From c8acf561ef0c66c03d9e15e46e753c98ab485050 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Pedro=20J=2E=20Est=C3=A9banez?= <pedrojrulez@gmail.com>
Date: Tue, 10 Sep 2024 11:29:54 +0200
Subject: [PATCH] Make languages' thread enter/exit more resilient

---
 core/object/script_language.cpp    | 17 +++++++++++++++++
 core/object/script_language.h      |  2 ++
 core/object/worker_thread_pool.cpp | 15 +++++++++------
 core/object/worker_thread_pool.h   |  2 --
 4 files changed, 28 insertions(+), 8 deletions(-)

diff --git a/core/object/script_language.cpp b/core/object/script_language.cpp
index 57e51951377..d5b7bc768da 100644
--- a/core/object/script_language.cpp
+++ b/core/object/script_language.cpp
@@ -41,6 +41,7 @@ ScriptLanguage *ScriptServer::_languages[MAX_LANGUAGES];
 int ScriptServer::_language_count = 0;
 bool ScriptServer::languages_ready = false;
 Mutex ScriptServer::languages_mutex;
+thread_local bool ScriptServer::thread_entered = false;
 
 bool ScriptServer::scripting_enabled = true;
 bool ScriptServer::reload_scripts_on_save = false;
@@ -326,6 +327,10 @@ bool ScriptServer::are_languages_initialized() {
 	return languages_ready;
 }
 
+bool ScriptServer::thread_is_entered() {
+	return thread_entered;
+}
+
 void ScriptServer::set_reload_scripts_on_save(bool p_enable) {
 	reload_scripts_on_save = p_enable;
 }
@@ -335,6 +340,10 @@ bool ScriptServer::is_reload_scripts_on_save_enabled() {
 }
 
 void ScriptServer::thread_enter() {
+	if (thread_entered) {
+		return;
+	}
+
 	MutexLock lock(languages_mutex);
 	if (!languages_ready) {
 		return;
@@ -342,9 +351,15 @@ void ScriptServer::thread_enter() {
 	for (int i = 0; i < _language_count; i++) {
 		_languages[i]->thread_enter();
 	}
+
+	thread_entered = true;
 }
 
 void ScriptServer::thread_exit() {
+	if (!thread_entered) {
+		return;
+	}
+
 	MutexLock lock(languages_mutex);
 	if (!languages_ready) {
 		return;
@@ -352,6 +367,8 @@ void ScriptServer::thread_exit() {
 	for (int i = 0; i < _language_count; i++) {
 		_languages[i]->thread_exit();
 	}
+
+	thread_entered = false;
 }
 
 HashMap<StringName, ScriptServer::GlobalScriptClass> ScriptServer::global_classes;
diff --git a/core/object/script_language.h b/core/object/script_language.h
index e38c344ae57..d9e2ab1d3c7 100644
--- a/core/object/script_language.h
+++ b/core/object/script_language.h
@@ -54,6 +54,7 @@ class ScriptServer {
 	static int _language_count;
 	static bool languages_ready;
 	static Mutex languages_mutex;
+	static thread_local bool thread_entered;
 
 	static bool scripting_enabled;
 	static bool reload_scripts_on_save;
@@ -101,6 +102,7 @@ public:
 	static void init_languages();
 	static void finish_languages();
 	static bool are_languages_initialized();
+	static bool thread_is_entered();
 };
 
 class PlaceHolderScriptInstance;
diff --git a/core/object/worker_thread_pool.cpp b/core/object/worker_thread_pool.cpp
index da503966b18..cf396c26760 100644
--- a/core/object/worker_thread_pool.cpp
+++ b/core/object/worker_thread_pool.cpp
@@ -63,17 +63,14 @@ void WorkerThreadPool::_process_task(Task *p_task) {
 		// Tasks must start with these at default values. They are free to set-and-forget otherwise.
 		set_current_thread_safe_for_nodes(false);
 		MessageQueue::set_thread_singleton_override(nullptr);
+
 		// Since the WorkerThreadPool is started before the script server,
 		// its pre-created threads can't have ScriptServer::thread_enter() called on them early.
 		// Therefore, we do it late at the first opportunity, so in case the task
 		// about to be run uses scripting, guarantees are held.
+		ScriptServer::thread_enter();
+
 		task_mutex.lock();
-		if (!curr_thread.ready_for_scripting && ScriptServer::are_languages_initialized()) {
-			task_mutex.unlock();
-			ScriptServer::thread_enter();
-			task_mutex.lock();
-			curr_thread.ready_for_scripting = true;
-		}
 		p_task->pool_thread_index = pool_thread_index;
 		prev_task = curr_thread.current_task;
 		curr_thread.current_task = p_task;
@@ -516,6 +513,12 @@ void WorkerThreadPool::yield() {
 	int th_index = get_thread_index();
 	ERR_FAIL_COND_MSG(th_index == -1, "This function can only be called from a worker thread.");
 	_wait_collaboratively(&threads[th_index], ThreadData::YIELDING);
+
+	// If this long-lived task started before the scripting server was initialized,
+	// now is a good time to have scripting languages ready for the current thread.
+	// Otherwise, such a piece of setup won't happen unless another task has been
+	// run during the collaborative wait.
+	ScriptServer::thread_enter();
 }
 
 void WorkerThreadPool::notify_yield_over(TaskID p_task_id) {
diff --git a/core/object/worker_thread_pool.h b/core/object/worker_thread_pool.h
index 5be4f209270..6374dbe8c7e 100644
--- a/core/object/worker_thread_pool.h
+++ b/core/object/worker_thread_pool.h
@@ -112,7 +112,6 @@ private:
 
 		uint32_t index = 0;
 		Thread thread;
-		bool ready_for_scripting : 1;
 		bool signaled : 1;
 		bool yield_is_over : 1;
 		Task *current_task = nullptr;
@@ -120,7 +119,6 @@ private:
 		ConditionVariable cond_var;
 
 		ThreadData() :
-				ready_for_scripting(false),
 				signaled(false),
 				yield_is_over(false) {}
 	};