Java生产者消费者是最基础的线程同步问题，java岗面试中还是很容易遇到的，之前没写过多线程的代码，面试中被问到很尬啊，面完回来恶补下。在网上查到大概有5种生产者消费者的写法，分别如下。
- 用synchronized对存储加锁，然后用object原生的wait() 和 notify()做同步。
- 用concurrent.locks.Lock，然后用condition的await() 和signal()做同步。
- 直接使用concurrent.BlockingQueue。
- 使用PipedInputStream/PipedOutputStream。
- 使用信号量semaphore。
我的理解，生产者消费者模式，其实只要保证在存储端同一时刻只有一个线程读或写就不会有问题，然后再去考虑线程同步。方法1 2 5都比较类似，都是加锁来限制同一时刻只能有一个读或写。而方法3 4其实是在存储内部去保证读和写的唯一的，最低层肯定还是通过锁机制来实现的，java底层代码都封装好了而已。
我自己尝试写了下前三种，代码如下：
synchronized版本
import java.util.LinkedList;
import java.util.Queue;
public class ProducerAndConsumer {
private final int MAX_LEN = 10;
private Queue<Integer> queue = new LinkedList<Integer>();
class Producer extends Thread {
@Override
public void run() {
producer();
}
private void producer() {
while(true) {
synchronized (queue) {
while (queue.size() == MAX_LEN) {
queue.notify();
System.out.println("当前队列满");
try {
queue.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
queue.add(1);
queue.notify();
System.out.println("生产者生产一条任务，当前队列长度为" + queue.size());
try {
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
}
class Consumer extends Thread {
@Override
public void run() {
consumer();
}
private void consumer() {
while (true) {
synchronized (queue) {
while (queue.size() == 0) {
queue.notify();
System.out.println("当前队列为空");
try {
queue.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
queue.poll();
queue.notify();
System.out.println("消费者消费一条任务，当前队列长度为" + queue.size());
try {
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
}
public static void main(String[] args) {
ProducerAndConsumer pc = new ProducerAndConsumer();
Producer producer = pc.new Producer();
Consumer consumer = pc.new Consumer();
producer.start();
consumer.start();
}
}
lock版实现，使用了condition做线程之间的同步。
import java.util.LinkedList;
import java.util.Queue;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* version 1 doesn't use synchronized to improve performance
*/
public class ProducerAndConsumer1 {
private final int MAX_LEN = 10;
private Queue<Integer> queue = new LinkedList<Integer>();
private final Lock lock = new ReentrantLock();
private final Condition condition = lock.newCondition();
class Producer extends Thread {
@Override
public void run() {
producer();
}
private void producer() {
while(true) {
lock.lock();
try {
while (queue.size() == MAX_LEN) {
System.out.println("当前队列满");
try {
condition.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
queue.add(1);
condition.signal();
System.out.println("生产者生产一条任务，当前队列长度为" + queue.size());
try {
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
} finally {
lock.unlock();
}
}
}
}
class Consumer extends Thread {
@Override
public void run() {
consumer();
}
private void consumer() {
while (true) {
lock.lock();
try {
while (queue.size() == 0) {
System.out.println("当前队列为空");
try {
condition.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
queue.poll();
condition.signal();
System.out.println("消费者消费一条任务，当前队列长度为" + queue.size());
try {
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
} finally {
lock.unlock();
}
}
}
}
public static void main(String[] args) {
ProducerAndConsumer pc = new ProducerAndConsumer();
Producer producer = pc.new Producer();
Consumer consumer = pc.new Consumer();
producer.start();
consumer.start();
}
}
BlockingQueue版实现
import java.util.Random;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingQueue;
public class ProducerAndConsumer {
private BlockingQueue<Integer> queue = new LinkedBlockingQueue<Integer>(10);
class Producer extends Thread {
@Override
public void run() {
producer();
}
private void producer() {
while(true) {
try {
queue.put(1);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("生产者生产一条任务，当前队列长度为" + queue.size());
try {
Thread.sleep(new Random().nextInt(1000)+500);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
class Consumer extends Thread {
@Override
public void run() {
consumer();
}
private void consumer() {
while (true) {
try {
queue.take();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("消费者消费一条任务，当前队列长度为" + queue.size());
try {
Thread.sleep(new Random().nextInt(1000)+500);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
public static void main(String[] args) {
ProducerAndConsumer pc = new ProducerAndConsumer();
Producer producer = pc.new Producer();
Consumer consumer = pc.new Consumer();
producer.start();
consumer.start();
}
}
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