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并发控制类:CountDownLatch、CyclicBarri

并发控制类:CountDownLatch、CyclicBarri

作者: 不停游动的鱼 | 来源:发表于2017-08-18 10:53 被阅读0次

    CountDownLatch

    • CountDownLatch是一个同步辅助类,在完成一组正在其他线程中执行的操作之前,它允许一个或多个线程一直等待。
    private static final CountDownLatch rongYao = new CountDownLatch(5);
    static class Hero implements Runnable {
        @Override
        public void run() {
            try {
                Thread.sleep(new Random().nextInt(10) * 1000);
                System.out.println("--> 英雄:" + Thread.currentThread().getName() + " 准备开始战斗.....");
                rongYao.countDown();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
    
    private static void testCountDownLatch() throws InterruptedException {
        // CountDownLatch测试
        Thread thread1 = new Thread(new Hero(), "鲁班七号");
        Thread thread2 = new Thread(new Hero(), "程咬金");
        Thread thread3 = new Thread(new Hero(), "黄忠");
        Thread thread4 = new Thread(new Hero(), "凯");
        Thread thread5 = new Thread(new Hero(), "嬴政");
    
        System.out.println("--> 所有英雄准备开始战斗....");
        System.out.println();
    
        thread1.start();
        thread2.start();
        thread3.start();
        thread4.start();
        thread5.start();
    
        rongYao.await();
        System.out.println("--> 所有英雄都准备好了,开撸吧...");
        System.out.println();
    }
    
    • 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。
    private static final CyclicBarrier cyclicBarrier = new CyclicBarrier(5, () -> System.out.println(">>>>>>>>>>>>>>>>>> 一个阶段完成 <<<<<<<<<<<<<<<<<"));
    private static final CountDownLatch cr = new CountDownLatch(5);
    
    static class Hero1 implements Runnable {
        @Override
        public void run() {
            try {
                Thread.sleep(new Random().nextInt(5) * 1000);
                System.out.println("--> 英雄:" + Thread.currentThread().getName() + " 已经到达中路,请求出击.....");
                cyclicBarrier.await();
                Thread.sleep(new Random().nextInt(10) * 1000);
                System.out.println("--> 英雄:" + Thread.currentThread().getName() + " 战胜了对手.....");
                cyclicBarrier.await();
                Thread.sleep(new Random().nextInt(3) * 1000);
                System.out.println("--> 英雄:" + Thread.currentThread().getName() + " 已经回城.....");
                cr.countDown();
            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (BrokenBarrierException e) {
                e.printStackTrace();
            }
        }
    }
    
    private static void testCyclicBarrier() throws InterruptedException {
        // CountDownLatch测试
        Thread thread1 = new Thread(new Hero1(), "鲁班七号");
        Thread thread2 = new Thread(new Hero1(), "程咬金");
        Thread thread3 = new Thread(new Hero1(), "黄忠");
        Thread thread4 = new Thread(new Hero1(), "凯");
        Thread thread5 = new Thread(new Hero1(), "嬴政");
    
        System.out.println("--> 中路战斗准备开始....");
        System.out.println();
    
        thread1.start();
        thread2.start();
        thread3.start();
        thread4.start();
        thread5.start();
    
        cr.await();
        System.out.println("--> 中路战斗结束...");
    }
    
    • Semaphore是一个计数信号量,它的本质是一个"[共享锁]"。
      信号量维护了一个信号量许可集。线程可以通过调用acquire()来获取信号量的许可;当信号量中有可用的许可时,线程能获取该许可;否则线程必须等待,直到有可用的许可为止。 线程可以通过release()来释放它所持有的信号量许可。
    private static final Semaphore semaphore = new Semaphore(5);
    
    private static void testSemaphore() {
        for (int i = 0; i < 10; i ++) {
            new Thread(new Runnable() {
                @Override
                public void run() {
                    try {
                        if (semaphore.tryAcquire(1, new Random().nextInt(10), TimeUnit.SECONDS)) {
                            Thread.sleep(new Random().nextInt(10) * 1000);
                            System.out.println(Thread.currentThread().getName() + " 获取到了执行的机会,已经完成了要做的工作...");
                        } else {
                            System.out.println(Thread.currentThread().getName() + " 在等待了一会之后没有获取到CPU资源,退出了...");
                        }
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    } finally {
                        semaphore.release();
                    }
                }
            }, "thread--" + i).start();
        }
    }
    

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