Java线程等待与唤醒

2018-10-06 08:06:28来源：博客园阅读 ()

class ThreadA extends Thread{

    public ThreadA(String name) {
        super(name);
    }

    public void run() {
        synchronized (this) {
            System.out.println(Thread.currentThread().getName()+" call notify()");
            notify();
        }
    }
}

public class WaitTest {

    public static void main(String[] args) {

        ThreadA t1 = new ThreadA("t1");

        synchronized(t1) {
            try {
                // 启动“线程t1”
                System.out.println(Thread.currentThread().getName()+" start t1");
                t1.start();

                // 主线程等待t1通过notify()唤醒。
                System.out.println(Thread.currentThread().getName()+" wait()");
                t1.wait();

                System.out.println(Thread.currentThread().getName()+" continue");
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

输出结果：main start t1 -> main wait() -> t1 call notify() -> main continue

其实调用t1.start()，t1为就绪状态，只是main方法中，t1被main线程锁住了，t1.wait()的时候，让当前线程等待，其实是让main线程等待了，然后释放了t1锁，t1线程执行，打印t1 call notify()，然后唤醒main线程，最后结束；

这里说一下wait()与sleep()的区别，他们的共同点都是让线程休眠，但是wait()会释放对象同步锁，而sleep()不会；下面的代码t1结束之后才会运行t2；能够证实这一点；

public class SleepLockTest{ 

    private static Object obj = new Object();

    public static void main(String[] args){ 
        ThreadA t1 = new ThreadA("t1"); 
        ThreadA t2 = new ThreadA("t2"); 
        t1.start(); 
        t2.start();
    } 

    static class ThreadA extends Thread{
        public ThreadA(String name){ 
            super(name); 
        } 
        public void run(){ 
            synchronized (obj) {
                try {
                    for(int i=0; i <10; i++){ 
                        System.out.printf("%s: %d\n", this.getName(), i); 
                        // i能被4整除时，休眠100毫秒
                        if (i%4 == 0)
                            Thread.sleep(100);
                    }
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        } 
    } 
}