本文屬于裝糊涂的豬原創(chuàng)，轉(zhuǎn)載請(qǐng)注明出處作者
背景交代：
??在上一篇OTA升級(jí)中有提到Nordic提供的升級(jí)庫(kù)，看源碼時(shí)發(fā)現(xiàn)如下一些代碼：
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還能這么玩的??？wait 、notify不是線程中的東東嗎？
mb.jpg
于是我找到官方的Object Class API,上面寫(xiě)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.
顯然是萬(wàn)類(lèi)之母啊，本周末就是母親節(jié)了，以本文獻(xiàn)祭給母親節(jié)了。
ty.gif
看下wait函數(shù)說(shuō)明（如下圖） ：
waitapi.png
再看下notify函數(shù)說(shuō)明（如下圖） ：
notify.jpg
歐了，大體的意思應(yīng)該是如下圖：
Wait and Notify Java Concurrency.jpg
于是擼出如下代碼：
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
但是這個(gè)究竟有什么應(yīng)用場(chǎng)景呢？
??比較典型的就是producer consumer problem，現(xiàn)在就以此為例：
??1)生產(chǎn)者線程每1秒生成一個(gè)新資源，并將其放入“taskQueue”中。
??2)消費(fèi)者線程需要1秒的時(shí)間來(lái)處理從“任務(wù)隊(duì)列”中消耗的資源。
??3)任務(wù)隊(duì)列的最大容量為5，在任何給定的時(shí)間內(nèi)，可以在“任務(wù)隊(duì)列”中存在最多5個(gè)資源。
??4)兩個(gè)線程都是無(wú)限運(yùn)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
```
下班寫(xiě)完這些，感覺(jué)自己
Don't worry，be happy!
[傳送門(mén)（代碼地址）](https://github.com/ftc300/JavaLaboratory.git)以后做實(shí)驗(yàn)的java代碼repo
參考資料：
官方Object說(shuō)明文檔：
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
線程池 ExecutorService 執(zhí)行完畢 ：
http://blog.csdn.net/truong/article/details/40227435
線程的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/
