java线程join方法会释放锁吗

Posted 2021-09-10 王者生辉

java线程join方法会释放锁吗，虽然join底层使用wait,wait是释放锁的

wait()和join()的调用方的区别：

object.wait()和thread.join()

join()的底层确实是wait()，wait()也确实释放锁，但是释放的是thread的对象锁

也就可以这么说

synchronized(obj){
    thread.join(); //join不释放锁
}
synchronized(thread){
    thread.join(); //join释放锁
}

下面是具体的例子：

public class JoinTest {


    public static void main(String[] args) {
        Object oo = new Object();


        MThread thread1 = new MThread("thread1 -- ", oo);
        thread1.start();

        // synchronized (thread1)
        synchronized (oo) {
            for (int i = 0; i < 100; i++) {
                if (i == 20) {
                    try {
                        thread1.join();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                System.out.println(Thread.currentThread().getName() + " -- " + i);
            }
        }
    }


}


class MThread extends Thread {


    private String name;
    private Object oo;


    public MThread(String name, Object oo) {
        this.name = name;
        this.oo = oo;
    }


    @Override
    public void run() {
        synchronized (oo) {
            for (int i = 0; i < 100; i++) {
                System.out.println(name + i);
            }
        }
    }


}

注意：上面代码是在i==20时加锁

当给对象oo加锁时，不释放锁（释放的是线程对象的锁而不是对象oo的锁），到20就卡住了

 

 

当给线程Thread1加锁时，释放锁