多线程并发工具类

CountDownLatch，CyclicBarrier，Semaphore，Exchanger

CountDownLatch

CountDownLatch，用于一个或多个线程等待其他线程完成操作。构造器中的计数值（count）实际上就是闭锁需要等待的线程数量。这个值只能被设置一次，主线程在启动其他线程后立即调用CountDownLatch.await()方法。这样主线程的操作就会在这个方法上阻塞，直到其他线程完成各自的任务。

听到这样的描述，相信有很多读者联想到了join方法，join的工作原理是，不停检查thread是否存活，如果存活则让当前线程永远wait，直到thread线程终止，线程的this.notifyAll 就会被调用。但是join与CountDownLatch还是存在着不少区别。join必须等到整个线程结束才行，但是CountDownLatch只要等到某一条件达成即可：
public class JoinWord implements Runnable{
@Override
public void run() {
System.out.println(Thread.currentThread().getName()+“first work”);
}
}

public class JoinTest {
public static void main(String[] args) throws InterruptedException {
Thread t1 = new Thread(new JoinWord());
Thread t2 = new Thread(new JoinWord());
t1.start();
t2.start();

    t1.join();
    t2.join();
    System.out.println(Thread.currentThread().getName()+"second work");
}

}

Thread-0first work
Thread-1first work
mainsecond work

public class Work implements Runnable{

CountDownLatch countDownLatch;

public  Work(CountDownLatch countDownLatch){
    this.countDownLatch = countDownLatch;
}
@Override
public void run() {
    System.out.println(Thread.currentThread().getName()+":first work");
    countDownLatch.countDown();
    try {
        Thread.sleep(500);
    }catch (InterruptedException e){
        e.printStackTrace();
    }
    System.out.println(Thread.currentThread().getName()+":third work");
}

}

public class CountDownLatchTest {
public static void main(String[] args) {
CountDownLatch countDownLatch = new CountDownLatch(2);
Thread t1 = new Thread(new Work(countDownLatch));
Thread t2 = new Thread(new Work(countDownLatch));
t1.start();
t2.start();
System.out.println(Thread.currentThread().getName()+“second work”);
}
}

mainsecond work
Thread-0:first work
Thread-1:first work
Thread-1:third work
Thread-0:third work

CyclicBarrier

可以实现让一组线程等待至某个状态之后再全部同时执行，且可以重用。CountDownLatch : 一个线程(或者多个)，等待另外N个线程完成某个事情之后才能执行。 CyclicBarrier : N个线程相互等待，任何一个线程完成之前，所有的线程都必须等待。相比较而言，CountDownLatch是一个倒计时计数器，CyclicBarrier是一个水闸。使用方法，通过一个int参数构造一个CyclicBarrier 。各个线程直接使用await进行等待。
public class Work1 implements Runnable{

CyclicBarrier cyclicBarrier;

public Work1(CyclicBarrier cyclicBarrier){
    this.cyclicBarrier = cyclicBarrier;
}
@Override
public void run() {
    System.out.println(Thread.currentThread().getName()+":first work");

    try {
        cyclicBarrier.await();
    }catch (Exception e){
        e.printStackTrace();
    }
    System.out.println(Thread.currentThread().getName()+":third work");
}

}

来源：CSDN

作者：Java开发小猿

链接：https://blog.csdn.net/weixin_36756317/article/details/103570930

标签

countdownlatch

线程

多线程

线程阻塞

work