java join源码分析

子线程.join()，主线程会等子线程执行完再执行，上代码

package qqqcloud.cn.Threads.JoinFunction;

import java.util.ArrayList;
import java.util.List;

public class hacker_02_mutil_join {

    public static void main(String[] args) throws InterruptedException {
        List<Thread> list=new ArrayList<>();   // 线程array

        for(int i=0;i<10;i++){
            list.add(new Thread(){
                @Override
                public void run(){
                    System.out.println(Thread.currentThread().getName()+"正在执行中。。。");
                }
            });
        }
        // 开启
        for(int i=0;i<list.size();i++){
            list.get(i).start();
        }
        // 子线程执行完，主线程再执行
        for(int i=0;i<list.size();i++){
            list.get(i).join();
        }

        System.out.println(Thread.currentThread().getName()+"主线程执行完。。。");

    }

}

上结果

线程.join，主线程会等子线程执行完再执行；线程.join是如何实现让主线程等待的，这是个值得探究的问题

查看源码

    public final void join() throws InterruptedException {
        join(0);
    }


    public final synchronized void join(long millis)
    throws InterruptedException {
        long base = System.currentTimeMillis();
        long now = 0;

        if (millis < 0) {
            throw new IllegalArgumentException("timeout value is negative");
        }

        if (millis == 0) {
            while (isAlive()) {
                wait(0);
            }
        } else {
            while (isAlive()) {
                long delay = millis - now;
                if (delay <= 0) {
                    break;
                }
                wait(delay);
                now = System.currentTimeMillis() - base;
            }
        }
    }

    public final native void wait(long timeout) throws InterruptedException;

wait(0),当前主线程进入队列等待唤醒，子线程执行完就唤醒主进程执行。