output.txt

26.03.2019 21:43:33 | Begin thread 13
26.03.2019 21:43:33 | Begin thread 15
26.03.2019 21:43:33 | Begin thread 14
26.03.2019 21:43:33 | Begin thread 16
26.03.2019 21:43:33 | Process account account_6 in thread 16
26.03.2019 21:43:33 | Process account account_7 in thread 14
26.03.2019 21:43:33 | Process account account_4 in thread 15
26.03.2019 21:43:33 | Process account account_5 in thread 13
26.03.2019 21:43:33 | Process account account_3 in thread 16
26.03.2019 21:43:33 | Process account account_2 in thread 14
26.03.2019 21:43:35 | Process account account_1 in thread 16
26.03.2019 21:43:36 | Process account account_1 locked for time: 26.03.2019 21:45:20
26.03.2019 21:43:36 | Process account account_8 in thread 16
26.03.2019 21:43:37 | Process account account_6 in thread 15
26.03.2019 21:43:37 | Process account account_7 in thread 13
26.03.2019 21:43:37 | Process account account_3 in thread 14
26.03.2019 21:43:38 | Process account account_5 in thread 15
26.03.2019 21:43:39 | Process account account_4 in thread 15
26.03.2019 21:43:40 | Process account account_2 in thread 15
26.03.2019 21:43:40 | Process account account_6 in thread 16
26.03.2019 21:43:40 | Process account account_5 in thread 14
26.03.2019 21:43:41 | Process account account_4 in thread 15
26.03.2019 21:43:41 | Process account account_7 locked for time: 26.03.2019 21:45:06
26.03.2019 21:43:41 | Process account account_8 in thread 13
26.03.2019 21:43:41 | Process account account_3 in thread 13
26.03.2019 21:43:42 | Process account account_2 in thread 15
26.03.2019 21:43:44 | Process account account_8 in thread 13
26.03.2019 21:43:44 | Process account account_4 in thread 14
26.03.2019 21:43:44 | Process account account_3 in thread 16
26.03.2019 21:43:45 | Process account account_5 in thread 14
26.03.2019 21:43:46 | Process account account_5 locked for time: 26.03.2019 21:45:29
26.03.2019 21:43:46 | Process account account_6 in thread 14
26.03.2019 21:43:46 | Process account account_4 in thread 15
26.03.2019 21:43:46 | Process account account_2 in thread 14
26.03.2019 21:43:47 | Process account account_6 in thread 16
26.03.2019 21:43:47 | Process account account_3 in thread 16
26.03.2019 21:43:48 | Process account account_8 locked for time: 26.03.2019 21:44:14
26.03.2019 21:43:48 | Process account account_6 in thread 13
26.03.2019 21:43:49 | Process account account_4 in thread 15
26.03.2019 21:43:49 | Process account account_2 in thread 14
26.03.2019 21:43:50 | Process account account_6 in thread 13
26.03.2019 21:43:51 | Process account account_3 locked for time: 26.03.2019 21:45:04
26.03.2019 21:43:51 | Process account account_2 in thread 16
26.03.2019 21:43:53 | Process account account_6 locked for time: 26.03.2019 21:44:00
26.03.2019 21:43:53 | Process account account_4 locked for time: 26.03.2019 21:44:25
26.03.2019 21:43:53 | Process account account_2 in thread 14
26.03.2019 21:43:57 | Process account account_2 in thread 13
26.03.2019 21:43:58 | Process account account_2 in thread 14
26.03.2019 21:44:00 | Process account account_6 in thread 13
26.03.2019 21:44:00 | Process account account_2 in thread 15
26.03.2019 21:44:02 | Process account account_2 in thread 16
26.03.2019 21:44:03 | Process account account_6 in thread 14
26.03.2019 21:44:03 | Process account account_6 in thread 15
26.03.2019 21:44:03 | Process account account_6 in thread 13
26.03.2019 21:44:03 | Process account account_2 in thread 14
26.03.2019 21:44:06 | Process account account_6 in thread 15
26.03.2019 21:44:06 | Process account account_2 in thread 16
26.03.2019 21:44:07 | Process account account_6 in thread 13
26.03.2019 21:44:07 | Process account account_6 in thread 14
26.03.2019 21:44:08 | Process account account_6 in thread 15
26.03.2019 21:44:08 | Process account account_2 in thread 13
26.03.2019 21:44:09 | Process account account_2 in thread 14
26.03.2019 21:44:10 | Process account account_2 in thread 16
26.03.2019 21:44:11 | Process account account_6 in thread 13
26.03.2019 21:44:13 | Process account account_6 in thread 14
26.03.2019 21:44:14 | Process account account_8 in thread 13
26.03.2019 21:44:14 | Process account account_6 in thread 15
26.03.2019 21:44:14 | Process account account_2 in thread 14
26.03.2019 21:44:15 | Process account account_2 locked for time: 26.03.2019 21:44:31
26.03.2019 21:44:17 | Process account account_8 locked for time: 26.03.2019 21:47:10
26.03.2019 21:44:18 | Process account account_6 in thread 16
26.03.2019 21:44:19 | Process account account_6 in thread 13
26.03.2019 21:44:21 | Process account account_6 locked for time: 26.03.2019 21:45:11
26.03.2019 21:44:25 | Process account account_4 in thread 13
26.03.2019 21:44:29 | Process account account_4 in thread 14
26.03.2019 21:44:30 | Process account account_4 in thread 15
26.03.2019 21:44:30 | Process account account_4 in thread 16
26.03.2019 21:44:31 | Process account account_4 in thread 13
26.03.2019 21:44:31 | Process account account_2 in thread 14
26.03.2019 21:44:34 | Process account account_4 in thread 15
26.03.2019 21:44:34 | Process account account_2 in thread 16
26.03.2019 21:44:35 | Process account account_4 in thread 13
26.03.2019 21:44:37 | Process account account_2 in thread 14
26.03.2019 21:44:37 | Process account account_2 in thread 15
26.03.2019 21:44:37 | Process account account_2 in thread 16

SimpleQueue.cs

using System;
using System.Collections.Concurrent;
using System.Linq;
using System.Threading;

namespace ConsoleApp1
{
    public class Program
    {
        static readonly Random Rng = new Random();
        const int WorkerCount = 4;
        const int AccountCount = 8;

        public static void Main()
        {
            var cancelSource = new CancellationTokenSource();
            var context = new Context
            {
                WaitQueue = new ConcurrentDictionary<string, Account>(),
                WorkQueue = new ConcurrentQueue<Account>(),
                Cancel = cancelSource.Token
            };
            for (var i = 0; i < WorkerCount; i++)
                new Thread(ProcessWorkQueue).Start(context);
            new Thread(ProcessWaitQueue).Start(context);
            for (var i = 0; i < AccountCount; i++)
            {
                var id = $"account_{i + 1}";
                context.WaitQueue.TryAdd(id, new Account {Id = id});
            }

            Thread.Sleep(60_000);
            cancelSource.Cancel();
        }

        static void ProcessWaitQueue(object obj)
        {
            var context = (Context) obj;
            while (!context.Cancel.IsCancellationRequested)
            {
                var ids = context.WaitQueue.Values
                    .Where(a => a.AvailableFrom < DateTime.Now)
                    .OrderBy(x => x.LastActivity)
                    .Select(x => x.Id)
                    .ToList();
                if (!ids.Any())
                    Thread.Sleep(100);
                foreach (var id in ids)
                    if (context.WaitQueue.TryRemove(id, out var account))
                        context.WorkQueue.Enqueue(account);
            }
        }

        static void ProcessWorkQueue(object obj)
        {
            var context = (Context) obj;
            Console.WriteLine("{0} | Begin thread {1}", DateTime.Now, Thread.CurrentThread.ManagedThreadId);
            while (!context.Cancel.IsCancellationRequested)
            {
                if (context.WorkQueue.TryDequeue(out var account))
                {
                    Console.WriteLine("{0} | Process account {1} in thread {2}", DateTime.Now, account.Id,
                        Thread.CurrentThread.ManagedThreadId);
                    Thread.Sleep(Rng.Next(0, 5) * 1000);
                    if (Rng.Next() % 5 == 0)
                    {
                        account.AvailableFrom = DateTime.Now.AddSeconds(Rng.Next(0, 200));
                        Console.WriteLine("{0} | Process account {1} locked for time: {2}", DateTime.Now, account.Id,
                            account.AvailableFrom);
                    }

                    account.LastActivity = DateTime.Now;
                    if (!context.WaitQueue.TryAdd(account.Id, account))
                        throw new InvalidOperationException("conflict");
                }
                else
                {
                    Thread.Sleep(100);
                }
            }

            Console.WriteLine("{0} | End thread {1}", DateTime.Now, Thread.CurrentThread.ManagedThreadId);
        }
    }

    class Context
    {
        public ConcurrentQueue<Account> WorkQueue { get; set; }
        public ConcurrentDictionary<string, Account> WaitQueue { get; set; }
        public CancellationToken Cancel { get; set; }
    }

    class Account
    {
        public string Id { get; set; }
        public DateTime AvailableFrom { get; set; } = DateTime.MinValue;
        public DateTime LastActivity { get; set; } = DateTime.MinValue;
    }
}