// https://github.com/dotnet/runtime/issues/111587

using System;

using System.Collections.Generic;

using System.Collections.Immutable;

using System.Linq;

using System.Threading;

​

public class Program

{

    class Genome : Queue<char>, IEquatable<Genome>

    {

        public bool Equals(Genome other) => this.SequenceEqual(other);

    }

​

    public static void Main()

    {

        var dictionary = ImmutableDictionary<int, Genome>.Empty;

        CancellationTokenSource cts = new(TimeSpan.FromSeconds(1));

        Thread[] threads = Enumerable.Range(1, 2).Select(i => new Thread(() =>

        {

            while (!cts.IsCancellationRequested)

            {

                Genome genome = ImmutableInterlocked.AddOrUpdate(ref dictionary,

                    1, _ => new(), (_, _) => new());

                lock (genome) genome.Enqueue('A');

            }

        })).ToArray();

        Array.ForEach(threads, t => t.Start());

        Array.ForEach(threads, t => t.Join());

    }

}

​