using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Threading;

namespace ConsoleApp1
{
    class Program
    {

        static SemaphoreSlim S = new SemaphoreSlim(1);
        static int postiLiberi = 200;

        static void Main(string[] args)
        {
            Parallel.Invoke(() => Cassa(1), () => Cassa(2));
        }

        static void Cassa(int numCassa)
        {
            int nb;
            Random r = new Random(numCassa);

            for (int i=0; i < 20; i++)
            {
                Thread.Sleep(r.Next(10, 15 + 1));
                nb = r.Next(1, 10 + 1);
                Console.WriteLine("cassa num: " + numCassa.ToString());
                Occupa(nb);
            }
            Console.WriteLine("cassa " + numCassa.ToString() + " chiusa");
        }

        static void Occupa(int quanti)
        {
            S.Wait();
            if (postiLiberi >= quanti)
            {
                postiLiberi -= quanti;
                Console.WriteLine("assegnati " + quanti.ToString() + " posti");
            }
            else
            {
                Console.WriteLine("posti non disponibili");
            }
            S.Release();
        }
    }
}