Can't specify the 'async' modifier on the 'Main' method of a console app

Question

I am new to asynchronous programming with the async modifier. I am trying to figure out how to make sure that my Main method of a console applicati

Answer 1

In C# 7.1 you will be able to do a proper async Main. The appropriate signatures for Main method has been extended to:

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

For e.g. you could be doing:

static async Task Main(string[] args)
{
    Bootstrapper bs = new Bootstrapper();
    var list = await bs.GetList();
}

At compile time, the async entry point method will be translated to call GetAwaitor().GetResult().

Details: https://blogs.msdn.microsoft.com/mazhou/2017/05/30/c-7-series-part-2-async-main

EDIT:

To enable C# 7.1 language features, you need to right-click on the project and click "Properties" then go to the "Build" tab. There, click the advanced button at the bottom:

From the language version drop-down menu, select "7.1" (or any higher value):

The default is "latest major version" which would evaluate (at the time of this writing) to C# 7.0, which does not support async main in console apps.

Answer 2

I'll add an important feature that all of the other answers have overlooked: cancellation.

One of the big things in TPL is cancellation support, and console apps have a method of cancellation built in (CTRL+C). It's very simple to bind them together. This is how I structure all of my async console apps:

static void Main(string[] args)
{
    CancellationTokenSource cts = new CancellationTokenSource();
    
    System.Console.CancelKeyPress += (s, e) =>
    {
        e.Cancel = true;
        cts.Cancel();
    };

    MainAsync(args, cts.Token).GetAwaiter.GetResult();
}

static async Task MainAsync(string[] args, CancellationToken token)
{
    ...
}

Answer 3

C# 7.1 (using vs 2017 update 3) introduces async main

You can write:

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

For more details C# 7 Series, Part 2: Async Main

Update:

You may get a compilation error:

Program does not contain a static 'Main' method suitable for an entry point

This error is due to that vs2017.3 is configured by default as c#7.0 not c#7.1.

You should explicitly modify the setting of your project to set c#7.1 features.

You can set c#7.1 by two methods:

Method 1: Using the project settings window:

• Open the settings of your project
• Select the Build tab
• Click the Advanced button
• Select the version you want As shown in the following figure:

Method2: Modify PropertyGroup of .csproj manually

Add this property:

    <LangVersion>7.1</LangVersion>

example:

    <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
        <PlatformTarget>AnyCPU</PlatformTarget>
        <DebugSymbols>true</DebugSymbols>
        <DebugType>full</DebugType>
        <Optimize>false</Optimize>
        <OutputPath>bin\Debug\</OutputPath>
        <DefineConstants>DEBUG;TRACE</DefineConstants>
        <ErrorReport>prompt</ErrorReport>
        <WarningLevel>4</WarningLevel>
        <Prefer32Bit>false</Prefer32Bit>
        <LangVersion>7.1</LangVersion>
    </PropertyGroup>    

Answer 4

Newest version of C# - C# 7.1 allows to create async console app. To enable C# 7.1 in project, you have to upgrade your VS to at least 15.3, and change C# version to C# 7.1 or C# latest minor version. To do this, go to Project properties -> Build -> Advanced -> Language version.

After this, following code will work:

internal class Program
{
    public static async Task Main(string[] args)
    {
         (...)
    }

Answer 5

In my case I had a list of jobs that I wanted to run in async from my main method, have been using this in production for quite sometime and works fine.

static void Main(string[] args)
{
    Task.Run(async () => { await Task.WhenAll(jobslist.Select(nl => RunMulti(nl))); }).GetAwaiter().GetResult();
}
private static async Task RunMulti(List<string> joblist)
{
    await ...
}

Answer 6

class Program
{
     public static EventHandler AsyncHandler;
     static void Main(string[] args)
     {
        AsyncHandler+= async (sender, eventArgs) => { await AsyncMain(); };
        AsyncHandler?.Invoke(null, null);
     }

     private async Task AsyncMain()
     {
        //Your Async Code
     }
}