using System;

using System.Threading;

using System.Threading.Tasks;   

using System.Collections;

using System.Collections.Generic;

using System.Collections.Concurrent;

public class Program

{

    public static async Task Main()

    {

        OnCancelThrowException();

        OnCancelReturn();

        await CancelTaskAndChildren();

    }

    private static void OnCancelThrowException()

    {

        var tokenSource = new CancellationTokenSource();

        var token = tokenSource.Token;

        var task = Task.Run(() => {

            token.ThrowIfCancellationRequested();

            while(true) {

                // if no clean up needed

                token.ThrowIfCancellationRequested();

                /*

                if clean up needed

                if(token.IsCancellationRequested)

                {

                    // cleanup code 

                    token.ThrowIfCancellationRequested();

                }

                */

            }

        }, token);

        tokenSource.Cancel();

        try 

        {

            task.Wait();

        }

        catch(AggregateException e) 

        {

            Console.WriteLine("Task Status: {0}, Error Messaage: {1}", task.Status, e.InnerException.Message);

        }

        finally 

        {

            tokenSource.Dispose();

        }

    }

    private static void OnCancelReturn() {

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

        var tokenSource = new CancellationTokenSource();

        var token = tokenSource.Token;

        int completedIterations = 0;

        for(int i=0; i<10; i++) {

            tasks.Add(Task.Run(() => {

                int x=0;

                for(x =0; x<200000; x++)

                {

                    if(token.IsCancellationRequested)

                        return x;

                }

                Interlocked.Increment(ref completedIterations);

                if(completedIterations > 5 && !tokenSource.IsCancellationRequested) {

                    tokenSource.Cancel();

                }

                return x;

            }, token));

        }

        try

        {

            Task.WaitAll(tasks.ToArray());

        }

        catch(AggregateException)

        {

            Console.WriteLine("{0, 10} {1,20} {2, 14}", "Task Id", "Status", "Iterations");

            foreach(var t in tasks)

            {

                Console.WriteLine("{0, 10} {1,20} {2, 14:N0}", t.Id, t.Status, t.Status != TaskStatus.Canceled ? t.Result.ToString(): "Not Started");

            }

        }

    }

    private static async Task CancelTaskAndChildren() 

    {

        var tasks = new ConcurrentBag<Task>();

        var tokenSource = new CancellationTokenSource();

        var token = tokenSource.Token;

        Task t1 = Task.Run(() => DoSomeWork(1, token), token);

        Console.WriteLine($"Task {t1.Id} executing");

        tasks.Add(t1);

        Task t2 = Task.Run(() => {

            Task t;

            for(int i=3; i<=10; i++) {

                t = Task.Factory.StartNew((obj) => DoSomeWork((int)obj, token), i, token);

                Console.WriteLine($"Task {t.Id} executing");

                tasks.Add(t);

            }

            DoSomeWork(2, token);

        }, token);

        Console.WriteLine($"Task {t2.Id} executing");

        tasks.Add(t2);

        Task.Delay(100).Wait();

        tokenSource.Cancel();

        Console.WriteLine($"Tasks cancellation requested");

        try

        {

            await Task.WhenAll(tasks.ToArray());

        }

        catch(OperationCanceledException e) 

        {

            Console.WriteLine(nameof(OperationCanceledException));

        }

        finally 

        {

            tokenSource.Dispose();

        }

        foreach(var task in tasks)

            Console.WriteLine($"Task {task.Id} {task.Status}");

    }

    private static void DoSomeWork(int taskNum, CancellationToken ct) 

    {

        if(ct.IsCancellationRequested) 

        {

            Console.WriteLine($"Task {taskNum} was cancelled before it got started");

            ct.ThrowIfCancellationRequested();

        }

        var sw = new SpinWait();

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

        {

            sw.SpinOnce();

            if(ct.IsCancellationRequested) 

            {

                Console.WriteLine($"Task {taskNum} cancelled");

                ct.ThrowIfCancellationRequested();

            }

        }

        Console.WriteLine($"Task {taskNum} completed");

    }

}