using System;

using System.Threading;

using System.Threading.Tasks;

public class Program

{

    public static async Task Main()

    {

        Foo.AsyncLocalVar = 1;

        await Bar.DoSomeWork("A");

        await Bar.DoSomeWork("B");

        // Sync flow also contains the variable 

        Bar.DoSomeWork("C");

        Console.WriteLine("Main:{0}", Foo.AsyncLocalVar);

        // This is still 1 because, AsyncLocalVar is outside of the Bar.DoSomeWork instance flow. 

        Console.WriteLine("Main Bar.GetAsyncLocalVar:{0}", Bar.GetAsyncLocalVar());

    }

}

​

public static class Foo

{

    private static AsyncLocal<int?> asyncLocalVar = new AsyncLocal<int?>();

    public static int AsyncLocalVar

    {

        get => (int)asyncLocalVar.Value;

        set => asyncLocalVar.Value = new int?(value);

    }

}

​

public static class Bar 

{

    private static Random rnd = new Random();

    public static async Task DoSomeWork(string s)

    {

        Foo.AsyncLocalVar = rnd.Next(1,99); 

        Console.WriteLine("{0}:{1}", s, Foo.AsyncLocalVar);

        Console.WriteLine("{0} GetAsyncLocalVar:{1}", s, Bar.GetAsyncLocalVar());

        await Task.Delay(1);

    }

    public static int GetAsyncLocalVar()

    {

        return Foo.AsyncLocalVar;

    }

}