java object wait notify notifyAll 的探究

先列出我的测试代码：

public static Object loc=new Object();

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

        Thread t1=new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    java.text.SimpleDateFormat sdf=new SimpleDateFormat("HH:mm:ss SSS");
                    System.out.println("["+sdf.format(new Date())+"] t1___等待锁...");
                    synchronized (loc) {
                        System.out.println("["+sdf.format(new Date())+"] t1___获得锁 ...");
                        Thread.sleep(5000);
                        System.out.println("["+sdf.format(new Date())+"] t1___loc..开始执行wait...");
                        loc.wait();
                        System.out.println("["+sdf.format(new Date())+"] t1___loc..执行wait后续...");
                        Thread.sleep(1000);
                    }
                    System.out.println("["+sdf.format(new Date())+"] t1___loc..离开锁...");
                }catch (Exception e){
                    e.printStackTrace();
                }
            }
        });
        Thread t3=new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    java.text.SimpleDateFormat sdf=new SimpleDateFormat("HH:mm:ss SSS");
                    System.out.println("["+sdf.format(new Date())+"] t3___等待锁...");
                    synchronized (loc) {
                        System.out.println("["+sdf.format(new Date())+"] t3___进入锁...");
                        Thread.sleep(5000);
                        System.out.println("["+sdf.format(new Date())+"] t3___loc..开始 wait...");
                        loc.wait();
                        System.out.println("["+sdf.format(new Date())+"] t3___loc..执行 wait后续...");
                        Thread.sleep(1000);
                    }
                    System.out.println("["+sdf.format(new Date())+"] t3___离开锁...");
                }catch (Exception e){
                    e.printStackTrace();
                }
            }
        });

        Thread t2=new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    java.text.SimpleDateFormat sdf=new SimpleDateFormat("HH:mm:ss SSS");
                    System.out.println("["+sdf.format(new Date())+"] t2___等待锁...");
                    synchronized (loc) {
                        System.out.println("["+sdf.format(new Date())+"] t2___获得锁...");
                        Thread.sleep(5000);
                        System.out.println("["+sdf.format(new Date())+"] t2___loc..开始执行 notify...");
                        loc.notify();
                        System.out.println("["+sdf.format(new Date())+"] t2___loc..执行 notify后续...");
                        Thread.sleep(1000);
                    }
                    System.out.println("["+sdf.format(new Date())+"] t2___loc 离开锁....");
                }catch (Exception e){
                    e.printStackTrace();
                }
            }
        });
        t1.start();
        t3.start();
        Thread.sleep(500);
        t2.start();


        System.out.println("t1___before join ....");
        t1.join();
        System.out.println("t2___before join ....");
        t2.join();
        System.out.println("t3____before join ....");
        t3.join();
        System.out.println("main exit....");
    }

执行结果:

[16:55:59 384] t1___等待锁...

[16:55:59 384] t1___获得锁 ...

[16:55:59 384] t3___等待锁...
t1___before join ....
[16:55:59 836] t2___等待锁...
[16:56:04 392] t1___loc..开始执行wait...

[16:56:04 392] t2___获得锁...
[16:56:09 392] t2___loc..开始执行 notify...
[16:56:09 392] t2___loc..执行 notify后续...
[16:56:10 392] t2___loc 离开锁....

[16:56:10 392] t3___进入锁...
[16:56:15 392] t3___loc..开始 wait...
[16:56:15 392] t1___loc..执行wait后续...
[16:56:16 392] t1___loc..离开锁...
t2___before join ....
t3____before join ....

总结：

  1. 执行wait后‘’暂时‘ 释放当前对象锁给其他线程，当前线程处于等待状态

  2. syn块中的wait收到notify通知后 唤醒cpu 继续判断锁状态 

  3. 执行notify且当前的对象锁释放后  wait等待的线程激活

  4. notifyAll  是一次唤醒所有的wait