Async and Await Keyword in C#

Async and Await keywords are used together to run a method asynchronously(not multi-threaded).  An async method will be run synchronously if it does not contain an await keyword. An async method either returns void or a task.

With these keywords, we run methods in an asynchronous way. Threads are optional. This style of code is more responsive. A network access can occur with no program freeze.

Eg: In the following example, the task run asynchronously. Thus, the two console.writeline statements are executed before the task completes.

using System;

using System.Threading.Tasks;

using System.Threading;

internal class Program
{
    private static void Main(string[] args)
    {
        var task = DoWork();
        Console.WriteLine("Task status: " + task.Status);
        Console.WriteLine("Waiting for ENTER");
        Console.ReadLine();
    }

    private static async Task DoWork()
    {
        Console.WriteLine("Entered DoWork(). Sleeping 3");
        // imitating time consuming code
        // in a real-world app this should be inside task, 
        // so method returns fast
        Thread.Sleep(3000);

        await Task.Run(() =>
            {
                for (int i = 0; i < 10; i++)
                {
                    Console.WriteLine("async task iteration " + i);
                    // imitating time consuming code
                    Thread.Sleep(1000);
                }
            });

        Console.WriteLine("Exiting DoWork()");
    }
}

Output:


Entered DoWork(). Sleeping 3

async task iteration 0

Task status: WaitingForActivation

Waiting for ENTER

async task iteration 1

async task iteration 2

async task iteration 3

async task iteration 4

async task iteration 5

async task iteration 6

async task iteration 7

async task iteration 8

async task iteration 9

Exiting DoWork()