SpinWait

/// <summary>
    /// SpinWait只有在SMP或多核CPU下才具有使用意义。在单处理器下，旋转非常浪费CPU时间，没有任何意义。
    /// 自旋锁特性导致其比较适用一些轻量级，极短时间的多核cpu系统上的锁保护。
    /// </summary>
    public struct SpinWait
    {
        public static readonly bool IsSingleProcessor;
        private const int yieldFrequency = 4000;
        private const int yieldOneFrequency = 3 * yieldFrequency;

        static SpinWait()
        {
            IsSingleProcessor = (Environment.ProcessorCount == 1);
        }

        private int count;

        public int Count
        {
            get { return count; }
        }

        public int Spin()
        {
            int oldCount = count;
            // On a single-CPU machine, we ensure our counter is always
            // a multiple of �s_yieldFrequency�, so we yield every time.
            // Else, we just increment by one.
            count += (IsSingleProcessor ? yieldFrequency : 1);
            // If not a multiple of �s_yieldFrequency� spin (w/ backoff).
            int countModFrequency = count % yieldFrequency;
            if (countModFrequency > 0)
            {
                Thread.SpinWait((int)(1 + (countModFrequency * 0.05f)));
            }
            else
            {
                Thread.Sleep(count <= yieldOneFrequency ? 0 : 1);
            }
            return oldCount;
        }

        public void Yield()
        {
            Thread.Sleep(count < yieldOneFrequency ? 0 : 1);
        }

        public void Reset()
        {
            count = 0;
        }
    }