Sequencer_1.cs

using System;
using System.Collections.Generic;
using System.Threading;

namespace Sequencer
{
    using System.Collections.Concurrent;

    public class Sequencer
    {
        private readonly ConcurrentQueue<Action> _pendingTasks = new ConcurrentQueue<Action>();
        private readonly object _running = new Object(); 

        public void Dispatch(Action action)
        {
            // Queue the task
            _pendingTasks.Enqueue(action);
            // Schedule a processing run (may be a noop)
            ThreadPool.QueueUserWorkItem( x=> Run());
        }

        // run when the pool has available cpu time for us.
        private void Run()
        {
            if (Monitor.TryEnter(_running))
            {
                try
                {
                    Action taskToRun;
                    while (_pendingTasks.TryDequeue(out taskToRun))
                    {
                        taskToRun();
                    }
                }
                finally
                {
                    Monitor.Exit(_running);
                }
            }
        }
    }
}