killchildren.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Akka.Actor;
using Akka.Dispatch.SysMsg;

namespace ConsoleApplication43
{
    class Program
    {
        static void Main(string[] args)
        {
            using (var system = ActorSystem.Create("sys"))
            {
                var parent = system.ActorOf<Parent>();
                parent.Tell("work");                
                parent.Tell("work");
                parent.Tell("terminate");
                //these will never be processed
                parent.Tell("work");
                parent.Tell("work");
                parent.Tell("work");

                Console.ReadLine();
            }
        }
    }

    public class Parent : ReceiveActor
    {
        private readonly HashSet<IActorRef> _children = new HashSet<IActorRef>();
        public Parent()
        {            
            for (int i = 0; i < 10; i++)
            {
                var child = Context.ActorOf<Worker>();
                Context.Watch(child);
                _children.Add(child);
            }

            Receive<string>(str => str == "work", s =>
            {
                foreach (var child in _children)
                {
                    //send some sort of work to child
                    child.Tell("work" + Guid.NewGuid());
                }
            });

            Receive<string>(str => str == "terminate", s =>
            {
                BecomeTerminating();
            });
        }

        private void BecomeTerminating()
        {
            foreach (var child in _children)
            {
                child.Tell(PoisonPill.Instance);
            }
            Become(Terminating);
        }

        private void Terminating()
        {
            Receive<Terminated>(t =>
            {
                _children.Remove(t.ActorRef);
                if (!_children.Any())
                {
                    //all children are dead
                    Context.Stop(Self);
                }
            });
        }

        protected override void PostStop()
        {
            Console.WriteLine("Stopping parent");
            base.PostStop();
        }
    }

    public class Worker : ReceiveActor
    {
        public Worker()
        {
            Receive<string>(s => Console.WriteLine($"Doing work {Self.Path}"));
        }
    }
}