Java生产者/消费者模型的一种实现

本文主要介绍java中生产者/消费者模式的实现，对java线程锁机制的一次深入理解。

生产者/消费者模型

生产者/消费者模型要保证，同一个资源在同一时间节点下只能被最多一个线程访问，这个在java中用锁就很容易实现。

下面的例子就是模拟多个生产者生产，多个消费者消费的demo

//抽象生产者
public abstract class AbstractProducer implements Runnable {

    abstract void produce() throws InterruptedException;

    @Override
    public void run() {
        try {
            while (true) {
                produce();
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

//抽象消费者
public abstract class AbstractConsumer implements Runnable {

    abstract void consume() throws InterruptedException;

    @Override
    public void run() {
        try {
            while (true) {
                consume();
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

public class ConsumerAndProducerDemo {

    private static final AtomicInteger ATOMIC_INTEGER = new AtomicInteger();

    private static final ReentrantLock LOCK = new ReentrantLock();

    private static final Condition CONDITION = LOCK.newCondition();

    private static final Queue<Product> PRODUCTS = new LinkedList<>();

    private static final int SIZE = 4;

    public static class Product {
        int id;

        Product(int id) {
            this.id = id;
        }
    }

    //实现消费者
    private static class Consumer extends AbstractConsumer {

        @Override
        void consume() throws InterruptedException {
            try {
                LOCK.lock();
                while (PRODUCTS.isEmpty()) {
                    CONDITION.await();
                }

                Product product = PRODUCTS.poll();
                Thread.sleep((long) (500 + Math.random() * 1000));
                System.out.println(" consume product " + product.id);
                CONDITION.signalAll();
            } finally {
                LOCK.unlock();
            }
        }
    }

    //实现生产者
    private static class Producer extends AbstractProducer {

        @Override
        void produce() throws InterruptedException {
            try {
                LOCK.lock();
                while (PRODUCTS.size() >= SIZE) {
                    CONDITION.await();
                }

                Thread.sleep(1000);
                Product product = new Product(ATOMIC_INTEGER.incrementAndGet());
                PRODUCTS.add(product);
                System.out.println("produce product " + product.id);

                CONDITION.signalAll();
            } finally {
                LOCK.unlock();
            }
        }
    }

    public static void main(String[] args) {
        for (int index = 0; index < 2; index++) {
            new Thread(new Producer()).start();
        }

        for (int index = 0; index < 3; index++) {
            new Thread(new Consumer()).start();
        }
    }
}

上面的demo这么实现

1. 启动多个线程模拟多个生产者和多个消费者
2. 同时使用了queue用来缓存产品
3. 当缓存区没满时生产者生产
4. 当缓冲区满时消费者开始消费

线程之间的同步，这里使用了ReentrantLock，ReentrantLock在之前的博客中有介绍过，当然也可以使用Object自带的wait()等方法，实现同步这里就不在修改demo另行实现了。