using System;

using System.Collections.Generic;

using System.Threading.Tasks;

using System.Threading;

​

public class Program

{

    static Dictionary<string, bool> map = new Dictionary<string, bool>();

    static async Task Runner()

    {

        Console.WriteLine("Started runner");

        for (var i=0; i < 100; i++)

        {

            map[i.ToString()] = true;

            await Task.Yield();

        }

    }

    static async Task Checker(CancellationToken cancellationToken)

    {

        Console.WriteLine("Started checker");

        while (!cancellationToken.IsCancellationRequested)

        {

            var result = map.Count == 0 ? true : !map.ContainsValue(false);

            if (result)

            {

                Console.WriteLine("All tasks are finished.");

            }

            else

            {

                Console.WriteLine("All tasks are not finished.");

            }

            await Task.Yield();

        }

    }

    public static void Main()

    {

        var cts = new CancellationTokenSource();

        var tasks = new List<Task>();

        var checker = Task.Run(async () => await Checker(cts.Token));

        for (var i=0; i < 50; i++)

        {

            tasks.Add(Task.Run(Runner));

        }

        Task.WhenAll(tasks).GetAwaiter().GetResult();

        cts.Cancel();

        checker.GetAwaiter().GetResult();

    }

}