Kernel: Scheduler can now check if tid is valid

Tid can become invalid if the thread is already terminated

kernel/include/kernel/Scheduler.h

@@ -31,6 +31,8 @@ namespace Kernel
 		Thread& current_thread();
 		static pid_t current_tid();
 
+		static bool is_valid_tid(pid_t tid);
+
 	private:
 		Scheduler() = default;
 

kernel/kernel/Scheduler.cpp

@@ -373,4 +373,26 @@ namespace Kernel
 		}
 	}
 
+	bool Scheduler::is_valid_tid(pid_t tid)
+	{
+		CriticalScope _;
+
+		if (s_instance == nullptr)
+			return tid == 0;
+
+		for (auto& thread : s_instance->m_active_threads)
+			if (thread.thread->tid() == tid)
+				return true;
+		
+		for (auto& thread : s_instance->m_sleeping_threads)
+			if (thread.thread->tid() == tid)
+				return true;
+
+		for (auto& thread : s_instance->m_blocking_threads)
+			if (thread.thread->tid() == tid)
+				return true;
+
+		return false;
+	}
+
 }