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.

9 files changed, 2 insertions, 113 deletions

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