How can I call an async method in Main?

Question

public class test
{
    public async Task Go()
    {
        await PrintAnswerToLife();
        Console.WriteLine("done");
    }

    public async Task PrintAnswerToLife()
    {
        int answer = await GetAnswerToLife();
        Console.WriteLine(answer);
    }

    public async Task<int> GetAnswerToLife()
    {
        await Task.Delay(5000);
        int answer = 21 * 2;
        return answer;
    }
}

if I want to call Go in main() method, how can I do that? I am trying out c# new features, I know i can hook the async method to a event and by triggering that event, async method can be called.

But what if I want to call it directly in main method? How can i do that?

I did something like

class Program
{
    static void Main(string[] args)
    {
        test t = new test();
        t.Go().GetAwaiter().OnCompleted(() =>
        {
            Console.WriteLine("finished");
        });
        Console.ReadKey();
    }


}

But seems it's a dead lock and nothing is printed on the screen.

Answer 1

Your Main method can be simplified. For C# 7.1 and newer:

static async Task Main(string[] args)
{
    test t = new test();
    await t.Go();
    Console.WriteLine("finished");
    Console.ReadKey();
}

For earlier versions of C#:

static void Main(string[] args)
{
    test t = new test();
    t.Go().Wait();
    Console.WriteLine("finished");
    Console.ReadKey();
}

This is part of the beauty of the async keyword (and related functionality): the use and confusing nature of callbacks is greatly reduced or eliminated.

Answer 2

Instead of Wait, you're better off using new test().Go().GetAwaiter().GetResult() since this will avoid exceptions being wrapped into AggregateExceptions, so you can just surround your Go() method with a try catch(Exception ex) block as usual.

Answer 3

Since the release of C# v7.1 async main methods have become available to use which avoids the need for the workarounds in the answers already posted. The following signatures have been added:

public static Task Main();
public static Task<int> Main();
public static Task Main(string[] args);
public static Task<int> Main(string[] args);

This allows you to write your code like this:

static async Task Main(string[] args)
{
    await DoSomethingAsync();
}

static async Task DoSomethingAsync()
{
    //...
}