1.join()方法介绍
join():使所属的线程对象x正常执行run()方法中的任务，而使当前线程z进行无限期的阻塞，等待线程x销毁后再继续执行z后面的代码。
join(long):等待一定时间。
- 在join过程中，如果当前线程被中断，则当前线程出现异常，但join所属的线程继续运行。
- join()在内部使用wait()方法进行等待，所以会释放锁
package chapter3.join;
public class MyThread extends Thread{
@Override
public void run() {
super.run();
try {
int secondValue = (int) (Math.random()*10000);
System.out.println(secondValue);
Thread.sleep(secondValue);
} catch (Exception e) {
e.printStackTrace();
}
}
}
package chapter3.join;
public class Test {
public static void main(String[] args) {
try {
MyThread myThread = new MyThread();
myThread.start();
myThread.join();
System.out.println("MyThread 执行完之后执行！");
} catch (Exception e) {
e.printStackTrace();
}
}
}
运行结果:
9574
MyThread 执行完之后执行！
2.join()方法后面的代码提前运行
join()方法源码:
//不带参数
public final void join() throws InterruptedException {
join(0);
}
//带参数
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; } } }
package chapter3.join;
public class ThreadA extends Thread{
private ThreadB threadB;
public ThreadA(ThreadB threadB) {
this.threadB = threadB;
}
@Override
public void run() {
super.run();
try {
synchronized (threadB) {
System.out.println("begin A ThreadName="+Thread.currentThread().getName()+"--"+System.currentTimeMillis());
Thread.sleep(3000);
System.out.println("end A ThreadName="+Thread.currentThread().getName()+"--"+System.currentTimeMillis());
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
package chapter3.join;
public class ThreadB extends Thread{
@Override
synchronized public void run() {
try {
super.run();
System.out.println("begin B ThreadName="+Thread.currentThread().getName()+"--"+System.currentTimeMillis());
Thread.sleep(3000);
System.out.println("end B ThreadName="+Thread.currentThread().getName()+"--"+System.currentTimeMillis());
} catch (Exception e) {
e.printStackTrace();
}
}
}
package chapter3.join;
public class Test {
public static void main(String[] args) {
try {
ThreadB threadB = new ThreadB();
ThreadA threadA = new ThreadA(threadB);
threadA.start();
threadB.start();
threadB.join(2000);
System.out.println("main end:"+System.currentTimeMillis());
} catch (Exception e) {
e.printStackTrace();
}
}
}
运行结果1:
begin A ThreadName=Thread-1--1561019085673
end A ThreadName=Thread-1--1561019088673
main end:1561019088673
begin B ThreadName=Thread-0--1561019088673
end B ThreadName=Thread-0--1561019091673
- threadB.join(2000)先抢到threadB锁,然后释放；
- ThreadA抢到锁，打印begin，sleep;
- 打印end,释放锁;
- threadB.join(2000)和ThreadB争抢锁，join再次抢到，发现时间已过，释放然后打印main end;
- ThreadB抢到锁，打印begin,end;
运行结果2:
begin A ThreadName=Thread-1--1561019572226
end A ThreadName=Thread-1--1561019575226
begin B ThreadName=Thread-0--1561019575226
end B ThreadName=Thread-0--1561019578226
main end:1561019578226
- threadB.join(2000)先抢到threadB锁,然后释放；
- ThreadA抢到锁，打印begin，sleep;
- 打印end,释放锁;
- threadB.join(2000)和ThreadB争抢锁，ThreadB抢到，打印begin,sleep,打印end后释放锁；
- mian end最后输出;