在JDK的官方的wait()方法的注释中明确表示线程可能被“虚假唤醒“，JDK也明确推荐使用while来判断状态信息。那么这种情况的发生的可能性有多大呢？

　　使用生产者消费者模型来说明，伪唤醒造成的后果是本来未被唤醒的线程被唤醒了，那么就破坏了生产者消费者中的判断条件，也就是例子中的while条件number == 0或者number == 1。最终导致的结果就死0和1不能交替出现。

　　JDK的两种同步方案均可能出现这种伪唤醒的问题（API说明明确表示会出现这种现象），这两种组合是synchronized+wait+notify和ReentrantLock+await+signal。下面的例子中，如果把while换成if，那么就0、1就不能交替出现，反制则会，例子中是100个线程进行增加，100个线程进行减少。

　　在Java并发编程书上面引用了Thinking In Java的一句话说，大概意思是：任何并发编程都是通过加锁来解决。其实JDK并发编程也是通过加锁解决，每个对象都有一个对象锁，并且有一个与这个锁相关的队列，来实现并发编程。区别在于加锁的粒度问题，读读可以并发（在读远大于写的场景下比较合适），其他三种情况不能并发。而关系型数据库也是利用这一思想，只不过做得更加彻底，除了写写不能并发，其他三种情况都能并发，这得益于MVCC模型。

public class Resource {    public int number = 0;    public synchronized void add() {        while (number == 1) {            try {                wait();            } catch (InterruptedException e) {                e.printStackTrace();            }        }        number++;        System.err.println(number + "-" + Thread.currentThread().getId());        notifyAll();    }    public synchronized void minus() {        while (number == 0) {            try {                wait();            } catch (InterruptedException e) {                e.printStackTrace();            }        }        number--;        System.err.println(number + "-" + Thread.currentThread().getId());        notifyAll();    }    public static class AddThread implements Runnable {        private Resource resource;        public AddThread(Resource resource) {            this.resource = resource;        }        @Override        public void run() {            for (;;) resource.add();        }    }    public static class MinusThread implements Runnable {        private Resource resource;        public MinusThread(Resource resource) {            this.resource = resource;        }        @Override        public void run() {            for (;;) resource.minus();        }    }    public static void main(String[] args) {        Resource resource = new Resource();        for (int i = 0; i < 100; i++) {            new Thread(new AddThread(resource)).start();            new Thread(new MinusThread(resource)).start();        }    }}

public class ResourceLock {    private int number = 0;    private final ReentrantLock lock = new ReentrantLock();    private final Condition condition = lock.newCondition();    public int getNumber() {        return this.number;    }    public void increase() {        lock.lock();        try {            while (number == 1) {                condition.await();            }            number++;            System.err.println(number + "-" + Thread.currentThread().getId());            condition.signalAll();        } catch (InterruptedException e) {            e.printStackTrace();        } finally {            if (lock.isHeldByCurrentThread()) {                lock.unlock();            }        }    }    public void decrease() {        lock.lock();        try {            while (number == 0) {                condition.await();            }            number--;            System.err.println(number + "-" + Thread.currentThread().getId());            condition.signalAll();        } catch (InterruptedException e) {            e.printStackTrace();        } finally {            if (lock.isHeldByCurrentThread()) {                lock.unlock();            }        }    }    static class IncreaseThread implements Runnable {        private ResourceLock resource;        public IncreaseThread(ResourceLock resource) {            this.resource = resource;        }        @Override        public void run() {            for (;;) resource.increase();        }    }    static class DecreaseThread implements Runnable {        private ResourceLock resource;        public DecreaseThread(ResourceLock resource) {            this.resource = resource;        }        @Override        public void run() {            for (;;) resource.decrease();        }    }    public static void main(String[] args) throws Exception {        ResourceLock resource = new ResourceLock();        ExecutorService es = Executors.newFixedThreadPool(5);        for (int i = 0; i < 100; i++) {            es.submit(new IncreaseThread(resource));            es.submit(new DecreaseThread(resource));        }    }}