java - 两个线程查询一个表

Question

我有一个大约 1 m 记录的巨大表，我想对所有记录进行一些处理，所以 1 线程方式，会说... 1000 条记录，处理它们，再获取 1000 条记录等...但是如果我想使用多任务处理呢？那是 2 个线程，每个线程获取 1000 条记录并并行处理，我如何确保每个线程将获取不同的 1000 条记录？注意:我正在使用 hibernate

看起来像那样

public void run() {


    partList=getKParts(10);
    operateOnList(partList);


}

Answer 1

当然，你可以同步代码。

public class MyClass {

    private final HibernateFetcher hibernateFetcher = new HibernateFetcher();

    private class Worker implements Runnable {    
       public run() {    
         List partList = hibernateFetcher.fetchRecords();
         operateOnList(partList);    
       }
    }

    public void myBatchProcessor() {

      while(!hibernateFetcher.isFinished()) {
      // create *n* workers and go!

      }    
   }       
}

class HibernateFetcher {        

  private int count = 0; 
  private final Object lock = new Object();
  private volatile boolean isFinished = false;  
  public List fetchRecords() {

      Criteria criteria = ...;

      synchronized(lock) {
         criteria.setFirstResult(count) // offset
                 .setMaxResults(1000);
         count=count+1000;
      }
      List result = criteria.list();
      isFinished = result.length > 0 ? false: true;
      return result;
  }

  public synchronized boolean isFinished(){
    return isFinished;
  }

}