Sentinel 深度剖析 之 流量控制中算法

public boolean canPass(Node node, int acquireCount, boolean prioritized) {
  // Pass when acquire count is less or equal than 0.
  if (acquireCount <= 0) {
    return true;
  }
  // Reject when count is less or equal than 0.
  // Otherwise,the costTime will be max of long and waitTime will overflow in some cases.
  if (count <= 0) {
    return false;
  }
  long currentTime = TimeUtil.currentTimeMillis();
  // Calculate the interval between every two requests.
  // 1) 两次请求的时间间隔
  long costTime = Math.round(1.0 * (acquireCount) / count * 1000);
  // Expected pass time of this request.
  // 2)计算这次请求的通过预留时间 = 上次请求通过时间+时间间隔
  long expectedTime = costTime + latestPassedTime.get();
  // 3)当预期时间 <= 当前时间, 则允许通过并更新上次请求时间戳
  if (expectedTime <= currentTime) {
    // Contention may exist here, but it's okay.
    latestPassedTime.set(currentTime);
    return true;
  } else {
    // Calculate the time to wait.
    // 4)当预期时间 > 当前时间, 则需要等待; 计算需要等待时间
    long waitTime = costTime + latestPassedTime.get() - TimeUtil.currentTimeMillis();
    // 5)需要等待的时间> 最⼤队列时间, 则拒绝 默认超时时间500毫秒
    if (waitTime > maxQueueingTimeMs) {
      return false;
    } else {
      long oldTime =
      latestPassedTime.addAndGet(costTime);
      try {
        waitTime = oldTime -
        TimeUtil.currentTimeMillis();
        // 6)
        if (waitTime > maxQueueingTimeMs) {
          latestPassedTime.addAndGet(-costTime);
          return false;
        }
        // in race condition waitTime may <= 0
        // 7)
        if (waitTime > 0) {
            Thread.sleep(waitTime);
        }
        return true;
      } catch (InterruptedException e) {
      }
    }
  }
  return false;
}