实现一个线程安全的阻塞队列

最新推荐文章于 2025-09-30 09:53:44 发布

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本文详细介绍了ArrayBlockingQueue的两种同步实现方式：一种是使用synchronized关键字，通过wait和notifyAll进行线程间的同步；另一种是使用ReentrantLock配合Condition，更加精确地控制线程的唤醒，提高效率。

1、使用synchronized实现。由于synchronized是同一把锁，所以使用notify()可能会唤醒非目标线程，notifyAll()唤醒全部线程则会带来大量的 CPU 上下文切换和锁竞争

public class ArrayBlockingQueue {
    private Object[] array; //数组
    private int head; //头
    private int tail; //尾
    private volatile int size; //元素个数

    public ArrayBlockingQueue(int capacity) {
        this.array = new Object[capacity];
    }

    //写入元素
    public synchronized void put(Object o) throws InterruptedException {
        //当队列满时，阻塞
        while (size == array.length) {
            this.wait();
        }
        array[tail++] = o;
        if (tail == array.length) {
            tail = 0;
        }
        size ++;
        //唤醒线程
        this.notifyAll();
    }

    //取出元素
    public synchronized Object get() throws InterruptedException {
        //当队列为空，阻塞
        while (size == 0) {
            this.wait();
        }
        Object o = array[head++];
        if (head == array.length) {
            head = 0;
        }
        size --;
        //唤醒线程
        this.notifyAll();
        return o;
    }

}

2、使用ReentrantLock，可以用Condition指定要唤醒的线程，所以效率更高

public class ArrayBlockingQueue {
    private Object[] array; //数组
    private int head; //头
    private int tail; //尾
    private volatile int size; //元素个数
    private ReentrantLock lock = new ReentrantLock(); //锁
    private Condition notEmpty = lock.newCondition(); //非空
    private Condition notFull = lock.newCondition();  //非满

    public ArrayBlockingQueue(int capacity) {
        this.array = new Object[capacity];
    }

    //写入元素
    public void put(Object o) throws InterruptedException {
        try{
            lock.lock();
            //当队列满时，阻塞
            while (size == array.length) {
                notFull.wait();
            }
            array[tail++] = o;
            if (tail == array.length) {
                tail = 0;
            }
            size ++;
            //唤醒线程
            notEmpty.notifyAll();
        } finally {
            lock.unlock();
        }
    }

    //取出元素
    public Object get() throws InterruptedException {
        lock.lock();
        try {
            //当队列为空，阻塞
            while (size == 0) {
                notEmpty.wait();
            }
            Object o = array[head++];
            if (head == array.length) {
                head = 0;
            }
            size --;
            //唤醒线程
            notFull.notifyAll();
            return o;
        } finally {
            lock.unlock();
        }
    }

}