C# LockFreeStack类

public class LockFreeStack : IEnumerable
    {
        private class SingleLinkedNode
        {
            public object Value;
            public SingleLinkedNode Next;
        }

        private SingleLinkedNode m_head;
        private int count;

        public int Count
        {
            get { return count; }
        }

        public void Push(object item)
        {
            SingleLinkedNode node = new SingleLinkedNode();
            node.Value = item;
            SingleLinkedNode head;
            do
            {
                head = m_head;
                node.Next = head;
            }
            while (m_head != head || Interlocked.CompareExchange(ref m_head, node, head) != head);
            Interlocked.Increment(ref count);
        }

        public object Peek()
        {
            SingleLinkedNode head = m_head;
            if (head == null)
            {
                throw new InvalidOperationException("Stack Empty!");
            }
            return head.Value;
        }

        public object Pop()
        {
            object result;
            if (TryPop(out result))
            {
                return result;
            }
            throw new InvalidOperationException("Stack Empty!");
        }

        /// <summary>
        /// 考虑到在多线程环境中，这里不抛出异常。我们需要人为判断其是否为空，即 !TryPop() or result != null
        /// </summary>
        /// <returns></returns>
        public bool TryPop(out object item)
        {
            SingleLinkedNode head;
            SingleLinkedNode next;
            do
            {
                head = m_head;
                if (head == null)
                {
                    item = null;
                    return false;
                }
                next = m_head.Next;
            }
            while (Interlocked.CompareExchange(ref m_head, next, head) != head);
            Interlocked.Decrement(ref count);
            item = head.Value;
            return true;
        }

        public object SpinPop()
        {
            SingleLinkedNode head;
            SpinWait spin = new SpinWait();
            while (true)
            {
                SingleLinkedNode next;
                do
                {
                    head = m_head;
                    if (head == null)
                    {
                        goto emptySpin;
                    }
                    next = head.Next;
                }
                while (m_head != head || Interlocked.CompareExchange(ref m_head, next, head) != head);
                break;
            emptySpin:
                spin.Spin();
            }
            Interlocked.Decrement(ref count);
            return head.Value;
        }

        public bool Contains(object item)
        {
            SingleLinkedNode head = m_head;
            while (m_head != null && head != null)
            {
                if (head.Value.Equals(item))
                {
                    return true;
                }
                head = head.Next;
            }
            return false;
        }

        public void Clear()
        {
            Interlocked.Exchange(ref m_head, null);
            Interlocked.Exchange(ref count, 0);
        }

        public IEnumerator GetEnumerator()
        {
            SingleLinkedNode head = m_head;
            while (m_head != null && head != null)
            {
                yield return head.Value;
                head = head.Next;
            }
        }
    }