Object wait notify notifyAll 方法详解

柔光的暖阳◎ 2021-09-27 16:28 351阅读 0赞

wait()方法表示，放弃当前对资源的占有权，等啊等啊，一直等到有人通知我，我才会运行后面的代码。

notify()方法表示，当前的线程已经放弃对资源的占有， 通知等待的线程来获得对资源的占有权，但是只有一个线程能够从wait状态中恢复，  
然后继续运行wait()后面的语句；

notifyAll()方法表示，当前的线程已经放弃对资源的占有， 通知所有的等待线程从wait()方法后的语句开始运行。 读出什么区别没有？  
wait，notify，notifyAll方法必须运行在synchronized代码块内

demo

import java.util.concurrent.BrokenBarrierException;
    import java.util.concurrent.CountDownLatch;
    import java.util.concurrent.CyclicBarrier;
    public class WaitNotifyDemo {
    	static final CountDownLatch lath = new CountDownLatch(2);
    	static final CyclicBarrier lathb = new CyclicBarrier(2);
    	
    	private static final Object syncObj = new Object();
    
    	static class WaitThread extends Thread {
    		@Override
    		public void run() {
    			System.out.println("wait begin enter synchronized");
    			synchronized (syncObj) {
    				try {
    					System.out.println("wait start");
    					// 线程等待
    					syncObj.wait();
    					System.out.println("wait end");
    				} catch (InterruptedException e) {
    					e.printStackTrace();
    				}
    
    			}
    			try {
    				lathb.await();
    			} catch (InterruptedException e) {
    				// TODO Auto-generated catch block
    				e.printStackTrace();
    			} catch (BrokenBarrierException e) {
    				// TODO Auto-generated catch block
    				e.printStackTrace();
    			}
    			lath.countDown();
    		}
    	}
    
    	static class NotifyThread extends Thread {
    		@Override
    		public void run() {
    			try {
    				Thread.sleep(10);
    			} catch (InterruptedException e) {
    				e.printStackTrace();
    			}
    			System.out.println("notify begin enter synchronized");
    			synchronized (syncObj) {
    				System.out.println("notify start");
    				// 当前线程运行完毕后 唤醒wait线程
    				syncObj.notify();
    
    				System.out.println("notify end");
    
    			}
    			try {
    				lathb.await();
    			} catch (InterruptedException e) {
    				// TODO Auto-generated catch block
    				e.printStackTrace();
    			} catch (BrokenBarrierException e) {
    				// TODO Auto-generated catch block
    				e.printStackTrace();
    			}
    			lath.countDown();
    		}
    	}
    
    	public static void main(String[] args) throws InterruptedException, BrokenBarrierException {
    
    		WaitThread wd = new WaitThread();
    		NotifyThread nd = new NotifyThread();
    		wd.start();
    		nd.start();
    		
    		//TODO主线程等待子线程的三种法法
    		//调用join
    		// nd.join();
    		// wd.join();
    		
    		//调用CountDownLatch
    		lath.await();
    		
    		//调用CyclicBarrier
    		// lathb.await();
    		System.out.println("=============");
    
    	}
    }