class GuiLock { // <--- changed struct to class
public:         // <--- added.
        GuiLock()  { EnterGuiMutex(); }
        ~GuiLock() { LeaveGuiMutex(); }
};

class GuiUnlock {
	int n;

public:
	GuiUnlock()  { n = LeaveGuiMutexAll(); }
	~GuiUnlock() { EnterGuiMutex(n); }
};