Java 并发编程

CountDownLatch

官网示例

import java.util.concurrent.CountDownLatch;

/**
 * 功能:
 * N个线程同时开始处理
 * 主线程等待N个线程处理完再继续
 *
 * @auther xh
 * @date 10/8/19 4:09 PM
 */
public class CountDownLatchTest {

    public static void main(String[] args) throws InterruptedException {
        int N = 10;
        //开始开关
        CountDownLatch startSignal = new CountDownLatch(1);
        //N个工作线程
        CountDownLatch doneSignal = new CountDownLatch(N);

        for (int i = 0; i < N; i++) {
            new Thread(new Worker(startSignal, doneSignal)).start();
        }
        System.out.println(Thread.currentThread().getName() + ": starting...");

        startSignal.countDown();
        //主线程等待 N 和线程处理完再继续
        doneSignal.await();
        System.out.println(Thread.currentThread().getName() + ": all finished");
    }
}

class Worker implements Runnable {
    private CountDownLatch startSignal;
    private CountDownLatch doneSignal;

    public Worker(CountDownLatch startSignal, CountDownLatch doneSignal) {
        this.startSignal = startSignal;
        this.doneSignal = doneSignal;
    }

    public void run() {

        try {
            //N 个线程同时开始处理
            startSignal.await();
            doWork();
            doneSignal.countDown();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    private void doWork() {
        System.out.println(Thread.currentThread().getName() + ":  doing work");
    }
}

运行结果:

main: starting...
Thread-0:  doing work
Thread-1:  doing work
Thread-2:  doing work
Thread-3:  doing work
Thread-4:  doing work
Thread-7:  doing work
Thread-6:  doing work
Thread-8:  doing work
Thread-5:  doing work
Thread-9:  doing work
main: all finished

改造为线程池:

    public static void main(String[] args) throws InterruptedException {
        int N = 10;
        //开始开关
        CountDownLatch startSignal = new CountDownLatch(1);
        //N个工作线程
        CountDownLatch doneSignal = new CountDownLatch(N);

        Executor executor = Executors.newCachedThreadPool();

        for (int i = 0; i < N; i++) {
            //new Thread(new Worker(startSignal, doneSignal)).start();
            executor.execute(new Worker(startSignal, doneSignal));
        }
        System.out.println(Thread.currentThread().getName() + ": starting...");

        startSignal.countDown();
        //主线程等待 N 和线程处理完再继续
        doneSignal.await();
        System.out.println(Thread.currentThread().getName() + ": all finished");
        //释放资源
        ((ExecutorService) executor).shutdown();
    }

结果:

main: starting...
pool-1-thread-2:  doing work
pool-1-thread-1:  doing work
pool-1-thread-3:  doing work
pool-1-thread-5:  doing work
pool-1-thread-4:  doing work
pool-1-thread-6:  doing work
pool-1-thread-7:  doing work
pool-1-thread-8:  doing work
pool-1-thread-9:  doing work
pool-1-thread-10:  doing work
main: all finished

BlockingQueue

public static void main(String[] args) throws InterruptedException {
        BlockingQueue<Integer> blockingQueue = new SynchronousQueue<>();
        blockingQueue.put(1);
        System.out.println(blockingQueue.offer(1));
        System.out.println(blockingQueue.offer(2));
        System.out.println(blockingQueue.offer(2));
        System.out.println(blockingQueue.offer(3));
        //System.out.println(blockingQueue.take());
        System.out.println(blockingQueue.size());
    }