using System;

using System.Collections.Generic;

using System.Text;

using System.Threading;

using System.Threading.Tasks;

using System.Linq;

​

public sealed class Runner

{

    public static int TotalCount = 0;

    private static ThreadLocal<Random> ThreadLocalRandom = new(() => new Random());

    int syncNum = 0;

    public async Task EnsureRunThingsExchangeAsync()

    {

        // Simulate contention

        await Task.Delay(TimeSpan.FromMilliseconds(ThreadLocalRandom.Value.Next(0, 10)));

        if (Interlocked.Increment(ref syncNum) > 1)

        {

            return;

        }

​

        do

        {

            Interlocked.Exchange(ref syncNum, 1);

            await ActualRunThingsAsync();

        }

        while (Interlocked.Decrement(ref syncNum) != 0);

    }

​

    private async Task ActualRunThingsAsync()

    {

        Interlocked.Increment(ref TotalCount);

    }

}

​

public class Program

{

    public static async Task Main()

    {

        var r = new Runner();

        const int totalThreads = 10_000;

        await Task.WhenAll(Enumerable.Range(0, totalThreads).Select(_ => r.EnsureRunThingsExchangeAsync()));

        if (totalThreads != Runner.TotalCount) 

        {

            Console.WriteLine($"Unexpected execution count. Found: {Runner.TotalCount}, expected: {totalThreads}.");    

        } else 

        {

            Console.WriteLine("Things worked according to plan!");

        }

    }

}