WorkerThreadPool (plus friends): Overhaul unlock allowance zones

This fixes a rare but possible deadlock, maybe due to undefined behavior. The new implementation is safer, at the cost of some added boilerplate.

(cherry picked from commit f4d76853b9d921e3645295f9bebc39eb73661e67)

12 files changed, 118 insertions, 110 deletions

diff --git a/SConstruct b/SConstruct
index 0ae8f1a387..2ccbd27638 100644
--- a/SConstruct
+++ b/SConstruct
@@ -856,7 +856,7 @@ else:  # GCC, Clang
             if cc_version_major >= 11:  # Broke on MethodBind templates before GCC 11.
                 env.Append(CCFLAGS=["-Wlogical-op"])
         elif methods.using_clang(env) or methods.using_emcc(env):
-            env.Append(CCFLAGS=["-Wimplicit-fallthrough"])
+            env.Append(CCFLAGS=["-Wimplicit-fallthrough", "-Wno-undefined-var-template"])
     elif env["warnings"] == "all":
         env.Append(CCFLAGS=["-Wall"] + common_warnings)
     elif env["warnings"] == "moderate":
diff --git a/core/io/resource_loader.cpp b/core/io/resource_loader.cpp
index c3c31d8823..fd4fbc36f7 100644
--- a/core/io/resource_loader.cpp
+++ b/core/io/resource_loader.cpp
@@ -1363,8 +1363,12 @@ thread_local int ResourceLoader::load_nesting = 0;
 thread_local Vector<String> ResourceLoader::load_paths_stack;
 thread_local HashMap<int, HashMap<String, Ref<Resource>>> ResourceLoader::res_ref_overrides;
 
+SafeBinaryMutex<ResourceLoader::BINARY_MUTEX_TAG> &_get_res_loader_mutex() {
+	return ResourceLoader::thread_load_mutex;
+}
+
 template <>
-thread_local uint32_t SafeBinaryMutex<ResourceLoader::BINARY_MUTEX_TAG>::count = 0;
+thread_local SafeBinaryMutex<ResourceLoader::BINARY_MUTEX_TAG>::TLSData SafeBinaryMutex<ResourceLoader::BINARY_MUTEX_TAG>::tls_data(_get_res_loader_mutex());
 SafeBinaryMutex<ResourceLoader::BINARY_MUTEX_TAG> ResourceLoader::thread_load_mutex;
 HashMap<String, ResourceLoader::ThreadLoadTask> ResourceLoader::thread_load_tasks;
 bool ResourceLoader::cleaning_tasks = false;
diff --git a/core/io/resource_loader.h b/core/io/resource_loader.h
index 217c14d7a3..f75bf019fb 100644
--- a/core/io/resource_loader.h
+++ b/core/io/resource_loader.h
@@ -194,7 +194,10 @@ private:
 	static thread_local int load_nesting;
 	static thread_local HashMap<int, HashMap<String, Ref<Resource>>> res_ref_overrides; // Outermost key is nesting level.
 	static thread_local Vector<String> load_paths_stack;
+
 	static SafeBinaryMutex<BINARY_MUTEX_TAG> thread_load_mutex;
+	friend SafeBinaryMutex<BINARY_MUTEX_TAG> &_get_res_loader_mutex();
+
 	static HashMap<String, ThreadLoadTask> thread_load_tasks;
 	static bool cleaning_tasks;
 
diff --git a/core/object/worker_thread_pool.cpp b/core/object/worker_thread_pool.cpp
index 155d963a2b..7fd43c4094 100644
--- a/core/object/worker_thread_pool.cpp
+++ b/core/object/worker_thread_pool.cpp
@@ -32,6 +32,7 @@
 
 #include "core/object/script_language.h"
 #include "core/os/os.h"
+#include "core/os/safe_binary_mutex.h"
 #include "core/os/thread_safe.h"
 
 WorkerThreadPool::Task *const WorkerThreadPool::ThreadData::YIELDING = (Task *)1;
@@ -46,7 +47,7 @@ void WorkerThreadPool::Task::free_template_userdata() {
 WorkerThreadPool *WorkerThreadPool::singleton = nullptr;
 
 #ifdef THREADS_ENABLED
-thread_local uintptr_t WorkerThreadPool::unlockable_mutexes[MAX_UNLOCKABLE_MUTEXES] = {};
+thread_local WorkerThreadPool::UnlockableLocks WorkerThreadPool::unlockable_locks[MAX_UNLOCKABLE_LOCKS];
 #endif
 
 void WorkerThreadPool::_process_task(Task *p_task) {
@@ -428,13 +429,9 @@ Error WorkerThreadPool::wait_for_task_completion(TaskID p_task_id) {
 
 void WorkerThreadPool::_lock_unlockable_mutexes() {
 #ifdef THREADS_ENABLED
-	for (uint32_t i = 0; i < MAX_UNLOCKABLE_MUTEXES; i++) {
-		if (unlockable_mutexes[i]) {
-			if ((((uintptr_t)unlockable_mutexes[i]) & 1) == 0) {
-				((Mutex *)unlockable_mutexes[i])->lock();
-			} else {
-				((BinaryMutex *)(unlockable_mutexes[i] & ~1))->lock();
-			}
+	for (uint32_t i = 0; i < MAX_UNLOCKABLE_LOCKS; i++) {
+		if (unlockable_locks[i].ulock) {
+			unlockable_locks[i].ulock->lock();
 		}
 	}
 #endif
@@ -442,13 +439,9 @@ void WorkerThreadPool::_lock_unlockable_mutexes() {
 
 void WorkerThreadPool::_unlock_unlockable_mutexes() {
 #ifdef THREADS_ENABLED
-	for (uint32_t i = 0; i < MAX_UNLOCKABLE_MUTEXES; i++) {
-		if (unlockable_mutexes[i]) {
-			if ((((uintptr_t)unlockable_mutexes[i]) & 1) == 0) {
-				((Mutex *)unlockable_mutexes[i])->unlock();
-			} else {
-				((BinaryMutex *)(unlockable_mutexes[i] & ~1))->unlock();
-			}
+	for (uint32_t i = 0; i < MAX_UNLOCKABLE_LOCKS; i++) {
+		if (unlockable_locks[i].ulock) {
+			unlockable_locks[i].ulock->unlock();
 		}
 	}
 #endif
@@ -675,37 +668,28 @@ WorkerThreadPool::TaskID WorkerThreadPool::get_caller_task_id() {
 }
 
 #ifdef THREADS_ENABLED
-uint32_t WorkerThreadPool::thread_enter_unlock_allowance_zone(Mutex *p_mutex) {
-	return _thread_enter_unlock_allowance_zone(p_mutex, false);
-}
-
-uint32_t WorkerThreadPool::thread_enter_unlock_allowance_zone(BinaryMutex *p_mutex) {
-	return _thread_enter_unlock_allowance_zone(p_mutex, true);
-}
-
-uint32_t WorkerThreadPool::_thread_enter_unlock_allowance_zone(void *p_mutex, bool p_is_binary) {
-	for (uint32_t i = 0; i < MAX_UNLOCKABLE_MUTEXES; i++) {
-		if (unlikely((unlockable_mutexes[i] & ~1) == (uintptr_t)p_mutex)) {
+uint32_t WorkerThreadPool::_thread_enter_unlock_allowance_zone(THREADING_NAMESPACE::unique_lock<THREADING_NAMESPACE::mutex> &p_ulock) {
+	for (uint32_t i = 0; i < MAX_UNLOCKABLE_LOCKS; i++) {
+		DEV_ASSERT((bool)unlockable_locks[i].ulock == (bool)unlockable_locks[i].rc);
+		if (unlockable_locks[i].ulock == &p_ulock) {
 			// Already registered in the current thread.
-			return UINT32_MAX;
-		}
-		if (!unlockable_mutexes[i]) {
-			unlockable_mutexes[i] = (uintptr_t)p_mutex;
-			if (p_is_binary) {
-				unlockable_mutexes[i] |= 1;
-			}
+			unlockable_locks[i].rc++;
+			return i;
+		} else if (!unlockable_locks[i].ulock) {
+			unlockable_locks[i].ulock = &p_ulock;
+			unlockable_locks[i].rc = 1;
 			return i;
 		}
 	}
-	ERR_FAIL_V_MSG(UINT32_MAX, "No more unlockable mutex slots available. Engine bug.");
+	ERR_FAIL_V_MSG(UINT32_MAX, "No more unlockable lock slots available. Engine bug.");
 }
 
 void WorkerThreadPool::thread_exit_unlock_allowance_zone(uint32_t p_zone_id) {
-	if (p_zone_id == UINT32_MAX) {
-		return;
+	DEV_ASSERT(unlockable_locks[p_zone_id].ulock && unlockable_locks[p_zone_id].rc);
+	unlockable_locks[p_zone_id].rc--;
+	if (unlockable_locks[p_zone_id].rc == 0) {
+		unlockable_locks[p_zone_id].ulock = nullptr;
 	}
-	DEV_ASSERT(unlockable_mutexes[p_zone_id]);
-	unlockable_mutexes[p_zone_id] = 0;
 }
 #endif
 
diff --git a/core/object/worker_thread_pool.h b/core/object/worker_thread_pool.h
index 57b67b32fa..5be4f20927 100644
--- a/core/object/worker_thread_pool.h
+++ b/core/object/worker_thread_pool.h
@@ -162,8 +162,12 @@ private:
 	static WorkerThreadPool *singleton;
 
 #ifdef THREADS_ENABLED
-	static const uint32_t MAX_UNLOCKABLE_MUTEXES = 2;
-	static thread_local uintptr_t unlockable_mutexes[MAX_UNLOCKABLE_MUTEXES];
+	static const uint32_t MAX_UNLOCKABLE_LOCKS = 2;
+	struct UnlockableLocks {
+		THREADING_NAMESPACE::unique_lock<THREADING_NAMESPACE::mutex> *ulock = nullptr;
+		uint32_t rc = 0;
+	};
+	static thread_local UnlockableLocks unlockable_locks[MAX_UNLOCKABLE_LOCKS];
 #endif
 
 	TaskID _add_task(const Callable &p_callable, void (*p_func)(void *), void *p_userdata, BaseTemplateUserdata *p_template_userdata, bool p_high_priority, const String &p_description);
@@ -192,7 +196,7 @@ private:
 	void _wait_collaboratively(ThreadData *p_caller_pool_thread, Task *p_task);
 
 #ifdef THREADS_ENABLED
-	static uint32_t _thread_enter_unlock_allowance_zone(void *p_mutex, bool p_is_binary);
+	static uint32_t _thread_enter_unlock_allowance_zone(THREADING_NAMESPACE::unique_lock<THREADING_NAMESPACE::mutex> &p_ulock);
 #endif
 
 	void _lock_unlockable_mutexes();
@@ -242,11 +246,14 @@ public:
 	static TaskID get_caller_task_id();
 
 #ifdef THREADS_ENABLED
-	static uint32_t thread_enter_unlock_allowance_zone(Mutex *p_mutex);
-	static uint32_t thread_enter_unlock_allowance_zone(BinaryMutex *p_mutex);
+	_ALWAYS_INLINE_ static uint32_t thread_enter_unlock_allowance_zone(const MutexLock<BinaryMutex> &p_lock) { return _thread_enter_unlock_allowance_zone(p_lock._get_lock()); }
+	template <int Tag>
+	_ALWAYS_INLINE_ static uint32_t thread_enter_unlock_allowance_zone(const SafeBinaryMutex<Tag> &p_mutex) { return _thread_enter_unlock_allowance_zone(p_mutex._get_lock()); }
 	static void thread_exit_unlock_allowance_zone(uint32_t p_zone_id);
 #else
-	static uint32_t thread_enter_unlock_allowance_zone(void *p_mutex) { return UINT32_MAX; }
+	static uint32_t thread_enter_unlock_allowance_zone(const MutexLock<BinaryMutex> &p_lock) { return UINT32_MAX; }
+	template <int Tag>
+	static uint32_t thread_enter_unlock_allowance_zone(const SafeBinaryMutex<Tag> &p_mutex) { return UINT32_MAX; }
 	static void thread_exit_unlock_allowance_zone(uint32_t p_zone_id) {}
 #endif
 
diff --git a/core/os/condition_variable.h b/core/os/condition_variable.h
index fa1355e98c..c819fa6b40 100644
--- a/core/os/condition_variable.h
+++ b/core/os/condition_variable.h
@@ -32,6 +32,7 @@
 #define CONDITION_VARIABLE_H
 
 #include "core/os/mutex.h"
+#include "core/os/safe_binary_mutex.h"
 
 #ifdef THREADS_ENABLED
 
@@ -56,7 +57,12 @@ class ConditionVariable {
 public:
 	template <typename BinaryMutexT>
 	_ALWAYS_INLINE_ void wait(const MutexLock<BinaryMutexT> &p_lock) const {
-		condition.wait(const_cast<THREADING_NAMESPACE::unique_lock<THREADING_NAMESPACE::mutex> &>(p_lock.lock));
+		condition.wait(const_cast<THREADING_NAMESPACE::unique_lock<THREADING_NAMESPACE::mutex> &>(p_lock._get_lock()));
+	}
+
+	template <int Tag>
+	_ALWAYS_INLINE_ void wait(const MutexLock<SafeBinaryMutex<Tag>> &p_lock) const {
+		condition.wait(const_cast<THREADING_NAMESPACE::unique_lock<THREADING_NAMESPACE::mutex> &>(p_lock.mutex._get_lock()));
 	}
 
 	_ALWAYS_INLINE_ void notify_one() const {
diff --git a/core/os/mutex.h b/core/os/mutex.h
index 3e7aa81bc1..773b31828d 100644
--- a/core/os/mutex.h
+++ b/core/os/mutex.h
@@ -72,13 +72,18 @@ public:
 
 template <typename MutexT>
 class MutexLock {
-	friend class ConditionVariable;
-
 	THREADING_NAMESPACE::unique_lock<typename MutexT::StdMutexType> lock;
 
 public:
 	explicit MutexLock(const MutexT &p_mutex) :
 			lock(p_mutex.mutex) {}
+
+	// Clarification: all the funny syntax is needed so this function exists only for binary mutexes.
+	template <typename T = MutexT>
+	_ALWAYS_INLINE_ THREADING_NAMESPACE::unique_lock<THREADING_NAMESPACE::mutex> &_get_lock(
+			typename std::enable_if<std::is_same<T, THREADING_NAMESPACE::mutex>::value> * = nullptr) const {
+		return const_cast<THREADING_NAMESPACE::unique_lock<THREADING_NAMESPACE::mutex> &>(lock);
+	}
 };
 
 using Mutex = MutexImpl<THREADING_NAMESPACE::recursive_mutex>; // Recursive, for general use
diff --git a/core/os/safe_binary_mutex.h b/core/os/safe_binary_mutex.h
index 1e98cc074c..4ca4b50b02 100644
--- a/core/os/safe_binary_mutex.h
+++ b/core/os/safe_binary_mutex.h
@@ -47,76 +47,76 @@
 // Also, don't forget to declare the thread_local variable on each use.
 template <int Tag>
 class SafeBinaryMutex {
-	friend class MutexLock<SafeBinaryMutex>;
+	friend class MutexLock<SafeBinaryMutex<Tag>>;
 
 	using StdMutexType = THREADING_NAMESPACE::mutex;
 
 	mutable THREADING_NAMESPACE::mutex mutex;
-	static thread_local uint32_t count;
+
+	struct TLSData {
+		mutable THREADING_NAMESPACE::unique_lock<THREADING_NAMESPACE::mutex> lock;
+		uint32_t count = 0;
+
+		TLSData(SafeBinaryMutex<Tag> &p_mutex) :
+				lock(p_mutex.mutex, THREADING_NAMESPACE::defer_lock) {}
+	};
+	static thread_local TLSData tls_data;
 
 public:
 	_ALWAYS_INLINE_ void lock() const {
-		if (++count == 1) {
-			mutex.lock();
+		if (++tls_data.count == 1) {
+			tls_data.lock.lock();
 		}
 	}
 
 	_ALWAYS_INLINE_ void unlock() const {
-		DEV_ASSERT(count);
-		if (--count == 0) {
-			mutex.unlock();
+		DEV_ASSERT(tls_data.count);
+		if (--tls_data.count == 0) {
+			tls_data.lock.unlock();
 		}
 	}
 
-	_ALWAYS_INLINE_ bool try_lock() const {
-		if (count) {
-			count++;
-			return true;
-		} else {
-			if (mutex.try_lock()) {
-				count++;
-				return true;
-			} else {
-				return false;
-			}
-		}
+	_ALWAYS_INLINE_ THREADING_NAMESPACE::unique_lock<THREADING_NAMESPACE::mutex> &_get_lock() const {
+		return const_cast<THREADING_NAMESPACE::unique_lock<THREADING_NAMESPACE::mutex> &>(tls_data.lock);
 	}
 
-	~SafeBinaryMutex() {
-		DEV_ASSERT(!count);
+	_ALWAYS_INLINE_ SafeBinaryMutex() {
+	}
+
+	_ALWAYS_INLINE_ ~SafeBinaryMutex() {
+		DEV_ASSERT(!tls_data.count);
 	}
 };
 
-// This specialization is needed so manual locking and MutexLock can be used
-// at the same time on a SafeBinaryMutex.
 template <int Tag>
 class MutexLock<SafeBinaryMutex<Tag>> {
 	friend class ConditionVariable;
 
-	THREADING_NAMESPACE::unique_lock<THREADING_NAMESPACE::mutex> lock;
+	const SafeBinaryMutex<Tag> &mutex;
 
 public:
-	_ALWAYS_INLINE_ explicit MutexLock(const SafeBinaryMutex<Tag> &p_mutex) :
-			lock(p_mutex.mutex) {
-		SafeBinaryMutex<Tag>::count++;
-	};
-	_ALWAYS_INLINE_ ~MutexLock() {
-		SafeBinaryMutex<Tag>::count--;
-	};
+	explicit MutexLock(const SafeBinaryMutex<Tag> &p_mutex) :
+			mutex(p_mutex) {
+		mutex.lock();
+	}
+
+	~MutexLock() {
+		mutex.unlock();
+	}
 };
 
 #else // No threads.
 
 template <int Tag>
-class SafeBinaryMutex : public MutexImpl {
-	static thread_local uint32_t count;
-};
+class SafeBinaryMutex {
+	struct TLSData {
+		TLSData(SafeBinaryMutex<Tag> &p_mutex) {}
+	};
+	static thread_local TLSData tls_data;
 
-template <int Tag>
-class MutexLock<SafeBinaryMutex<Tag>> {
 public:
-	MutexLock(const SafeBinaryMutex<Tag> &p_mutex) {}
-	~MutexLock() {}
+	void lock() const {}
+	void unlock() const {}
 };
 
 #endif // THREADS_ENABLED
diff --git a/core/templates/command_queue_mt.cpp b/core/templates/command_queue_mt.cpp
index ef75a70868..5fa767263f 100644
--- a/core/templates/command_queue_mt.cpp
+++ b/core/templates/command_queue_mt.cpp
@@ -33,14 +33,6 @@
 #include "core/config/project_settings.h"
 #include "core/os/os.h"
 
-void CommandQueueMT::lock() {
-	mutex.lock();
-}
-
-void CommandQueueMT::unlock() {
-	mutex.unlock();
-}
-
 CommandQueueMT::CommandQueueMT() {
 	command_mem.reserve(DEFAULT_COMMAND_MEM_SIZE_KB * 1024);
 }
diff --git a/core/templates/command_queue_mt.h b/core/templates/command_queue_mt.h
index 1e6c6e42a9..8ef5dd3064 100644
--- a/core/templates/command_queue_mt.h
+++ b/core/templates/command_queue_mt.h
@@ -362,23 +362,24 @@ class CommandQueueMT {
 			return;
 		}
 
-		lock();
+		MutexLock lock(mutex);
 
-		uint32_t allowance_id = WorkerThreadPool::thread_enter_unlock_allowance_zone(&mutex);
 		while (flush_read_ptr < command_mem.size()) {
 			uint64_t size = *(uint64_t *)&command_mem[flush_read_ptr];
 			flush_read_ptr += 8;
 			CommandBase *cmd = reinterpret_cast<CommandBase *>(&command_mem[flush_read_ptr]);
+			uint32_t allowance_id = WorkerThreadPool::thread_enter_unlock_allowance_zone(lock);
 			cmd->call();
+			WorkerThreadPool::thread_exit_unlock_allowance_zone(allowance_id);
 
 			// Handle potential realloc due to the command and unlock allowance.
 			cmd = reinterpret_cast<CommandBase *>(&command_mem[flush_read_ptr]);
 
 			if (unlikely(cmd->sync)) {
 				sync_head++;
-				unlock(); // Give an opportunity to awaiters right away.
+				lock.~MutexLock(); // Give an opportunity to awaiters right away.
 				sync_cond_var.notify_all();
-				lock();
+				new (&lock) MutexLock(mutex);
 				// Handle potential realloc happened during unlock.
 				cmd = reinterpret_cast<CommandBase *>(&command_mem[flush_read_ptr]);
 			}
@@ -387,14 +388,11 @@ class CommandQueueMT {
 
 			flush_read_ptr += size;
 		}
-		WorkerThreadPool::thread_exit_unlock_allowance_zone(allowance_id);
 
 		command_mem.clear();
 		flush_read_ptr = 0;
 
 		_prevent_sync_wraparound();
-
-		unlock();
 	}
 
 	_FORCE_INLINE_ void _wait_for_sync(MutexLock<BinaryMutex> &p_lock) {
@@ -410,9 +408,6 @@ class CommandQueueMT {
 	void _no_op() {}
 
 public:
-	void lock();
-	void unlock();
-
 	/* NORMAL PUSH COMMANDS */
 	DECL_PUSH(0)
 	SPACE_SEP_LIST(DECL_PUSH, 15)
@@ -446,9 +441,8 @@ public:
 	}
 
 	void set_pump_task_id(WorkerThreadPool::TaskID p_task_id) {
-		lock();
+		MutexLock lock(mutex);
 		pump_task_id = p_task_id;
-		unlock();
 	}
 
 	CommandQueueMT();
diff --git a/modules/gdscript/gdscript_cache.cpp b/modules/gdscript/gdscript_cache.cpp
index 3b6526ffd9..b3c0744bdf 100644
--- a/modules/gdscript/gdscript_cache.cpp
+++ b/modules/gdscript/gdscript_cache.cpp
@@ -144,6 +144,14 @@ GDScriptParserRef::~GDScriptParserRef() {
 
 GDScriptCache *GDScriptCache::singleton = nullptr;
 
+SafeBinaryMutex<GDScriptCache::BINARY_MUTEX_TAG> &_get_gdscript_cache_mutex() {
+	return GDScriptCache::mutex;
+}
+
+template <>
+thread_local SafeBinaryMutex<GDScriptCache::BINARY_MUTEX_TAG>::TLSData SafeBinaryMutex<GDScriptCache::BINARY_MUTEX_TAG>::tls_data(_get_gdscript_cache_mutex());
+SafeBinaryMutex<GDScriptCache::BINARY_MUTEX_TAG> GDScriptCache::mutex;
+
 void GDScriptCache::move_script(const String &p_from, const String &p_to) {
 	if (singleton == nullptr || p_from == p_to) {
 		return;
@@ -369,7 +377,7 @@ Ref<GDScript> GDScriptCache::get_full_script(const String &p_path, Error &r_erro
 
 	// Allowing lifting the lock might cause a script to be reloaded multiple times,
 	// which, as a last resort deadlock prevention strategy, is a good tradeoff.
-	uint32_t allowance_id = WorkerThreadPool::thread_enter_unlock_allowance_zone(&singleton->mutex);
+	uint32_t allowance_id = WorkerThreadPool::thread_enter_unlock_allowance_zone(singleton->mutex);
 	r_error = script->reload(true);
 	WorkerThreadPool::thread_exit_unlock_allowance_zone(allowance_id);
 	if (r_error) {
diff --git a/modules/gdscript/gdscript_cache.h b/modules/gdscript/gdscript_cache.h
index f7f2cd90e9..4903da92b4 100644
--- a/modules/gdscript/gdscript_cache.h
+++ b/modules/gdscript/gdscript_cache.h
@@ -34,7 +34,7 @@
 #include "gdscript.h"
 
 #include "core/object/ref_counted.h"
-#include "core/os/mutex.h"
+#include "core/os/safe_binary_mutex.h"
 #include "core/templates/hash_map.h"
 #include "core/templates/hash_set.h"
 
@@ -95,7 +95,12 @@ class GDScriptCache {
 
 	bool cleared = false;
 
-	Mutex mutex;
+public:
+	static const int BINARY_MUTEX_TAG = 2;
+
+private:
+	static SafeBinaryMutex<BINARY_MUTEX_TAG> mutex;
+	friend SafeBinaryMutex<BINARY_MUTEX_TAG> &_get_gdscript_cache_mutex();
 
 public:
 	static void move_script(const String &p_from, const String &p_to);