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實例講解Java并發(fā)編程之閉鎖

更新時間：2015年04月13日 10:50:45 投稿：junjie

這篇文章主要介紹了實例講解Java并發(fā)編程之閉鎖,閉鎖相當(dāng)于一扇門,在閉鎖到達(dá)結(jié)束狀態(tài)之前,這扇門一直是關(guān)閉著的,沒有任何線程可以通過,當(dāng)?shù)竭_(dá)結(jié)束狀態(tài)時,這扇門才會打開并容許所有線程通過,需要的朋友可以參考下

閉鎖相當(dāng)于一扇門，在閉鎖到達(dá)結(jié)束狀態(tài)之前，這扇門一直是關(guān)閉著的，沒有任何線程可以通過，當(dāng)?shù)竭_(dá)結(jié)束狀態(tài)時，這扇門才會打開并容許所有線程通過。它可以使一個或多個線程等待一組事件發(fā)生。閉鎖狀態(tài)包括一個計數(shù)器，初始化為一個正式，正數(shù)表示需要等待的事件數(shù)量。countDown方法遞減計數(shù)器，表示一個事件已經(jīng)發(fā)生，而await方法等待計數(shù)器到達(dá)0，表示等待的事件已經(jīng)發(fā)生。CountDownLatch強(qiáng)調(diào)的是一個線程（或多個）需要等待另外的n個線程干完某件事情之后才能繼續(xù)執(zhí)行。

場景應(yīng)用：
10個運動員準(zhǔn)備賽跑，他們等待裁判一聲令下就開始同時跑，當(dāng)最后一個人通過終點的時候，比賽結(jié)束。10個運動相當(dāng)于10個線程，這里關(guān)鍵是控制10個線程同時跑起來，還有怎么判斷最后一個線程到達(dá)終點?？梢杂?個閉鎖，第一個閉鎖用來控制10個線程等待裁判的命令，第二個閉鎖控制比賽結(jié)束。

import java.util.concurrent.CountDownLatch;
 
class Aworker implements Runnable {
 private int num;
 private CountDownLatch begin;
 private CountDownLatch end;
 
 public Aworker(int num, final CountDownLatch begin, final CountDownLatch end) {
 this.num = num;
 this.begin = begin;
 this.end = end;
 }
 
 @Override
 public void run() {
 // TODO Auto-generated method stub
 try {
  System.out.println(num + "th people is ready");
  begin.await();  //準(zhǔn)備就緒
 } catch (InterruptedException e) {
  e.printStackTrace();
 } finally {
  end.countDown();  //計數(shù)器減一，到達(dá)終點
  System.out.println(num + "th people arrive");
 }
 }
}
 
public class Race {
 public static void main(String[] args) {
 int num = 10;
 CountDownLatch begin = new CountDownLatch(1);
 CountDownLatch end = new CountDownLatch(num);
 
 for (int i = 1; i <= num; i++) {
  new Thread(new Aworker(i, begin, end)).start();
 }
 
 try {
  Thread.sleep((long) (Math.random() * 5000));
 } catch (InterruptedException e1) {
  // TODO Auto-generated catch block
  e1.printStackTrace();
 } 
 System.out.println("judge say : run !");
 begin.countDown(); //裁判一聲令下開始跑
 long startTime = System.nanoTime();
 try {
  end.await(); //等待結(jié)束
 } catch (InterruptedException e) {
  // TODO Auto-generated catch block
  e.printStackTrace();
 } finally {
  long endTime = System.nanoTime();
  System.out.println("judge say : all arrived !");
  System.out.println("spend time: " + (endTime - startTime));
 }
 }
}

輸出

1th people is ready
2th people is ready
4th people is ready
6th people is ready
3th people is ready
10th people is ready
8th people is ready
5th people is ready
7th people is ready
9th people is ready
judge say : run !
1th people arrive
4th people arrive
10th people arrive
5th people arrive
2th people arrive
judge say : all arrived !
9th people arrive
7th people arrive
8th people arrive
3th people arrive
6th people arrive
spend time: 970933

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