by searchers within the `package.searchers` function list. In addition to this, Lua-CSharp provides `ILuaModuleLoader` as a module loading mechanism.

sandbox/Benchmark/Benchmark.csproj

@@ -15,6 +15,12 @@
 
   <ItemGroup>
     <ProjectReference Include="..\..\src\Lua\Lua.csproj" />
+    <ProjectReference Include="..\..\src\Lua.Annotations\Lua.Annotations.csproj" />
+    <ProjectReference
+      Include="..\..\src\Lua.SourceGenerator\Lua.SourceGenerator.csproj"
+      OutputItemType="Analyzer"
+      ReferenceOutputAssembly="false"
+    />
   </ItemGroup>
 
   <ItemGroup>

sandbox/Benchmark/CoroutineTransferBenchmark.cs

@@ -0,0 +1,61 @@
+using BenchmarkDotNet.Attributes;
+using Lua;
+using Lua.Runtime;
+using Lua.Standard;
+
+[Config(typeof(ComparisonConfig))]
+public class CoroutineTransferBenchmark
+{
+    [Params("resume", "wrap")]
+    public string Operation { get; set; } = "resume";
+
+    [Params(1, 64, 4096)]
+    public int ResultCount { get; set; }
+
+    [Params(false, true)]
+    public bool Cancellable { get; set; }
+
+    LuaState state = default!;
+    LuaClosure closure = default!;
+    CancellationTokenSource cancellation = default!;
+
+    [GlobalSetup]
+    public void Setup()
+    {
+        state = LuaState.Create();
+        state.OpenStandardLibraries();
+        cancellation = new();
+        state.Environment["packet"] = new LuaFunction(
+            (context, _) =>
+            {
+                context.GetReturnBuffer(ResultCount).Fill(42);
+                return new(ResultCount);
+            }
+        );
+        closure = state.Load(
+            Operation == "wrap"
+                ? "local run=coroutine.wrap(function() for i=1,64 do coroutine.yield(packet()) end end); for i=1,64 do run() end; run(); return 42"
+                : "local co=coroutine.create(function() for i=1,64 do coroutine.yield(packet()) end end); for i=1,64 do coroutine.resume(co) end; coroutine.resume(co); return 42",
+            "coroutine-transfer"
+        );
+        if (Run() != 42)
+            throw new InvalidOperationException("Unexpected coroutine transfer result");
+    }
+
+    [Benchmark(OperationsPerInvoke = 64)]
+    public int Run()
+    {
+        state
+            .RunAsync(closure, 0, Cancellable ? cancellation.Token : default)
+            .GetAwaiter()
+            .GetResult();
+        return state.Stack.Pop().Read<int>();
+    }
+
+    [GlobalCleanup]
+    public void Cleanup()
+    {
+        cancellation.Dispose();
+        state.Dispose();
+    }
+}

sandbox/Benchmark/GeneratedUserDataBenchmark.cs

@@ -0,0 +1,71 @@
+using BenchmarkDotNet.Attributes;
+using Lua;
+using Lua.Runtime;
+
+[Config(typeof(ComparisonConfig))]
+public class GeneratedUserDataBenchmark
+{
+    [Params("field", "method", "comparison", "write")]
+    public string Case { get; set; } = "field";
+
+    [Params(false, true)]
+    public bool OverrideMetatable { get; set; }
+
+    LuaState state = default!;
+    LuaClosure closure = default!;
+
+    [GlobalSetup]
+    public void Setup()
+    {
+        state = LuaState.Create();
+        var first = new GeneratedBenchmarkObject { Value = 7 };
+        var second = new GeneratedBenchmarkObject { Value = 8 };
+        if (OverrideMetatable)
+        {
+            ILuaUserData left = first;
+            ILuaUserData right = second;
+            left.Metatable = left.Metatable;
+            right.Metatable = right.Metatable;
+        }
+        state.Environment["first"] = first;
+        state.Environment["second"] = second;
+        var (source, expected) = Case switch
+        {
+            "field" => ("local v=first;local n=0;for i=1,1000 do n=n+v.Value end;return n", 7000),
+            "method" => ("local v=first;local n=0;for i=1,1000 do n=n+v:Add(1) end;return n", 8000),
+            "comparison" => (
+                "local a,b=first,second;local n=0;for i=1,1000 do if a<b then n=n+1 end end;return n",
+                1000
+            ),
+            "write" => ("local v=first;for i=1,1000 do v.Value=i end;return v.Value", 1000),
+            _ => throw new ArgumentOutOfRangeException(nameof(Case)),
+        };
+        closure = state.Load(source, Case);
+        if (Run() != expected)
+            throw new InvalidOperationException($"Unexpected result for {Case}");
+    }
+
+    [Benchmark(OperationsPerInvoke = 1000)]
+    public int Run()
+    {
+        state.RunAsync(closure).GetAwaiter().GetResult();
+        return state.Stack.Pop().Read<int>();
+    }
+
+    [GlobalCleanup]
+    public void Cleanup() => state.Dispose();
+}
+
+[LuaObject]
+public partial class GeneratedBenchmarkObject
+{
+    [LuaMember]
+    public int Value { get; set; }
+
+    [LuaMember]
+    public int Add(int value) => Value + value;
+
+    [LuaMetamethod(LuaObjectMetamethod.Lt)]
+    public static bool Less(GeneratedBenchmarkObject left, GeneratedBenchmarkObject right) =>
+        left.Value < right.Value;
+}

sandbox/Benchmark/Program.cs

@@ -29,6 +29,8 @@
             typeof(InterpreterComparison),
             typeof(CompilationComparison),
             typeof(StartupComparison),
+            typeof(GeneratedUserDataBenchmark),
+            typeof(CoroutineTransferBenchmark),
         ])
         .Run(args);
 

sandbox/Benchmark/README.md

@@ -25,6 +25,8 @@ measure Unicode encoding or arbitrary binary strings.
 | `InterpreterComparison` | Execute a retained compiled chunk and read one numeric result | Numeric loops, Lua calls/varargs, table access/sort, metamethods, math, strings, patterns, coroutines, host callbacks, n-body |
 | `CompilationComparison` | Compile source in an existing state; no execution | Small loop, n-body, control flow, identifiers, plain strings, escaped strings |
 | `StartupComparison` | Create a state, open libraries, dispose where supported | One lifecycle per engine |
+| `GeneratedUserDataBenchmark` | Execute 1,000 generated C# member accesses or comparisons; report time per operation | Property reads/writes, method calls, comparisons, with default and explicitly replaced metatables |
+| `CoroutineTransferBenchmark` | Transfer 64 yielded packets; report time per transfer | `resume` and `wrap`, 1–4,096 results per packet, with and without cancellation |
 
 Only the engine being measured is initialized for a benchmark. Execution
 excludes source compilation and state setup. Scripts rebuild their mutable
@@ -52,6 +54,8 @@ equivalent deterministic disposal API.
 dotnet bin/Release/net10.0/Benchmark.dll --filter '*InterpreterComparison*host-calls*'
 dotnet bin/Release/net10.0/Benchmark.dll --filter '*CompilationComparison*'
 dotnet bin/Release/net10.0/Benchmark.dll --filter '*StartupComparison*'
+dotnet bin/Release/net10.0/Benchmark.dll --filter '*GeneratedUserDataBenchmark*'
+dotnet bin/Release/net10.0/Benchmark.dll --filter '*CoroutineTransferBenchmark*'
 dotnet bin/Release/net10.0/Benchmark.dll --legacy --filter '*GSubBenchmark*'
 ```
 

src/Lua.SourceGenerator/LuaObjectGenerator.Emit.cs

@@ -236,10 +236,7 @@ TempCollections tempCollections
 
             metamethodSet.Add(LuaObjectMetamethod.NewIndex);
 
-            if (!TryEmitMetatable(builder, metamethodSet, context))
-            {
-                return false;
-            }
+            EmitMetatable(builder, metamethodSet);
 
             // implicit operator
             builder.AppendLine(
@@ -1342,62 +1339,74 @@ static void EmitMethodFunctionBody(
         }
     }
 
-    static bool TryEmitMetatable(
-        CodeBuilder builder,
-        IEnumerable<LuaObjectMetamethod> metamethods,
-        in SourceProductionContext context
-    )
+    static void EmitMetatable(CodeBuilder builder, IEnumerable<LuaObjectMetamethod> metamethods)
     {
         builder.AppendLine("global::Lua.LuaTable? global::Lua.ILuaUserData.Metatable");
         using (builder.BeginBlockScope())
-        {
-            builder.AppendLine("get => Metatable;");
-            builder.AppendLine("set => Metatable = value;");
-        }
-        builder.AppendLine("static global::Lua.LuaTable? Metatable");
-        using (builder.BeginBlockScope())
         {
             builder.AppendLine("get");
             using (builder.BeginBlockScope())
             {
                 builder.AppendLine(
-                    "var metatable = global::System.Threading.Volatile.Read(ref __metatable);"
-                );
-                builder.AppendLine("if (metatable != null) return metatable;");
-                builder.AppendLine();
-                builder.AppendLine("metatable = new();");
-                foreach (var metamethod in metamethods)
-                {
-                    var metaMethodName = metamethod.ToString();
-                    var lowerName = metaMethodName.ToLower();
-                    builder.AppendLine(
-                        $"metatable[global::Lua.Runtime.Metamethods.{metaMethodName}] = __metamethod_{lowerName};"
-                    );
-                }
-
-                builder.AppendLine(
-                    "// Publish only a complete table. Concurrent readers share the winning instance,"
+                    "var overrides = global::System.Threading.Volatile.Read(ref __metatableOverrides);"
                 );
                 builder.AppendLine(
-                    "// including a custom metatable installed while initialization was in progress."
+                    "return overrides != null && overrides.TryGetValue(this, out var entry) ? entry.Value : __metatable;"
                 );
+            }
+            builder.AppendLine("set");
+            using (builder.BeginBlockScope())
+            {
                 builder.AppendLine(
-                    "return global::System.Threading.Interlocked.CompareExchange(ref __metatable, metatable, null) ?? metatable;"
+                    "__GetMetatableOverrides().GetValue(this, _ => new __MetatableOverride(value)).Value = value;"
                 );
             }
+        }
 
-            builder.AppendLine("set");
-            using (builder.BeginBlockScope())
+        builder.AppendLine("static global::Lua.LuaTable __CreateMetatable()");
+        using (builder.BeginBlockScope())
+        {
+            builder.AppendLine("var metatable = new global::Lua.LuaTable();");
+            foreach (var metamethod in metamethods)
             {
+                var metaMethodName = metamethod.ToString();
+                var lowerName = metaMethodName.ToLower();
                 builder.AppendLine(
-                    "global::System.Threading.Volatile.Write(ref __metatable, value);"
+                    $"metatable[global::Lua.Runtime.Metamethods.{metaMethodName}] = __metamethod_{lowerName};"
                 );
             }
+            builder.AppendLine("metatable.Freeze();");
+            builder.AppendLine("return metatable;");
         }
 
-        builder.AppendLine("static global::Lua.LuaTable? __metatable;");
+        builder.AppendLine("sealed class __MetatableOverride");
+        using (builder.BeginBlockScope())
+        {
+            builder.AppendLine("public volatile global::Lua.LuaTable? Value;");
+            builder.AppendLine(
+                "public __MetatableOverride(global::Lua.LuaTable? value) => Value = value;"
+            );
+        }
+        builder.AppendLine(
+            "static global::System.Runtime.CompilerServices.ConditionalWeakTable<object, __MetatableOverride>? __metatableOverrides;"
+        );
+        builder.AppendLine(
+            "static global::System.Runtime.CompilerServices.ConditionalWeakTable<object, __MetatableOverride> __GetMetatableOverrides()"
+        );
+        using (builder.BeginBlockScope())
+        {
+            builder.AppendLine(
+                "var overrides = global::System.Threading.Volatile.Read(ref __metatableOverrides);"
+            );
+            builder.AppendLine("if (overrides != null) return overrides;");
+            builder.AppendLine("overrides = new();");
+            builder.AppendLine(
+                "return global::System.Threading.Interlocked.CompareExchange(ref __metatableOverrides, overrides, null) ?? overrides;"
+            );
+        }
+        builder.AppendLine(
+            "static readonly global::Lua.LuaTable __metatable = __CreateMetatable();"
+        );
         builder.AppendLine();
-
-        return true;
     }
 }