concurrent（六）同步辅助器CyclicBarrier & 源码分析

参考文档：
Java多线程系列--“JUC锁”10之 CyclicBarrier原理和示例：https://www.cnblogs.com/skywang12345/p/3533995.html
简介
CyclicBarrier是一个同步辅助类，允许一组线程互相等待，直到到达某个公共屏障点 (common barrier point)。因为该 barrier 在释放等待线程后可以重用，所以称它为循环的 barrier。基于ReentrantLock实现
举个栗子

/**
 * 简单模拟一下对战平台中玩家需要完全准备好了,才能进入游戏的场景。
 * 
 * @author BFD_526
 * 
 */
public class CyclicBarrierTest {

    public static void main(String[] args) {
        test();
    }
    // 同步屏障
    static void test() {
        ExecutorService service = Executors.newFixedThreadPool(5);
        CyclicBarrier barrier = new CyclicBarrier(5);
        for (int i = 0; i < 5; i++) {
            service.execute(new Player("玩家" + i, barrier));
        }
        service.shutdown();
    }
    // 同步屏障重置
    static void test1() {
        ExecutorService service = Executors.newFixedThreadPool(5);
        CyclicBarrier barrier = new CyclicBarrier(5);
        for (int i = 0; i < 5; i++) {
            service.execute(new Player("玩家" + i, barrier));
        }
        for (int i = 5; i < 10; i++) {
            service.execute(new Player("玩家" + i, barrier));
        }
        service.shutdown();
    }
    // 在同步屏障结束后，启动优先线程
    static void test2() {
        ExecutorService service = Executors.newFixedThreadPool(5);
        CyclicBarrier ba = new CyclicBarrier(5, new Runnable() {
            @Override
            public void run() {
                System.out.println("所有玩家已就位");
            }
        });
        for (int i = 0; i < 5; i++) {
            service.execute(new Player("玩家" + i, ba));
        }
    }
}

class Player implements Runnable {
    private final String name;
    private final CyclicBarrier barrier;

    public Player(String name, CyclicBarrier barrier) {
        this.name = name;
        this.barrier = barrier;
    }

    public void run() {
        try {
            TimeUnit.SECONDS.sleep(1 + (new Random().nextInt(3)));
            System.out.println(name + "已准备,等待其他玩家准备...");
            barrier.await();
            TimeUnit.SECONDS.sleep(1 + (new Random().nextInt(3)));
            System.out.println(name + "已加入游戏");
        } catch (InterruptedException e) {
            System.out.println(name + "离开游戏");
        } catch (BrokenBarrierException e) {
            System.out.println(name + "离开游戏");
        }
    }
}

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