Fix dangling Variants (3.2)

core/object.cpp

@@ -33,6 +33,7 @@
 #include "core/class_db.h"
 #include "core/core_string_names.h"
 #include "core/message_queue.h"
+#include "core/object_rc.h"
 #include "core/os/os.h"
 #include "core/print_string.h"
 #include "core/resource.h"
@@ -968,6 +969,37 @@ void Object::cancel_delete() {
 	_predelete_ok = true;
 }
 
+#ifdef DEBUG_ENABLED
+ObjectRC *Object::_use_rc() {
+
+	// The RC object is lazily created the first time it's requested;
+	// that way, there's no need to allocate and release it at all if this Object
+	// is not being referred by any Variant at all.
+
+	// Although when dealing with Objects from multiple threads some locking
+	// mechanism should be used, this at least makes safe the case of first
+	// assignment.
+
+	ObjectRC *rc = nullptr;
+	ObjectRC *const creating = reinterpret_cast<ObjectRC *>(1);
+	if (unlikely(_rc.compare_exchange_strong(rc, creating, std::memory_order_acq_rel))) {
+		// Not created yet
+		rc = memnew(ObjectRC(this));
+		_rc.store(rc, std::memory_order_release);
+		return rc;
+	}
+
+	// Spin-wait until we know it's created (or just return if it's already created)
+	for (;;) {
+		if (likely(rc != creating)) {
+			rc->increment();
+			return rc;
+		}
+		rc = _rc.load(std::memory_order_acquire);
+	}
+}
+#endif
+
 void Object::set_script_and_instance(const RefPtr &p_script, ScriptInstance *p_instance) {
 
 	//this function is not meant to be used in any of these ways
@@ -1944,6 +1976,9 @@ Object::Object() {
 	instance_binding_count = 0;
 	memset(_script_instance_bindings, 0, sizeof(void *) * MAX_SCRIPT_INSTANCE_BINDINGS);
 	script_instance = NULL;
+#ifdef DEBUG_ENABLED
+	_rc.store(nullptr, std::memory_order_release);
+#endif
 #ifdef TOOLS_ENABLED
 
 	_edited = false;
@@ -1957,6 +1992,15 @@ Object::Object() {
 
 Object::~Object() {
 
+#ifdef DEBUG_ENABLED
+	ObjectRC *rc = _rc.load(std::memory_order_acquire);
+	if (rc) {
+		if (rc->invalidate()) {
+			memfree(rc);
+		}
+	}
+#endif
+
 	if (script_instance)
 		memdelete(script_instance);
 	script_instance = NULL;

core/object.h

@@ -34,11 +34,16 @@
 #include "core/hash_map.h"
 #include "core/list.h"
 #include "core/map.h"
+#include "core/object_id.h"
 #include "core/os/rw_lock.h"
 #include "core/set.h"
 #include "core/variant.h"
 #include "core/vmap.h"
 
+#ifdef DEBUG_ENABLED
+#include <atomic> // For ObjectRC*
+#endif
+
 #define VARIANT_ARG_LIST const Variant &p_arg1 = Variant(), const Variant &p_arg2 = Variant(), const Variant &p_arg3 = Variant(), const Variant &p_arg4 = Variant(), const Variant &p_arg5 = Variant()
 #define VARIANT_ARG_PASS p_arg1, p_arg2, p_arg3, p_arg4, p_arg5
 #define VARIANT_ARG_DECLARE const Variant &p_arg1, const Variant &p_arg2, const Variant &p_arg3, const Variant &p_arg4, const Variant &p_arg5
@@ -397,7 +402,7 @@ public:                                                        \
 private:
 
 class ScriptInstance;
-typedef uint64_t ObjectID;
+class ObjectRC;
 
 class Object {
 public:
@@ -477,6 +482,9 @@ class Object {
 	int _predelete_ok;
 	Set<Object *> change_receptors;
 	ObjectID _instance_id;
+#ifdef DEBUG_ENABLED
+	std::atomic<ObjectRC *> _rc;
+#endif
 	bool _predelete();
 	void _postinitialize();
 	bool _can_translate;
@@ -587,6 +595,10 @@ class Object {
 		return &ptr;
 	}
 
+#ifdef DEBUG_ENABLED
+	ObjectRC *_use_rc();
+#endif
+
 	bool _is_gpl_reversed() const { return false; }
 
 	_FORCE_INLINE_ ObjectID get_instance_id() const { return _instance_id; }

core/object_id.h

@@ -0,0 +1,38 @@
+/*************************************************************************/
+/*  object_rc.h                                                          */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2020 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2020 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+#ifndef OBJECTID_H
+#define OBJECTID_H
+
+#include "core/int_types.h"
+
+typedef uint64_t ObjectID;
+
+#endif

core/object_rc.h

@@ -0,0 +1,75 @@
+/*************************************************************************/
+/*  object_rc.h                                                          */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2020 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2020 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+#ifndef OBJECTRC_H
+#define OBJECTRC_H
+
+#ifdef DEBUG_ENABLED
+
+#include "core/os/memory.h"
+#include "core/typedefs.h"
+
+#include <atomic>
+
+class Object;
+
+// Used to track Variants pointing to a non-Reference Object
+class ObjectRC {
+	std::atomic<Object *> _ptr;
+	std::atomic<uint32_t> _users;
+
+public:
+	_FORCE_INLINE_ void increment() {
+		_users.fetch_add(1, std::memory_order_relaxed);
+	}
+
+	_FORCE_INLINE_ bool decrement() {
+		return _users.fetch_sub(1, std::memory_order_relaxed) == 1;
+	}
+
+	_FORCE_INLINE_ bool invalidate() {
+		_ptr.store(nullptr, std::memory_order_release);
+		return decrement();
+	}
+
+	_FORCE_INLINE_ Object *get_ptr() {
+		return _ptr.load(std::memory_order_acquire);
+	}
+
+	_FORCE_INLINE_ ObjectRC(Object *p_object) {
+		// 1 (the Object) + 1 (the first user)
+		_users.store(2, std::memory_order_relaxed);
+		_ptr.store(p_object, std::memory_order_release);
+	}
+};
+
+#endif
+
+#endif