using System;

using System.Threading;

using System.Threading.Tasks;

using System.Threading.Tasks.Dataflow;

using System.Diagnostics;

​

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        task1().Wait();

        Console.WriteLine("Finished");

    }

​

    private static async Task task1()

    {

        Stopwatch sw = Stopwatch.StartNew();

        Console.WriteLine("1");

        //await task3(1); // Directly await task

        await task2(); // Await actionblock

        Console.WriteLine("8");

        Console.WriteLine("Elapsed time is " + sw.ElapsedMilliseconds);

    }

​

    private static async Task task2()

    {

        var actionBlock = new ActionBlock<int>(task3, new ExecutionDataflowBlockOptions{MaxDegreeOfParallelism = 1, BoundedCapacity = 7, EnsureOrdered = true, });

        await actionBlock.SendAsync(10).ConfigureAwait(false);

        actionBlock.Complete();

        await actionBlock.Completion.ConfigureAwait(false);

    }

​

    private static async Task task3(int x)

    {

        await Task.Delay(1000);

        Console.WriteLine("2");

        Console.WriteLine("3");

        Console.WriteLine("4");

        Console.WriteLine("5");

        await Task.Delay(1000);

        Console.WriteLine("6");

        Console.WriteLine("7");

    }

}