Program.cs

using System;
using System.Linq;
using System.Threading.Tasks;
using log4net;
using log4net.Config;

namespace ItsBigItsHeavyItsWood
{
    class Program
    {
        private static readonly ILog s_logger = LogManager.GetLogger("Logger");
        private static readonly Random s_random = new Random();

        static void Main()
        {
            BasicConfigurator.Configure();
            var items = new[]
            {
                "a",
                "b",
                "c",
                "d",
                "e",
                "f",
            };

            s_logger.Info("starting all tasks");

            var tasks = items.Select(Process).ToArray();

            s_logger.Info("started all tasks");

            Task.WaitAll(tasks);
        }

        private static async Task Process(string item)
        {
            using (NDC.Push(String.Format("[item {0}]", item)))
            {
                s_logger.InfoFormat("starting stuff with item {0}", item);
                await Task.Delay(TimeSpan.FromSeconds(s_random.Next(30)));
                s_logger.InfoFormat("doing more stuff with item {0}", item);
                await Task.Delay(TimeSpan.FromSeconds(s_random.Next(30)));
                s_logger.InfoFormat("done with item {0}", item);
            }
        }
    }
}