TaskBulder for TPL in MVC4

TaskBuilder.cs

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

namespace Utils
{
    using System.Threading;

    public interface ITaskBuilder
    {
        TaskBuilder AddTask(Action action);

        TaskBuilder Run();
    }

    public class TaskBuilder : ITaskBuilder
    {
        private const int MaxWaitHandleWaitAllAllowed = 64;
        private int waitHandleCount;
        private ManualResetEventSlim[] mres;
        private readonly List<Action> taskList; 
        
        public TaskBuilder()
        {
            waitHandleCount = 0;
            taskList = new List<Action>();
        }

        /// <summary>
        /// Add a task
        /// </summary>
        /// <param name="action"></param>
        /// <returns></returns>
        public TaskBuilder AddTask(Action action)
        {
            taskList.Add(action);
            waitHandleCount++;

            return this;
        }

        /// <summary>
        /// Run a batch of tasks
        /// </summary>
        /// <returns></returns>
        public TaskBuilder Run()
        {
            mres = new ManualResetEventSlim[waitHandleCount];

            for ( var i = 0; i < mres.Length; i++ )
            {
                mres[i] = new ManualResetEventSlim( false );
            }

            var index = 0;
            foreach (var task in taskList)
            {
                int idx = index;
                Task.Factory.StartNew( task + ( () => this.mres[idx].Set() ) );
                index++;
            }

            WaitHandle.WaitAll((from x in mres select x.WaitHandle).ToArray());

            return this;
        }
    }
}

Use.cs

DataSet ds1  = null;
DataSet ds2 = null;

var tb = new TaskBuilder();

tb.AddTask(
    () =>
        {
            ds1 = GetDataSet1(params);
        });
tb.AddTask(
    () =>
        {
            ds2 = ds1 = GetDataSet2(params);
        });

tb.Run();