C# Online Compiler | .NET Fiddle

using Akka.Actor;
using Akka.Configuration;
using System.Threading.Tasks;
using System;

public class Program
{
    public static void Main()
    {
        // this configuration is required ony in .NET Fiddle
        var config = ConfigurationFactory.ParseString(@"akka.actor.default-dispatcher { type = ""Akka.Dispatch.TaskDispatcherConfigurator""}");

        var system = ActorSystem.Create("Sample", config);

        var actor = system.ActorOf<FreeBusyActor>();

        Task.Run(async () =>
        {

            for (var i = 0; i < 10; i++)
            {
                actor.Tell("get busy");
                await Task.Delay(40);
            }
			
			// alow some time for .NET Fiddle to flush
			await Task.Delay(500);
        }).Wait();
    }

    public class FreeBusyActor : ReceiveActor
    {
        public FreeBusyActor()
        {
            // the actor starts as "Free"
            Free();
        }

        void Free()
        {
            // when free, only "get busy" commands are handled
            Receive<string>(s => {

                if (s == "get busy")
                {
                    Console.WriteLine("Getting busy...");

                    // the actor becomes busy, so the next messages are handled differently
                    Become(Busy);

                    // the actor starts some work in the background
                    // when it's done tell itself it's free
                    Task.Delay(80).ContinueWith(_ => "you're free").PipeTo(Self, Self);
                }
            });
        }

        void Busy()
        {
            Receive<string>(s =>
            {
                // when busy, only accept messages from itself to get free
                if (s == "you're free" && Sender.Equals(Self))
                {
                    Console.WriteLine("Getting free...");
                    Become(Free);
                }
                // otherwise we won't do anything
                else
                {
                    Console.WriteLine("Not doing anything, I'm busy...");
                }
            });
        }
    }
}

 
using Akka.Actor;
using Akka.Configuration;
using System.Threading.Tasks;
using System;
​
public class Program
{
    public static void Main()
    {
        // this configuration is required ony in .NET Fiddle
        var config = ConfigurationFactory.ParseString(@"akka.actor.default-dispatcher { type = ""Akka.Dispatch.TaskDispatcherConfigurator""}");
​
        var system = ActorSystem.Create("Sample", config);
​
        var actor = system.ActorOf<FreeBusyActor>();
​
        Task.Run(async () =>
        {
​
            for (var i = 0; i < 10; i++)
            {
                actor.Tell("get busy");
                await Task.Delay(40);
            }