java多线程wait和join_java多线程join和wait

join作用是阻塞主线程一直到子线程运行完毕

package com.ydy.thread;

import java.util.concurrent.atomic.AtomicInteger;

class Add implements Runnable{

private AtomicInteger count=new AtomicInteger(0);

@Override

public void run() {

// TODO Auto-generated method stub

for(int i=0;i<100000000;i++) {

count.incrementAndGet();

}

}

public AtomicInteger getCount() {

return count;

}

}

public class JoinTest {

public static void main(String[] args) throws Exception {

Add add=new Add();

Thread t1=new Thread(add);

Thread t2=new Thread(add);

t1.start();

t2.start();

t1.join();//阻塞main线程,一直到t1线程运行完毕

System.out.println("t1.join()");

t2.join();

System.out.println("t2.join()");

System.out.println("countAll"+add.getCount());

}

}

join实现原理是基于wait机制,以下代码选自java.lang.Thread

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;

}

}

}