Java并发-类库新组件 - CountDownLatch 理解

</pre><pre name="code" class="java">

直接附加上练习代码

package com.xyw.concurrent.blog;

import java.util.concurrent.*;
import java.util.*;

/*
* CountDownLatch 是进行同步一个或者多个任务，强制他们等待由其他任务执行的一组操作完成。
* 其有个初始的计数值，wait 的值都将被阻塞，直到计数值达到零的情况。 并且CountDownLatch 只能进行一次触发。计数器不能被重置。
* 如果被重置，请看下一期的讲解的情况。
*/
class TaskPortion implements Runnable{
private  static int counter = 0;
private final int id = counter++; // 进行设置自增的ID 的选项
private static Random rand = new Random(47);
private final CountDownLatch latch;
TaskPortion(CountDownLatch latch){
this.latch = latch;
}
public void run(){
try{
doWork();
latch.countDown();
}catch(InterruptedException ex){

}
}
public void doWork() throws InterruptedException{
TimeUnit.MILLISECONDS.sleep(rand.nextInt(2000));
System.out.println(this + "completed!");
}
public String toString(){
return String.format("%1$-3d",	id);
}
}// 这是个进行分开执行的任务， performs some portion of a task

class WaitingTask implements Runnable{
private static int counter = 0;
private final int id = counter++;
private final CountDownLatch latch;
WaitingTask(CountDownLatch latch){
this.latch = latch;
}
public void run(){
try{
latch.await(); // 进行等待，知道 计数值为 零的时候，发生其中的停止的情况
System.out.println("Latch barrier passed for " + this);
//System.out.println(latch.getCount()); // 这个是用来进行监视，是不是其中运行的关键值得情况。
}catch(InterruptedException e){
System.out.println(this + " interrupted");
}
}
public String toString(){
return String.format("WaitingTask %1$-3d", id);
}
}

public class CountDownLatchDemo {
static final int SIZE = 10; // 你可以进行改变 SIZE 的值来进行了解 CountDownLatch 类的原理的情况
public static void main(String[] args) throws Exception{
ExecutorService exec = Executors.newCachedThreadPool();
CountDownLatch latch = new CountDownLatch(SIZE);
for(int i = 0; i< 100; i++){
exec.execute(new WaitingTask(latch));
}
for(int i = 0; i < SIZE; i++){
exec.execute(new TaskPortion(latch)); // 这些都是线程的进行的工作，并且只有
// 其中的情况，等于一百的时候， WaitingTask 才进行运行，注意其中线程的先后的关系不是唯一确定的情况。
}
System.out.println("Launched all tasks");
exec.shutdown(); // 当所有任务结束时完成
System.out.print(latch.getCount()+ "\n");
}
}

// 运行结果

<pre name="code" class="java">Launched all tasks
10
7  completed!
9  completed!
5  completed!
8  completed!
1  completed!
2  completed!
6  completed!
4  completed!
0  completed!
3  completed!
Latch barrier passed for WaitingTask 6
Latch barrier passed for WaitingTask 2
Latch barrier passed for WaitingTask 9
Latch barrier passed for WaitingTask 0
Latch barrier passed for WaitingTask 4
Latch barrier passed for WaitingTask 5
Latch barrier passed for WaitingTask 8
Latch barrier passed for WaitingTask 3
Latch barrier passed for WaitingTask 7
Latch barrier passed for WaitingTask 1