Java Concurrency/Threads（3）——join详解

参考自：https://www.cnblogs.com/enjiex/p/3661551.html

1. Java Thread join 方法作用：

将当前线程A变为wait，执行join操作的线程B直到B结束。如果该B线程在执行中被中断.

2. join方法的三个重载：

public final void join()；//此方法会把当前线程变为wait，直到执行join操作的线程结束，如果该线程在执行中被中断，则会抛出InterruptedException
public final synchronized void join(long milis); //此方法会把当前线程变为wait，直到执行join操作的线程结束或者在执行join后等待millis的时间。因为线程调度依赖于操作系统的实现，因为这并不能保证当前线程一定会在millis时间变为RUnnable。
public final synchronized void join(long milis, int nanos); //此方法会把当前线程变为wait，直到执行join操作的线程结束或者在join后等待millis+nanos的时间。

package com.guoqiang;

import static com.guoqiang.ThreadColor.*;


public class Main {

    public static void main(String[] args) {
        Thread t1 = new Thread(new MyRunnable(), "t1");
        Thread t2 = new Thread(new MyRunnable(), "t2");
        Thread t3 = new Thread(new MyRunnable(), "t3");

        t1.start();

        //start second thread after waiting for 2 seconds or if it's dead
        try {
            t1.join(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        t2.start();

        //start third thread only when first thread is dead
        try {
            t1.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        t3.start();

        //let all threads finish execution before finishing main thread
        try {
            t1.join();
            t2.join();
            t3.join();
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        System.out.println("All threads are dead, exiting main thread");
    }
}
class MyRunnable implements Runnable{

    @Override
    public void run() {
        System.out.println("Thread started:::"+Thread.currentThread().getName());
        try {
            Thread.sleep(4000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("Thread ended:::"+Thread.currentThread().getName());
    }
}

OUT:
Thread started:::t1
Thread started:::t2
Thread ended:::t1
Thread started:::t3
Thread ended:::t2
Thread ended:::t3
All threads are dead, exiting main thread