redis——队列

一、用list实现队列

rpush和lpop右进左出，lpush和rpop左进右出实现FIFO单向队列。

public class QueueTest<T> extends AbstractQueue {

    private String qName;

    public QueueTest(String qName){
        this.qName = qName;
    }

    @Override
    public Iterator iterator() {
        throw new UnsupportedOperationException();
    }

    @Override
    public int size() {
        return RedisUtils.llen(qName).intValue();
    }

    @Override
    public boolean offer(Object t) {
        //String value = JSON.toJSONString(t);
        return RedisUtils.rpush(qName,t.toString()) == 1;
    }

    @Override
    public String poll() {
        return RedisUtils.lpop(qName);
    }

    @Override
    public String peek() {
        return RedisUtils.lindex(qName,0L);
    }

    public static void main(String[] args){
        QueueTest queue = new QueueTest("queue");
        queue.offer(1);
        queue.offer(2);
        queue.offer(3);
        System.out.println("size : " + queue.size());
        System.out.println("peek : " + queue.peek());
        System.out.println(queue.poll());
        System.out.println(queue.poll());
        System.out.println(queue.poll());
        System.out.println(queue.poll());
        RedisUtils.close();
    }
}

二、用zset实现延迟队列

public class DelayQueueTest<E extends Delayed> extends AbstractQueue {

    private String qName;
    public DelayQueueTest(String qName){
        this.qName = qName;
    }

    @Override
    public Iterator iterator() {
        throw new UnsupportedOperationException();
    }

    @Override
    public int size() {
        return RedisUtils.zcard(qName).intValue();
    }

    @Override
    public boolean offer(Object o) {
        //延时5s
        return RedisUtils.zadd(qName,System.currentTimeMillis() + 5000,o.toString()) == 0;
    }

    @Override
    public String poll() {
        Set<String> values = RedisUtils.zrangeByscore(qName,0, System.currentTimeMillis(),0,1);
        if(values != null && !values.isEmpty()){
            String value = values.iterator().next();
            if(RedisUtils.zrem(qName,value) > 0){
                return value;
            }
        }
        return null;
    }

    @Override
    public String peek() {
        Set<String> values = RedisUtils.zrange(qName,0L,0L);
        if (values != null && !values.isEmpty()){
            String value = values.iterator().next();
            return value;
        }
        return null;
    }

    public static void main(String[] args) throws InterruptedException{
        DelayQueueTest delayQueue = new DelayQueueTest("delayQueue");
        Thread thread = new Thread(new Runnable() {
            @Override
            public void run() {
                for (int i = 0; i < 10; i++) {
                    delayQueue.offer(i);
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        });
        thread.start();
        Thread.sleep(10000);
        thread.join();
        for (;;){
            if(delayQueue.peek() == null){
                break;
            }
            String value = delayQueue.poll();
            if(value != null){
                System.out.println(value);
            }
            Thread.sleep(2000);
        }
        RedisUtils.close();
    }
}

①、延迟队列空了，会无限peek 、poll重试，空轮询不但拉高了服务器的CPU消耗，Redis的QPS也会被拉高，可以让线程sleep一会儿

②、阻塞读，用brpop/blpop代替rpop/lpop，队列没有数据时，会立即进入休眠状态，一旦数据来了，立即醒过来。但空闲连接会自动断开，一直阻塞，闲置过久，会主动断开连接，此时brpop/blpop会抛出异常