Fix possible multi-platform race-condition (depending on kernel)

As well as remove another pthread_self call.

Utilities/Thread.cpp

@@ -2337,6 +2337,7 @@ void thread_base::start()
 	ensure(::ResumeThread(reinterpret_cast<HANDLE>(+m_thread)) != static_cast<DWORD>(-1));
 #elif defined(__APPLE__)
 	pthread_attr_t attrs;
+	pthread_t thread_id{};
 	struct sched_param sp;
     memset(&sp, 0, sizeof(struct sched_param));
     sp.sched_priority=99;
@@ -2346,20 +2347,43 @@ void thread_base::start()
 	pthread_attr_set_qos_class_np(&attrs, QOS_CLASS_USER_INTERACTIVE, 0);
 	pthread_attr_setschedpolicy(&attrs, SCHED_RR);
 	pthread_attr_setschedparam(&attrs, &sp);
-	ensure(pthread_create(reinterpret_cast<pthread_t*>(&m_thread.raw()), &attrs, entry_point, this) == 0);
+	ensure(pthread_create(&thread_id, &attrs, entry_point, this) == 0);
 #else
-	ensure(pthread_create(reinterpret_cast<pthread_t*>(&m_thread.raw()), nullptr, entry_point, this) == 0);
+	pthread_t thread_id{};
+	ensure(pthread_create(&thread_id, nullptr, entry_point, this) == 0);
+#endif
+
+#ifndef _WIN32
+	// Update m_thread atomically
+	u64 dest_id = 0;
+	std::memcpy(&dest_id, &thread_id, sizeof(thread_id));
+
+	if (!m_thread && !m_thread.compare_and_swap_test(0, dest_id))
+	{
+		ensure(m_thread == dest_id);
+	}
 #endif
 }
 
 void thread_base::initialize(void (*error_cb)())
 {
 #ifndef _WIN32
-#ifdef ANDROID
+#ifdef __APPLE__
-	m_thread.release(pthread_self());
+	while (!m_thread)
+	{
+		busy_wait();
+	}
+	[[maybe_unused]] u64 new_tid = 0;
+#elif defined(ANDROID)
+	const u64 new_tid = pthread_self();
 #else
-	m_thread.release(reinterpret_cast<u64>(pthread_self()));
+	const u64 new_tid = reinterpret_cast<u64>(pthread_self());
 #endif
+
+	if (!m_thread && !m_thread.compare_and_swap_test(0, new_tid))
+	{
+		ensure(m_thread == new_tid);
+	}
 #endif
 
 	// Initialize TLS variables