Example 1-36. Using the lock keyword

using System;
using System.Threading.Tasks;

namespace Chapter1
{
    public class Program
    {
        static void Main()
        {
            int n = 0;

            object _lock = new object();

            var up = Task.Run(() =>
            {

                for (int i = 0; i < 1000000; i++)
                    lock (_lock)
                        n++;
            });

            for (int i = 0; i < 1000000; i++)
                lock (_lock)
                    n--;

            up.Wait();
            Console.WriteLine(n);
        }
    }
}