iterators.cs

using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Threading.Tasks;

namespace IteratorTests
{
    public static class Program
    {
        public static void Main()
        {
            try
            {
                Test1();
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.ToString());
            }

            Console.ReadKey();
            Console.WriteLine();

            try
            {
                Test2();
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.ToString());
            }


            Console.ReadKey();
            Console.WriteLine();

            try
            {
                Test3();
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.ToString());
            }


            Console.ReadKey();
        }

        private static void Test1()
        {
            var ten = RangeIterator(1, 10);

            Run(ten);
        }

        private static void Test2()
        {
            var ten = new [] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };

            Run(ten);
        }

        private static void Test3()
        {
            var ten = new[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };

            var counters = new ConcurrentDictionary<int, int>();
            Parallel.ForEach(ten, item => counters.AddOrUpdate(item, key => 1, (key, value) => ++value));
            foreach (var counter in counters)
            {
                Print(counter);
            }
        }

        private static void Run(IEnumerable<int> enumerator)
        {
            var counters = new ConcurrentDictionary<int, int>();

            var tasks = new List<Task>();
            for (int i = 0; i < 16; i++)
            {
                tasks.Add(Task.Run(() =>
                                       {
                                           foreach (var item in enumerator)
                                           {
                                               counters.AddOrUpdate(item, key => 1, (key, value) => ++value);
                                           }
                                       }));
            }

            Task.WaitAll(tasks.ToArray());

            foreach (var counter in counters)
            {
                Print(counter);
            }
        }

        private static void Print(KeyValuePair<int, int> pair)
        {
            Console.WriteLine($"{pair.Key}: {pair.Value}");
        }

        private static IEnumerable<int> RangeIterator(int start, int count)
        {
            for (var i = 0; i < count; i++)
            {
                yield return start + i;
            }
        }
    }
}