notify通知的遗漏很容易理解，即threadA还没开始wait的时候，threadB已经notify了，这样，threadB通知是没有任何响应的，当threadB退出synchronized代码块后，threadA再开始wait，便会一直阻塞等待，直到被别的线程打断。

遗漏通知的代码

下面给出一段代码演示通知是如何遗漏的，如下：

public class MissedNotify extends Object {
	private Object proceedLock;

	public MissedNotify() {
		print(in MissedNotify());
		proceedLock = new Object();
	}

	public void waitToProceed() throws InterruptedException {
		print(in waitToProceed() - entered);

		synchronized ( proceedLock ) {
			print(in waitToProceed() - about to wait());
			proceedLock.wait();
			print(in waitToProceed() - back from wait());
		}

		print(in waitToProceed() - leaving);
	}

	public void proceed() {
		print(in proceed() - entered);

		synchronized ( proceedLock ) {
			print(in proceed() - about to notifyAll());
			proceedLock.notifyAll();
			print(in proceed() - back from notifyAll());
		}

		print(in proceed() - leaving);
	}

	private static void print(String msg) {
		String name = Thread.currentThread().getName();
		System.out.println(name + :  + msg);
	}

	public static void main(String[] args) {
		final MissedNotify mn = new MissedNotify();

		Runnable runA = new Runnable() {
				public void run() {
					try {
						//休眠1000ms，大于runB中的500ms，
						//是为了后调用waitToProceed，从而先notifyAll，后wait，
						//从而造成通知的遗漏
						Thread.sleep(1000);
						mn.waitToProceed();
					} catch ( InterruptedException x ) {
						x.printStackTrace();
					}
				}
			};

		Thread threadA = new Thread(runA, threadA);
		threadA.start();

		Runnable runB = new Runnable() {
				public void run() {
					try {
						//休眠500ms，小于runA中的1000ms，
						//是为了先调用proceed，从而先notifyAll，后wait，
						//从而造成通知的遗漏
						Thread.sleep(500);
						mn.proceed();
					} catch ( InterruptedException x ) {
						x.printStackTrace();
					}
				}
			};

		Thread threadB = new Thread(runB, threadB);
		threadB.start();

		try { 
			Thread.sleep(10000);
		} catch ( InterruptedException x ) {}

		//试图打断wait阻塞
		print(about to invoke interrupt() on threadA);
		threadA.interrupt();
	}
}

执行结果如下：

分析：由于threadB在执行mn.proceed（）之前只休眠了500ms，而threadA在执行mn.waitToProceed（）之前休眠了1000ms，因此，threadB会先苏醒，继而执行mn.proceed（），获取到proceedLock的对象锁，继而执行其中的notifyAll（），当退出proceed（）方法中的synchronized代码块时，threadA才有机会获取proceedLock的对象锁，继而执行其中的wait（）方法，但此时notifyAll（）方法已经执行完毕，threadA便漏掉了threadB的通知，便会阻塞下去。后面主线程休眠10秒后，尝试中断threadA线程，使其抛出InterruptedException。

修正后的代码

为了修正MissedNotify，需要添加一个boolean指示变量，该变量只能在同步代码块内部访问和修改。修改后的代码如下：

public class MissedNotifyFix extends Object {
	private Object proceedLock;
	//该标志位用来指示线程是否需要等待
	private boolean okToProceed;

	public MissedNotifyFix() {
		print(in MissedNotify());
		proceedLock = new Object();
		//先设置为false
		okToProceed = false;
	}

	public void waitToProceed() throws InterruptedException {
		print(in waitToProceed() - entered);

		synchronized ( proceedLock ) {
			print(in waitToProceed() - entered sync block);
			//while循环判断，这里不用if的原因是为了防止早期通知
			while ( okToProceed == false ) {
				print(in waitToProceed() - about to wait());
				proceedLock.wait();
				print(in waitToProceed() - back from wait());
			}

			print(in waitToProceed() - leaving sync block);
		}

		print(in waitToProceed() - leaving);
	}

	public void proceed() {
		pr