多線程之（CountDownLatch）

CountDownLatch，一個同步輔助類，在完成一組正在其他線程中執行的操作之前，它允許一個或多個線程一直等待。

主要方法

public CountDownLatch(int count);

public void countDown();

public void await() throws InterruptedException

構造方法參數指定了計數的次數

countDown方法，當前線程調用此方法，則計數減一

awaint方法，調用此方法會一直阻塞當前線程，直到計時器的值爲0

package multiThread;
import java.util.concurrent.CountDownLatch;
public class Demon3 {
    public static void main(String[] args) {
        CountDownLatch countDownLatch = new CountDownLatch(3);
        new MyThread(countDownLatch, "thread1").start();
        new MyThread(countDownLatch, "thread2").start();
        new MyThread(countDownLatch, "thread3").start();
          
        try {
            //等待所有進程執行完
            countDownLatch.await();
            System.out.println("All thread stopped");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}
class MyThread extends Thread {
      
    private CountDownLatch countDownLatch;
    private String threadName;
    public MyThread(CountDownLatch countDownLatch, String threadName) {
        this.countDownLatch = countDownLatch;
        this.threadName = threadName;
    }
    @Override
    public void run() {
          
        System.out.println(threadName + "RUN!!");
          
        try {
            Thread.sleep(10000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
          
        System.out.println(threadName + "Stopped!!");
        countDownLatch.countDown(); //執行完減1
    }
      
}