Remove NO_THREADS fallback code, Godot 4 requires thread support

This also removes `OS::can_use_threads` from the public API since it's always
true.

16 files changed, 8 insertions, 431 deletions

diff --git a/core/core_bind.cpp b/core/core_bind.cpp
index a164221fc2..9152b4a215 100644
--- a/core/core_bind.cpp
+++ b/core/core_bind.cpp
@@ -425,10 +425,6 @@ void OS::delay_msec(int p_msec) const {
 	::OS::get_singleton()->delay_usec(int64_t(p_msec) * 1000);
 }
 
-bool OS::can_use_threads() const {
-	return ::OS::get_singleton()->can_use_threads();
-}
-
 bool OS::is_userfs_persistent() const {
 	return ::OS::get_singleton()->is_userfs_persistent();
 }
@@ -561,8 +557,6 @@ void OS::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("is_userfs_persistent"), &OS::is_userfs_persistent);
 	ClassDB::bind_method(D_METHOD("is_stdout_verbose"), &OS::is_stdout_verbose);
 
-	ClassDB::bind_method(D_METHOD("can_use_threads"), &OS::can_use_threads);
-
 	ClassDB::bind_method(D_METHOD("is_debug_build"), &OS::is_debug_build);
 
 	ClassDB::bind_method(D_METHOD("get_static_memory_usage"), &OS::get_static_memory_usage);
diff --git a/core/core_bind.h b/core/core_bind.h
index ba22971d78..4a89f4f13b 100644
--- a/core/core_bind.h
+++ b/core/core_bind.h
@@ -218,8 +218,6 @@ public:
 	uint64_t get_ticks_msec() const;
 	uint64_t get_ticks_usec() const;
 
-	bool can_use_threads() const;
-
 	bool is_userfs_persistent() const;
 
 	bool is_stdout_verbose() const;
diff --git a/core/debugger/remote_debugger_peer.cpp b/core/debugger/remote_debugger_peer.cpp
index e9362b4ea4..525362ec7c 100644
--- a/core/debugger/remote_debugger_peer.cpp
+++ b/core/debugger/remote_debugger_peer.cpp
@@ -79,10 +79,8 @@ RemoteDebuggerPeerTCP::RemoteDebuggerPeerTCP(Ref<StreamPeerTCP> p_tcp) {
 	tcp_client = p_tcp;
 	if (tcp_client.is_valid()) { // Attaching to an already connected stream.
 		connected = true;
-#ifndef NO_THREADS
 		running = true;
 		thread.start(_thread_func, this);
-#endif
 	} else {
 		tcp_client.instantiate();
 	}
@@ -183,10 +181,8 @@ Error RemoteDebuggerPeerTCP::connect_to_host(const String &p_host, uint16_t p_po
 		return FAILED;
 	}
 	connected = true;
-#ifndef NO_THREADS
 	running = true;
 	thread.start(_thread_func, this);
-#endif
 	return OK;
 }
 
@@ -208,9 +204,7 @@ void RemoteDebuggerPeerTCP::_thread_func(void *p_ud) {
 }
 
 void RemoteDebuggerPeerTCP::poll() {
-#ifdef NO_THREADS
-	_poll();
-#endif
+	// Nothing to do, polling is done in thread.
 }
 
 void RemoteDebuggerPeerTCP::_poll() {
diff --git a/core/debugger/remote_debugger_peer.h b/core/debugger/remote_debugger_peer.h
index 473fd8d712..2ab641d537 100644
--- a/core/debugger/remote_debugger_peer.h
+++ b/core/debugger/remote_debugger_peer.h
@@ -43,12 +43,12 @@ protected:
 
 public:
 	virtual bool is_peer_connected() = 0;
+	virtual int get_max_message_size() const = 0;
 	virtual bool has_message() = 0;
 	virtual Error put_message(const Array &p_arr) = 0;
 	virtual Array get_message() = 0;
 	virtual void close() = 0;
 	virtual void poll() = 0;
-	virtual int get_max_message_size() const = 0;
 	virtual bool can_block() const { return true; } // If blocking io is allowed on main thread (debug).
 
 	RemoteDebuggerPeer();
@@ -81,12 +81,12 @@ public:
 
 	Error connect_to_host(const String &p_host, uint16_t p_port);
 
-	void poll() override;
 	bool is_peer_connected() override;
+	int get_max_message_size() const override;
 	bool has_message() override;
-	Array get_message() override;
 	Error put_message(const Array &p_arr) override;
-	int get_max_message_size() const override;
+	Array get_message() override;
+	void poll() override;
 	void close() override;
 
 	RemoteDebuggerPeerTCP(Ref<StreamPeerTCP> p_stream = Ref<StreamPeerTCP>());
diff --git a/core/os/mutex.cpp b/core/os/mutex.cpp
index 1d4400bfc1..512db1737a 100644
--- a/core/os/mutex.cpp
+++ b/core/os/mutex.cpp
@@ -40,11 +40,7 @@ void _global_unlock() {
 	_global_mutex.unlock();
 }
 
-#ifndef NO_THREADS
-
 template class MutexImpl<std::recursive_mutex>;
 template class MutexImpl<std::mutex>;
 template class MutexLock<MutexImpl<std::recursive_mutex>>;
 template class MutexLock<MutexImpl<std::mutex>>;
-
-#endif
diff --git a/core/os/mutex.h b/core/os/mutex.h
index a51248807b..eb58418bd6 100644
--- a/core/os/mutex.h
+++ b/core/os/mutex.h
@@ -34,8 +34,6 @@
 #include "core/error/error_list.h"
 #include "core/typedefs.h"
 
-#if !defined(NO_THREADS)
-
 #include <mutex>
 
 template <class StdMutexT>
@@ -79,29 +77,4 @@ extern template class MutexImpl<std::mutex>;
 extern template class MutexLock<MutexImpl<std::recursive_mutex>>;
 extern template class MutexLock<MutexImpl<std::mutex>>;
 
-#else
-
-class FakeMutex {
-	FakeMutex() {}
-};
-
-template <class MutexT>
-class MutexImpl {
-public:
-	_ALWAYS_INLINE_ void lock() const {}
-	_ALWAYS_INLINE_ void unlock() const {}
-	_ALWAYS_INLINE_ Error try_lock() const { return OK; }
-};
-
-template <class MutexT>
-class MutexLock {
-public:
-	explicit MutexLock(const MutexT &p_mutex) {}
-};
-
-using Mutex = MutexImpl<FakeMutex>;
-using BinaryMutex = MutexImpl<FakeMutex>; // Non-recursive, handle with care
-
-#endif // !NO_THREADS
-
 #endif // MUTEX_H
diff --git a/core/os/os.cpp b/core/os/os.cpp
index ee8da21751..2bdede889f 100644
--- a/core/os/os.cpp
+++ b/core/os/os.cpp
@@ -328,14 +328,6 @@ String OS::get_processor_name() const {
 	return "";
 }
 
-bool OS::can_use_threads() const {
-#ifdef NO_THREADS
-	return false;
-#else
-	return true;
-#endif
-}
-
 void OS::set_has_server_feature_callback(HasServerFeatureCallback p_callback) {
 	has_server_feature_callback = p_callback;
 }
diff --git a/core/os/os.h b/core/os/os.h
index aa45a3b8a8..1a5e45968d 100644
--- a/core/os/os.h
+++ b/core/os/os.h
@@ -299,8 +299,6 @@ public:
 
 	virtual String get_unique_id() const;
 
-	virtual bool can_use_threads() const;
-
 	bool has_feature(const String &p_feature);
 
 	void set_has_server_feature_callback(HasServerFeatureCallback p_callback);
diff --git a/core/os/rw_lock.h b/core/os/rw_lock.h
index a046f474ea..d3206547c7 100644
--- a/core/os/rw_lock.h
+++ b/core/os/rw_lock.h
@@ -33,8 +33,6 @@
 
 #include "core/error/error_list.h"
 
-#if !defined(NO_THREADS)
-
 #include <shared_mutex>
 
 class RWLock {
@@ -72,21 +70,6 @@ public:
 	}
 };
 
-#else
-
-class RWLock {
-public:
-	void read_lock() const {}
-	void read_unlock() const {}
-	Error read_try_lock() const { return OK; }
-
-	void write_lock() {}
-	void write_unlock() {}
-	Error write_try_lock() { return OK; }
-};
-
-#endif
-
 class RWLockRead {
 	const RWLock &lock;
 
diff --git a/core/os/semaphore.h b/core/os/semaphore.h
index 72df52dd34..1a93d3ee2c 100644
--- a/core/os/semaphore.h
+++ b/core/os/semaphore.h
@@ -34,8 +34,6 @@
 #include "core/error/error_list.h"
 #include "core/typedefs.h"
 
-#if !defined(NO_THREADS)
-
 #include <condition_variable>
 #include <mutex>
 
@@ -70,15 +68,4 @@ public:
 	}
 };
 
-#else
-
-class Semaphore {
-public:
-	_ALWAYS_INLINE_ void post() const {}
-	_ALWAYS_INLINE_ void wait() const {}
-	_ALWAYS_INLINE_ bool try_wait() const { return true; }
-};
-
-#endif
-
 #endif // SEMAPHORE_H
diff --git a/core/os/thread.cpp b/core/os/thread.cpp
index c8072b7280..e8ebb4597f 100644
--- a/core/os/thread.cpp
+++ b/core/os/thread.cpp
@@ -34,9 +34,6 @@
 #include "thread.h"
 
 #include "core/object/script_language.h"
-
-#if !defined(NO_THREADS)
-
 #include "core/templates/safe_refcount.h"
 
 Error (*Thread::set_name_func)(const String &) = nullptr;
@@ -128,5 +125,4 @@ Thread::~Thread() {
 	}
 }
 
-#endif
 #endif // PLATFORM_THREAD_OVERRIDE
diff --git a/core/os/thread.h b/core/os/thread.h
index 0fb283e224..7462ec17fb 100644
--- a/core/os/thread.h
+++ b/core/os/thread.h
@@ -35,15 +35,14 @@
 #ifdef PLATFORM_THREAD_OVERRIDE
 #include "platform_thread.h"
 #else
+
 #ifndef THREAD_H
 #define THREAD_H
 
+#include "core/templates/safe_refcount.h"
 #include "core/typedefs.h"
 
-#if !defined(NO_THREADS)
-#include "core/templates/safe_refcount.h"
 #include <thread>
-#endif
 
 class String;
 
@@ -65,7 +64,6 @@ public:
 	};
 
 private:
-#if !defined(NO_THREADS)
 	friend class Main;
 
 	static ID main_thread_id;
@@ -82,7 +80,6 @@ private:
 	static void (*set_priority_func)(Thread::Priority);
 	static void (*init_func)();
 	static void (*term_func)();
-#endif
 
 public:
 	static void _set_platform_funcs(
@@ -91,7 +88,6 @@ public:
 			void (*p_init_func)() = nullptr,
 			void (*p_term_func)() = nullptr);
 
-#if !defined(NO_THREADS)
 	_FORCE_INLINE_ ID get_id() const { return id; }
 	// get the ID of the caller thread
 	_FORCE_INLINE_ static ID get_caller_id() { return caller_id; }
@@ -107,19 +103,6 @@ public:
 
 	Thread();
 	~Thread();
-#else
-	_FORCE_INLINE_ ID get_id() const { return 0; }
-	// get the ID of the caller thread
-	_FORCE_INLINE_ static ID get_caller_id() { return 0; }
-	// get the ID of the main thread
-	_FORCE_INLINE_ static ID get_main_id() { return 0; }
-
-	static Error set_name(const String &p_name) { return ERR_UNAVAILABLE; }
-
-	void start(Thread::Callback p_callback, void *p_user, const Settings &p_settings = Settings()) {}
-	bool is_started() const { return false; }
-	void wait_to_finish() {}
-#endif
 };
 
 #endif // THREAD_H
diff --git a/core/os/threaded_array_processor.h b/core/os/threaded_array_processor.h
index 935fc7a360..95a2253f14 100644
--- a/core/os/threaded_array_processor.h
+++ b/core/os/threaded_array_processor.h
@@ -49,8 +49,6 @@ struct ThreadArrayProcessData {
 	}
 };
 
-#ifndef NO_THREADS
-
 template <class T>
 void process_array_thread(void *ud) {
 	T &data = *(T *)ud;
@@ -86,21 +84,4 @@ void thread_process_array(uint32_t p_elements, C *p_instance, M p_method, U p_us
 	memdelete_arr(threads);
 }
 
-#else
-
-template <class C, class M, class U>
-void thread_process_array(uint32_t p_elements, C *p_instance, M p_method, U p_userdata) {
-	ThreadArrayProcessData<C, U> data;
-	data.method = p_method;
-	data.instance = p_instance;
-	data.userdata = p_userdata;
-	data.index.set(0);
-	data.elements = p_elements;
-	for (uint32_t i = 0; i < p_elements; i++) {
-		data.process(i);
-	}
-}
-
-#endif
-
 #endif // THREADED_ARRAY_PROCESSOR_H
diff --git a/core/templates/cowdata.h b/core/templates/cowdata.h
index f98b2308c9..1482e3eef1 100644
--- a/core/templates/cowdata.h
+++ b/core/templates/cowdata.h
@@ -46,9 +46,7 @@ class CharString;
 template <class T, class V>
 class VMap;
 
-#if !defined(NO_THREADS)
 SAFE_NUMERIC_TYPE_PUN_GUARANTEES(uint32_t)
-#endif
 
 // Silence a false positive warning (see GH-52119).
 #if defined(__GNUC__) && !defined(__clang__)
diff --git a/core/templates/safe_list.h b/core/templates/safe_list.h
index e850f3bd5e..95e8ca1a14 100644
--- a/core/templates/safe_list.h
+++ b/core/templates/safe_list.h
@@ -33,11 +33,9 @@
 
 #include "core/os/memory.h"
 #include "core/typedefs.h"
-#include <functional>
-
-#if !defined(NO_THREADS)
 
 #include <atomic>
+#include <functional>
 #include <type_traits>
 
 // Design goals for these classes:
@@ -239,159 +237,4 @@ public:
 	}
 };
 
-#else // NO_THREADS
-
-// Effectively the same structure without the atomics. It's probably possible to simplify it but the semantics shouldn't differ greatly.
-template <class T, class A = DefaultAllocator>
-class SafeList {
-	struct SafeListNode {
-		SafeListNode *next = nullptr;
-
-		// If the node is logically deleted, this pointer will typically point to the previous list item in time that was also logically deleted.
-		SafeListNode *graveyard_next = nullptr;
-
-		std::function<void(T)> deletion_fn = [](T t) { return; };
-
-		T val;
-	};
-
-	SafeListNode *head = nullptr;
-	SafeListNode *graveyard_head = nullptr;
-
-	unsigned int active_iterator_count = 0;
-
-public:
-	class Iterator {
-		friend class SafeList;
-
-		SafeListNode *cursor = nullptr;
-		SafeList *list = nullptr;
-
-	public:
-		Iterator(SafeListNode *p_cursor, SafeList *p_list) :
-				cursor(p_cursor), list(p_list) {
-			list->active_iterator_count++;
-		}
-
-		~Iterator() {
-			list->active_iterator_count--;
-		}
-
-		T &operator*() {
-			return cursor->val;
-		}
-
-		Iterator &operator++() {
-			cursor = cursor->next;
-			return *this;
-		}
-
-		// These two operators are mostly useful for comparisons to nullptr.
-		bool operator==(const void *p_other) const {
-			return cursor == p_other;
-		}
-
-		bool operator!=(const void *p_other) const {
-			return cursor != p_other;
-		}
-
-		// These two allow easy range-based for loops.
-		bool operator==(const Iterator &p_other) const {
-			return cursor == p_other.cursor;
-		}
-
-		bool operator!=(const Iterator &p_other) const {
-			return cursor != p_other.cursor;
-		}
-	};
-
-public:
-	// Calling this will cause an allocation.
-	void insert(T p_value) {
-		SafeListNode *new_node = memnew_allocator(SafeListNode, A);
-		new_node->val = p_value;
-		new_node->next = head;
-		head = new_node;
-	}
-
-	Iterator find(T p_value) {
-		for (Iterator it = begin(); it != end(); ++it) {
-			if (*it == p_value) {
-				return it;
-			}
-		}
-		return end();
-	}
-
-	void erase(T p_value, std::function<void(T)> p_deletion_fn) {
-		erase(find(p_value), p_deletion_fn);
-	}
-
-	void erase(T p_value) {
-		erase(find(p_value), [](T t) { return; });
-	}
-
-	void erase(Iterator p_iterator, std::function<void(T)> p_deletion_fn) {
-		p_iterator.cursor->deletion_fn = p_deletion_fn;
-		erase(p_iterator);
-	}
-
-	void erase(Iterator p_iterator) {
-		Iterator prev = begin();
-		for (; prev != end(); ++prev) {
-			if (prev.cursor && prev.cursor->next == p_iterator.cursor) {
-				break;
-			}
-		}
-		if (prev == end()) {
-			// Not in the list, nothing to do.
-			return;
-		}
-		// First, remove the node from the list.
-		prev.cursor->next = p_iterator.cursor->next;
-
-		// Then queue it for deletion by putting it in the node graveyard. Don't touch `next` because an iterator might still be pointing at this node.
-		p_iterator.cursor->graveyard_next = graveyard_head;
-		graveyard_head = p_iterator.cursor;
-	}
-
-	Iterator begin() {
-		return Iterator(head, this);
-	}
-
-	Iterator end() {
-		return Iterator(nullptr, this);
-	}
-
-	// Calling this will cause zero to many deallocations.
-	bool maybe_cleanup() {
-		SafeListNode *cursor = graveyard_head;
-		if (active_iterator_count != 0) {
-			// It's not safe to clean up with an active iterator, because that iterator could be pointing to an element that we want to delete.
-			return false;
-		}
-		graveyard_head = nullptr;
-		// Our graveyard list is now unreachable by any active iterators, detached from the main graveyard head and ready for deletion.
-		while (cursor) {
-			SafeListNode *tmp = cursor;
-			cursor = cursor->next;
-			tmp->deletion_fn(tmp->val);
-			memdelete_allocator<SafeListNode, A>(tmp);
-		}
-		return true;
-	}
-
-	~SafeList() {
-#ifdef DEBUG_ENABLED
-		if (!maybe_cleanup()) {
-			ERR_PRINT("There are still iterators around when destructing a SafeList. Memory will be leaked. This is a bug.");
-		}
-#else
-		maybe_cleanup();
-#endif
-	}
-};
-
-#endif
-
 #endif // SAFE_LIST_H
diff --git a/core/templates/safe_refcount.h b/core/templates/safe_refcount.h
index 1f6551762e..c4ffe5ca02 100644
--- a/core/templates/safe_refcount.h
+++ b/core/templates/safe_refcount.h
@@ -33,8 +33,6 @@
 
 #include "core/typedefs.h"
 
-#if !defined(NO_THREADS)
-
 #include <atomic>
 #include <type_traits>
 
@@ -191,141 +189,4 @@ public:
 	}
 };
 
-#else
-
-template <class T>
-class SafeNumeric {
-protected:
-	T value;
-
-public:
-	_ALWAYS_INLINE_ void set(T p_value) {
-		value = p_value;
-	}
-
-	_ALWAYS_INLINE_ T get() const {
-		return value;
-	}
-
-	_ALWAYS_INLINE_ T increment() {
-		return ++value;
-	}
-
-	_ALWAYS_INLINE_ T postincrement() {
-		return value++;
-	}
-
-	_ALWAYS_INLINE_ T decrement() {
-		return --value;
-	}
-
-	_ALWAYS_INLINE_ T postdecrement() {
-		return value--;
-	}
-
-	_ALWAYS_INLINE_ T add(T p_value) {
-		return value += p_value;
-	}
-
-	_ALWAYS_INLINE_ T postadd(T p_value) {
-		T old = value;
-		value += p_value;
-		return old;
-	}
-
-	_ALWAYS_INLINE_ T sub(T p_value) {
-		return value -= p_value;
-	}
-
-	_ALWAYS_INLINE_ T postsub(T p_value) {
-		T old = value;
-		value -= p_value;
-		return old;
-	}
-
-	_ALWAYS_INLINE_ T exchange_if_greater(T p_value) {
-		if (value < p_value) {
-			value = p_value;
-		}
-		return value;
-	}
-
-	_ALWAYS_INLINE_ T conditional_increment() {
-		if (value == 0) {
-			return 0;
-		} else {
-			return ++value;
-		}
-	}
-
-	_ALWAYS_INLINE_ explicit SafeNumeric<T>(T p_value = static_cast<T>(0)) :
-			value(p_value) {
-	}
-};
-
-class SafeFlag {
-protected:
-	bool flag;
-
-public:
-	_ALWAYS_INLINE_ bool is_set() const {
-		return flag;
-	}
-
-	_ALWAYS_INLINE_ void set() {
-		flag = true;
-	}
-
-	_ALWAYS_INLINE_ void clear() {
-		flag = false;
-	}
-
-	_ALWAYS_INLINE_ void set_to(bool p_value) {
-		flag = p_value;
-	}
-
-	_ALWAYS_INLINE_ explicit SafeFlag(bool p_value = false) :
-			flag(p_value) {}
-};
-
-class SafeRefCount {
-	uint32_t count = 0;
-
-public:
-	_ALWAYS_INLINE_ bool ref() { // true on success
-		if (count != 0) {
-			++count;
-			return true;
-		} else {
-			return false;
-		}
-	}
-
-	_ALWAYS_INLINE_ uint32_t refval() { // none-zero on success
-		if (count != 0) {
-			return ++count;
-		} else {
-			return 0;
-		}
-	}
-
-	_ALWAYS_INLINE_ bool unref() { // true if must be disposed of
-		return --count == 0;
-	}
-
-	_ALWAYS_INLINE_ uint32_t unrefval() { // 0 if must be disposed of
-		return --count;
-	}
-
-	_ALWAYS_INLINE_ uint32_t get() const {
-		return count;
-	}
-
-	_ALWAYS_INLINE_ void init(uint32_t p_value = 1) {
-		count = p_value;
-	}
-};
-
-#endif
-
 #endif // SAFE_REFCOUNT_H