多线程 实际场景应用篇

Posted 2020-10-23 狂风骤起

以下示例均来自jdk concurrent包。
/**
 * 有一个任务，它要等待其他几个任务
 * 执行完毕 之后才能执行
 *
 *
 * 倒计时器
 */
public class CountDownLatchTest {



    public static void main(String[] args){
        final CountDownLatch count = new CountDownLatch(2);
        new Thread(){
            public void run(){
                try {
                    TimeUnit.MILLISECONDS.sleep(1000);
                    System.out.println("线程"+Thread.currentThread().getName()+"正在执行...");
                    TimeUnit.MILLISECONDS.sleep(1000);
                    System.out.println("线程"+Thread.currentThread().getName()+"执行完毕 ");
                    count.countDown();

                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            };
        }.start();



        //任务2
        new Thread(){
            public void run(){
                try {
                    TimeUnit.MILLISECONDS.sleep(1000);
                    System.out.println("线程"+Thread.currentThread().getName()+"正在执行...");
                    TimeUnit.MILLISECONDS.sleep(1000);
                    System.out.println("线程"+Thread.currentThread().getName()+"执行完毕 ");
                    count.countDown();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            };
        }.start();

        try {
            count.await();
            System.out.println("主线程"+Thread.currentThread().getName()+"执行完毕 ");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

    }
}

/**
 *   周末部门聚餐
 *  所有人到齐了 之后 才能开始。。。
 *
 *
 * 可循环的同步屏障 */
public class CyclicBarrierTest {


    public static void main(String[] args){
        final CyclicBarrier barrier = new CyclicBarrier(20);
        ExecutorService threadPool = Executors.newCachedThreadPool();
        //模拟20个用户
        for(int i=1;i<=20;i++){
            final int t=i;
            Runnable r = new Runnable(){
                public void run(){
                    //模拟每个人来的时间
                    try {
                        TimeUnit.MILLISECONDS.sleep(1000);
                        System.out.println(t+" 用户到达"+(barrier.getNumberWaiting()+1)+"人到达");
                        barrier.await();
                        if(t==1){  //控制打印一条
                            System.out.println("人员全部到齐，开始吃饭");
                        }
                        Thread.sleep(300);
                        System.out.println(t+"用户吃完，可以回家 了");
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            };
            threadPool.execute(r);
        }

        threadPool.shutdown();
    }
}

/**
 * 团伙a 绑了B，放言要100万， 与家属c达到 一致意见在某个地方
 * 交换人质，于是A和c同时来到交换地点，同时一手交钱一手交货
 * 使用exchanger实现
 */
public class ExchangerTest {

    public static void main(String[] args){
        ExecutorService threadPool = Executors.newCachedThreadPool();
        Exchanger<String> exchanger = new Exchanger<String>();

        threadPool.execute(new Runnable() {
            @Override
            public void run() {
                String data ="人质B";
                try {
                    String response = exchanger.exchange(data);
                    System.out.println("绑架者用B换回"+response);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });

        //家属c
        threadPool.execute(new Runnable() {
            @Override
            public void run() {
                String data ="1000万";
                try {
                    String response = exchanger.exchange(data);
                    System.out.println("C用1000万换回"+response);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });

        threadPool.shutdown();
    }
}

/**
 * 信号量控制并发
 * 20个人  2个窗口买票
 *
 */
public class SemaphoreTest {
    private void execute(){
        Semaphore semaphore = new Semaphore(2);
        //线程池
        ExecutorService threadPool = Executors.newCachedThreadPool();
        //模拟20个线程
        for(int i=0;i<20;i++) {
            threadPool.execute(new MyTask(semaphore,i));
        }
    }

    class MyTask implements Runnable{
        private Semaphore semaphore; //信号 量 2个许可
        private int userNo;
        public MyTask(Semaphore semaphore,int userNo){
            this.semaphore=semaphore;
            this.userNo =userNo;
        }
        public void run(){
            //执行买票

            try {
                //获取信号量许可，如果获取不到 在此阻塞
                semaphore.acquire();

                //如果 获取到， 可以往下执行 也就是买票
                System.out.println("用户"+userNo+" 进入窗口，准备买票");
                TimeUnit.MILLISECONDS.sleep(1000);

                System.out.println("用户"+userNo+" 买票完成，准备离开 ");
                TimeUnit.MILLISECONDS.sleep(1000);
                System.out.println("用户"+userNo+" 买票完成，离开窗口 ");
                semaphore.release();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
    public static void main(String[] args){
        SemaphoreTest test = new SemaphoreTest();
        test.execute();

    }
}