using System;

using System.Collections.Generic;

using System.Linq;

using System.Threading;

​

public class Program

{

    public static void Main()

    {

        QueuedLock queuedLock = new QueuedLock();

        foreach (var batch in Enumerable.Range(1, 10))

        {

            int index = 0;

            var sequence = Enumerable.Range(1, 10);

            var tickets = new List<int>();

            var threads = sequence.Select(_ =>

            {

                Thread.Sleep(20);

                var thread = new Thread(() =>

                {

                    var ticket = Interlocked.Increment(ref index);

                    queuedLock.Enter(); try { tickets.Add(ticket); Thread.Sleep(40); }

                    finally { queuedLock.Exit(); }

                });

                thread.Start();

                return thread;

            }).ToArray();

            foreach (var thread in threads) thread.Join();

            Console.WriteLine($"Batch #{batch}, tickets: {String.Join(", ", tickets)} - "

                + (tickets.SequenceEqual(sequence) ? "OK" : "NOT FIFO!"));

        }

    }

​

    public class QueuedLock

    {

        private readonly object _locker = new object();

        private int _ticketsCount = 0;

        private int _ticketToRide = 1;

​

        public void Enter()

        {

            if (Monitor.IsEntered(_locker)) throw new InvalidOperationException();

            int myTicket = Interlocked.Increment(ref _ticketsCount);

            Monitor.Enter(_locker);

            while (myTicket != Volatile.Read(ref _ticketToRide))

                Monitor.Wait(_locker);

        }

​

        public void Exit()

        {

            if (!Monitor.IsEntered(_locker)) throw new InvalidOperationException();

            Interlocked.Increment(ref _ticketToRide);

            Monitor.PulseAll(_locker);

            Monitor.Exit(_locker);

        }

    }

}

​