Java的高并发编程系列（六）生产者消费者面试题解析

面试题：写一个固定容量同步容器，拥有Put和get方法，以及getCount方法能够支持两个生产者线程以及10个消费者线程的阻塞调用

使用wait和notify/notifyAll来实现：

public class MyContainer1 {
    private final LinkedList lists = new LinkedList<>();
    private final int MAX = 10; //最多10个元素
    private int count = 0;
    public synchronized void put(T t){
        while (lists.size() == MAX) { //while正常情况下和wait()一起使用，
            try {
                this.wait(); //effective java
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        lists.add(t);
        ++ count;
        this.notifyAll(); //通知消费者线程进行消费
    }
    public synchronized T get(){
        T t = null;
        while (lists.size() == 0) {
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        t = lists.removeFirst();
        count --;
        this.notifyAll(); //通知生产者进行生产
        return t;
    }
    public static void main(String[] args) {
        MyContainer1 c = new MyContainer1<>();
        //启动消费者线程
        for (int i = 0; i < 100; i++) {
            new Thread(()->{
                for (int j = 0; j < 5; j++) {
                    System.out.println(c.get());
                }
            }, "c" + i).start();
        }

        try {
            TimeUnit.SECONDS.sleep(2);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        //启动生产者线程
        for (int i = 0; i < 2; i++) {
            new Thread(()->{
                for (int j = 0; j < 25; j++) {
                    c.put(Thread.currentThread().getName() + "" + j);
                }
            }, "p" + i).start();
        }
    }
}

使用Lock和Condition来实现，对比两种方式，Condition的方式可以更加精确的指定哪些线程被唤醒。

public class MyContainer2 {
    private final LinkedList lists = new LinkedList<>();
    private final int MAX = 10;
    private int count = 0;
    private Lock lock = new ReentrantLock();
    private Condition producer = lock.newCondition();
    private Condition consumer = lock.newCondition();

    public void put(T t){
        try {
            lock.lock();
            while (lists.size() == MAX) {
                producer.await();
            }       
            lists.add(t);
            ++count;
            consumer.signalAll(); //通知消费者线程进行消费
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }

    public T get(){
        T t = null;
        try {
            lock.lock();
            while (lists.size() == 0) {
                consumer.await();
            }

            lists.removeFirst();
            count --;
            producer.signalAll(); //通知生产者进行生产
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }   
        return t;
    }

    public static void main(String[] args) {
        MyContainer2 c = new MyContainer2<>();
        //启消费者线程
        for (int i = 0; i < 100; i++) {
            new Thread(()->{
                for (int j = 0; j < 5; j++) {
                    System.out.println(c.get());
                }
            }, "c" + i).start();
        }

        try {
            TimeUnit.SECONDS.sleep(2);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        //启动生产者线程
        for (int i = 0; i < 2; i++) {
            new Thread(()->{
                for (int j = 0; j < 25; j++) {
                    c.put(Thread.currentThread().getName() + "" + j);
                }
            }, "p" + i).start();
        }
    }
}