生产者和消费者问题是线程模型中的经典问题：生产者和消费者在同一时间段内共用同一个存储空间，如下图所示，生产者向空间里存放数据，而消费者取用数据，
如果不加以协调可能会出现以下情况：
存储空间已满，而生产者占用着它，消费者等着生产者让出空间从而去除产品，生产者等着消费者消费产品，从而向空间中添加产品。互相等待，从而发生死锁。
存储空间为空，而消费者占用着它，生产者等着消费者让出空间从而添加产品，消费者等着生产者生产产品，从而从空间中去除产品。互相等待，从而发生死锁。
JAVA解决线程模型的三种方式
1、wait()和notify()
import java.util.LinkedList;
public class ProducerConsumer {
private LinkedList<Object> storeHouse = new LinkedList<Object>();
private int MAX = 10;
public ProducerConsumer() {
}
public void start() {
new Producer().start();
new Comsumer().start();
}
class Producer extends Thread {
public void run() {
while (true) {
synchronized (storeHouse) {
try {
while (storeHouse.size() == MAX) {
System.out.println("storeHouse is full , please wait");
storeHouse.wait();
}
Object newOb = new Object();
if (storeHouse.add(newOb)) {
System.out.println("Producer put a Object to storeHouse");
Thread.sleep((long) (Math.random() * 3000));
storeHouse.notify();
}
} catch (InterruptedException ie) {
System.out.println("producer is interrupted!");
}
}
}
}
}
class Comsumer extends Thread {
public void run() {
while (true) {
synchronized (storeHouse) {
try {
while (storeHouse.size() == 0) {
System.out.println("storeHouse is empty , please wait");
storeHouse.wait();
}
storeHouse.removeLast();
System.out.println("Comsumer get a Object from storeHouse");
Thread.sleep((long) (Math.random() * 3000));
storeHouse.notify();
} catch (InterruptedException ie) {
System.out.println("Consumer is interrupted");
}
}
}
}
}
public static void main(String[] args) throws Exception {
ProducerConsumer pc = new ProducerConsumer();
pc.start();
}
}
2、await()和signal()，即线程锁的方式
package sort;
import java.util.LinkedList;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
public class ProducerConsumer {
private LinkedList<Object> myList = new LinkedList<Object>();
private int MAX = 10;
private final Lock lock = new ReentrantLock();
private final Condition full = lock.newCondition();
private final Condition empty = lock.newCondition();
public ProducerConsumer() {
}
public void start() {
new Producer().start();
new Consumer().start();
}
public static void main(String[] args) throws Exception {
ProducerConsumer s2 = new ProducerConsumer();
s2.start();
}
class Producer extends Thread {
public void run() {
while (true) {
lock.lock();
try {
while (myList.size() == MAX) {
System.out.println("warning: it's full!");
full.await();
}
Object o = new Object();
if (myList.add(o)) {
System.out.println("Producer: " + o);
empty.signal();
}
} catch (InterruptedException ie) {
System.out.println("producer is interrupted!");
} finally {
lock.unlock();
}
}
}
}
class Consumer extends Thread {
public void run() {
while (true) {
lock.lock();
try {
while (myList.size() == 0) {
System.out.println("warning: it's empty!");
empty.await();
}
Object o = myList.removeLast();
System.out.println("Consumer: " + o);
full.signal();
} catch (InterruptedException ie) {
System.out.println("consumer is interrupted!");
} finally {
lock.unlock();
}
}
}
}
}
3、阻塞队列的方式
import java.util.concurrent.*;
public class ProducerConsumer {
// 建立一个阻塞队列
private LinkedBlockingQueue<Object> queue = new LinkedBlockingQueue<Object>(10);
public ProducerConsumer() {
}
public void start() {
new Producer().start();
new Consumer().start();
}
public static void main(String[] args) throws Exception {
ProducerConsumer s3 = new ProducerConsumer();
s3.start();
}
class Producer extends Thread {
public void run() {
while (true) {
try {
Object o = new Object();
// 取出一个对象
queue.put(o);
System.out.println("Producer: " + o);
} catch (InterruptedException e) {
System.out.println("producer is interrupted!");
}
// }
}
}
}
class Consumer extends Thread {
public void run() {
while (true) {
try {
// 取出一个对象
Object o = queue.take();
System.out.println("Consumer: " + o);
} catch (InterruptedException e) {
System.out.println("producer is interrupted!");
}
// }
}
}
}
}
三种方式原理一致，都是对独占空间加锁，阻塞和唤醒线程，第一种方式比较传统，第三种方式最简单，只需存储和取用，线程同步的操作交由LinkedBlockingQueue全权处理。
wait()和notify()其他例子
产品类
//生产的产品
public class Product {
private int productId;
public Product(int productId) {
this.productId = productId;
}
public int getProductId() {
return productId;
}
public void setProductId(int productId) {
this.productId = productId;
}
@Override
public String toString() {
return "product_"+productId;
}
}
仓库类
import java.util.ArrayList;
import java.util.List;
public class StoreHouse {
private static final Integer initialSize = 10;
private List<Product> list = null;
public StoreHouse() {
this.list = new ArrayList<Product>(initialSize);
}
public synchronized void put(Product product) {
if (list.size() == StoreHouse.initialSize) {
try {
System.out.println("仓库已满，等待消费者消费");
this.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
list.add(product);
System.out.println("放入仓库" + product);
notifyAll();
}
public synchronized void get() {
if (list.size() == 0) {
try {
System.out.println("仓库为空，等待生产者生产");
this.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
Product product = list.get(list.size()-1);
System.out.println("从仓库取出" + product);
list.remove(list.size()-1);
notifyAll();
}
}
生产者
public class Producer implements Runnable {
StoreHouse storeHouse = null;
public Producer(StoreHouse storeHouse) {
this.storeHouse = storeHouse;
}
@Override
public void run() {
int i = 0;
while (true) {
Product product = new Product(++i);
storeHouse.put(product);
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
return;
}
}
}
}
消费者
public class Consumer implements Runnable {
StoreHouse storeHouse = null;
public Consumer(StoreHouse storeHouse) {
this.storeHouse = storeHouse;
}
@Override
public void run() {
int i = 0;
while (true) {
storeHouse.get();
try {
Thread.sleep(1500);
} catch (InterruptedException e) {
return;
}
}
}
}
客户端测试
public class Client {
public static void main(String[] args) {
StoreHouse storeHouse = new StoreHouse();
Runnable producer = new Producer(storeHouse);
Runnable consumer = new Consumer(storeHouse);
Thread produceThread = new Thread(producer);
Thread consumeThread = new Thread(consumer);
produceThread.start();
consumeThread.start();
}
}
