本文属于装糊涂的猪原创，转载请注明出处作者
背景交代：
在上一篇OTA升级中有提到Nordic提供的升级库，看源码时发现如下一些代码：
private final Object mLock = new Object();
synchronized (mLock)
{
mLock.notify();
}
synchronized (mLock)
{
while ((mConnectionState == STATE_CONNECTING
|| mConnectionState ==STATE_CONNECTED) && mError == 0)
mLock.wait();
}
心生疑惑，Object还能这么玩的啊？wait 、notify不是线程中的东东吗？
mb.jpg
于是我找到官方的Object Class API,上面写道：
Class Object is the root of the class hierarchy. Every class has Object as a superclass. All objects, including arrays, implement the methods of this class.
显然是万类之母啊，本周末就是母亲节了，以本文献祭给母亲节了。
ty.gif
看下wait函数说明（如下图） ：
waitapi.png
再看下notify函数说明（如下图） ：
notify.jpg
欧了，大体的意思应该是如下图：
Wait and Notify Java Concurrency.jpg
于是撸出如下代码：
public class LockTest01 {
static Object lock = new Object();
static boolean b =true;
/**
* @param args
*/
public static void main(String[] args) {
new Thread(){
public void run() {
synchronized (lock) {
while (b){
try {
System.out.println("wait start");
lock.wait();
try {
//do something
Thread.sleep(2000);
b=false;
System.out.println("wait sleep 2s");
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("wait end");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
};
}.start();
new Thread(){
public void run() {
synchronized (lock) {
System.out.println("notify start");
try {
//do something
Thread.sleep(2000);
System.out.println("notify sleep 2s");
} catch (InterruptedException e) {
e.printStackTrace();
}
lock.notify();
System.out.println("notify end");
}
};
}.start();
}
}
Output:
wait start
notify start
notify sleep 2s
notify end
wait sleep 2s
wait end
但是这个究竟有什么应用场景呢？
比较典型的就是producer consumer problem，现在就以此为例：
1)生产者线程每1秒生成一个新资源，并将其放入“taskQueue”中。
2)消费者线程需要1秒的时间来处理从“任务队列”中消耗的资源。
3)任务队列的最大容量为5，在任何给定的时间内，可以在“任务队列”中存在最多5个资源。
4)两个线程都是无限运行的。
Producer Design
class Producer implements Runnable
{
private final List<Integer> taskQueue;
private final int MAX_CAPACITY;
public Producer(List<Integer> sharedQueue, int size)
{
this.taskQueue = sharedQueue;
this.MAX_CAPACITY = size;
}
@Override
public void run()
{
int counter = 0;
while (true)
{
try
{
produce(counter++);
}
catch (InterruptedException ex)
{
ex.printStackTrace();
}
}
}
private void produce(int i) throws InterruptedException
{
synchronized (taskQueue)
{
while (taskQueue.size() == MAX_CAPACITY)
{
System.out.println("Queue is full " + Thread.currentThread().getName() + " is waiting , size: " + taskQueue.size());
taskQueue.wait();
}
Thread.sleep(1000);
taskQueue.add(i);
System.out.println("Produced: " + i);
taskQueue.notifyAll();
}
}
}
Consumer Design
class Consumer implements Runnable
{
private final List<Integer> taskQueue;
public Consumer(List<Integer> sharedQueue)
{
this.taskQueue = sharedQueue;
}
@Override
public void run()
{
while (true)
{
try
{
consume();
} catch (InterruptedException ex)
{
ex.printStackTrace();
}
}
}
private void consume() throws InterruptedException
{
synchronized (taskQueue)
{
while (taskQueue.isEmpty())
{
System.out.println("Queue is empty " + Thread.currentThread().getName() + " is waiting , size: " + taskQueue.size());
taskQueue.wait();
}
Thread.sleep(1000);
int i = (Integer) taskQueue.remove(0);
System.out.println("Consumed: " + i);
taskQueue.notifyAll();
}
}
}
Application
public class ProducerConsumerExampleWithWaitAndNotify
{
public static void main(String[] args)
{
List<Integer> taskQueue = new ArrayList<Integer>();
int MAX_CAPACITY = 5;
Thread tProducer = new Thread(new Producer(taskQueue, MAX_CAPACITY), "Producer");
Thread tConsumer = new Thread(new Consumer(taskQueue), "Consumer");
tProducer.start();
tConsumer.start();
}
}
Output:
Produced: 0
Produced: 1
Produced: 2
Produced: 3
Produced: 4
Queue is full Producer is waiting , size: 5
Consumed: 0
Consumed: 1
Consumed: 2
Consumed: 3
Consumed: 4
Queue is empty Consumer is waiting , size: 0
Produced: 5
Produced: 6
Produced: 7
Produced: 8
Produced: 9
Queue is full Producer is waiting , size: 5
Consumed: 5
Consumed: 6
Consumed: 7
Consumed: 8
Consumed: 9
Queue is empty Consumer is waiting , size: 0
```
下班写完这些，感觉自己
Don't worry，be happy!
[传送门（代码地址）](https://github.com/ftc300/JavaLaboratory.git)以后做实验的java代码repo
参考资料：
官方Object说明文档：
https://docs.oracle.com/javase/7/docs/api/java/lang/Object.html
stackoverflow :
http://stackoverflow.com/questions/886722/how-to-use-wait-and-notify-in-java
线程池 ExecutorService 执行完毕 ：
http://blog.csdn.net/truong/article/details/40227435
线程的wait/notify：
http://www.programcreek.com/2009/02/notify-and-wait-example/
how-to-work-with-wait-notify-and-notifyall-in-java :
http://howtodoinjava.com/core-java/multi-threading/how-to-work-with-wait-notify-and-notifyall-in-java/
