Await and async

One example of await and async from the book Pro C# 9 with .NET 5: Foundational Principles and Practices in Programming

using System;
using System.Threading;
using System.Threading.Tasks;

namespace AwaitAsyncExample
{
    class Program
    {
        static void Main(string[] args)
        {
            Task.Run(async () =>
            {
                await MultipleAwaits();
            });

            Console.ReadKey();
        }

        static async Task MultipleAwaits()
        {
            Task task1 = Task.Run(() =>
            {
                Thread.Sleep(2_000);
                Console.WriteLine("Done with first task!");
            });
            Task task2 = Task.Run(() =>
            {
                Thread.Sleep(1_000);
                Console.WriteLine("Done with second task!");
            });
            Task task3 = Task.Run(() =>
            {
                Thread.Sleep(1_000);
                Console.WriteLine("Done with third task!");
            });
            await Task.WhenAll(task1, task2, task3);
        }
    }
}

Another example:

private static readonly Object ThisLock = new Object();

static void Main(string[] args)
{
  Task.Run(async () =>
  {
	await MultipleAwaits();
  });

  Console.ReadKey();
}

static async Task MultipleAwaits()
{
  Task task1 = Task.Run(() =>
  {
	lock (ThisLock)
	{
	  File.AppendAllText("test.txt", "test 1");
	}
  });
  Task task2 = Task.Run(() =>
  {
	lock (ThisLock)
	{
	  File.AppendAllText("test.txt", "test 2");
	}
  });
  Task task3 = Task.Run(() =>
  {
	lock (ThisLock)
	{
	  File.AppendAllText("test.txt", "test 3");
	}
  });
  await Task.WhenAll(task1, task2, task3);
}

Notice:

lock (ThisLock)
{
  File.AppendAllText("test.txt", "test 2");
}

Without lock exception "The process cannot access the file 'test.txt' because it is being used by another process." will be raised.

One more example in Windows forms:

namespace AsyncTest;

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
        btnStart.Click += DoSomeWork;
    }

    async void DoSomeWork(object sender, EventArgs e)
    {
        label1.Text = "start";
        string text = await DoWait();
        label1.Text = text;
    }

    private Task<string> DoWait()
    {
        Task<string> task1 = Task.Run(() =>
        {
            Thread.Sleep(2_000);
            return Task.FromResult("did it");
        });

        return task1;
    }
}