Are async console applications supported in .NET Core?

At some point in time the CoreCLR supported async main entry points. See http://blog.stephencleary.com/2015/03/async-console-apps-on-net-coreclr.html

However both the following programs are not working in .NET Core RTM

using System;
using System.Threading.Tasks;

namespace ConsoleApplication
{
    public class Program
    {
        public static async Task Main(string[] args)
        {
            await Task.Delay(1000);
            Console.WriteLine("Hello World!");
        }
    }
}

or

using System;
using System.Threading.Tasks;

namespace ConsoleApplication
{
    public class Program
    {
        public async Task Main(string[] args)
        {
            await Task.Delay(1000);
            Console.WriteLine("Hello World!");
        }
    }
}

These both fail with the error:

> error CS5001: Program does not contain a static 'Main' method suitable for an entry point

Are async console applications supported in .NET Core RTM?

Yes, the async Main functions are supported since .NET Core 2.0.

dotnet --info
.NET Command Line Tools (2.0.0)

Product Information:
 Version:            2.0.0
 Commit SHA-1 hash:  cdcd1928c9

Runtime Environment:
 OS Name:     ubuntu
 OS Version:  16.04
 OS Platform: Linux
 RID:         ubuntu.16.04-x64
 Base Path:   /usr/share/dotnet/sdk/2.0.0/

Microsoft .NET Core Shared Framework Host

  Version  : 2.0.0
  Build    : e8b8861ac7faf042c87a5c2f9f2d04c98b69f28d

The support for the async Main functions is introduced in C# version 7.1. However, this functionality is not available out of the box. To make use of this feature you need explicitly specify the C# version 7.1 in your .csproj file, either by including

<LangVersion>latest</LangVersion>

or by

<LangVersion>7.1</LangVersion>

For example for the ASP.NET core 2.0 project:

<Project Sdk="Microsoft.NET.Sdk.Web">
  <PropertyGroup>
    <TargetFramework>netcoreapp2.0</TargetFramework>
    <LangVersion>latest</LangVersion>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.AspNetCore.All" Version="2.0.0" />
  </ItemGroup>
  <ItemGroup>
    <DotNetCliToolReference Include="Microsoft.VisualStudio.Web.CodeGeneration.Tools" Version="2.0.0" />
    <DotNetCliToolReference Include="Microsoft.EntityFrameworkCore.Tools.DotNet" Version="2.0.0" />
    <DotNetCliToolReference Include="Microsoft.DotNet.Watcher.Tools" Version="2.0.0" />
  </ItemGroup>
</Project>

where the Main function can be rewritten as following:

using System.Threading.Tasks;

...
public static async Task Main(string[] args)
{
   await BuildWebHost(args).RunAsync();
}
...

References:

1. C# 7 Series, Part 2: Async Main
2. Champion "Async Main" (C# 7.1)

Update: Async main is supported natively by C# 7.1! See Evgeny's answer above.

I'll keep the below workaround for posterity, but it is no longer needed. async main is way simpler, use that if you can!

---

This is my preferred workaround in C# less than 7.1:

using System;
using System.Threading.Tasks;

namespace ConsoleApplication
{
    public class Program
    {
        public static void Main(string[] args)
        {
            MainAsync(args).GetAwaiter().GetResult();

            Console.ReadKey();
        }

        public static async Task MainAsync(string[] args)
        {
            await Task.Delay(1000);
            Console.WriteLine("Hello World!");
        }
    }
}

GetAwaiter().GetResult() is the same as .Wait (blocking synchronously), but is preferred because it unwraps exceptions.

Support for async entry points was removed a while back.

See this issue on the aspnet/announcements github.

> We decided to move towards unification of entry point semantics with > desktop CLR. > > Obsolete in RC1: > > Support for async/Task<> Main. > > Support for instantiating of entry point type (Program). > > The Main method should be public static void Main or public static int Main. > >Support for injecting dependencies into the Program class's constructor and Main method. > >Use PlatformServices and CompilationServices instead. > >To get to IApplicationEnvironment, IRuntimeEnvironment, IAssemblyLoaderContainer, IAssemblyLoadContextAccessor, > ILibraryManager > use Microsoft.Extensions.PlatformAbstractions.PlatformServices.Default > static object. > >To get to ILibraryExporter, ICompilerOptionsProvider use the Microsoft.Extensions.CompilationAbstractions.CompilationServices.Default > static object. > >Support for CallContextServiceLocator. Use PlatformServices and CompilationServices instead. > >Same as above. > > These would be removed in RC2: #106