From 37b6a36cc4b5a4dec6c2c2996864ca06c7f37672 Mon Sep 17 00:00:00 2001
From: Lyuma <xn.lyuma@gmail.com>
Date: Sun, 1 Nov 2020 00:44:15 -0700
Subject: [PATCH] Avoid reentrant OBJTYPE_RLOCK in ClassDB

Fixes #43020 when a thread uses ClassDB while main thread calls is_parent_class().
---
 core/class_db.cpp | 26 +++++++++++++++++---------
 core/class_db.h   |  5 +++++
 2 files changed, 22 insertions(+), 9 deletions(-)

diff --git a/core/class_db.cpp b/core/class_db.cpp
index ad85cd0d623..81bc9015618 100644
--- a/core/class_db.cpp
+++ b/core/class_db.cpp
@@ -242,21 +242,25 @@ HashMap<StringName, ClassDB::ClassInfo> ClassDB::classes;
 HashMap<StringName, StringName> ClassDB::resource_base_extensions;
 HashMap<StringName, StringName> ClassDB::compat_classes;
 
-bool ClassDB::is_parent_class(const StringName &p_class, const StringName &p_inherits) {
-	OBJTYPE_RLOCK;
-
+bool ClassDB::_is_parent_class(const StringName &p_class, const StringName &p_inherits) {
 	StringName inherits = p_class;
 
 	while (inherits.operator String().length()) {
 		if (inherits == p_inherits) {
 			return true;
 		}
-		inherits = get_parent_class(inherits);
+		inherits = _get_parent_class(inherits);
 	}
 
 	return false;
 }
 
+bool ClassDB::is_parent_class(const StringName &p_class, const StringName &p_inherits) {
+	OBJTYPE_RLOCK;
+
+	return _is_parent_class(p_class, p_inherits);
+}
+
 void ClassDB::get_class_list(List<StringName> *p_classes) {
 	OBJTYPE_RLOCK;
 
@@ -275,7 +279,7 @@ void ClassDB::get_inheriters_from_class(const StringName &p_class, List<StringNa
 	const StringName *k = nullptr;
 
 	while ((k = classes.next(k))) {
-		if (*k != p_class && is_parent_class(*k, p_class)) {
+		if (*k != p_class && _is_parent_class(*k, p_class)) {
 			p_classes->push_back(*k);
 		}
 	}
@@ -287,7 +291,7 @@ void ClassDB::get_direct_inheriters_from_class(const StringName &p_class, List<S
 	const StringName *k = nullptr;
 
 	while ((k = classes.next(k))) {
-		if (*k != p_class && get_parent_class(*k) == p_class) {
+		if (*k != p_class && _get_parent_class(*k) == p_class) {
 			p_classes->push_back(*k);
 		}
 	}
@@ -315,14 +319,18 @@ StringName ClassDB::get_compatibility_remapped_class(const StringName &p_class)
 	return p_class;
 }
 
-StringName ClassDB::get_parent_class(const StringName &p_class) {
-	OBJTYPE_RLOCK;
-
+StringName ClassDB::_get_parent_class(const StringName &p_class) {
 	ClassInfo *ti = classes.getptr(p_class);
 	ERR_FAIL_COND_V_MSG(!ti, StringName(), "Cannot get class '" + String(p_class) + "'.");
 	return ti->inherits;
 }
 
+StringName ClassDB::get_parent_class(const StringName &p_class) {
+	OBJTYPE_RLOCK;
+
+	return _get_parent_class(p_class);
+}
+
 ClassDB::APIType ClassDB::get_api_type(const StringName &p_class) {
 	OBJTYPE_RLOCK;
 
diff --git a/core/class_db.h b/core/class_db.h
index 4734b06c7a6..22072066d93 100644
--- a/core/class_db.h
+++ b/core/class_db.h
@@ -164,6 +164,11 @@ public:
 	static HashMap<StringName, HashMap<StringName, Variant>> default_values;
 	static Set<StringName> default_values_cached;
 
+private:
+	// Non-locking variants of get_parent_class and is_parent_class.
+	static StringName _get_parent_class(const StringName &p_class);
+	static bool _is_parent_class(const StringName &p_class, const StringName &p_inherits);
+
 public:
 	// DO NOT USE THIS!!!!!! NEEDS TO BE PUBLIC BUT DO NOT USE NO MATTER WHAT!!!
 	template <class T>