并发编程之Barrier

import java.util.Random;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.CyclicBarrier;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class Main {
public static void main(String[] args) throws Exception {

    CyclicBarrier cyclicBarrier = new CyclicBarrier(3);

    ExecutorService executorService = Executors.newFixedThreadPool(3);
    
    executorService.submit(new Thread(new Runner(cyclicBarrier, "horse1")));
    executorService.submit(new Thread(new Runner(cyclicBarrier, "horse2")));
    executorService.submit(new Thread(new Runner(cyclicBarrier, "horse3")));
    executorService.shutdown();
}}

class Runner implements Runnable {

private CyclicBarrier cyclicBarrier;
private String name;

public Runner(CyclicBarrier cyclicBarrier, String name) {
    super();
    this.name = name;
    this.cyclicBarrier = cyclicBarrier;
}

@Override
public void run() {
    try {
        Thread.sleep(1000 * (new Random()).nextInt(10));
        System.out.println(name + "准备好了");
        cyclicBarrier.await();
    } catch (Exception e) {
        e.printStackTrace();
    }
    System.out.println(name + "起跑");
}

}
执行结果：

只有当三匹马都准备好时候才能同时起跑。 另外： CyclicBarrier(n）控制的线程数n如果大于实际执行过程中的线程数，那么所有await的线程都将无限等待。

另外可以为cyclicBarrier设置超时时间，当线程等待时候超过了超时时间时候，就会不再等待，直接执行，CyclicBarrier抛出BrokenBarrierException 。其余应该受到cyclicBarrier约束的线程也因BrokenBarrierExceptio不再受到约束，转为直接执行。

import java.util.Random;
import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

public class Main {

public static void main(String[] args) throws Exception {

    CyclicBarrier cyclicBarrier = new CyclicBarrier(3);

    ExecutorService executorService = Executors.newFixedThreadPool(3);

    executorService.submit(new Thread(new Runner(cyclicBarrier, "horse1")));
    executorService.submit(new Thread(new Runner(cyclicBarrier, "horse2")));
    executorService.submit(new Thread(new Runner(cyclicBarrier, "horse3")));

    executorService.shutdown();
}

}

class Runner implements Runnable {

private CyclicBarrier cyclicBarrier;
private String name;

public Runner(CyclicBarrier cyclicBarrier, String name) {
    super();
    this.name = name;
    this.cyclicBarrier = cyclicBarrier;
}

@Override
public void run() {
    try {
        long time = 1000 * (new Random()).nextInt(10);
        Thread.sleep(time);
        System.out.println(name + "准备好了,准备好之前睡了：" + time);
        cyclicBarrier.await(1, TimeUnit.SECONDS);
    } catch (InterruptedException e) {
        System.out.println(name + "中断异常");
    } catch (BrokenBarrierException e) {
        System.out.println(name + "栅栏已经损坏了");
    } catch (TimeoutException e) {
        System.out.println(name + "等待超时");
    }
    System.out.println(name + "起跑");
}

}

执行结果：

另外存在这种场景CyclicBarrier控制n个线程，其中n-1个为副线程，另外一个为主线程。主线程等到其余n-1个线程执行完毕之后方可执行：

import java.util.Random;
import java.util.concurrent.CyclicBarrier;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class Main {

public static void main(String[] args) throws Exception {

    CyclicBarrier cyclicBarrier = new CyclicBarrier(4);

    new Thread(new Runner(cyclicBarrier, "horse1")).start();
    new Thread(new Runner(cyclicBarrier, "horse2")).start();
    new Thread(new Runner(cyclicBarrier, "horse3")).start();

    cyclicBarrier.await();
    System.out.println("mainHorse start running after horse 1-3");
}

}

class Runner implements Runnable {

private CyclicBarrier cyclicBarrier;
private String name;

public Runner(CyclicBarrier cyclicBarrier, String name) {
    super();
    this.name = name;
    this.cyclicBarrier = cyclicBarrier;
}

@Override
public void run() {
    try {
        Thread.sleep(2000);
        System.out.println(name + "准备好了");
        cyclicBarrier.await();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

}