using System;
using System.Threading;

namespace ConsoleApp
{
    public class Program
    {
        const int interations = 100;
        const int spinWaitIterations = 1000000;
        private static Random random = new();
        static void Main()
        {
            using var countdownEvent = new CountdownEvent(2 * interations);
            for (var i = 0; i < interations; i++)
            {
                ThreadPool.UnsafeQueueUserWorkItem(FixedDuration, countdownEvent, false);
                ThreadPool.UnsafeQueueUserWorkItem(VariableDuration, countdownEvent, false);
            }
            countdownEvent.Wait();
        }

        private static void FixedDuration(object state)
        {
            Thread.SpinWait(spinWaitIterations * 2);
            (state as CountdownEvent).Signal();
        }

        private static void VariableDuration(object state)
        {
            if (random.Next(0, 4) == 0)
            {
                Thread.SpinWait(spinWaitIterations * 5);
            }
            else
            {
                Thread.SpinWait(spinWaitIterations);
            }
            (state as CountdownEvent).Signal();
        }
    }
}