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1. Hbase源码10_插曲StealJobQueue
   1. 1. 简介
   2. 源码

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Hbase源码10_插曲StealJobQueue

1. 简介

在HBase做Compact过程, 会分两个线程池来处理大Compact和小Compact, 用的就是StealJobQueue队列, 设计的挺巧, 可以看下。

大致思路如下：

• StealJobQueue本身是个队列, 类里面又定义了一个队列stealFromQueue
• StealJobQueue的获取是先从本身的获取, 获取不到从stealFromQueue偷取。stealFromQueue就是一个正常的队列。
• 然后大Compact使用StealJobQueue, 小Compact 使用stealFromQueue
• 这样就能优化大Compact的线程池, 当大Compact的线程池空闲的时候, 就可以从小Compact中偷取小任务执行。

源码

package org.apache.hadoop.hbase.util;

import org.apache.hadoop.hbase.classification.InterfaceAudience;

import java.util.concurrent.BlockingQueue;
import java.util.concurrent.PriorityBlockingQueue;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

/**
 * This queue allows a ThreadPoolExecutor to steal jobs from another ThreadPoolExecutor.
 * This queue also acts as the factory for creating the PriorityBlockingQueue to be used in the
 * steal-from ThreadPoolExecutor. The behavior of this queue is the same as a normal
 * PriorityBlockingQueue except the take/poll(long,TimeUnit) methods would also check whether there
 * are jobs in the steal-from queue if this q ueue is empty.
 *
 * Note the workers in ThreadPoolExecutor must be pre-started so that they can steal job from the
 * other queue, otherwise the worker will only be started after there are jobs submitted to main
 * queue.
 */
@InterfaceAudience.Private
public class StealJobQueue<T> extends PriorityBlockingQueue<T> {

  private BlockingQueue<T> stealFromQueue;

  private final Lock lock = new ReentrantLock();
  private final Condition notEmpty = lock.newCondition();

  public StealJobQueue() {
    this.stealFromQueue = new PriorityBlockingQueue<T>() {
      @Override
      public boolean offer(T t) {
        lock.lock();
        try {
          notEmpty.signal();
          return super.offer(t);
        } finally {
          lock.unlock();
        }
      }
    };
  }

  public BlockingQueue<T> getStealFromQueue() {
    return stealFromQueue;
  }

  @Override
  public boolean offer(T t) {
    lock.lock();
    try {
      notEmpty.signal();
      return super.offer(t);
    } finally {
      lock.unlock();
    }
  }

  @Override
  public T take() throws InterruptedException {
    lock.lockInterruptibly();
    try {
      while (true) {
        T retVal = this.poll();
        if (retVal == null) {
          retVal = stealFromQueue.poll();
        }
        if (retVal == null) {
          notEmpty.await();
        } else {
          return retVal;
        }
      }
    } finally {
      lock.unlock();
    }
  }

  @Override
  public T poll(long timeout, TimeUnit unit) throws InterruptedException {
    long nanos = unit.toNanos(timeout);
    lock.lockInterruptibly();
    try {
      while (true) {
        T retVal = this.poll();
        if (retVal == null) {
          retVal = stealFromQueue.poll();
        }
        if (retVal == null) {
          if (nanos <= 0)
            return null;
          nanos = notEmpty.awaitNanos(nanos);
        } else {
          return retVal;
        }
      }
    } finally {
      lock.unlock();
    }
  }
}