C#: Ensure native handles are freed after switch to .NET Core

Finalizers are longer guaranteed to be called on exit now that
we switched to .NET Core. This results in native instances leaking.

The only solution I can think of so far is to keep a list of all
instances alive to dispose when the AssemblyLoadContext.Unloading
event is raised.

modules/mono/csharp_script.cpp

@@ -1581,6 +1581,7 @@ void CSharpLanguage::tie_managed_to_unmanaged_with_pre_setup(GCHandleIntPtr p_gc
 	CSharpInstance *instance = CAST_CSHARP_INSTANCE(p_unmanaged->get_script_instance());
 
 	if (!instance) {
+		// Native bindings don't need post-setup
 		return;
 	}
 

modules/mono/editor/bindings_generator.cpp

@@ -75,6 +75,10 @@ StringBuilder &operator<<(StringBuilder &r_sb, const char *p_cstring) {
 #define CLOSE_BLOCK_L3 INDENT3 CLOSE_BLOCK
 #define CLOSE_BLOCK_L4 INDENT4 CLOSE_BLOCK
 
+#define BINDINGS_GLOBAL_SCOPE_CLASS "GD"
+#define BINDINGS_PTR_FIELD "NativePtr"
+#define BINDINGS_NATIVE_NAME_FIELD "NativeName"
+
 #define CS_PARAM_MEMORYOWN "memoryOwn"
 #define CS_PARAM_METHODBIND "method"
 #define CS_PARAM_INSTANCE "ptr"

modules/mono/glue/GodotSharp/GodotSharp/Core/Array.cs

@@ -13,16 +13,21 @@ namespace Godot.Collections
     /// interfacing with the engine. Otherwise prefer .NET collections
     /// such as <see cref="System.Array"/> or <see cref="List{T}"/>.
     /// </summary>
-    public sealed class Array : IList, IDisposable
+    public sealed class Array :
+        IList,
+        IDisposable
     {
         internal godot_array.movable NativeValue;
 
+        private WeakReference<IDisposable> _weakReferenceToSelf;
+
         /// <summary>
         /// Constructs a new empty <see cref="Array"/>.
         /// </summary>
         public Array()
         {
             NativeValue = (godot_array.movable)NativeFuncs.godotsharp_array_new();
+            _weakReferenceToSelf = DisposablesTracker.RegisterDisposable(this);
         }
 
         /// <summary>
@@ -51,6 +56,8 @@ namespace Godot.Collections
                 throw new ArgumentNullException(nameof(array));
 
             NativeValue = (godot_array.movable)NativeFuncs.godotsharp_array_new();
+            _weakReferenceToSelf = DisposablesTracker.RegisterDisposable(this);
+
             int length = array.Length;
 
             Resize(length);
@@ -64,6 +71,7 @@ namespace Godot.Collections
             NativeValue = (godot_array.movable)(nativeValueToOwn.IsAllocated ?
                 nativeValueToOwn :
                 NativeFuncs.godotsharp_array_new());
+            _weakReferenceToSelf = DisposablesTracker.RegisterDisposable(this);
         }
 
         // Explicit name to make it very clear
@@ -88,6 +96,7 @@ namespace Godot.Collections
         {
             // Always dispose `NativeValue` even if disposing is true
             NativeValue.DangerousSelfRef.Dispose();
+            DisposablesTracker.UnregisterDisposable(_weakReferenceToSelf);
         }
 
         /// <summary>

modules/mono/glue/GodotSharp/GodotSharp/Core/Bridge/ManagedCallbacks.cs

@@ -33,6 +33,7 @@ namespace Godot.Bridge
         public delegate* unmanaged<IntPtr, void> GCHandleBridge_FreeGCHandle;
         public delegate* unmanaged<void> DebuggingUtils_InstallTraceListener;
         public delegate* unmanaged<void> Dispatcher_InitializeDefaultGodotTaskScheduler;
+        public delegate* unmanaged<void> DisposablesTracker_OnGodotShuttingDown;
         // @formatter:on
 
         public static ManagedCallbacks Create()
@@ -65,6 +66,7 @@ namespace Godot.Bridge
                 GCHandleBridge_FreeGCHandle = &GCHandleBridge.FreeGCHandle,
                 DebuggingUtils_InstallTraceListener = &DebuggingUtils.InstallTraceListener,
                 Dispatcher_InitializeDefaultGodotTaskScheduler = &Dispatcher.InitializeDefaultGodotTaskScheduler,
+                DisposablesTracker_OnGodotShuttingDown = &DisposablesTracker.OnGodotShuttingDown,
                 // @formatter:on
             };
         }

modules/mono/glue/GodotSharp/GodotSharp/Core/Bridge/ScriptManagerBridge.cs

@@ -44,16 +44,19 @@ namespace Godot.Bridge
         internal static unsafe IntPtr CreateManagedForGodotObjectBinding(godot_string_name* nativeTypeName,
             IntPtr godotObject)
         {
+            // TODO: Optimize with source generators and delegate pointers
+
             try
             {
                 Type nativeType = TypeGetProxyClass(nativeTypeName);
                 var obj = (Object)FormatterServices.GetUninitializedObject(nativeType);
 
-                obj.NativePtr = godotObject;
-
                 var ctor = nativeType.GetConstructor(
                     BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance,
                     null, Type.EmptyTypes, null);
+
+                obj.NativePtr = godotObject;
+
                 _ = ctor!.Invoke(obj, null);
 
                 return GCHandle.ToIntPtr(GCHandle.Alloc(obj));
@@ -70,14 +73,14 @@ namespace Godot.Bridge
             IntPtr godotObject,
             godot_variant** args, int argCount)
         {
+            // TODO: Optimize with source generators and delegate pointers
+
             try
             {
                 // Performance is not critical here as this will be replaced with source generators.
                 Type scriptType = _scriptBridgeMap[scriptPtr];
                 var obj = (Object)FormatterServices.GetUninitializedObject(scriptType);
 
-                obj.NativePtr = godotObject;
-
                 var ctor = scriptType
                     .GetConstructors(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance)
                     .Where(c => c.GetParameters().Length == argCount)
@@ -108,7 +111,11 @@ namespace Godot.Bridge
                         *args[i], parameters[i].ParameterType);
                 }
 
-                ctor.Invoke(obj, invokeParams);
+                obj.NativePtr = godotObject;
+
+                _ = ctor.Invoke(obj, invokeParams);
+
+
                 return true.ToGodotBool();
             }
             catch (Exception e)

modules/mono/glue/GodotSharp/GodotSharp/Core/Dictionary.cs

@@ -18,12 +18,15 @@ namespace Godot.Collections
     {
         internal godot_dictionary.movable NativeValue;
 
+        private WeakReference<IDisposable> _weakReferenceToSelf;
+
         /// <summary>
         /// Constructs a new empty <see cref="Dictionary"/>.
         /// </summary>
         public Dictionary()
         {
             NativeValue = (godot_dictionary.movable)NativeFuncs.godotsharp_dictionary_new();
+            _weakReferenceToSelf = DisposablesTracker.RegisterDisposable(this);
         }
 
         /// <summary>
@@ -45,6 +48,7 @@ namespace Godot.Collections
             NativeValue = (godot_dictionary.movable)(nativeValueToOwn.IsAllocated ?
                 nativeValueToOwn :
                 NativeFuncs.godotsharp_dictionary_new());
+            _weakReferenceToSelf = DisposablesTracker.RegisterDisposable(this);
         }
 
         // Explicit name to make it very clear
@@ -69,6 +73,7 @@ namespace Godot.Collections
         {
             // Always dispose `NativeValue` even if disposing is true
             NativeValue.DangerousSelfRef.Dispose();
+            DisposablesTracker.UnregisterDisposable(_weakReferenceToSelf);
         }
 
         /// <summary>

modules/mono/glue/GodotSharp/GodotSharp/Core/DisposablesTracker.cs

@@ -0,0 +1,101 @@
+using System;
+using System.Collections.Concurrent;
+using System.Runtime.InteropServices;
+using System.Runtime.Loader;
+using Godot.NativeInterop;
+
+#nullable enable
+
+namespace Godot
+{
+    internal static class DisposablesTracker
+    {
+        static DisposablesTracker()
+        {
+            AssemblyLoadContext.Default.Unloading += _ => OnUnloading();
+        }
+
+        [UnmanagedCallersOnly]
+        internal static void OnGodotShuttingDown()
+        {
+            try
+            {
+                OnUnloading();
+            }
+            catch (Exception e)
+            {
+                ExceptionUtils.DebugUnhandledException(e);
+            }
+        }
+
+        private static void OnUnloading()
+        {
+            bool isStdoutVerbose;
+
+            try
+            {
+                isStdoutVerbose = OS.IsStdoutVerbose();
+            }
+            catch (ObjectDisposedException)
+            {
+                // OS singleton already disposed. Maybe OnUnloading was called twice.
+                isStdoutVerbose = false;
+            }
+
+            if (isStdoutVerbose)
+                GD.Print("Unloading: Disposing tracked instances...");
+
+            // Dispose Godot Objects first, and only then dispose other disposables
+            // like StringName, NodePath, Godot.Collections.Array/Dictionary, etc.
+            // The Godot Object Dispose() method may need any of the later instances.
+
+            foreach (WeakReference<Object> item in GodotObjectInstances.Keys)
+            {
+                if (item.TryGetTarget(out Object? self))
+                    self.Dispose();
+            }
+
+            foreach (WeakReference<IDisposable> item in OtherInstances.Keys)
+            {
+                if (item.TryGetTarget(out IDisposable? self))
+                    self.Dispose();
+            }
+
+            if (isStdoutVerbose)
+                GD.Print("Unloading: Finished disposing tracked instances.");
+        }
+
+        // ReSharper disable once RedundantNameQualifier
+        private static ConcurrentDictionary<WeakReference<Godot.Object>, object?> GodotObjectInstances { get; } =
+            new();
+
+        private static ConcurrentDictionary<WeakReference<IDisposable>, object?> OtherInstances { get; } =
+            new();
+
+        public static WeakReference<Object> RegisterGodotObject(Object godotObject)
+        {
+            var weakReferenceToSelf = new WeakReference<Object>(godotObject);
+            GodotObjectInstances.TryAdd(weakReferenceToSelf, null);
+            return weakReferenceToSelf;
+        }
+
+        public static WeakReference<IDisposable> RegisterDisposable(IDisposable disposable)
+        {
+            var weakReferenceToSelf = new WeakReference<IDisposable>(disposable);
+            OtherInstances.TryAdd(weakReferenceToSelf, null);
+            return weakReferenceToSelf;
+        }
+
+        public static void UnregisterGodotObject(WeakReference<Object> weakReference)
+        {
+            if (!GodotObjectInstances.TryRemove(weakReference, out _))
+                throw new ArgumentException("Godot Object not registered", nameof(weakReference));
+        }
+
+        public static void UnregisterDisposable(WeakReference<IDisposable> weakReference)
+        {
+            if (!OtherInstances.TryRemove(weakReference, out _))
+                throw new ArgumentException("Disposable not registered", nameof(weakReference));
+        }
+    }
+}

modules/mono/glue/GodotSharp/GodotSharp/Core/NodePath.cs

@@ -43,6 +43,8 @@ namespace Godot
     {
         internal godot_node_path.movable NativeValue;
 
+        private WeakReference<IDisposable> _weakReferenceToSelf;
+
         ~NodePath()
         {
             Dispose(false);
@@ -61,11 +63,13 @@ namespace Godot
         {
             // Always dispose `NativeValue` even if disposing is true
             NativeValue.DangerousSelfRef.Dispose();
+            DisposablesTracker.UnregisterDisposable(_weakReferenceToSelf);
         }
 
         private NodePath(godot_node_path nativeValueToOwn)
         {
             NativeValue = (godot_node_path.movable)nativeValueToOwn;
+            _weakReferenceToSelf = DisposablesTracker.RegisterDisposable(this);
         }
 
         // Explicit name to make it very clear
@@ -111,7 +115,10 @@ namespace Godot
         public NodePath(string path)
         {
             if (!string.IsNullOrEmpty(path))
+            {
                 NativeValue = (godot_node_path.movable)NativeFuncs.godotsharp_node_path_new_from_string(path);
+                _weakReferenceToSelf = DisposablesTracker.RegisterDisposable(this);
+            }
         }
 
         /// <summary>

modules/mono/glue/GodotSharp/GodotSharp/Core/Object.base.cs

@@ -11,7 +11,9 @@ namespace Godot
         private Type _cachedType = typeof(Object);
 
         internal IntPtr NativePtr;
-        internal bool MemoryOwn;
+        private bool _memoryOwn;
+
+        private WeakReference<Object> _weakReferenceToSelf;
 
         /// <summary>
         /// Constructs a new <see cref="Object"/>.
@@ -34,6 +36,8 @@ namespace Godot
                     GetType(), _cachedType);
             }
 
+            _weakReferenceToSelf = DisposablesTracker.RegisterGodotObject(this);
+
             _InitializeGodotScriptInstanceInternals();
         }
 
@@ -61,7 +65,7 @@ namespace Godot
 
         internal Object(bool memoryOwn)
         {
-            MemoryOwn = memoryOwn;
+            _memoryOwn = memoryOwn;
         }
 
         /// <summary>
@@ -74,7 +78,12 @@ namespace Godot
             if (instance == null)
                 return IntPtr.Zero;
 
-            if (instance._disposed)
+            // We check if NativePtr is null because this may be called by the debugger.
+            // If the debugger puts a breakpoint in one of the base constructors, before
+            // NativePtr is assigned, that would result in UB or crashes when calling
+            // native functions that receive the pointer, which can happen because the
+            // debugger calls ToString() and tries to get the value of properties.
+            if (instance._disposed || instance.NativePtr == IntPtr.Zero)
                 throw new ObjectDisposedException(instance.GetType().FullName);
 
             return instance.NativePtr;
@@ -104,9 +113,8 @@ namespace Godot
 
             if (NativePtr != IntPtr.Zero)
             {
-                if (MemoryOwn)
+                if (_memoryOwn)
                 {
-                    MemoryOwn = false;
                     NativeFuncs.godotsharp_internal_refcounted_disposed(NativePtr, (!disposing).ToGodotBool());
                 }
                 else
@@ -117,6 +125,8 @@ namespace Godot
                 NativePtr = IntPtr.Zero;
             }
 
+            DisposablesTracker.UnregisterGodotObject(_weakReferenceToSelf);
+
             _disposed = true;
         }
 

modules/mono/glue/GodotSharp/GodotSharp/Core/StringName.cs

@@ -14,6 +14,8 @@ namespace Godot
     {
         internal godot_string_name.movable NativeValue;
 
+        private WeakReference<IDisposable> _weakReferenceToSelf;
+
         ~StringName()
         {
             Dispose(false);
@@ -32,11 +34,13 @@ namespace Godot
         {
             // Always dispose `NativeValue` even if disposing is true
             NativeValue.DangerousSelfRef.Dispose();
+            DisposablesTracker.UnregisterDisposable(_weakReferenceToSelf);
         }
 
         private StringName(godot_string_name nativeValueToOwn)
         {
             NativeValue = (godot_string_name.movable)nativeValueToOwn;
+            _weakReferenceToSelf = DisposablesTracker.RegisterDisposable(this);
         }
 
         // Explicit name to make it very clear
@@ -57,7 +61,10 @@ namespace Godot
         public StringName(string name)
         {
             if (!string.IsNullOrEmpty(name))
+            {
                 NativeValue = (godot_string_name.movable)NativeFuncs.godotsharp_string_name_new_from_string(name);
+                _weakReferenceToSelf = DisposablesTracker.RegisterDisposable(this);
+            }
         }
 
         /// <summary>
@@ -138,5 +145,15 @@ namespace Godot
         {
             return NativeValue.DangerousSelfRef == other;
         }
+
+        public override bool Equals(object obj)
+        {
+            return ReferenceEquals(this, obj) || (obj is StringName other && Equals(other));
+        }
+
+        public override int GetHashCode()
+        {
+            return NativeValue.GetHashCode();
+        }
     }
 }

modules/mono/glue/GodotSharp/GodotSharp/GodotSharp.csproj

@@ -60,6 +60,7 @@
     <Compile Include="Core\GodotTaskScheduler.cs" />
     <Compile Include="Core\GodotTraceListener.cs" />
     <Compile Include="Core\GodotUnhandledExceptionEvent.cs" />
+    <Compile Include="Core\DisposablesTracker.cs" />
     <Compile Include="Core\Interfaces\IAwaitable.cs" />
     <Compile Include="Core\Interfaces\IAwaiter.cs" />
     <Compile Include="Core\Interfaces\ISerializationListener.cs" />

modules/mono/godotsharp_defs.h

@@ -33,15 +33,10 @@
 
 #define BINDINGS_NAMESPACE "Godot"
 #define BINDINGS_NAMESPACE_COLLECTIONS BINDINGS_NAMESPACE ".Collections"
-#define BINDINGS_NAMESPACE_BRIDGE BINDINGS_NAMESPACE ".Bridge"
-#define BINDINGS_GLOBAL_SCOPE_CLASS "GD"
-#define BINDINGS_PTR_FIELD "NativePtr"
-#define BINDINGS_NATIVE_NAME_FIELD "NativeName"
 #define API_SOLUTION_NAME "GodotSharp"
 #define CORE_API_ASSEMBLY_NAME "GodotSharp"
 #define EDITOR_API_ASSEMBLY_NAME "GodotSharpEditor"
 #define TOOLS_ASM_NAME "GodotTools"
-#define TOOLS_PROJECT_EDITOR_ASM_NAME "GodotTools.ProjectEditor"
 
 #define BINDINGS_CLASS_NATIVECALLS "NativeCalls"
 #define BINDINGS_CLASS_NATIVECALLS_EDITOR "EditorNativeCalls"

modules/mono/mono_gd/gd_mono.cpp

@@ -471,26 +471,17 @@ GDMono::GDMono() {
 }
 
 GDMono::~GDMono() {
+	finalizing_scripts_domain = true;
+
 	if (is_runtime_initialized()) {
-#warning "TODO assembly unloading for cleanup of disposables (including managed RefCounteds)"
-#if 0
-		if (scripts_domain) {
-			Error err = _unload_scripts_domain();
-			if (err != OK) {
-				ERR_PRINT("Mono: Failed to unload scripts domain.");
-			}
+		if (GDMonoCache::godot_api_cache_updated) {
+			GDMonoCache::managed_callbacks.DisposablesTracker_OnGodotShuttingDown();
 		}
-
-		print_verbose("Mono: Runtime cleanup...");
-
-		mono_jit_cleanup(root_domain);
-
-		print_verbose("Mono: Finalized");
-#endif
-
-		runtime_initialized = false;
 	}
 
+	finalizing_scripts_domain = false;
+	runtime_initialized = false;
+
 #if defined(ANDROID_ENABLED)
 	gdmono::android::support::cleanup();
 #endif

modules/mono/mono_gd/gd_mono_cache.cpp

@@ -68,6 +68,7 @@ void update_godot_api_cache(const ManagedCallbacks &p_managed_callbacks) {
 	CHECK_CALLBACK_NOT_NULL(GCHandleBridge, FreeGCHandle);
 	CHECK_CALLBACK_NOT_NULL(DebuggingUtils, InstallTraceListener);
 	CHECK_CALLBACK_NOT_NULL(Dispatcher, InitializeDefaultGodotTaskScheduler);
+	CHECK_CALLBACK_NOT_NULL(DisposablesTracker, OnGodotShuttingDown);
 
 	managed_callbacks = p_managed_callbacks;
 

modules/mono/mono_gd/gd_mono_cache.h

@@ -78,6 +78,7 @@ struct ManagedCallbacks {
 	using FuncGCHandleBridge_FreeGCHandle = void(GD_CLR_STDCALL *)(GCHandleIntPtr);
 	using FuncDebuggingUtils_InstallTraceListener = void(GD_CLR_STDCALL *)();
 	using FuncDispatcher_InitializeDefaultGodotTaskScheduler = void(GD_CLR_STDCALL *)();
+	using FuncDisposablesTracker_OnGodotShuttingDown = void(GD_CLR_STDCALL *)();
 
 	FuncSignalAwaiter_SignalCallback SignalAwaiter_SignalCallback;
 	FuncDelegateUtils_InvokeWithVariantArgs DelegateUtils_InvokeWithVariantArgs;
@@ -104,6 +105,7 @@ struct ManagedCallbacks {
 	FuncGCHandleBridge_FreeGCHandle GCHandleBridge_FreeGCHandle;
 	FuncDebuggingUtils_InstallTraceListener DebuggingUtils_InstallTraceListener;
 	FuncDispatcher_InitializeDefaultGodotTaskScheduler Dispatcher_InitializeDefaultGodotTaskScheduler;
+	FuncDisposablesTracker_OnGodotShuttingDown DisposablesTracker_OnGodotShuttingDown;
 };
 
 extern ManagedCallbacks managed_callbacks;