一种父线程阻塞等待子线程的有效方法

最近在做一个查询优化时，考虑到一次查询耗时较多，所以打算用多线程来做，之前是串行查询。比如一个用户查询触发50个线程，在只有一个用户的情况下，性能比串行查询确实提高了许多，但当多个用户同时触发查询的时候，CPU却飙高得很厉害，比串行查询好不了多少。

因为一次查询是同步查询，即要等待所有的线程完成后才返回结果，所以一开始想到的办法是每次查询都起一个线程池，这个线程池里面有50个线程，这个线程池阻塞等待所有的线程完成然后返回结果，从而造成50个用户同时查询时起了50个线程池，cpu资源消耗殆尽。能不能做到所用用户查询触发的线程统一由一个线程池控制呢？百度后终于找到了解决办法。

 1 import java.util.concurrent.CountDownLatch;
 2 
 3 public class ThreadA implements Runnable {
 4 
 5     private CountDownLatch cDownLatch;
 6 
 7     private String name;
 8 
 9     public ThreadA(CountDownLatch cDownLatch, String threadName) {
10         this.cDownLatch = cDownLatch;
11         this.name = threadName;
12     }
13 
14     @Override
15     public void run() {
16         System.out.println(name + " begin.");
17         try {
18             Thread.sleep(500);
19         } catch (InterruptedException e) {
20             e.printStackTrace();
21         }
22         System.out.println(name + " end.");
23         cDownLatch.countDown();
24     }
25 }

线程执行体

 1 import java.util.concurrent.BlockingQueue;
 2 import java.util.concurrent.LinkedBlockingQueue;
 3 import java.util.concurrent.ThreadPoolExecutor;
 4 import java.util.concurrent.TimeUnit;
 5 
 6 public class MyThreadPool extends ThreadPoolExecutor {
 7 
 8     private static MyThreadPool myPool = new MyThreadPool(10, 100, 1,
 9             TimeUnit.DAYS, new LinkedBlockingQueue<Runnable>());
10 
11     private MyThreadPool(int corePoolSize, int maximumPoolSize,
12             long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue) {
13         super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
14     }
15 
16     public static MyThreadPool getInstance() {
17         return myPool;
18     }
19 }

线程池

import java.util.concurrent.CountDownLatch;public class MainThread {public static void main(String[] args) {ThreadExecutor executor = new ThreadExecutor("A", 3);executor.execute();}
}class ThreadExecutor {private String prefix;private int size;public ThreadExecutor(String prefix, int size) {this.prefix = prefix;this.size = size;}public void execute() {System.out.println(prefix + " begin.");ThreadA temp = null;CountDownLatch cDownLatch = new CountDownLatch(size);for (int i = 0; i < size; i++) {temp = new ThreadA(cDownLatch, prefix + i);MyThreadPool.getInstance().execute(temp);}try {cDownLatch.await();} catch (InterruptedException e) {e.printStackTrace();}System.out.println(prefix + " end.");}
}