Thread.join()的用法

最新推荐文章于 2021-11-01 22:11:54 发布

原创最新推荐文章于 2021-11-01 22:11:54 发布 · 137 阅读

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本文通过一个实例展示了如何使用Java的线程join方法来确保所有子线程执行完毕后再进行汇总操作，具体实现了一个计数器线程类，并在主函数中创建并启动多个此类线程，通过调用join方法等待所有线程完成执行。

原文：http://www.j2medev.com/bbs/dispbbs.asp?boardid=3&Id=34846

thread.join()应该是让当前线程block住，等thread执行完之后，再继续执行。比如有3个线程在执行计算任务，必须等三个线程都执行完才能汇总，那么这时候在主线程里面让三个线程join，最后计算结果既可。代码显示如下。

import java.util.Random;

public class ThreadTest {

    public static void main(String[] args) {
        System.out.println("in " + Thread.currentThread().getName());
        long start = System.currentTimeMillis();
        CounterThread[] ct = new CounterThread[3];
        for (int i = 0; i < ct.length; i++) {
            ct[i] = new CounterThread();
            ct[i].start();
            try {
                ct[i].join();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        long end = System.currentTimeMillis();
        System.out.println("join total time = " + (end - start));
        int result = 0;
        for (int j = 0; j < ct.length; j++) {
            result += ct[j].getResult();
        }
        System.out.println("the result is " + result);

    }

}

class CounterThread extends Thread {

    public CounterThread() {
    }

    private int result;

    public int getResult() {
        return result;
    }

    public void run() {
        try {
            int time = (new Random().nextInt() >>> 1) % 5000;
            Thread.sleep(time);
            System.out.println(Thread.currentThread().getName()
                    + " is blocked for " + time + "ms");
        } catch (InterruptedException ex) {

        }
        result = 5;
    }
}

输出结果：

in main
Thread-0 is blocked for 205ms
Thread-1 is blocked for 4226ms
Thread-2 is blocked for 4469ms
join total time = 8906
the result is 15