Clean up instance bindings for engine singletons to prevent crash

binding_generator.py

@@ -1504,6 +1504,10 @@ def generate_engine_class_header(class_api, used_classes, fully_used_classes, us
         result.append(f"\tGDEXTENSION_CLASS({class_name}, {inherits})")
     result.append("")
 
+    if is_singleton:
+        result.append(f"\tstatic {class_name} *singleton;")
+        result.append("")
+
     result.append("public:")
     result.append("")
 
@@ -1584,6 +1588,11 @@ def generate_engine_class_header(class_api, used_classes, fully_used_classes, us
 
     result.append("\t}")
     result.append("")
+
+    if is_singleton:
+        result.append(f"\t~{class_name}();")
+        result.append("")
+
     result.append("public:")
 
     # Special cases.
@@ -1733,6 +1742,7 @@ def generate_engine_class_source(class_api, used_classes, fully_used_classes, us
 
     result.append(f"#include <godot_cpp/classes/{snake_class_name}.hpp>")
     result.append("")
+    result.append("#include <godot_cpp/core/class_db.hpp>")
     result.append("#include <godot_cpp/core/engine_ptrcall.hpp>")
     result.append("#include <godot_cpp/core/error_macros.hpp>")
     result.append("")
@@ -1747,9 +1757,10 @@ def generate_engine_class_source(class_api, used_classes, fully_used_classes, us
     result.append("")
 
     if is_singleton:
+        result.append(f"{class_name} *{class_name}::singleton = nullptr;")
+        result.append("")
         result.append(f"{class_name} *{class_name}::get_singleton() {{")
         # We assume multi-threaded access is OK because each assignment will assign the same value every time
-        result.append(f"\tstatic {class_name} *singleton = nullptr;")
         result.append("\tif (unlikely(singleton == nullptr)) {")
         result.append(
             f"\t\tGDExtensionObjectPtr singleton_obj = internal::gdextension_interface_global_get_singleton({class_name}::get_class_static()._native_ptr());"
@@ -1763,11 +1774,22 @@ def generate_engine_class_source(class_api, used_classes, fully_used_classes, us
         result.append("#ifdef DEBUG_ENABLED")
         result.append("\t\tERR_FAIL_NULL_V(singleton, nullptr);")
         result.append("#endif // DEBUG_ENABLED")
+        result.append("\t\tif (likely(singleton)) {")
+        result.append(f"\t\t\tClassDB::_register_engine_singleton({class_name}::get_class_static(), singleton);")
+        result.append("\t\t}")
         result.append("\t}")
         result.append("\treturn singleton;")
         result.append("}")
         result.append("")
 
+        result.append(f"{class_name}::~{class_name}() {{")
+        result.append("\tif (singleton == this) {")
+        result.append(f"\t\tClassDB::_unregister_engine_singleton({class_name}::get_class_static());")
+        result.append("\t\tsingleton = nullptr;")
+        result.append("\t}")
+        result.append("}")
+        result.append("")
+
     if "methods" in class_api:
         for method in class_api["methods"]:
             if method["is_virtual"]:

include/godot_cpp/core/class_db.hpp

@@ -45,6 +45,7 @@
 #include <godot_cpp/variant/callable_method_pointer.hpp>
 
 #include <list>
+#include <mutex>
 #include <set>
 #include <string>
 #include <unordered_map>
@@ -104,6 +105,8 @@ class ClassDB {
 	static std::unordered_map<StringName, const GDExtensionInstanceBindingCallbacks *> instance_binding_callbacks;
 	// Used to remember the custom class registration order.
 	static std::vector<StringName> class_register_order;
+	static std::unordered_map<StringName, Object *> engine_singletons;
+	static std::mutex engine_singletons_mutex;
 
 	static MethodBind *bind_methodfi(uint32_t p_flags, MethodBind *p_bind, const MethodDefinition &method_name, const void **p_defs, int p_defcount);
 	static void initialize_class(const ClassInfo &cl);
@@ -153,6 +156,21 @@ class ClassDB {
 		instance_binding_callbacks[p_name] = p_callbacks;
 	}
 
+	static void _register_engine_singleton(const StringName &p_class_name, Object *p_singleton) {
+		std::lock_guard<std::mutex> lock(engine_singletons_mutex);
+		std::unordered_map<StringName, Object *>::const_iterator i = engine_singletons.find(p_class_name);
+		if (i != engine_singletons.end()) {
+			ERR_FAIL_COND((*i).second != p_singleton);
+			return;
+		}
+		engine_singletons[p_class_name] = p_singleton;
+	}
+
+	static void _unregister_engine_singleton(const StringName &p_class_name) {
+		std::lock_guard<std::mutex> lock(engine_singletons_mutex);
+		engine_singletons.erase(p_class_name);
+	}
+
 	template <typename N, typename M, typename... VarArgs>
 	static MethodBind *bind_method(N p_method_name, M p_method, VarArgs... p_args);
 

include/godot_cpp/godot.hpp

@@ -160,6 +160,7 @@ extern "C" GDExtensionInterfaceObjectDestroy gdextension_interface_object_destro
 extern "C" GDExtensionInterfaceGlobalGetSingleton gdextension_interface_global_get_singleton;
 extern "C" GDExtensionInterfaceObjectGetInstanceBinding gdextension_interface_object_get_instance_binding;
 extern "C" GDExtensionInterfaceObjectSetInstanceBinding gdextension_interface_object_set_instance_binding;
+extern "C" GDExtensionInterfaceObjectFreeInstanceBinding gdextension_interface_object_free_instance_binding;
 extern "C" GDExtensionInterfaceObjectSetInstance gdextension_interface_object_set_instance;
 extern "C" GDExtensionInterfaceObjectGetClassName gdextension_interface_object_get_class_name;
 extern "C" GDExtensionInterfaceObjectCastTo gdextension_interface_object_cast_to;

src/core/class_db.cpp

@@ -43,6 +43,8 @@ namespace godot {
 std::unordered_map<StringName, ClassDB::ClassInfo> ClassDB::classes;
 std::unordered_map<StringName, const GDExtensionInstanceBindingCallbacks *> ClassDB::instance_binding_callbacks;
 std::vector<StringName> ClassDB::class_register_order;
+std::unordered_map<StringName, Object *> ClassDB::engine_singletons;
+std::mutex ClassDB::engine_singletons_mutex;
 GDExtensionInitializationLevel ClassDB::current_level = GDEXTENSION_INITIALIZATION_CORE;
 
 MethodDefinition D_METHOD(StringName p_name) {
@@ -419,6 +421,22 @@ void ClassDB::deinitialize(GDExtensionInitializationLevel p_level) {
 		});
 		class_register_order.erase(it, class_register_order.end());
 	}
+
+	if (p_level == GDEXTENSION_INITIALIZATION_CORE) {
+		// Make a new list of the singleton objects, since freeing the instance bindings will lead to
+		// elements getting removed from engine_singletons.
+		std::vector<Object *> singleton_objects;
+		{
+			std::lock_guard<std::mutex> lock(engine_singletons_mutex);
+			singleton_objects.reserve(engine_singletons.size());
+			for (const std::pair<StringName, Object *> &pair : engine_singletons) {
+				singleton_objects.push_back(pair.second);
+			}
+		}
+		for (std::vector<Object *>::iterator i = singleton_objects.begin(); i != singleton_objects.end(); i++) {
+			internal::gdextension_interface_object_free_instance_binding((*i)->_owner, internal::token);
+		}
+	}
 }
 
 } // namespace godot

src/godot.cpp

@@ -166,6 +166,7 @@ GDExtensionInterfaceObjectDestroy gdextension_interface_object_destroy = nullptr
 GDExtensionInterfaceGlobalGetSingleton gdextension_interface_global_get_singleton = nullptr;
 GDExtensionInterfaceObjectGetInstanceBinding gdextension_interface_object_get_instance_binding = nullptr;
 GDExtensionInterfaceObjectSetInstanceBinding gdextension_interface_object_set_instance_binding = nullptr;
+GDExtensionInterfaceObjectFreeInstanceBinding gdextension_interface_object_free_instance_binding = nullptr;
 GDExtensionInterfaceObjectSetInstance gdextension_interface_object_set_instance = nullptr;
 GDExtensionInterfaceObjectGetClassName gdextension_interface_object_get_class_name = nullptr;
 GDExtensionInterfaceObjectCastTo gdextension_interface_object_cast_to = nullptr;
@@ -406,6 +407,7 @@ GDExtensionBool GDExtensionBinding::init(GDExtensionInterfaceGetProcAddress p_ge
 	LOAD_PROC_ADDRESS(global_get_singleton, GDExtensionInterfaceGlobalGetSingleton);
 	LOAD_PROC_ADDRESS(object_get_instance_binding, GDExtensionInterfaceObjectGetInstanceBinding);
 	LOAD_PROC_ADDRESS(object_set_instance_binding, GDExtensionInterfaceObjectSetInstanceBinding);
+	LOAD_PROC_ADDRESS(object_free_instance_binding, GDExtensionInterfaceObjectFreeInstanceBinding);
 	LOAD_PROC_ADDRESS(object_set_instance, GDExtensionInterfaceObjectSetInstance);
 	LOAD_PROC_ADDRESS(object_get_class_name, GDExtensionInterfaceObjectGetClassName);
 	LOAD_PROC_ADDRESS(object_cast_to, GDExtensionInterfaceObjectCastTo);

test/project/main.gd

@@ -256,6 +256,9 @@ func _ready():
 	assert_equal(example.test_virtual_implemented_in_script("Virtual", 939), "Implemented")
 	assert_equal(custom_signal_emitted, ["Virtual", 939])
 
+	# Test that we can access an engine singleton.
+	assert_equal(example.test_use_engine_singleton(), OS.get_name())
+
 	# Test that notifications happen on both parent and child classes.
 	var example_child = $ExampleChild
 	assert_equal(example_child.get_value1(), 11)

test/src/example.cpp

@@ -11,6 +11,7 @@
 #include <godot_cpp/classes/label.hpp>
 #include <godot_cpp/classes/multiplayer_api.hpp>
 #include <godot_cpp/classes/multiplayer_peer.hpp>
+#include <godot_cpp/classes/os.hpp>
 #include <godot_cpp/variant/utility_functions.hpp>
 
 using namespace godot;
@@ -239,6 +240,8 @@ void Example::_bind_methods() {
 	GDVIRTUAL_BIND(_do_something_virtual, "name", "value");
 	ClassDB::bind_method(D_METHOD("test_virtual_implemented_in_script"), &Example::test_virtual_implemented_in_script);
 
+	ClassDB::bind_method(D_METHOD("test_use_engine_singleton"), &Example::test_use_engine_singleton);
+
 	ClassDB::bind_static_method("Example", D_METHOD("test_static", "a", "b"), &Example::test_static);
 	ClassDB::bind_static_method("Example", D_METHOD("test_static2"), &Example::test_static2);
 
@@ -671,6 +674,10 @@ String Example::test_virtual_implemented_in_script(const String &p_name, int p_v
 	return "Unimplemented";
 }
 
+String Example::test_use_engine_singleton() const {
+	return OS::get_singleton()->get_name();
+}
+
 void ExampleRuntime::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("set_prop_value", "value"), &ExampleRuntime::set_prop_value);
 	ClassDB::bind_method(D_METHOD("get_prop_value"), &ExampleRuntime::get_prop_value);

test/src/example.h

@@ -186,6 +186,8 @@ class Example : public Control {
 
 	GDVIRTUAL2R(String, _do_something_virtual, String, int);
 	String test_virtual_implemented_in_script(const String &p_name, int p_value);
+
+	String test_use_engine_singleton() const;
 };
 
 VARIANT_ENUM_CAST(Example::Constants);