using System;

using System.Collections.Generic;

using System.Threading;

using System.Threading.Tasks;

public class Program

{

    public static void Main()

    {

        var cancellationTokenSource = new CancellationTokenSource(TimeSpan.FromSeconds(30));

        var tasks = new List<Task> {    

            StartTask(1, cancellationTokenSource.Token),

            StartTask(2, cancellationTokenSource.Token),

            StartTask(3, cancellationTokenSource.Token),

            StartTask(4, cancellationTokenSource.Token),

            StartTask(5, cancellationTokenSource.Token),

            StartTask(6, cancellationTokenSource.Token),

            StartTask(7, cancellationTokenSource.Token),

            StartTask(8, cancellationTokenSource.Token),

            StartTask(9, cancellationTokenSource.Token),

            StartTask(10, cancellationTokenSource.Token)

        };

        cancellationTokenSource.CancelAfter(TimeSpan.FromSeconds(9));

        var allTasks = new List<Task>(tasks);

        var stopAsyncToken = new CancellationTokenSource(TimeSpan.FromSeconds(30)).Token;

        Task.WaitAll(allTasks.ToArray(), stopAsyncToken);

    }

    private static async Task StartTask(int waitTime, CancellationToken cancellationToken){

        await Task.Run(async () => {

            await Task.Run(() => Console.WriteLine($"{waitTime}: waiting {waitTime} seconds"));

            await Task.Delay(TimeSpan.FromSeconds(waitTime), cancellationToken);

            await Task.Run(() => Console.WriteLine($"{waitTime}: waited {waitTime} seconds"));

        }, cancellationToken);

    }   

}