java实现生产者消费者问题
引言
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：
生产者消费者图
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。
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!");}// } }}}}
结论
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。