IndexOutOfRangeException with RoundRobinRoutingLogic & SmallestMailboxRoutingLogic

[jordansjones]

Assuming Routee[] routees has 1 or more elements in the array, when Interlocked.Increment(ref _next) rolls over to a negative number, an IndexOutOfRangeException will be thrown.

The following is a simplistic example that demonstrates what is happening:

var items = new [] { 1, 2, 3, 4, 5 };
var count = int.MaxValue - 5;

for (var i = 0; i < 20; i++)
{
    items[Interlocked.Increment(ref count) % items.Length].Dump();
}

The following is a simplistic program that demonstrates the above while using Akka.

public class Program
{

    public const long Total = ((long) int.MaxValue) + 15;

    public static Stopwatch Stopwatch;

    public static void DoIt()
    {
        var system = ActorSystem.Create("GreetSystem");
        var greeter = system.ActorOf(
            Props.Create(() => new OutputActor())
                    .WithRouter(new RoundRobinPool(10).WithResizer(new DefaultResizer(5, 150)))
            );

        Stopwatch = Stopwatch.StartNew();
        for (var i = 0L; i < Total; i++)
        {
            greeter.Tell(i);
        }
    }

    public static void Main(string[] args)
    {
        DoIt();
    }

    public class OutputActor : ReceiveActor
    {

        private static long _count = -1;

        private static float _percent = -1f;

        private static readonly object Guard = new object();

        public OutputActor()
        {
            Receive<long>(x => DoStuff(x));
        }

        protected void DoStuff(long message)
        {
            var count = Interlocked.Increment(ref _count);
            lock (Guard)
            {
                var percent = (float) Math.Round((double) count / Total, 4);
                if (Math.Abs(percent - _percent) < .00001F) { return; }

                _percent = percent;
                Console.SetCursorPosition(0, 0);
                Console.Write("                    ");
                Console.SetCursorPosition(0, 0);
                Console.Write("{0:P2}", _percent);
            }
        }

    }

}