生产者、消费者模式被广泛的运用在解耦、消息队列场景中。使用生产者和消费者模式，通常在他们之间增加一个阻塞队列作为媒介，有了媒介之后，相当于有了一个缓冲，平衡了两者之间的能力。
生产者消费者模式设计
如图所示，生产者线程会向阻塞队里面加数据，满了则阻塞，而消费者线程会向阻塞队里里面取出数据。阻塞队列的作用就是平衡图中3和4的过程。
生产者消费者模式（图片来源于拉勾）.png
生产者、消费者模式的实现
利用BlockingQueue实现
代码如下所示，表面上看起来简单，实际上BlockingQueue给我们做了很多工作，比如队列满了就去阻塞生产者线程，队列有空就去唤醒生产者线程等。
public class BlockingQueueDemo {
public static void main(String[] args) {
//创建ArrayBlockingQueue类型的BlockingQueue
BlockingQueue<Object> arrayQueue = new ArrayBlockingQueue<>(10);
Runnable producer = () -> {
while (true) {
try {
//生产者往队列中存放数据
log.info("execute arrayQueue put......");
arrayQueue.put(new Object());
} catch (InterruptedException e) {
e.printStackTrace();
}
}
};
//启动两个生产者线程
new Thread(producer).start();
new Thread(producer).start();
Runnable customer = () -> {
while (true) {
try {
log.info("execute arrayQueue take......");
//消费者从队列中取出数据
arrayQueue.take();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
};
//启动两个消费者线程
new Thread(customer).start();
new Thread(customer).start();
}
}
利用Condition实现
@Slf4j
public class BlockingQueueForCondition {
private Queue queue;
private int max = 16;
private ReentrantLock lock = new ReentrantLock();
//在lock锁的基础上创建两个条件，notEmptyCondition：队列没有空的条件，notFullCondition队列没有满的条件
private Condition notEmptyCondition = lock.newCondition();
private Condition notFullCondition = lock.newCondition();
public BlockingQueueForCondition(int size) {
this.max = size;
queue = new LinkedList();
}
public void put(Object object) throws InterruptedException {
//多线程场景需要一定的同步措施来保证线程安全，因此需要加锁操作
lock.lock();
try {
//检测队列是否已经满了
while (queue.size() == max) {
//此时队列已经满了，阻塞生产者线程并且释放lock锁
notFullCondition.await();
}
//如果没有满则往队列里面存放数据，并且调用notEmptyCondition.signalAll()通知正在等待的消费者，
//并且唤醒等待的消费者
queue.add(object);
notEmptyCondition.signalAll();
} finally {
//最后释放锁,否则可能会产生无法释放锁的情况
lock.unlock();
}
}
public Object take() throws InterruptedException {
try {
while (queue.isEmpty()) {
notEmptyCondition.await();
}
Object item = queue.remove();
notFullCondition.signalAll();
return item;
} finally {
lock.unlock();
}
}
public static void main(String[] args) throws InterruptedException {
BlockingQueueForCondition block = new BlockingQueueForCondition(20);
for (int i = 0; i < 100; i++) {
block.put(new Object());
}
}
}
利用Wait、Notify实现
BlockingQueueForWaitNotify: 实现阻塞队列内部的put、take细节，以及线程的等待、通知和唤醒
@Slf4j
public class BlockingQueueForWaitNotify {
private int maxSize;
private LinkedList<Integer> storage;
private final Random random = new Random();
public BlockingQueueForWaitNotify(int size) {
this.maxSize = size;
storage = new LinkedList<>();
}
public synchronized void put(int item) throws InterruptedException {
while (storage.size() == maxSize) {
wait();
}
storage.add(item);
notifyAll();
}
public synchronized int take() throws InterruptedException{
while (storage.isEmpty()){
wait();
}
int item = storage.remove();
notifyAll();
return item;
}
}
BlockingQueueTest： 定义生产者、消费者线程测试阻塞队列
@Slf4j
public class BlockingQueueTest {
public static void main(String[] args) {
BlockingQueueForWaitNotify blockingQueue = new BlockingQueueForWaitNotify(20);
Producer producer = new Producer(blockingQueue);
Consumer consumer = new Consumer(blockingQueue);
new Thread(producer).start();
new Thread(consumer).start();
}
}
@Slf4j
class Producer implements Runnable {
private BlockingQueueForWaitNotify blockingQueue;
public Producer(BlockingQueueForWaitNotify blockingQueue) {
this.blockingQueue = blockingQueue;
}
// @SneakyThrows
@Override
public void run() {
for (int i = 0; i < 100; i++) {
try {
log.info("produce begin to put");
blockingQueue.put(i);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
@Slf4j
class Consumer implements Runnable {
private BlockingQueueForWaitNotify blockingQueue;
public Consumer(BlockingQueueForWaitNotify blockingQueue) {
this.blockingQueue = blockingQueue;
}
@Override
public void run() {
for (int i = 0; i < 100; i++) {
try {
int item = blockingQueue.take();
log.info("consumer take:{}", item);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
总结
本文介绍了3种实现生产者、消费者模式的方法，分别是基于ArrayBlockingQueue、Condition、Wait和Notify来实现。利用jdk自带的ArrayBlockingQueue比较简单，它内部已经帮你实现了队列满了就去阻塞生产者线程，队列有空就去唤醒生产者线程等逻辑，而利用Condition、Wait和Notify实现相当于我们写了BlockingQueue的一些内部细节，供生产者消费者使用。
参考：
1.拉勾教育《java并发编程78讲》
2.https://github.com/nuptkwz/high-concurrency/tree/master/src/main/java/com/practice/concurrency/highconcurrency/producerandcustomer
