java多线程join()方法的作用和实现原理解析(应用场景)

package com.Lock;
 
/**
 * join方法示例
 * 比如有三个人小红、小李、小王， 三个人相约一起去酒店吃饭，菜已经点好了， 三个人从不同的地方出发，只有三个人都到了酒店之后才会开始上菜；那么这三个人就分别代表三个线程，这三个线程执行完之后才会执行 “上菜” 的代码逻辑，
 */
public class ConutDownLatchJoinDemo implements Runnable {
 
 
    @Override
    public void run() {
 
        System.out.println(Thread.currentThread().getName() + "开始出发了");
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(Thread.currentThread().getName() + "到酒店了");
 
 
    }
}
 
// 酒店线程
class Hotel2 implements  Runnable{
 
    Thread thread;
 
    public Hotel2 ( Thread thread){
        this.thread = thread;
    }
    @Override
    public void run() {
 
        System.out.println(Thread.currentThread().getName() +"正在等待大家的到来.....");
        try {
            // 待其他线程执行完成后在执行下面的代码
            thread.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("人齐了，"+Thread.currentThread().getName() +"服务员开始上菜");
    }
}
class Main2 {
    public static void main(String[] args) throws InterruptedException {
 
        Thread t1 = new Thread(new ConutDownLatchJoinDemo(), "小红");
        Thread t2 = new Thread(new ConutDownLatchJoinDemo(), "小王");
        Thread t3 = new Thread(new ConutDownLatchJoinDemo(), "小李");
 
        // 三个人同时出发
        t1.start();
        t2.start();
        t3.start();
 
        // 酒店也开始着手准备好将要上的菜
        new Thread(new Hotel2(t3),"酒店").start();
 
 
    }
}

Thread.currentThread().join();

// 酒店线程
class Hotel2 implements  Runnable{
 
    Thread thread;
 
    public Hotel2 ( Thread thread){
        this.thread = thread;
    }
    @Override
    public void run() {
 
        System.out.println(Thread.currentThread().getName() +"正在等待大家的到来.....");
        try {
            //  将  t3.join(); 改为 Thread.currentThread().join();
            Thread.currentThread().join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("人齐了，"+Thread.currentThread().getName() +"服务员开始上菜");
    }
}

oid JavaThread::exit(booldestory_vm, ExitTypeexit_type);
static void ensure_join(JavaThread*thread) {
	Handle threadObj(thread, thread -> threadObj());
	ObjectLocker lock(threadObj, thread);
	thread -> clear_pending_exception();
	java_lang_Thread::set_thread_status(threadObj(), java_lang_Thread::TERMINATED);
	java_lang_Thread::set_thread(threadObj(), NULL);
     //下行执行了notifyAll()操作
	lock.notify_all(thread);
	thread -> clear_pending_exception();
}