Revert recently added approach to cross-thread lambda survival

Commits reverted:
- 1ed69191483002ee62ec5b4d5adb16d3bc315ef3
- 271511726b02848783904429c8dde857f6266429

4 files changed, 16 insertions, 107 deletions

diff --git a/modules/gdscript/gdscript.cpp b/modules/gdscript/gdscript.cpp
index b098a0d3d5..a2be6a86d7 100644
--- a/modules/gdscript/gdscript.cpp
+++ b/modules/gdscript/gdscript.cpp
@@ -1392,17 +1392,14 @@ String GDScript::debug_get_script_name(const Ref<Script> &p_script) {
 #endif
 
 thread_local GDScript::UpdatableFuncPtr GDScript::func_ptrs_to_update_thread_local;
-GDScript::UpdatableFuncPtr *GDScript::func_ptrs_to_update_main_thread = &func_ptrs_to_update_thread_local;
 
-List<GDScript::UpdatableFuncPtrElement>::Element *GDScript::_add_func_ptr_to_update(GDScriptFunction **p_func_ptr_ptr) {
-	MutexLock lock(func_ptrs_to_update_mutex);
-
-	List<UpdatableFuncPtrElement>::Element *result = func_ptrs_to_update_elems.push_back(UpdatableFuncPtrElement());
+GDScript::UpdatableFuncPtrElement GDScript::_add_func_ptr_to_update(GDScriptFunction **p_func_ptr_ptr) {
+	UpdatableFuncPtrElement result = {};
 
 	{
-		MutexLock lock2(func_ptrs_to_update_thread_local.mutex);
-		result->get().element = func_ptrs_to_update_thread_local.ptrs.push_back(p_func_ptr_ptr);
-		result->get().mutex = &func_ptrs_to_update_thread_local.mutex;
+		MutexLock lock(func_ptrs_to_update_thread_local.mutex);
+		result.element = func_ptrs_to_update_thread_local.ptrs.push_back(p_func_ptr_ptr);
+		result.mutex = &func_ptrs_to_update_thread_local.mutex;
 
 		if (likely(func_ptrs_to_update_thread_local.initialized)) {
 			return result;
@@ -1411,89 +1408,17 @@ List<GDScript::UpdatableFuncPtrElement>::Element *GDScript::_add_func_ptr_to_upd
 		func_ptrs_to_update_thread_local.initialized = true;
 	}
 
+	MutexLock lock(func_ptrs_to_update_mutex);
 	func_ptrs_to_update.push_back(&func_ptrs_to_update_thread_local);
 
 	return result;
 }
 
-void GDScript::_remove_func_ptr_to_update(List<UpdatableFuncPtrElement>::Element *p_func_ptr_element) {
-	// None of these checks should ever fail, unless there's a bug.
-	// They can be removed once we are sure they never catch anything.
-	// Left here now due to extra safety needs late in the release cycle.
-	ERR_FAIL_NULL(p_func_ptr_element);
-	MutexLock lock(func_ptrs_to_update_thread_local.mutex);
-	ERR_FAIL_NULL(p_func_ptr_element->get().element);
-	ERR_FAIL_NULL(p_func_ptr_element->get().mutex);
-	MutexLock lock2(*p_func_ptr_element->get().mutex);
-	p_func_ptr_element->get().element->erase();
-	p_func_ptr_element->erase();
-}
-
-void GDScript::_fixup_thread_function_bookkeeping() {
-	// Transfer the ownership of these update items to the main thread,
-	// because the current one is dying, leaving theirs orphan, dangling.
-
-	HashSet<GDScript *> scripts;
-
-	DEV_ASSERT(!Thread::is_main_thread());
-	MutexLock lock(func_ptrs_to_update_main_thread->mutex);
-
-	{
-		MutexLock lock2(func_ptrs_to_update_thread_local.mutex);
-
-		while (!func_ptrs_to_update_thread_local.ptrs.is_empty()) {
-			// Transfer the thread-to-script records from the dying thread to the main one.
-
-			List<GDScriptFunction **>::Element *E = func_ptrs_to_update_thread_local.ptrs.front();
-			List<GDScriptFunction **>::Element *new_E = func_ptrs_to_update_main_thread->ptrs.push_front(E->get());
-
-			GDScript *script = (*E->get())->get_script();
-			if (!scripts.has(script)) {
-				scripts.insert(script);
-
-				// Replace dying thread by the main thread in the script-to-thread records.
-
-				MutexLock lock3(script->func_ptrs_to_update_mutex);
-				DEV_ASSERT(script->func_ptrs_to_update.find(&func_ptrs_to_update_thread_local));
-				{
-					for (List<UpdatableFuncPtrElement>::Element *F = script->func_ptrs_to_update_elems.front(); F; F = F->next()) {
-						bool is_dying_thread_entry = F->get().mutex == &func_ptrs_to_update_thread_local.mutex;
-						if (is_dying_thread_entry) {
-							// This may lead to multiple main-thread entries, but that's not a problem
-							// and allows to reuse the element, which is needed, since it's tracked by pointer.
-							F->get().element = new_E;
-							F->get().mutex = &func_ptrs_to_update_main_thread->mutex;
-						}
-					}
-				}
-			}
-
-			E->erase();
-		}
-	}
-	func_ptrs_to_update_main_thread->initialized = true;
-
-	{
-		// Remove orphan thread-to-script entries from every script.
-		// FIXME: This involves iterating through every script whenever a thread dies.
-		//        While it's OK that thread creation/destruction are heavy operations,
-		//        additional bookkeeping can be used to outperform this brute-force approach.
-
-		GDScriptLanguage *gd_lang = GDScriptLanguage::get_singleton();
-
-		MutexLock lock2(gd_lang->mutex);
-
-		for (SelfList<GDScript> *s = gd_lang->script_list.first(); s; s = s->next()) {
-			GDScript *script = s->self();
-			for (List<UpdatableFuncPtr *>::Element *E = script->func_ptrs_to_update.front(); E; E = E->next()) {
-				bool is_dying_thread_entry = &E->get()->mutex == &func_ptrs_to_update_thread_local.mutex;
-				if (is_dying_thread_entry) {
-					E->erase();
-					break;
-				}
-			}
-		}
-	}
+void GDScript::_remove_func_ptr_to_update(const UpdatableFuncPtrElement p_func_ptr_element) {
+	ERR_FAIL_NULL(p_func_ptr_element.element);
+	ERR_FAIL_NULL(p_func_ptr_element.mutex);
+	MutexLock lock(*p_func_ptr_element.mutex);
+	p_func_ptr_element.element->erase();
 }
 
 void GDScript::clear(ClearData *p_clear_data) {
@@ -1521,7 +1446,6 @@ void GDScript::clear(ClearData *p_clear_data) {
 				*func_ptr_ptr = nullptr;
 			}
 		}
-		func_ptrs_to_update_elems.clear();
 	}
 
 	RBSet<GDScript *> must_clear_dependencies = get_must_clear_dependencies();
@@ -2141,10 +2065,6 @@ void GDScriptLanguage::remove_named_global_constant(const StringName &p_name) {
 	named_globals.erase(p_name);
 }
 
-void GDScriptLanguage::thread_exit() {
-	GDScript::_fixup_thread_function_bookkeeping();
-}
-
 void GDScriptLanguage::init() {
 	//populate global constants
 	int gcc = CoreConstants::get_global_constant_count();
diff --git a/modules/gdscript/gdscript.h b/modules/gdscript/gdscript.h
index 8d62334d69..9717dd7ff1 100644
--- a/modules/gdscript/gdscript.h
+++ b/modules/gdscript/gdscript.h
@@ -128,16 +128,11 @@ class GDScript : public Script {
 		Mutex *mutex = nullptr;
 	};
 	static thread_local UpdatableFuncPtr func_ptrs_to_update_thread_local;
-	static thread_local LocalVector<List<UpdatableFuncPtr *>::Element> func_ptrs_to_update_entries_thread_local;
-	static UpdatableFuncPtr *func_ptrs_to_update_main_thread;
 	List<UpdatableFuncPtr *> func_ptrs_to_update;
-	List<UpdatableFuncPtrElement> func_ptrs_to_update_elems;
 	Mutex func_ptrs_to_update_mutex;
 
-	List<UpdatableFuncPtrElement>::Element *_add_func_ptr_to_update(GDScriptFunction **p_func_ptr_ptr);
-	static void _remove_func_ptr_to_update(List<UpdatableFuncPtrElement>::Element *p_func_ptr_element);
-
-	static void _fixup_thread_function_bookkeeping();
+	UpdatableFuncPtrElement _add_func_ptr_to_update(GDScriptFunction **p_func_ptr_ptr);
+	static void _remove_func_ptr_to_update(const UpdatableFuncPtrElement p_func_ptr_element);
 
 #ifdef TOOLS_ENABLED
 	// For static data storage during hot-reloading.
@@ -559,10 +554,6 @@ public:
 	virtual void add_named_global_constant(const StringName &p_name, const Variant &p_value) override;
 	virtual void remove_named_global_constant(const StringName &p_name) override;
 
-	/* MULTITHREAD FUNCTIONS */
-
-	virtual void thread_exit() override;
-
 	/* DEBUGGER FUNCTIONS */
 
 	virtual String debug_get_error() const override;
diff --git a/modules/gdscript/gdscript_lambda_callable.cpp b/modules/gdscript/gdscript_lambda_callable.cpp
index 339d1ac08e..547f5607d3 100644
--- a/modules/gdscript/gdscript_lambda_callable.cpp
+++ b/modules/gdscript/gdscript_lambda_callable.cpp
@@ -296,7 +296,5 @@ GDScriptLambdaSelfCallable::GDScriptLambdaSelfCallable(Object *p_self, GDScriptF
 }
 
 GDScriptLambdaSelfCallable::~GDScriptLambdaSelfCallable() {
-	if (updatable_func_ptr_element) {
-		GDScript::_remove_func_ptr_to_update(updatable_func_ptr_element);
-	}
+	GDScript::_remove_func_ptr_to_update(updatable_func_ptr_element);
 }
diff --git a/modules/gdscript/gdscript_lambda_callable.h b/modules/gdscript/gdscript_lambda_callable.h
index 405d7c1823..ee7d547544 100644
--- a/modules/gdscript/gdscript_lambda_callable.h
+++ b/modules/gdscript/gdscript_lambda_callable.h
@@ -45,7 +45,7 @@ class GDScriptLambdaCallable : public CallableCustom {
 	GDScriptFunction *function = nullptr;
 	Ref<GDScript> script;
 	uint32_t h;
-	List<GDScript::UpdatableFuncPtrElement>::Element *updatable_func_ptr_element = nullptr;
+	GDScript::UpdatableFuncPtrElement updatable_func_ptr_element;
 
 	Vector<Variant> captures;
 
@@ -72,7 +72,7 @@ class GDScriptLambdaSelfCallable : public CallableCustom {
 	Ref<RefCounted> reference; // For objects that are RefCounted, keep a reference.
 	Object *object = nullptr; // For non RefCounted objects, use a direct pointer.
 	uint32_t h;
-	List<GDScript::UpdatableFuncPtrElement>::Element *updatable_func_ptr_element = nullptr;
+	GDScript::UpdatableFuncPtrElement updatable_func_ptr_element;
 
 	Vector<Variant> captures;