kernel: Add a kernel_wait_for_event() function to avoid weird calls to kernel_wait in kthreads

kernel/src/arch/x86_64/CPU.cpp

@@ -128,10 +128,10 @@ void io_thread()
     while (true)
     {
         u8 scancode;
-        while (!scancode_queue.try_pop(scancode)) { kernel_wait(0); }
+        while (!scancode_queue.try_pop(scancode)) kernel_wait_for_event();
 
         char key;
-        if (Keyboard::decode_scancode(scancode).try_set_value(key)) { ConsoleDevice::did_press_key(key); }
+        if (Keyboard::decode_scancode(scancode).try_set_value(key)) ConsoleDevice::did_press_key(key);
     }
 }
 

kernel/src/main.cpp

@@ -30,7 +30,7 @@ void reap_thread()
 
         dying_threads.consume([](Thread* thread) { Scheduler::reap_thread(thread); });
 
-        kernel_wait(0);
+        kernel_wait_for_event();
     }
 }
 

kernel/src/thread/Scheduler.cpp

@@ -365,6 +365,12 @@ void kernel_wait(pid_t pid)
     kernel_yield();
 }
 
+void kernel_wait_for_event()
+{
+    g_current->state = ThreadState::Waiting;
+    kernel_yield();
+}
+
 [[noreturn]] void kernel_exit()
 {
     g_current->state = ThreadState::Dying;

kernel/src/thread/Scheduler.h

@@ -56,3 +56,6 @@ extern "C" void kernel_yield();
 void kernel_wait(pid_t pid);
 void kernel_sleep(u64 ms);
 [[noreturn]] void kernel_exit();
+
+// Freezes the current thread until someone else calls wake_up() on this thread.
+void kernel_wait_for_event();