Java并发编程：线程间的协作wait()、notify()、n
java并发编程协作有两种方式：
- 利用Object对象下面的wait()、notify()或者notifyAll()
- 利用Condition的await()、singnal()或者singnalAll()
其中需要注意的是：
对于方式1、调用wait()、notify()或者notifyAll() 必须在同步块或者同步方法中进行（synchronized块或者synchronized方法）。
对于方式2、await()、singnal()或者singnalAll()必须在lock()和unlock()方法中进行。
下面以常见的生成着和消费者模型为例，说明这两种方式的使用。我们以购物车为例，当购物车为空的时候，不允许从购物车中拿操作，当购物车满5个商品的时候为满，不允许再放入商品。本例仅仅为说明以上两个方式的使用，不具有说明实际意义
使用方式1
ShoppingCar.java
public class ShoppingCar {
private Queue<String> queue = null;
Lock lock = new ReentrantLock();
public ShoppingCar(Queue<String> queue) {
super();
this.queue = queue;
}
public void getGood(String i){
synchronized (queue) {
System.out.println("current queue size is "+queue.size()+" car"+i+" start get good");
while(queue.isEmpty()){
try {
System.out.println("car "+i+" get good stop");//当queue空的时候，等待，并让出对象锁
queue.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
String g = queue.poll();
System.out.println("car "+i+" get good "+ g +" suceed");
queue.notifyAll();
}
}
public void addGood(String i,String g){
synchronized (queue) {
System.out.println("current queue size is "+queue.size()+" car"+i+" start add "+g);
while(queue.size()>=5){
try {
System.out.println("car"+i+" add"+g+" stop");//当queue满的时候，等待，并让出对象锁
queue.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println("car "+i+" add "+g+" suceed");
queue.add(g);
queue.notifyAll();
}
}
}
使用方式2
ShoppingCar2.java
public class ShoppingCar2 {
private Queue<String> queue = null;
Lock lock = new ReentrantLock();
Condition empty = lock.newCondition();
Condition full = lock.newCondition();
public ShoppingCar2(Queue<String> queue) {
super();
this.queue = queue;
}
public void getGood(String i){
lock.lock();
try{
System.out.println("current queue size is "+queue.size()+" car"+i+" start get good");
while(queue.isEmpty()){
try {
System.out.println("car "+i+" get good stop");//当queue空的时候，等待，并让出对象锁
empty.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
String g = queue.poll();
System.out.println("car "+i+" get good "+ g +" sssuceed");
full.signalAll();
}finally{
lock.unlock();
}
}
public void addGood(String i,String g){
lock.lock();
try{
System.out.println("current queue size is "+queue.size()+" car"+i+" start add "+g);
while(queue.size()>=5){
try {
System.out.println("car"+i+" add "+g+" stop");//当queue满的时候，等待，并让出对象锁
full.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println("car "+i+" add "+g+" suceed");
queue.add(g);
empty.signalAll();
}finally{
lock.unlock();
}
}
}
调用：
public class Demo {
public static void main(String[] args) {
ShoppingCar2 car = new ShoppingCar2(new LinkedList<String>());
ExecutorService addser = Executors.newCachedThreadPool();
ExecutorService getser = Executors.newCachedThreadPool();
for(int i=0;i<10;i++)
addser.submit(new AddThread(i, car));
for(int i=0;i<10;i++)
getser.submit(new GetThread(i, car));
addser.shutdown();
getser.shutdown();
}
public static class AddThread implements Runnable{
ShoppingCar2 car = null;
int id;
public AddThread(int i,ShoppingCar2 car){
this.car = car;
this.id = i;
}
@Override
public void run() {
while(true){
car.addGood(String.valueOf(id),String.valueOf((int)(100*Math.random())));
try {
Thread.currentThread().sleep((int)(1000*Math.random())*10);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
public static class GetThread implements Runnable{
ShoppingCar2 car = null;
int id;
public GetThread(int i,ShoppingCar2 car){
this.car = car;
this.id = i;
}
@Override
public void run() {
while(true){
car.getGood(String.valueOf(id));
try {
Thread.currentThread().sleep((int)(1000*Math.random())*10);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
}
说明：购物车有两个操作，一个get商品、一个add商品、在Demo类中我们有一个AddThread类专门去add商品、一个GetThread类专门去get商品。main方法中，我们分别产出10个Get线程和10个Add线程去执行商品的add和get操作。
商品用一个随机生成的数字代替，get和add商品的时间也随机指定。执行结果如下：
current queue size is 0 car0 start add 53
car 0 add 53 suceed
current queue size is 1 car3 start add 58
car 3 add 58 suceed
current queue size is 2 car4 start add 82
car 4 add 82 suceed
current queue size is 3 car2 start add 33
car 2 add 33 suceed
current queue size is 4 car6 start add 99
car 6 add 99 suceed
current queue size is 5 car7 start add 53
car7 add 53 stop</span>
current queue size is 5 car1 start add 45
car1 add 45 stop
current queue size is 5 car8 start add 59
car8 add 59 stop
current queue size is 5 car5 start add 58
car5 add 58 stop
current queue size is 5 car9 start add 88
car9 add 88 stop
current queue size is 5 car0 start get good
car 0 get good 53 sssuceed
current queue size is 4 car3 start get good
car 3 get good 58 sssuceed
current queue size is 3 car1 start get good
car 1 get good 82 sssuceed
current queue size is 2 car2 start get good
car 2 get good 33 sssuceed
current queue size is 1 car4 start get good
car 4 get good 99 sssuceed
car 7 add 53 suceed</span>
car 1 add 45 suceed
car 8 add 59 suceed
car 5 add 58 suceed
car 9 add 88 suceed
current queue size is 5 car5 start get good
car 5 get good 53 sssuceed
current queue size is 4 car6 start get good
car 6 get good 45 sssuceed
current queue size is 3 car8 start get good
car 8 get good 59 sssuceed
current queue size is 2 car9 start get good
car 9 get good 58 sssuceed
current queue size is 1 car7 start get good
car 7 get good 88 sssuceed
current queue size is 0 car4 start add 88
car 4 add 88 suceed
current queue size is 1 car9 start get good
car 9 get good 88 sssuceed
current queue size is 0 car5 start add 1
car 5 add 1 suceed
current queue size is 1 car9 start get good
car 9 get good 1 sssuceed
current queue size is 0 car9 start get good
car 9 get good stop
current queue size is 0 car1 start add 70
car 1 add 70 suceed
我们选取部分的结果分析，看标注的两个地方
car7 add 53 stop
执行到这里时，购物车满了，没有添加到购物车
car 7 add 53 suceed
到这里时候，由于有线程在get商品，此时购物车中商品小于5个了，可以添加商品了，就添加成功
