Sleepy barber problem with traffic lights

Question

I found this code online while studying and I couldn’t understand two things:

1. What the traffic light "seatbelt" does?

2. Why isn’t the barber checking the waiting room after finishing a cut? (It goes directly to the state "Resting")

Thank you very much!

static void Main(string[] args)
{
    Random Rand = new Random();
    const int MaxCustomers = 3;
    const int NumChairs = 3;
    Semaphore waitingRoom = new Semaphore(NumChairs, NumChairs);
    Semaphore barberChair = new Semaphore(1, 1);
    Semaphore barberSleepChair = new Semaphore(0, 1);
    Semaphore seatBelt = new Semaphore(0, 1);
    bool AllDone = false;
    void Barber()
    {
        while (!AllDone)
        {
            Console.WriteLine("Barbeiro dormindo.");
            barberSleepChair.WaitOne();
            if (waitingRoom.ToString() == "3")
            {
                Console.WriteLine("Barbeiro tem que cortar.");
                Thread.Sleep(Rand.Next(1, 3) * 1000);
                Console.WriteLine("Barbeiro corta o cabelo.");
                seatBelt.Release();
                Console.WriteLine("Barbeiro checa a sala de espera");  
            }
            else
            {
                Console.WriteLine("Barbeiro dormindo.");
            }
        }
        return;
    }
    void Customer(Object number)
    {
        int Number = (int)number;
        Console.WriteLine("O cliente {0} vai ao salão.", Number);
        Thread.Sleep(Rand.Next(1, 5) * 1000);
        Console.WriteLine("Cliente {0} está no salão.", Number);
        waitingRoom.WaitOne();
        Console.WriteLine("Cliente {0} entra na sala de espera.", Number);
        barberChair.WaitOne();
        waitingRoom.Release();
        Console.WriteLine("O cliente acorda o barbeiro", Number);
        barberSleepChair.Release();
        seatBelt.WaitOne();
        barberChair.Release();
        Console.WriteLine("Cliente {0} sai do salão.", Number);
    }
    Thread BarberThread = new Thread(Barber);
    BarberThread.Start();
    Thread[] Customers = new Thread[MaxCustomers];
    for (int i = 0; i < MaxCustomers; i++)
    {
        Customers[i] = new Thread(new ParameterizedThreadStart(Customer));
        Customers[i].Start(i);
    }
    for (int i = 0; i < MaxCustomers; i++)
    {
        Customers[i].Join();
    }
    AllDone = true;
    barberSleepChair.Release();
    BarberThread.Join();
    Console.WriteLine("Fim do trabalho!");
    Console.ReadKey();
}

Answer 1

See what I got from the code. The seatbelt is a traffic light that signals whether the barber’s chair is available to customers. It starts empty (0) and when a customer wakes the barber, he sits in the chair (seatBelt.WaitOne()). When the barber has finished shaving, he releases the chair (seatBelt.Release()).

According to your code, the barber checks the room until AllDone for true, that is, until

for (int i = 0; i < MaxCustomers; i++)
{
   Customers[i].Join();
}

close. Soon, it should meet three customers and then close its work.