问一个 Java 的 Condition 问题

V2EX = way to explore

V2EX 是一个关于分享和探索的地方

现在注册

已注册用户请登录

这是一个创建于 1478 天前的主题，其中的信息可能已经有所发展或是发生改变。

有两个线程，一个生产者，一个消费者，不断的在队列里面插数据和取数据。有个问题 notFull.signalAll()这句代码一个放在 try 里面，一个放在 finally 里面控制台输出结果为什么不一样？


public class ConditionDemo2 {

    private int queueSize = 10;
    private PriorityQueue<Integer> queue = new PriorityQueue<Integer>(queueSize);
    private Lock lock = new ReentrantLock();
    private Condition notFull = lock.newCondition();
    private Condition notEmpty = lock.newCondition();

    public static void main(String[] args) {
        ConditionDemo2 conditionDemo2 = new ConditionDemo2();
        Producer producer = conditionDemo2.new Producer();
        Consumer consumer = conditionDemo2.new Consumer();
        producer.start();
        consumer.start();
    }

    class Consumer extends Thread {

        @Override
        public void run() {
            consume();
        }

        private void consume() {
            while (true) {
                lock.lock();
                try {
                    while (queue.size() == 0) {
                        System.out.println("队列空，等待数据");
                        try {
                            notEmpty.await();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                    queue.poll();
                    notFull.signalAll();//看这里----------------------
                    System.out.println("从队列里取走了一个数据，队列剩余" + queue.size() + "个元素");
                } finally {
                    lock.unlock();
                }
            }
        }
    }

    class Producer extends Thread {

        @Override
        public void run() {
            produce();
        }

        private void produce() {
            while (true) {
                lock.lock();
                try {
                    while (queue.size() == queueSize) {
                        System.out.println("队列满，等待有空余");
                        try {
                            notFull.await();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                    queue.offer(1);
                    notEmpty.signalAll();//看这里----------------------
                    System.out.println("向队列插入了一个元素，队列剩余空间" + (queueSize - queue.size()));
                } finally {
                    lock.unlock();
                }
            }
        }
    }

}


public class ConditionDemo3 {

    private int queueSize = 10;
    private PriorityQueue<Integer> queue = new PriorityQueue<Integer>(queueSize);
    private Lock lock = new ReentrantLock();
    private Condition notFull = lock.newCondition();
    private Condition notEmpty = lock.newCondition();

    public static void main(String[] args) {
        ConditionDemo3 conditionDemo2 = new ConditionDemo3();
        Producer producer = conditionDemo2.new Producer();
        Consumer consumer = conditionDemo2.new Consumer();
        producer.start();
        consumer.start();
    }

    class Consumer extends Thread {

        @Override
        public void run() {
            consume();
        }

        private void consume() {
            while (true) {
                lock.lock();
                try {
                    while (queue.size() == 0) {
                        System.out.println("队列空，等待数据");
                        try {
                            notEmpty.await();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                    queue.poll();
                    System.out.println("从队列里取走了一个数据，队列剩余" + queue.size() + "个元素");
                } finally {
                    notFull.signalAll();//看这里----------------------
                    lock.unlock();
                }
            }
        }
    }

    class Producer extends Thread {

        @Override
        public void run() {
            produce();
        }

        private void produce() {
            while (true) {
                lock.lock();
                try {
                    while (queue.size() == queueSize) {
                        System.out.println("队列满，等待有空余");
                        try {
                            notFull.await();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                    queue.offer(1);
                    System.out.println("向队列插入了一个元素，队列剩余空间" + (queueSize - queue.size()));
                } finally {
                    System.out.println("final");
                    notFull.signalAll();//看这里----------------------
                    lock.unlock();
                }
            }
        }
    }

}

3 条回复 • 2020-12-03 16:12:48 +08:00