/// <summary>
/// 循環(huán)一次
/// </summary>
/// <remarks>
/// This is typically called in a loop, and may change in behavior based on the number of times a
/// <see cref="SpinOnce"/> has been called thus far on this instance.
/// </remarks>
public void SpinOnce()
{
  if (NextSpinWillYield)
  {
    int yieldsSoFar = (m_count >= YIELD_THRESHOLD ? m_count - YIELD_THRESHOLD : m_count);
    //③循環(huán)到20次時(shí)，執(zhí)行Thread.Sleep(01)
    if ((yieldsSoFar % SLEEP_1_EVERY_HOW_MANY_TIMES) == (SLEEP_1_EVERY_HOW_MANY_TIMES - 1))
    {
      //當(dāng)前線程掛起，讓出cpu
      //所有掛起的線程都有機(jī)會(huì)競(jìng)爭(zhēng)當(dāng)前時(shí)間片段，不限制線程優(yōu)先級(jí)
      Thread.Sleep(1);
    }
    //②執(zhí)行Thread.Yield()5次后，執(zhí)行Thread.Sleep(0)  
    else if ((yieldsSoFar % SLEEP_0_EVERY_HOW_MANY_TIMES) == (SLEEP_0_EVERY_HOW_MANY_TIMES - 1))
    {
      //當(dāng)前線程掛起，讓出cpu
      //(只允許那些優(yōu)先級(jí)相等或更高的線程使用當(dāng)前的CPU。
      //如果沒(méi)有，那當(dāng)前線程會(huì)重新使用CPU時(shí)間片)
      //（上面已說(shuō)明，后續(xù)補(bǔ)充實(shí)現(xiàn)）
      Thread.Sleep(0);
    }
    else
    {
      //當(dāng)前線程掛起（執(zhí)行狀態(tài)->就緒狀態(tài)）， 讓出cpu，
      //（后續(xù)補(bǔ)充實(shí)現(xiàn)邏輯）
      Thread.Yield();
    }
  }
  else
  {
    //線程等待
    //4,8,16,32,64...位運(yùn)算，2的n次方
    //①循環(huán)10次
    Thread.SpinWait(4 << m_count);
  }
  // m_count 遞增; m_count 達(dá)到最大值后回滾Count =10
  m_count = (m_count == int.MaxValue ? YIELD_THRESHOLD : m_count + 1);
}

/// <summary>
/// 重置循環(huán)計(jì)數(shù)器
/// </summary>
public void Reset()
{
  m_count = 0;
}
#region Static Methods
/// <summary>
/// 循環(huán).直到condition返回True
/// </summary>
public static void SpinUntil(Func<bool> condition)
{
  SpinUntil(condition, Timeout.Infinite);
}
/// <summary>
/// 循環(huán)，直到condition返回True或者時(shí)間達(dá)到timeout
/// </summary>
public static bool SpinUntil(Func<bool> condition, TimeSpan timeout)
{
  //校驗(yàn)時(shí)間格式是否正確
  Int64 totalMilliseconds = (Int64)timeout.TotalMilliseconds;
  if (totalMilliseconds < -1 || totalMilliseconds > Int32.MaxValue)
  {
    throw new System.ArgumentOutOfRangeException(
      "timeout", timeout, "SpinWait_SpinUntil_TimeoutWrong");
  }
  return SpinUntil(condition, (int)timeout.TotalMilliseconds);
}
/// <summary>
/// 直到condition返回True或者時(shí)間達(dá)到timeout.
/// </summary>
public static bool SpinUntil(Func<bool> condition, int millisecondsTimeout)
{
  //校驗(yàn)時(shí)間格式
  if (millisecondsTimeout < Timeout.Infinite)
  {
    throw new ArgumentOutOfRangeException(
      "millisecondsTimeout", millisecondsTimeout, "SpinWait_SpinUntil_TimeoutWrong");
  }
  //空值校驗(yàn)
  if (condition == null)
  {
    throw new ArgumentNullException("condition", "SpinWait_SpinUntil_ArgumentNull");
  }
  uint startTime = 0;
  if (millisecondsTimeout != 0 && millisecondsTimeout != Timeout.Infinite)
  {
    //自上次啟動(dòng)計(jì)算機(jī)以來(lái)所經(jīng)過(guò)的時(shí)間（以毫秒為單位）。
    startTime = TimeoutHelper.GetTime();
  }
  SpinWait spinner = new SpinWait();
  while (!condition())
  {
    if (millisecondsTimeout == 0)
    {
      return false;
    }
    spinner.SpinOnce();
    //計(jì)時(shí)
    if (millisecondsTimeout != Timeout.Infinite && spinner.NextSpinWillYield)
    {
      if (millisecondsTimeout <= (TimeoutHelper.GetTime() - startTime))
      {
        return false;
      }
    }
  }
  return true;
}

#endregion