Async/Await in C# - A quick how to

Using asynchronous programming in C#, you can improve your application’s responsiveness by avoiding the activities which are blocked in a synchronous operation. This post will explain in short so you will understand how to use Async and Await keywords in C#.

Assume you go to a coffee shop and order coffee with cake.

Here are the list of thing that a worker needs to do:

1. Accept the order and payment, takes 3 minutes

2. Make the coffee, and put it on a tray, takes 5 minutes

3. Put a slice of cake you have ordered and put it on the tray, takes 1 minutes

Synchronous

In a synchronous world, it’s like the coffee shop has only one staff and has to work on the tasks one after another. Here it takes 9 minutes for the worker to complete all above three tasks.

namespace Demo
{
    public class CoffeeShop
    {
        public const int MIN = 60 * 60 * 1000
        public void AcceptPayment()         => Thread.Sleep(3 * MIN);
        public void MakeCoffee()            => Thread.Sleep(5 * MIN);
        public void PrepareSliceOfCake()    => Thread.Sleep(1 * MIN);
    }

    class Program
    {
        static void Main()
        {
            var shop = new CoffeeShop();
            shop.AcceptPayment();
            shop.MakeCoffee();
            shop.PrepareSliceOfCake();
        }
    }
}

Asynchronous

But if we use asynchronous programming, we can me it less.

using System.Threading.Tasks;
namespace Demo
{
    public class CoffeeShop
    {
        ...
        public async Task AcceptPayment()       => await Task.Delay(3 * MIN);
        public async Task MakeCoffee()          => await Task.Delay(5 * MIN);
        public async Task PrepareSliceOfCake()  => await Task.Delay(1 * MIN);
        ...
    }

    class Program
    {
        static void Main()
        {
            var shop = new CoffeeShop();
            var acceptPaymentTask = shop.AcceptPayment();
            var makeCoffeeTask = shop.MakeCoffee();
            var prepareSliceOfCake = shop.PrepareSliceOfCake();

            Task.WaitAll(acceptPaymentTask, makeCoffeeTask, prepareSliceOfCake);
        }
    }
}

We changed the return types of the functions from void to async Task and used Task.WaitAll to wait for all the task to complete so we can drink our coffee with the slice of cake.

Using await in Main needs async Main

We may want to have the coffee even if without the cake, because we are thirsty?

    ...
        static async Task Main()
        {
            var shop = new CoffeeShop();
            var acceptPaymentTask = shop.AcceptPayment();
            var makeCoffeeTask = shop.MakeCoffee();

            Task.WaitAll(acceptPaymentTask, makeCoffeeTask);

            // Drink the coffee while waiting for...

            await shop.PrepareSliceOfCake();

            // The cake is ready :yum:
        }
    ...

You can see we had to add async Task to the Main method as well, because we are using await keyword inside it.

Conclusion

This post was a quick introduction to using async/await in C# which I hope it was helpful. Parallel tasks are still tasks and needs to be done in the same time as the synchronous tasks, but running them asynchronously helps us getting the coffee sooner if we are thirsty. :)