CyclicBarrier、CountDownLatch、Callable、FutureTask

import java.util.Random;
import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;
/**
 * 三个运动员各自准备，等到三个人都准备好后，再一起跑</br>
 * @author yang.han</br>
   @see    1:先创建一个公共 CyclicBarrier 对象，设置 同时等待 的线程数，CyclicBarrier cyclicBarrier = new CyclicBarrier(3);</br>
    2:这些线程同时开始自己做准备，自身准备完毕后，需要等待别人准备完毕，这时调用 cyclicBarrier.await(); 即可开始等待别人；</br>
    3:当指定的 同时等待 的线程数都调用了 cyclicBarrier.await();时，意味着这些线程都准备完毕好，然后这些线程才 同时继续执行。</br>
 *
 */
public class TestCyclicBarrier {

    public static void main(String[] args) {
        int runner = 3;
        final CyclicBarrier cycliBarrier = new CyclicBarrier(runner);
        final Random random = new Random();
        
        for (char runnerName = ‘A‘; runnerName <= ‘C‘; runnerName++) {
            final String rName = String.valueOf(runnerName);
            new Thread(new Runnable(){
                @Override
                public void run() {
                    long prepareTime = random.nextInt(10000)+100;
                    System.out.println(rName + " is preparing for time: " + prepareTime);
                    try {
                        Thread.sleep(prepareTime);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println(rName + " is prepared, waiting for others");
                    try {
                        cycliBarrier.await(); // 当前运动员准备完毕，等待别人准备好
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    } catch (BrokenBarrierException e) {
                        e.printStackTrace();
                    }
                    System.out.println(rName + " starts running"); // 所有运动员都准备好了，一起开始跑
                }
                
            }).start();
        }
    }

}

import java.util.concurrent.CountDownLatch;
/**
 * 四个线程 A B C D，其中 D 要等到 A B C 全执行完毕后才执行，而且 A B C 是同步运行的
 * @author yang.han</br>
 @see 1:创建一个计数器，设置初始值，CountdownLatch countDownLatch = new CountDownLatch(2);</br>
    2:在 等待线程 里调用 countDownLatch.await() 方法，进入等待状态，直到计数值变成 0；</br>
    3:在 其他线程 里，调用 countDownLatch.countDown() 方法，该方法会将计数值减小 1；</br>
    4:当 其他线程 的 countDown() 方法把计数值变成 0 时，等待线程 里的 countDownLatch.await() 立即退出，继续执行下面的代码。</br>
 *
 */
public class TestCountDownLatch {

    public static void main(String[] args) {
        int workerNum = 3;
        final CountDownLatch countDownlatch = new CountDownLatch(workerNum);
        
        new Thread(new Runnable(){
            @Override
            public void run() {
                System.out.println("D is waiting for other three threads");
                try {
                    countDownlatch.await();
                    System.out.println("D is start work");
                    Thread.sleep(100);
                    System.out.println("D finsh Work");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }).start();
        
        for (char threadName = ‘A‘; threadName <= ‘C‘; threadName++) {
            final String tName = String.valueOf(threadName);
            new Thread(new Runnable(){
                @Override
                public void run() {
                    System.out.println(tName + " is working");
                    try {
                        Thread.sleep(100);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println(tName + " finished");
                    countDownlatch.countDown();
                }
            }).start();
        }
    }

}

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;
/**
 * 我们想让子线程去计算从 1 加到 100，并把算出的结果返回到主线程</br>
 * @author yang.han</br>
 * @see
 *     如何把子线程的结果回传回来呢？在 Java 里，有一个类是配合 Callable 使用的：FutureTask，不过注意，它获取结果的 get 方法会阻塞主线程。
 *
 */
public class TestCallableAndFutureTask {

    public static void main(String[] args) {
        Callable<Integer> callAble = new Callable<Integer>() {
            @Override
            public Integer call() throws Exception {
                System.out.println("Task starts");
                Thread.sleep(100);
                int result = 0;
                for (int i = 0; i <= 100; i++) {
                    result += i;
                }
                System.out.println("Task finished and return result");
                return result;
            }
        };
        
        FutureTask<Integer> futureTask = new FutureTask<Integer>(callAble);
        new Thread(futureTask).start();
        
        try {
            System.out.println("Before futureTask.get()");
            System.out.println("Result: " + futureTask.get());
            System.out.println("After futureTask.get()");
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }
    }

}