使用队列来做:
class QueueTest
    {
        private Queue thisQu = Queue.Synchronized(new Queue(1000));
        public void Push(object obj)
        {
            lock(thisQu)
                this.thisQu.Enqueue(obj);
        }
        public object Pop()
        {            
            lock(thisQu)
            {
                if(thisQu.Count >0)
                    this.thisQu.Dequeue();
                else
                    return null;
            }
        }
        public int Count
        {
            get
            {
                return thisQu.Count;
            }
        }
        public void Clear()
        {
            lock(thisQu)
            {
                this.thisQu.Clear();
            }
        }
    }

C#本身有堆栈的功能，private Stack switchCheckStack = new Stack();