using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading;

using System.Threading.Tasks;

public class Program

{

    public static async Task Main()

    {

        var p = new Progress<int>();

        p.ProgressChanged += P_ProgressChanged;

​

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

            await DoStuffAsync(p);

    }

    private static void P_ProgressChanged(object sender, int e)

    {

           Console.WriteLine(e);

    }

    public static async Task DoStuffAsync(IProgress<int> progress)

    {

        int totalPercentDone = 0;

        var semaphore =  new SemaphoreSlim(1,1);

​

        Task[] tasks = Enumerable.Range(1, 2).Select(n => Task.Run(async () =>

        {

            for (int i = 0; i < 5; i++)

            {

                await Task.Delay(100); // Simulate an I/O operation

                await semaphore.WaitAsync();

​

                try

                {

                    totalPercentDone += 10;

                    progress.Report(totalPercentDone);

                }

                finally

                {

                    semaphore.Release();

                }

            }

        })).ToArray();

​

        await Task.WhenAll(tasks);

    }

}