Thread.sleep((long) (Math.random() * 5000));
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("judge say : run !");
begin.countDown();
long startTime = System.currentTimeMillis();
try {
end.await();
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
long endTime = System.currentTimeMillis();
System.out.println("judge say : all arrived !");
System.out.println("spend time: " + (endTime - startTime));
}
}
}
class AWork implements Runnable {
final CountDownLatch begin;
final CountDownLatch end;
final int id;
public AWork(final int id, final CountDownLatch begin, final CountDownLatch end) {
this.id = id;
this.begin = begin;
this.end = end;
}
@Override
public void run() {
try {
System.out.println(this.id + " ready !");
begin.await();
// run...
Thread.sleep((long) (Math.random() * 10000));
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
System.out.println(this.id + " arrived !");
end.countDown();
}
}
}
输出结果：
0 ready !
1 ready !
2 ready !
4 ready !
3 ready !
judge say : run !
3 arrived !
4 arrived !
2 arrived !
1 arrived !
0 arrived !
judge say : all arrived !
spend time: 6785
CountDownLatch强调的是一个线程（或多个）需要等待另外的n个线程干完某件事情之后才能继续执行。 上述例子，main线程是裁判，5个AWorker是跑步的。运动员先准备，裁判喊跑，运动员才开始跑（这是第一次同步，对应begin）。5个人谁跑到终点了，countdown一下，直到5个人全部到达，裁判喊停（这是第二次同步，对应end），然后算时间。
2、cyclicbarrier
定义：是一个同步辅助类，它允许一组线程互相等待，直到到达某个公共的屏障点，所有线程一起继续执行或者返回。一个特性就是CyclicBarrier支持一个可选的Runnable命令，在一组线程中的最后一个线程到达之后，该命令只在每个屏障点运行一次。若在继续所有参与线程之前更新此共享状态，此屏障操作很有用。
用法：用计数 N 初始化CyclicBarrier, 每调用一次await，线程阻塞，并且计数+1（计数起始是0），当计数增长到指定计数N时，所有阻塞线程会被唤醒。继续调用await也将迅速返回。
规定五个人只要都跑到终点了，大家可以喝啤酒。但是，只要有一个人没到终点，就不能喝。 这里也没有要求大家要同时起跑。
package com.concurrent;
import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;
/**
-
@author riemann
-
@date 2019/08/12 22:54
*/
public class CyclicBarrierTest {
public static void main(String[] args) {
final int count = 5;
final CyclicBarrier barrier = new CyclicBarrier(count, new Runnable() {
@Override
public void run() {
System.out.println("drink beer!");
}
});
for (int i = 0; i < count; i++) {
new Thread(new Worker(i, barrier)).start();
}
}
}
class Worker implements Runnable {
final int id;
final CyclicBarrier barrier;
public Worker(final int id, final CyclicBarrier barrier) {
this.id = id;
this.barrier = barrier;
}
@Override
public void run() {
try {
System.out.println(this.id + "starts to run !");
Thread.sleep((long) (Math.random() * 10000));
System.out.println(this.id + "arrived !");
this.barrier.await();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (BrokenBarrierException e) {
e.printStackTrace();
}
}
}
输出结果：
0starts to run !
2starts to run !
3starts to run !
4starts to run !
1starts to run !
2arrived !
4arrived !
0arrived !
1arrived !
3arrived !
drink beer!
