4 files changed, 41 insertions, 10 deletions

diff --git a/core/object/script_language.cpp b/core/object/script_language.cpp
index 011f4203ea..2bdbfb5ad1 100644
--- a/core/object/script_language.cpp
+++ b/core/object/script_language.cpp
@@ -39,10 +39,11 @@
 
 ScriptLanguage *ScriptServer::_languages[MAX_LANGUAGES];
 int ScriptServer::_language_count = 0;
+bool ScriptServer::languages_ready = false;
+Mutex ScriptServer::languages_mutex;
 
 bool ScriptServer::scripting_enabled = true;
 bool ScriptServer::reload_scripts_on_save = false;
-SafeFlag ScriptServer::languages_finished; // Used until GH-76581 is fixed properly.
 ScriptEditRequestFunction ScriptServer::edit_request_func = nullptr;
 
 void Script::_notification(int p_what) {
@@ -160,12 +161,13 @@ bool ScriptServer::is_scripting_enabled() {
 }
 
 ScriptLanguage *ScriptServer::get_language(int p_idx) {
+	MutexLock lock(languages_mutex);
 	ERR_FAIL_INDEX_V(p_idx, _language_count, nullptr);
-
 	return _languages[p_idx];
 }
 
 Error ScriptServer::register_language(ScriptLanguage *p_language) {
+	MutexLock lock(languages_mutex);
 	ERR_FAIL_NULL_V(p_language, ERR_INVALID_PARAMETER);
 	ERR_FAIL_COND_V_MSG(_language_count >= MAX_LANGUAGES, ERR_UNAVAILABLE, "Script languages limit has been reach, cannot register more.");
 	for (int i = 0; i < _language_count; i++) {
@@ -179,6 +181,8 @@ Error ScriptServer::register_language(ScriptLanguage *p_language) {
 }
 
 Error ScriptServer::unregister_language(const ScriptLanguage *p_language) {
+	MutexLock lock(languages_mutex);
+
 	for (int i = 0; i < _language_count; i++) {
 		if (_languages[i] == p_language) {
 			_language_count--;
@@ -219,17 +223,31 @@ void ScriptServer::init_languages() {
 		}
 	}
 
-	for (int i = 0; i < _language_count; i++) {
-		_languages[i]->init();
+	{
+		MutexLock lock(languages_mutex);
+
+		for (int i = 0; i < _language_count; i++) {
+			_languages[i]->init();
+		}
+
+		languages_ready = true;
 	}
 }
 
 void ScriptServer::finish_languages() {
+	MutexLock lock(languages_mutex);
+
 	for (int i = 0; i < _language_count; i++) {
 		_languages[i]->finish();
 	}
 	global_classes_clear();
-	languages_finished.set();
+
+	languages_ready = false;
+}
+
+bool ScriptServer::are_languages_initialized() {
+	MutexLock lock(languages_mutex);
+	return languages_ready;
 }
 
 void ScriptServer::set_reload_scripts_on_save(bool p_enable) {
@@ -241,7 +259,8 @@ bool ScriptServer::is_reload_scripts_on_save_enabled() {
 }
 
 void ScriptServer::thread_enter() {
-	if (!languages_finished.is_set()) {
+	MutexLock lock(languages_mutex);
+	if (!languages_ready) {
 		return;
 	}
 	for (int i = 0; i < _language_count; i++) {
@@ -250,7 +269,8 @@ void ScriptServer::thread_enter() {
 }
 
 void ScriptServer::thread_exit() {
-	if (!languages_finished.is_set()) {
+	MutexLock lock(languages_mutex);
+	if (!languages_ready) {
 		return;
 	}
 	for (int i = 0; i < _language_count; i++) {
diff --git a/core/object/script_language.h b/core/object/script_language.h
index 3e4041d173..85e64c8d62 100644
--- a/core/object/script_language.h
+++ b/core/object/script_language.h
@@ -52,9 +52,11 @@ class ScriptServer {
 
 	static ScriptLanguage *_languages[MAX_LANGUAGES];
 	static int _language_count;
+	static bool languages_ready;
+	static Mutex languages_mutex;
+
 	static bool scripting_enabled;
 	static bool reload_scripts_on_save;
-	static SafeFlag languages_finished; // Used until GH-76581 is fixed properly.
 
 	struct GlobalScriptClass {
 		StringName language;
@@ -98,8 +100,7 @@ public:
 
 	static void init_languages();
 	static void finish_languages();
-
-	static bool are_languages_finished() { return languages_finished.is_set(); }
+	static bool are_languages_initialized();
 };
 
 class PlaceHolderScriptInstance;
diff --git a/core/object/worker_thread_pool.cpp b/core/object/worker_thread_pool.cpp
index 2fcd0867e6..784acadab4 100644
--- a/core/object/worker_thread_pool.cpp
+++ b/core/object/worker_thread_pool.cpp
@@ -30,6 +30,7 @@
 
 #include "worker_thread_pool.h"
 
+#include "core/object/script_language.h"
 #include "core/os/os.h"
 #include "core/os/thread_safe.h"
 
@@ -60,6 +61,14 @@ void WorkerThreadPool::_process_task(Task *p_task) {
 		set_current_thread_safe_for_nodes(false);
 		pool_thread_index = thread_ids[Thread::get_caller_id()];
 		ThreadData &curr_thread = threads[pool_thread_index];
+		// 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.
+		if (!curr_thread.ready_for_scripting && ScriptServer::are_languages_initialized()) {
+			ScriptServer::thread_enter();
+			curr_thread.ready_for_scripting = true;
+		}
 		task_mutex.lock();
 		p_task->pool_thread_index = pool_thread_index;
 		if (low_priority) {
diff --git a/core/object/worker_thread_pool.h b/core/object/worker_thread_pool.h
index d4d9387765..f323a979f7 100644
--- a/core/object/worker_thread_pool.h
+++ b/core/object/worker_thread_pool.h
@@ -106,6 +106,7 @@ private:
 		uint32_t index;
 		Thread thread;
 		Task *current_low_prio_task = nullptr;
+		bool ready_for_scripting = false;
 	};
 
 	TightLocalVector<ThreadData> threads;