ibatis里面流控的实现

ibatis里面的流控实现是通过Throttle这个类来实现，既信号量，实例化时指定最大的访问量，每次请求时从这里获取一个信号量，如果已经达到阈值将阻塞或者抛出异常，以免大量的请求导致服务当机，每次请求时申请一个，请求结束返回，既信号量的实现，代码如下

申请资源
public void increment() {
    synchronized (LOCK) {
      long totalWaitTime = 0;
      while (count >= limit) {
        if (maxWait > 0) {
          long waitTime = System.currentTimeMillis();
          try {
            LOCK.wait(maxWait - totalWaitTime);
          } catch (InterruptedException e) {
            //ignore
          }
          totalWaitTime += System.currentTimeMillis() - waitTime;
          if (totalWaitTime > maxWait) {
            throw new RuntimeException("Throttle waited too long (" + totalWaitTime + " milliseconds) for lock.");
          }
        } else {
          try {
            LOCK.wait();
          } catch (InterruptedException e) {
            //ignore
          }
        }
      }
      count++;
    }
  }

释放资源
 /**
   * Remove a reference
   */
  public void decrement() {
    synchronized (LOCK) {
      count--;
      LOCK.notify();
    }
  }

客户端调用方式

  /**
   * Pop an object from the pool
   * @return - the Object
   */
  public Object pop() {
    throttle.increment();
    return pool.remove(0);
  }

  /**
   * Push an object onto the pool
   * @param o - the object to put into the pool
   */
  public void push(Object o) {
    if (o != null && o.getClass() == type) {
      pool.add(o);
      throttle.decrement();
    }
  }