using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
class Async
{
    public class Number
    {
        public int Id;
        public int Num;
    }
    public static async Task Main(string[] args)
    {
        List<Number> nums = new List<Number>();

        //One would expect that the following code runs truly asynchronously, on the same thread.
        //However:
        Task task1 = FooAsync(1, nums); //This runs on one thread
        Task task2 = FooAsync(2, nums); //This runs on another thread
        await task1;
        await task2;

        foreach(var num in nums)
        {
            Console.WriteLine($"{num.Num} (Id: {num.Id})");
        }
    }
    public static async Task FooAsync(int id, List<Number> nums)
    {
        Console.WriteLine($"Starting async task (id: {id}) in Thread {Thread.CurrentThread.ManagedThreadId}");
        await Task.Delay(1000);
        for (int i = 0; i < 100; i++)
        {
            nums.Add(new Number() { Id = id, Num = i });
        }
        Console.WriteLine($"Finished async task (id: {id}) in Thread {Thread.CurrentThread.ManagedThreadId}");
    }
}