Mono/C#: Optimize the way we store GC handles for scripts

Don't store GC handles for C# script instances and instance bindings as 'Ref<MonoGCHandle>'; store the raw data instead. Initially this was not possible as we needed to store a Variant, but this had not been the case for a looong time yet the stored type was never updated.

modules/mono/csharp_script.cpp

@@ -150,8 +150,8 @@ void CSharpLanguage::finish() {
 	for (Map<Object *, CSharpScriptBinding>::Element *E = script_bindings.front(); E; E = E->next()) {
 		CSharpScriptBinding &script_binding = E->value();
 
-		if (script_binding.gchandle.is_valid()) {
-			script_binding.gchandle->release();
+		if (!script_binding.gchandle.is_released()) {
+			script_binding.gchandle.release();
 			script_binding.inited = false;
 		}
 	}
@@ -676,7 +676,7 @@ void CSharpLanguage::pre_unsafe_unreference(Object *p_obj) {
 void CSharpLanguage::frame() {
 
 	if (gdmono && gdmono->is_runtime_initialized() && gdmono->get_core_api_assembly() != NULL) {
-		const Ref<MonoGCHandle> &task_scheduler_handle = GDMonoCache::cached_data.task_scheduler_handle;
+		const Ref<MonoGCHandleRef> &task_scheduler_handle = GDMonoCache::cached_data.task_scheduler_handle;
 
 		if (task_scheduler_handle.is_valid()) {
 			MonoObject *task_scheduler = task_scheduler_handle->get_target();
@@ -804,7 +804,7 @@ void CSharpLanguage::reload_assemblies(bool p_soft_reload) {
 		for (SelfList<ManagedCallable> *elem = ManagedCallable::instances.first(); elem; elem = elem->next()) {
 			ManagedCallable *managed_callable = elem->self();
 
-			MonoDelegate *delegate = (MonoDelegate *)managed_callable->delegate_handle->get_target();
+			MonoDelegate *delegate = (MonoDelegate *)managed_callable->delegate_handle.get_target();
 
 			Array serialized_data;
 			MonoObject *managed_serialized_data = GDMonoMarshal::variant_to_mono_object(serialized_data);
@@ -1278,6 +1278,7 @@ bool CSharpLanguage::debug_break(const String &p_error, bool p_allow_continue) {
 void CSharpLanguage::_on_scripts_domain_unloaded() {
 	for (Map<Object *, CSharpScriptBinding>::Element *E = script_bindings.front(); E; E = E->next()) {
 		CSharpScriptBinding &script_binding = E->value();
+		script_binding.gchandle.release();
 		script_binding.inited = false;
 	}
 
@@ -1286,7 +1287,7 @@ void CSharpLanguage::_on_scripts_domain_unloaded() {
 
 		for (SelfList<ManagedCallable> *elem = ManagedCallable::instances.first(); elem; elem = elem->next()) {
 			ManagedCallable *managed_callable = elem->self();
-			managed_callable->delegate_handle.unref();
+			managed_callable->delegate_handle.release();
 			managed_callable->delegate_invoke = NULL;
 		}
 	}
@@ -1328,33 +1329,33 @@ void CSharpLanguage::set_language_index(int p_idx) {
 	lang_idx = p_idx;
 }
 
-void CSharpLanguage::release_script_gchandle(Ref<MonoGCHandle> &p_gchandle) {
+void CSharpLanguage::release_script_gchandle(MonoGCHandleData &p_gchandle) {
 
-	if (!p_gchandle->is_released()) { // Do not lock unnecessarily
+	if (!p_gchandle.is_released()) { // Do not lock unnecessarily
 		MutexLock lock(get_singleton()->script_gchandle_release_mutex);
-		p_gchandle->release();
+		p_gchandle.release();
 	}
 }
 
-void CSharpLanguage::release_script_gchandle(MonoObject *p_expected_obj, Ref<MonoGCHandle> &p_gchandle) {
+void CSharpLanguage::release_script_gchandle(MonoObject *p_expected_obj, MonoGCHandleData &p_gchandle) {
 
-	uint32_t pinned_gchandle = MonoGCHandle::new_strong_handle_pinned(p_expected_obj); // We might lock after this, so pin it
+	uint32_t pinned_gchandle = GDMonoUtils::new_strong_gchandle_pinned(p_expected_obj); // We might lock after this, so pin it
 
-	if (!p_gchandle->is_released()) { // Do not lock unnecessarily
+	if (!p_gchandle.is_released()) { // Do not lock unnecessarily
 		MutexLock lock(get_singleton()->script_gchandle_release_mutex);
 
-		MonoObject *target = p_gchandle->get_target();
+		MonoObject *target = p_gchandle.get_target();
 
 		// We release the gchandle if it points to the MonoObject* we expect (otherwise it was
 		// already released and could have been replaced) or if we can't get its target MonoObject*
 		// (which doesn't necessarily mean it was released, and we want it released in order to
 		// avoid locking other threads unnecessarily).
 		if (target == p_expected_obj || target == NULL) {
-			p_gchandle->release();
+			p_gchandle.release();
 		}
 	}
 
-	MonoGCHandle::free_handle(pinned_gchandle);
+	GDMonoUtils::free_gchandle(pinned_gchandle);
 }
 
 CSharpLanguage::CSharpLanguage() {
@@ -1399,7 +1400,7 @@ bool CSharpLanguage::setup_csharp_script_binding(CSharpScriptBinding &r_script_b
 	r_script_binding.inited = true;
 	r_script_binding.type_name = type_name;
 	r_script_binding.wrapper_class = type_class; // cache
-	r_script_binding.gchandle = MonoGCHandle::create_strong(mono_object);
+	r_script_binding.gchandle = MonoGCHandleData::new_strong_handle(mono_object);
 	r_script_binding.owner = p_object;
 
 	// Tie managed to unmanaged
@@ -1464,10 +1465,11 @@ void CSharpLanguage::free_instance_binding_data(void *p_data) {
 		if (script_binding.inited) {
 			// Set the native instance field to IntPtr.Zero, if not yet garbage collected.
 			// This is done to avoid trying to dispose the native instance from Dispose(bool).
-			MonoObject *mono_object = script_binding.gchandle->get_target();
+			MonoObject *mono_object = script_binding.gchandle.get_target();
 			if (mono_object) {
 				CACHED_FIELD(GodotObject, ptr)->set_value_raw(mono_object, NULL);
 			}
+			script_binding.gchandle.release();
 		}
 
 		script_bindings.erase(data);
@@ -1487,26 +1489,26 @@ void CSharpLanguage::refcount_incremented_instance_binding(Object *p_object) {
 	CRASH_COND(!data);
 
 	CSharpScriptBinding &script_binding = ((Map<Object *, CSharpScriptBinding>::Element *)data)->get();
-	Ref<MonoGCHandle> &gchandle = script_binding.gchandle;
+	MonoGCHandleData &gchandle = script_binding.gchandle;
 
 	if (!script_binding.inited)
 		return;
 
-	if (ref_owner->reference_get_count() > 1 && gchandle->is_weak()) { // The managed side also holds a reference, hence 1 instead of 0
+	if (ref_owner->reference_get_count() > 1 && gchandle.is_weak()) { // The managed side also holds a reference, hence 1 instead of 0
 		GD_MONO_SCOPE_THREAD_ATTACH;
 
 		// The reference count was increased after the managed side was the only one referencing our owner.
 		// This means the owner is being referenced again by the unmanaged side,
 		// so the owner must hold the managed side alive again to avoid it from being GCed.
 
-		MonoObject *target = gchandle->get_target();
+		MonoObject *target = gchandle.get_target();
 		if (!target)
 			return; // Called after the managed side was collected, so nothing to do here
 
 		// Release the current weak handle and replace it with a strong handle.
-		uint32_t strong_gchandle = MonoGCHandle::new_strong_handle(target);
-		gchandle->release();
-		gchandle->set_handle(strong_gchandle, MonoGCHandle::STRONG_HANDLE);
+		MonoGCHandleData strong_gchandle = MonoGCHandleData::new_strong_handle(target);
+		gchandle.release();
+		gchandle = strong_gchandle;
 	}
 }
 
@@ -1523,27 +1525,27 @@ bool CSharpLanguage::refcount_decremented_instance_binding(Object *p_object) {
 	CRASH_COND(!data);
 
 	CSharpScriptBinding &script_binding = ((Map<Object *, CSharpScriptBinding>::Element *)data)->get();
-	Ref<MonoGCHandle> &gchandle = script_binding.gchandle;
+	MonoGCHandleData &gchandle = script_binding.gchandle;
 
 	int refcount = ref_owner->reference_get_count();
 
 	if (!script_binding.inited)
 		return refcount == 0;
 
-	if (refcount == 1 && gchandle.is_valid() && !gchandle->is_weak()) { // The managed side also holds a reference, hence 1 instead of 0
+	if (refcount == 1 && !gchandle.is_released() && !gchandle.is_weak()) { // The managed side also holds a reference, hence 1 instead of 0
 		GD_MONO_SCOPE_THREAD_ATTACH;
 
 		// If owner owner is no longer referenced by the unmanaged side,
 		// the managed instance takes responsibility of deleting the owner when GCed.
 
-		MonoObject *target = gchandle->get_target();
+		MonoObject *target = gchandle.get_target();
 		if (!target)
 			return refcount == 0; // Called after the managed side was collected, so nothing to do here
 
 		// Release the current strong handle and replace it with a weak handle.
-		uint32_t weak_gchandle = MonoGCHandle::new_weak_handle(target);
-		gchandle->release();
-		gchandle->set_handle(weak_gchandle, MonoGCHandle::WEAK_HANDLE);
+		MonoGCHandleData weak_gchandle = MonoGCHandleData::new_weak_handle(target);
+		gchandle.release();
+		gchandle = weak_gchandle;
 
 		return false;
 	}
@@ -1551,7 +1553,7 @@ bool CSharpLanguage::refcount_decremented_instance_binding(Object *p_object) {
 	return refcount == 0;
 }
 
-CSharpInstance *CSharpInstance::create_for_managed_type(Object *p_owner, CSharpScript *p_script, const Ref<MonoGCHandle> &p_gchandle) {
+CSharpInstance *CSharpInstance::create_for_managed_type(Object *p_owner, CSharpScript *p_script, const MonoGCHandleData &p_gchandle) {
 
 	CSharpInstance *instance = memnew(CSharpInstance(Ref<CSharpScript>(p_script)));
 
@@ -1571,8 +1573,8 @@ CSharpInstance *CSharpInstance::create_for_managed_type(Object *p_owner, CSharpS
 
 MonoObject *CSharpInstance::get_mono_object() const {
 
-	ERR_FAIL_COND_V(gchandle.is_null(), NULL);
-	return gchandle->get_target();
+	ERR_FAIL_COND_V(gchandle.is_released(), NULL);
+	return gchandle.get_target();
 }
 
 Object *CSharpInstance::get_owner() {
@@ -1945,10 +1947,6 @@ bool CSharpInstance::_unreference_owner_unsafe() {
 }
 
 MonoObject *CSharpInstance::_internal_new_managed() {
-#ifdef DEBUG_ENABLED
-	CRASH_COND(!gchandle.is_valid());
-#endif
-
 	// Search the constructor first, to fail with an error if it's not found before allocating anything else.
 	GDMonoMethod *ctor = script->script_class->get_method(CACHED_STRING_NAME(dotctor), 0);
 	ERR_FAIL_NULL_V_MSG(ctor, NULL,
@@ -1975,7 +1973,7 @@ MonoObject *CSharpInstance::_internal_new_managed() {
 	}
 
 	// Tie managed to unmanaged
-	gchandle = MonoGCHandle::create_strong(mono_object);
+	gchandle = MonoGCHandleData::new_strong_handle(mono_object);
 
 	if (base_ref)
 		_reference_owner_unsafe(); // Here, after assigning the gchandle (for the refcount_incremented callback)
@@ -1994,7 +1992,7 @@ void CSharpInstance::mono_object_disposed(MonoObject *p_obj) {
 
 #ifdef DEBUG_ENABLED
 	CRASH_COND(base_ref);
-	CRASH_COND(gchandle.is_null());
+	CRASH_COND(gchandle.is_released());
 #endif
 	CSharpLanguage::get_singleton()->release_script_gchandle(p_obj, gchandle);
 }
@@ -2003,7 +2001,7 @@ void CSharpInstance::mono_object_disposed_baseref(MonoObject *p_obj, bool p_is_f
 
 #ifdef DEBUG_ENABLED
 	CRASH_COND(!base_ref);
-	CRASH_COND(gchandle.is_null());
+	CRASH_COND(gchandle.is_released());
 #endif
 
 	r_remove_script_instance = false;
@@ -2069,7 +2067,7 @@ void CSharpInstance::refcount_incremented() {
 
 	Reference *ref_owner = Object::cast_to<Reference>(owner);
 
-	if (ref_owner->reference_get_count() > 1 && gchandle->is_weak()) { // The managed side also holds a reference, hence 1 instead of 0
+	if (ref_owner->reference_get_count() > 1 && gchandle.is_weak()) { // The managed side also holds a reference, hence 1 instead of 0
 		GD_MONO_SCOPE_THREAD_ATTACH;
 
 		// The reference count was increased after the managed side was the only one referencing our owner.
@@ -2077,9 +2075,9 @@ void CSharpInstance::refcount_incremented() {
 		// so the owner must hold the managed side alive again to avoid it from being GCed.
 
 		// Release the current weak handle and replace it with a strong handle.
-		uint32_t strong_gchandle = MonoGCHandle::new_strong_handle(gchandle->get_target());
-		gchandle->release();
-		gchandle->set_handle(strong_gchandle, MonoGCHandle::STRONG_HANDLE);
+		MonoGCHandleData strong_gchandle = MonoGCHandleData::new_strong_handle(gchandle.get_target());
+		gchandle.release();
+		gchandle = strong_gchandle;
 	}
 }
 
@@ -2094,16 +2092,16 @@ bool CSharpInstance::refcount_decremented() {
 
 	int refcount = ref_owner->reference_get_count();
 
-	if (refcount == 1 && !gchandle->is_weak()) { // The managed side also holds a reference, hence 1 instead of 0
+	if (refcount == 1 && !gchandle.is_weak()) { // The managed side also holds a reference, hence 1 instead of 0
 		GD_MONO_SCOPE_THREAD_ATTACH;
 
 		// If owner owner is no longer referenced by the unmanaged side,
 		// the managed instance takes responsibility of deleting the owner when GCed.
 
 		// Release the current strong handle and replace it with a weak handle.
-		uint32_t weak_gchandle = MonoGCHandle::new_weak_handle(gchandle->get_target());
-		gchandle->release();
-		gchandle->set_handle(weak_gchandle, MonoGCHandle::WEAK_HANDLE);
+		MonoGCHandleData weak_gchandle = MonoGCHandleData::new_weak_handle(gchandle.get_target());
+		gchandle.release();
+		gchandle = weak_gchandle;
 
 		return false;
 	}
@@ -2269,7 +2267,7 @@ CSharpInstance::~CSharpInstance() {
 
 	destructing_script_instance = true;
 
-	if (gchandle.is_valid()) {
+	if (!gchandle.is_released()) {
 		if (!predelete_notified && !ref_dying) {
 			// This destructor is not called from the owners destructor.
 			// This could be being called from the owner's set_script_instance method,
@@ -2277,7 +2275,7 @@ CSharpInstance::~CSharpInstance() {
 			// we must call Dispose here, because Dispose calls owner->set_script_instance(NULL)
 			// and that would mess up with the new script instance if called later.
 
-			MonoObject *mono_object = gchandle->get_target();
+			MonoObject *mono_object = gchandle.get_target();
 
 			if (mono_object) {
 				MonoException *exc = NULL;
@@ -2289,7 +2287,7 @@ CSharpInstance::~CSharpInstance() {
 			}
 		}
 
-		gchandle->release(); // Make sure the gchandle is released
+		gchandle.release(); // Make sure the gchandle is released
 	}
 
 	// If not being called from the owner's destructor, and we still hold a reference to the owner
@@ -2449,7 +2447,7 @@ bool CSharpScript::_update_exports() {
 			return false;
 		}
 
-		uint32_t tmp_pinned_gchandle = MonoGCHandle::new_strong_handle_pinned(tmp_object); // pin it (not sure if needed)
+		uint32_t tmp_pinned_gchandle = GDMonoUtils::new_strong_gchandle_pinned(tmp_object); // pin it (not sure if needed)
 
 		GDMonoMethod *ctor = script_class->get_method(CACHED_STRING_NAME(dotctor), 0);
 
@@ -2464,7 +2462,7 @@ bool CSharpScript::_update_exports() {
 		if (ctor_exc) {
 			// TODO: Should we free 'tmp_native' if the exception was thrown after its creation?
 
-			MonoGCHandle::free_handle(tmp_pinned_gchandle);
+			GDMonoUtils::free_gchandle(tmp_pinned_gchandle);
 			tmp_object = NULL;
 
 			ERR_PRINT("Exception thrown from constructor of temporary MonoObject:");
@@ -2543,7 +2541,7 @@ bool CSharpScript::_update_exports() {
 			GDMonoUtils::debug_print_unhandled_exception(exc);
 		}
 
-		MonoGCHandle::free_handle(tmp_pinned_gchandle);
+		GDMonoUtils::free_gchandle(tmp_pinned_gchandle);
 		tmp_object = NULL;
 
 		if (tmp_native && !base_ref) {
@@ -3109,8 +3107,8 @@ CSharpInstance *CSharpScript::_create_instance(const Variant **p_args, int p_arg
 		CRASH_COND(data == NULL);
 
 		CSharpScriptBinding &script_binding = ((Map<Object *, CSharpScriptBinding>::Element *)data)->get();
-		if (script_binding.inited && script_binding.gchandle.is_valid()) {
-			MonoObject *mono_object = script_binding.gchandle->get_target();
+		if (script_binding.inited && !script_binding.gchandle.is_released()) {
+			MonoObject *mono_object = script_binding.gchandle.get_target();
 			if (mono_object) {
 				MonoException *exc = NULL;
 				GDMonoUtils::dispose(mono_object, &exc);
@@ -3120,6 +3118,7 @@ CSharpInstance *CSharpScript::_create_instance(const Variant **p_args, int p_arg
 				}
 			}
 
+			script_binding.gchandle.release(); // Just in case
 			script_binding.inited = false;
 		}
 	}
@@ -3148,7 +3147,7 @@ CSharpInstance *CSharpScript::_create_instance(const Variant **p_args, int p_arg
 	}
 
 	// Tie managed to unmanaged
-	instance->gchandle = MonoGCHandle::create_strong(mono_object);
+	instance->gchandle = MonoGCHandleData::new_strong_handle(mono_object);
 
 	if (instance->base_ref)
 		instance->_reference_owner_unsafe(); // Here, after assigning the gchandle (for the refcount_incremented callback)

modules/mono/csharp_script.h

@@ -240,7 +240,7 @@ class CSharpInstance : public ScriptInstance {
 	bool destructing_script_instance = false;
 
 	Ref<CSharpScript> script;
-	Ref<MonoGCHandle> gchandle;
+	MonoGCHandleData gchandle;
 
 	Vector<Callable> event_signal_callables;
 
@@ -258,7 +258,7 @@ class CSharpInstance : public ScriptInstance {
 
 	// Do not use unless you know what you are doing
 	friend void GDMonoInternals::tie_managed_to_unmanaged(MonoObject *, Object *);
-	static CSharpInstance *create_for_managed_type(Object *p_owner, CSharpScript *p_script, const Ref<MonoGCHandle> &p_gchandle);
+	static CSharpInstance *create_for_managed_type(Object *p_owner, CSharpScript *p_script, const MonoGCHandleData &p_gchandle);
 
 	void _call_multilevel(MonoObject *p_mono_object, const StringName &p_method, const Variant **p_args, int p_argcount);
 
@@ -326,8 +326,14 @@ struct CSharpScriptBinding {
 	bool inited;
 	StringName type_name;
 	GDMonoClass *wrapper_class;
-	Ref<MonoGCHandle> gchandle;
+	MonoGCHandleData gchandle;
 	Object *owner;
+
+	CSharpScriptBinding() :
+			inited(false),
+			wrapper_class(NULL),
+			owner(NULL) {
+	}
 };
 
 class ManagedCallableMiddleman : public Object {
@@ -414,8 +420,8 @@ public:
 	_FORCE_INLINE_ EditorPlugin *get_godotsharp_editor() const { return godotsharp_editor; }
 #endif
 
-	static void release_script_gchandle(Ref<MonoGCHandle> &p_gchandle);
-	static void release_script_gchandle(MonoObject *p_expected_obj, Ref<MonoGCHandle> &p_gchandle);
+	static void release_script_gchandle(MonoGCHandleData &p_gchandle);
+	static void release_script_gchandle(MonoObject *p_expected_obj, MonoGCHandleData &p_gchandle);
 
 	bool debug_break(const String &p_error, bool p_allow_continue = true);
 	bool debug_break_parse(const String &p_file, int p_line, const String &p_error);

modules/mono/glue/base_object_glue.cpp

@@ -70,8 +70,8 @@ void godot_icall_Object_Disposed(MonoObject *p_obj, Object *p_ptr) {
 	if (data) {
 		CSharpScriptBinding &script_binding = ((Map<Object *, CSharpScriptBinding>::Element *)data)->get();
 		if (script_binding.inited) {
-			Ref<MonoGCHandle> &gchandle = script_binding.gchandle;
-			if (gchandle.is_valid()) {
+			MonoGCHandleData &gchandle = script_binding.gchandle;
+			if (!gchandle.is_released()) {
 				CSharpLanguage::release_script_gchandle(p_obj, gchandle);
 			}
 		}
@@ -117,8 +117,8 @@ void godot_icall_Reference_Disposed(MonoObject *p_obj, Object *p_ptr, MonoBoolea
 		if (data) {
 			CSharpScriptBinding &script_binding = ((Map<Object *, CSharpScriptBinding>::Element *)data)->get();
 			if (script_binding.inited) {
-				Ref<MonoGCHandle> &gchandle = script_binding.gchandle;
-				if (gchandle.is_valid()) {
+				MonoGCHandleData &gchandle = script_binding.gchandle;
+				if (!gchandle.is_released()) {
 					CSharpLanguage::release_script_gchandle(p_obj, gchandle);
 				}
 			}

modules/mono/managed_callable.cpp

@@ -44,8 +44,8 @@ bool ManagedCallable::compare_equal(const CallableCustom *p_a, const CallableCus
 	const ManagedCallable *a = static_cast<const ManagedCallable *>(p_a);
 	const ManagedCallable *b = static_cast<const ManagedCallable *>(p_b);
 
-	MonoDelegate *delegate_a = (MonoDelegate *)a->delegate_handle->get_target();
-	MonoDelegate *delegate_b = (MonoDelegate *)b->delegate_handle->get_target();
+	MonoDelegate *delegate_a = (MonoDelegate *)a->delegate_handle.get_target();
+	MonoDelegate *delegate_b = (MonoDelegate *)b->delegate_handle.get_target();
 
 	if (!delegate_a || !delegate_b) {
 		if (!delegate_a && !delegate_b)
@@ -66,7 +66,7 @@ bool ManagedCallable::compare_less(const CallableCustom *p_a, const CallableCust
 uint32_t ManagedCallable::hash() const {
 	// hmm
 	uint32_t hash = delegate_invoke->get_name().hash();
-	return hash_djb2_one_64(delegate_handle.ptr()->handle, hash);
+	return hash_djb2_one_64(delegate_handle.handle, hash);
 }
 
 String ManagedCallable::get_as_text() const {
@@ -92,12 +92,12 @@ void ManagedCallable::call(const Variant **p_arguments, int p_argcount, Variant
 #ifdef GD_MONO_HOT_RELOAD
 	// Lost during hot-reload
 	ERR_FAIL_NULL(delegate_invoke);
-	ERR_FAIL_COND(delegate_handle.is_null());
+	ERR_FAIL_COND(delegate_handle.is_released());
 #endif
 
 	ERR_FAIL_COND(delegate_invoke->get_parameters_count() < p_argcount);
 
-	MonoObject *delegate = delegate_handle->get_target();
+	MonoObject *delegate = delegate_handle.get_target();
 
 	MonoException *exc = NULL;
 	MonoObject *ret = delegate_invoke->invoke(delegate, p_arguments, &exc);
@@ -111,7 +111,7 @@ void ManagedCallable::call(const Variant **p_arguments, int p_argcount, Variant
 }
 
 void ManagedCallable::set_delegate(MonoDelegate *p_delegate) {
-	delegate_handle = MonoGCHandle::create_strong((MonoObject *)p_delegate);
+	delegate_handle = MonoGCHandleData::new_strong_handle((MonoObject *)p_delegate);
 	MonoMethod *delegate_invoke_raw = mono_get_delegate_invoke(mono_object_get_class((MonoObject *)p_delegate));
 	const StringName &delegate_invoke_name = CSharpLanguage::get_singleton()->get_string_names().delegate_invoke_method_name;
 	delegate_invoke = memnew(GDMonoMethod(delegate_invoke_name, delegate_invoke_raw)); // TODO: Use pooling for this GDMonoMethod instances
@@ -132,12 +132,14 @@ ManagedCallable::ManagedCallable(MonoDelegate *p_delegate) {
 #endif
 }
 
-#ifdef GD_MONO_HOT_RELOAD
 ManagedCallable::~ManagedCallable() {
+#ifdef GD_MONO_HOT_RELOAD
 	{
 		MutexLock lock(instances_mutex);
 		instances.remove(&self_instance);
 		instances_pending_reload.erase(this);
 	}
-}
 #endif
+
+	delegate_handle.release();
+}

modules/mono/managed_callable.h

@@ -42,7 +42,7 @@
 
 class ManagedCallable : public CallableCustom {
 	friend class CSharpLanguage;
-	Ref<MonoGCHandle> delegate_handle;
+	MonoGCHandleData delegate_handle;
 	GDMonoMethod *delegate_invoke;
 
 #ifdef GD_MONO_HOT_RELOAD
@@ -60,7 +60,7 @@ public:
 	ObjectID get_object() const override;
 	void call(const Variant **p_arguments, int p_argcount, Variant &r_return_value, Callable::CallError &r_call_error) const override;
 
-	_FORCE_INLINE_ MonoDelegate *get_delegate() { return (MonoDelegate *)delegate_handle->get_target(); }
+	_FORCE_INLINE_ MonoDelegate *get_delegate() { return (MonoDelegate *)delegate_handle.get_target(); }
 
 	void set_delegate(MonoDelegate *p_delegate);
 
@@ -71,9 +71,7 @@ public:
 	static constexpr CompareEqualFunc compare_less_func_ptr = &ManagedCallable::compare_less;
 
 	ManagedCallable(MonoDelegate *p_delegate);
-#ifdef GD_MONO_HOT_RELOAD
 	~ManagedCallable();
-#endif
 };
 
 #endif // MANAGED_CALLABLE_H

modules/mono/mono_gc_handle.cpp

@@ -32,56 +32,35 @@
 
 #include "mono_gd/gd_mono.h"
 
-uint32_t MonoGCHandle::new_strong_handle(MonoObject *p_object) {
-
-	return mono_gchandle_new(p_object, /* pinned: */ false);
-}
-
-uint32_t MonoGCHandle::new_strong_handle_pinned(MonoObject *p_object) {
-
-	return mono_gchandle_new(p_object, /* pinned: */ true);
-}
-
-uint32_t MonoGCHandle::new_weak_handle(MonoObject *p_object) {
-
-	return mono_gchandle_new_weakref(p_object, /* track_resurrection: */ false);
-}
-
-void MonoGCHandle::free_handle(uint32_t p_gchandle) {
+void MonoGCHandleData::release() {
+#ifdef DEBUG_ENABLED
+	CRASH_COND(handle && GDMono::get_singleton() == NULL);
+#endif
 
-	mono_gchandle_free(p_gchandle);
+	if (handle && GDMono::get_singleton()->is_runtime_initialized()) {
+		GDMonoUtils::free_gchandle(handle);
+		handle = 0;
+	}
 }
 
-Ref<MonoGCHandle> MonoGCHandle::create_strong(MonoObject *p_object) {
-
-	return memnew(MonoGCHandle(new_strong_handle(p_object), STRONG_HANDLE));
+MonoGCHandleData MonoGCHandleData::new_strong_handle(MonoObject *p_object) {
+	return MonoGCHandleData(GDMonoUtils::new_strong_gchandle(p_object), gdmono::GCHandleType::STRONG_HANDLE);
 }
 
-Ref<MonoGCHandle> MonoGCHandle::create_weak(MonoObject *p_object) {
-
-	return memnew(MonoGCHandle(new_weak_handle(p_object), WEAK_HANDLE));
+MonoGCHandleData MonoGCHandleData::new_strong_handle_pinned(MonoObject *p_object) {
+	return MonoGCHandleData(GDMonoUtils::new_strong_gchandle_pinned(p_object), gdmono::GCHandleType::STRONG_HANDLE);
 }
 
-void MonoGCHandle::release() {
-
-#ifdef DEBUG_ENABLED
-	CRASH_COND(!released && GDMono::get_singleton() == NULL);
-#endif
-
-	if (!released && GDMono::get_singleton()->is_runtime_initialized()) {
-		free_handle(handle);
-		released = true;
-	}
+MonoGCHandleData MonoGCHandleData::new_weak_handle(MonoObject *p_object) {
+	return MonoGCHandleData(GDMonoUtils::new_weak_gchandle(p_object), gdmono::GCHandleType::WEAK_HANDLE);
 }
 
-MonoGCHandle::MonoGCHandle(uint32_t p_handle, HandleType p_handle_type) {
+Ref<MonoGCHandleRef> MonoGCHandleRef::create_strong(MonoObject *p_object) {
 
-	released = false;
-	weak = p_handle_type == WEAK_HANDLE;
-	handle = p_handle;
+	return memnew(MonoGCHandleRef(MonoGCHandleData::new_strong_handle(p_object)));
 }
 
-MonoGCHandle::~MonoGCHandle() {
+Ref<MonoGCHandleRef> MonoGCHandleRef::create_weak(MonoObject *p_object) {
 
-	release();
+	return memnew(MonoGCHandleRef(MonoGCHandleData::new_weak_handle(p_object)));
 }

modules/mono/mono_gc_handle.h

@@ -35,44 +35,79 @@
 
 #include "core/reference.h"
 
-class MonoGCHandle : public Reference {
+namespace gdmono {
 
-	GDCLASS(MonoGCHandle, Reference);
+enum class GCHandleType : char {
+	NIL,
+	STRONG_HANDLE,
+	WEAK_HANDLE
+};
 
-	bool released;
-	bool weak;
+}
 
-	friend class ManagedCallable;
+// Manual release of the GC handle must be done when using this struct
+struct MonoGCHandleData {
 	uint32_t handle;
+	gdmono::GCHandleType type;
 
-public:
-	enum HandleType {
-		STRONG_HANDLE,
-		WEAK_HANDLE
-	};
+	_FORCE_INLINE_ bool is_released() const { return !handle; }
+	_FORCE_INLINE_ bool is_weak() const { return type == gdmono::GCHandleType::WEAK_HANDLE; }
 
-	static uint32_t new_strong_handle(MonoObject *p_object);
-	static uint32_t new_strong_handle_pinned(MonoObject *p_object);
-	static uint32_t new_weak_handle(MonoObject *p_object);
-	static void free_handle(uint32_t p_gchandle);
+	_FORCE_INLINE_ MonoObject *get_target() const { return handle ? mono_gchandle_get_target(handle) : NULL; }
 
-	static Ref<MonoGCHandle> create_strong(MonoObject *p_object);
-	static Ref<MonoGCHandle> create_weak(MonoObject *p_object);
+	void release();
 
-	_FORCE_INLINE_ bool is_released() { return released; }
-	_FORCE_INLINE_ bool is_weak() { return weak; }
+	MonoGCHandleData &operator=(const MonoGCHandleData &p_other) {
+#ifdef DEBUG_ENABLED
+		CRASH_COND(!is_released());
+#endif
+		handle = p_other.handle;
+		type = p_other.type;
+		return *this;
+	}
 
-	_FORCE_INLINE_ MonoObject *get_target() const { return released ? NULL : mono_gchandle_get_target(handle); }
+	MonoGCHandleData(const MonoGCHandleData &) = default;
 
-	_FORCE_INLINE_ void set_handle(uint32_t p_handle, HandleType p_handle_type) {
-		released = false;
-		weak = p_handle_type == WEAK_HANDLE;
-		handle = p_handle;
+	MonoGCHandleData() :
+			handle(0),
+			type(gdmono::GCHandleType::NIL) {
 	}
-	void release();
 
-	MonoGCHandle(uint32_t p_handle, HandleType p_handle_type);
-	~MonoGCHandle();
+	MonoGCHandleData(uint32_t p_handle, gdmono::GCHandleType p_type) :
+			handle(p_handle),
+			type(p_type) {
+	}
+
+	static MonoGCHandleData new_strong_handle(MonoObject *p_object);
+	static MonoGCHandleData new_strong_handle_pinned(MonoObject *p_object);
+	static MonoGCHandleData new_weak_handle(MonoObject *p_object);
+};
+
+class MonoGCHandleRef : public Reference {
+
+	GDCLASS(MonoGCHandleRef, Reference);
+
+	MonoGCHandleData data;
+
+public:
+	static Ref<MonoGCHandleRef> create_strong(MonoObject *p_object);
+	static Ref<MonoGCHandleRef> create_weak(MonoObject *p_object);
+
+	_FORCE_INLINE_ bool is_released() const { return data.is_released(); }
+	_FORCE_INLINE_ bool is_weak() const { return data.is_weak(); }
+
+	_FORCE_INLINE_ MonoObject *get_target() const { return data.get_target(); }
+
+	void release() { data.release(); }
+
+	_FORCE_INLINE_ void set_handle(uint32_t p_handle, gdmono::GCHandleType p_handle_type) {
+		data = MonoGCHandleData(p_handle, p_handle_type);
+	}
+
+	MonoGCHandleRef(const MonoGCHandleData &p_gc_handle_data) :
+			data(p_gc_handle_data) {
+	}
+	~MonoGCHandleRef() { release(); }
 };
 
 #endif // CSHARP_GC_HANDLE_H

modules/mono/mono_gd/gd_mono_cache.cpp

@@ -186,7 +186,7 @@ void CachedData::clear_godot_api_cache() {
 
 	// End of MarshalUtils methods
 
-	task_scheduler_handle = Ref<MonoGCHandle>();
+	task_scheduler_handle = Ref<MonoGCHandleRef>();
 }
 
 #define GODOT_API_CLASS(m_class) (GDMono::get_singleton()->get_core_api_assembly()->get_class(BINDINGS_NAMESPACE, #m_class))
@@ -316,7 +316,7 @@ void update_godot_api_cache() {
 	// TODO Move to CSharpLanguage::init() and do handle disposal
 	MonoObject *task_scheduler = mono_object_new(mono_domain_get(), GODOT_API_CLASS(GodotTaskScheduler)->get_mono_ptr());
 	GDMonoUtils::runtime_object_init(task_scheduler, GODOT_API_CLASS(GodotTaskScheduler));
-	cached_data.task_scheduler_handle = MonoGCHandle::create_strong(task_scheduler);
+	cached_data.task_scheduler_handle = MonoGCHandleRef::create_strong(task_scheduler);
 
 	cached_data.godot_api_cache_updated = true;
 }

modules/mono/mono_gd/gd_mono_cache.h

@@ -156,7 +156,7 @@ struct CachedData {
 
 	// End of MarshalUtils methods
 
-	Ref<MonoGCHandle> task_scheduler_handle;
+	Ref<MonoGCHandleRef> task_scheduler_handle;
 
 	bool corlib_cache_updated;
 	bool godot_api_cache_updated;

modules/mono/mono_gd/gd_mono_internals.cpp

@@ -75,7 +75,7 @@ void tie_managed_to_unmanaged(MonoObject *managed, Object *unmanaged) {
 		script_binding.inited = true;
 		script_binding.type_name = NATIVE_GDMONOCLASS_NAME(klass);
 		script_binding.wrapper_class = klass;
-		script_binding.gchandle = ref ? MonoGCHandle::create_weak(managed) : MonoGCHandle::create_strong(managed);
+		script_binding.gchandle = ref ? MonoGCHandleData::new_weak_handle(managed) : MonoGCHandleData::new_strong_handle(managed);
 		script_binding.owner = unmanaged;
 
 		if (ref) {
@@ -101,7 +101,7 @@ void tie_managed_to_unmanaged(MonoObject *managed, Object *unmanaged) {
 		return;
 	}
 
-	Ref<MonoGCHandle> gchandle = ref ? MonoGCHandle::create_weak(managed) : MonoGCHandle::create_strong(managed);
+	MonoGCHandleData gchandle = ref ? MonoGCHandleData::new_weak_handle(managed) : MonoGCHandleData::new_strong_handle(managed);
 
 	Ref<CSharpScript> script = CSharpScript::create_for_managed_type(klass, native);
 

modules/mono/mono_gd/gd_mono_utils.cpp

@@ -86,10 +86,9 @@ MonoObject *unmanaged_get_managed(Object *unmanaged) {
 		}
 	}
 
-	Ref<MonoGCHandle> &gchandle = script_binding.gchandle;
-	ERR_FAIL_COND_V(gchandle.is_null(), NULL);
+	MonoGCHandleData &gchandle = script_binding.gchandle;
 
-	MonoObject *target = gchandle->get_target();
+	MonoObject *target = gchandle.get_target();
 
 	if (target)
 		return target;
@@ -106,7 +105,7 @@ MonoObject *unmanaged_get_managed(Object *unmanaged) {
 	MonoObject *mono_object = GDMonoUtils::create_managed_for_godot_object(script_binding.wrapper_class, script_binding.type_name, unmanaged);
 	ERR_FAIL_NULL_V(mono_object, NULL);
 
-	gchandle->set_handle(MonoGCHandle::new_strong_handle(mono_object), MonoGCHandle::STRONG_HANDLE);
+	gchandle = MonoGCHandleData::new_strong_handle(mono_object);
 
 	// Tie managed to unmanaged
 	Reference *ref = Object::cast_to<Reference>(unmanaged);
@@ -156,6 +155,22 @@ bool is_thread_attached() {
 	return mono_domain_get() != NULL;
 }
 
+uint32_t new_strong_gchandle(MonoObject *p_object) {
+	return mono_gchandle_new(p_object, /* pinned: */ false);
+}
+
+uint32_t new_strong_gchandle_pinned(MonoObject *p_object) {
+	return mono_gchandle_new(p_object, /* pinned: */ true);
+}
+
+uint32_t new_weak_gchandle(MonoObject *p_object) {
+	return mono_gchandle_new_weakref(p_object, /* track_resurrection: */ false);
+}
+
+void free_gchandle(uint32_t p_gchandle) {
+	mono_gchandle_free(p_gchandle);
+}
+
 void runtime_object_init(MonoObject *p_this_obj, GDMonoClass *p_class, MonoException **r_exc) {
 	GDMonoMethod *ctor = p_class->get_method(".ctor", 0);
 	ERR_FAIL_NULL(ctor);

modules/mono/mono_gd/gd_mono_utils.h

@@ -92,6 +92,11 @@ _FORCE_INLINE_ bool is_main_thread() {
 	return mono_domain_get() != NULL && mono_thread_get_main() == mono_thread_current();
 }
 
+uint32_t new_strong_gchandle(MonoObject *p_object);
+uint32_t new_strong_gchandle_pinned(MonoObject *p_object);
+uint32_t new_weak_gchandle(MonoObject *p_object);
+void free_gchandle(uint32_t p_gchandle);
+
 void runtime_object_init(MonoObject *p_this_obj, GDMonoClass *p_class, MonoException **r_exc = NULL);
 
 bool mono_delegate_equal(MonoDelegate *p_a, MonoDelegate *p_b);

modules/mono/signal_awaiter_utils.cpp

@@ -114,8 +114,15 @@ void SignalAwaiterCallable::call(const Variant **p_arguments, int p_argcount, Va
 		mono_array_setref(signal_args, i, boxed);
 	}
 
+	MonoObject *awaiter = awaiter_handle.get_target();
+
+	if (!awaiter) {
+		r_call_error.error = Callable::CallError::CALL_ERROR_INSTANCE_IS_NULL;
+		return;
+	}
+
 	MonoException *exc = NULL;
-	CACHED_METHOD_THUNK(SignalAwaiter, SignalCallback).invoke(awaiter_handle->get_target(), signal_args, &exc);
+	CACHED_METHOD_THUNK(SignalAwaiter, SignalCallback).invoke(awaiter, signal_args, &exc);
 
 	if (exc) {
 		GDMonoUtils::set_pending_exception(exc);
@@ -127,10 +134,14 @@ void SignalAwaiterCallable::call(const Variant **p_arguments, int p_argcount, Va
 
 SignalAwaiterCallable::SignalAwaiterCallable(Object *p_target, MonoObject *p_awaiter, const StringName &p_signal) :
 		target_id(p_target->get_instance_id()),
-		awaiter_handle(MonoGCHandle::create_strong(p_awaiter)),
+		awaiter_handle(MonoGCHandleData::new_strong_handle(p_awaiter)),
 		signal(p_signal) {
 }
 
+SignalAwaiterCallable::~SignalAwaiterCallable() {
+	awaiter_handle.release();
+}
+
 bool EventSignalCallable::compare_equal(const CallableCustom *p_a, const CallableCustom *p_b) {
 	const EventSignalCallable *a = static_cast<const EventSignalCallable *>(p_a);
 	const EventSignalCallable *b = static_cast<const EventSignalCallable *>(p_b);
@@ -159,7 +170,6 @@ String EventSignalCallable::get_as_text() const {
 	String class_name = owner->get_class();
 	Ref<Script> script = owner->get_script();
 	if (script.is_valid() && script->get_path().is_resource_file()) {
-
 		class_name += "(" + script->get_path().get_file() + ")";
 	}
 	StringName signal = event_signal->field->get_name();

modules/mono/signal_awaiter_utils.h

@@ -40,7 +40,7 @@ Error gd_mono_connect_signal_awaiter(Object *p_source, const StringName &p_signa
 
 class SignalAwaiterCallable : public CallableCustom {
 	ObjectID target_id;
-	Ref<MonoGCHandle> awaiter_handle;
+	MonoGCHandleData awaiter_handle;
 	StringName signal;
 
 public:
@@ -64,6 +64,7 @@ public:
 	void call(const Variant **p_arguments, int p_argcount, Variant &r_return_value, Callable::CallError &r_call_error) const override;
 
 	SignalAwaiterCallable(Object *p_target, MonoObject *p_awaiter, const StringName &p_signal);
+	~SignalAwaiterCallable();
 };
 
 class EventSignalCallable : public CallableCustom {