Sequencer implementation: iteration 1

Sequencer_1.cs

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

namespace Sequencer
{
    public class Sequencer
    {
        private Queue<Action> _pendingTasks = new Queue<Action>();
        private bool _isRunning;
        private readonly object _lock = new Object(); 

        public void Dispatch(Action action)
        {
            // here we queue a call to our own logic
            ThreadPool.QueueUserWorkItem( (x)=> Run((Action) x), action );
        }

        // run when the pool has available cpu time for us.
        private void Run(Action action)
        {
            lock(_lock) {
                if (_isRunning) {
                    // we need to store and stop
                    _pendingTasks.Enqueue(action);
                    return;
                }
                // ok, we can run
                _isRunning = true;
            }

            while (true) {
                // execute the next action
                action ();
                // we check if others are available
                lock (_lock) {
                    if (_pendingTasks.Count == 0) {
                        _isRunning = false;
                        return;
                    }
                    // pop the next task
                    action = _pendingTasks.Dequeue();
                }
            }
        }
    }
}