Java object wait notify notifyAll代码解析

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

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