聊聊redisson的DelayedQueue

序

本文主要研究一下redisson的DelayedQueue

maven

        <dependency>
            <groupId>org.redisson</groupId>
            <artifactId>redisson</artifactId>
            <version>3.8.1</version>
        </dependency>

实例

    @Test
    public void testDelayedQueue() throws InterruptedException {
        Config config = new Config();
        config.useSingleServer()
                .setAddress("redis://192.168.99.100:6379");
        RedissonClient redisson = Redisson.create(config);
        RBlockingQueue<String> blockingQueue = redisson.getBlockingQueue("dest_queue1");
        RDelayedQueue<String> delayedQueue = redisson.getDelayedQueue(blockingQueue);
        delayedQueue.offer("demo", 10, TimeUnit.SECONDS);
        Assert.assertFalse(blockingQueue.contains("demo"));
        TimeUnit.SECONDS.sleep(15);
        Assert.assertTrue(blockingQueue.contains("demo"));
    }

• 这里使用了两个queue，对delayedQueue的offer操作是直接进入delayedQueue，但是delay是作用在目标队列上，这里就是RBlockingQueue

源码解析

RDelayedQueue.offer

redisson-3.8.1-sources.jar!/org/redisson/RedissonDelayedQueue.java

public class RedissonDelayedQueue<V> extends RedissonExpirable implements RDelayedQueue<V> {

    private final QueueTransferService queueTransferService;
    private final String channelName;
    private final String queueName;
    private final String timeoutSetName;
    
    protected RedissonDelayedQueue(QueueTransferService queueTransferService, Codec codec, final CommandAsyncExecutor commandExecutor, String name) {
        super(codec, commandExecutor, name);
        channelName = prefixName("redisson_delay_queue_channel", getName());
        queueName = prefixName("redisson_delay_queue", getName());
        timeoutSetName = prefixName("redisson_delay_queue_timeout", getName());
        
        //QueueTransferTask task = ......
        
        queueTransferService.schedule(queueName, task);
        
        this.queueTransferService = queueTransferService;
    }

    public void offer(V e, long delay, TimeUnit timeUnit) {
        get(offerAsync(e, delay, timeUnit));
    }
    
    public RFuture<Void> offerAsync(V e, long delay, TimeUnit timeUnit) {
        long delayInMs = timeUnit.toMillis(delay);
        long timeout = System.currentTimeMillis() + delayInMs;
     
        long randomId = PlatformDependent.threadLocalRandom().nextLong();
        return commandExecutor.evalWriteAsync(getName(), codec, RedisCommands.EVAL_VOID,
                "local value = struct.pack('dLc0', tonumber(ARGV[2]), string.len(ARGV[3]), ARGV[3]);" 
              + "redis.call('zadd', KEYS[2], ARGV[1], value);"
              + "redis.call('rpush', KEYS[3], value);"
              // if new object added to queue head when publish its startTime 
              // to all scheduler workers 
              + "local v = redis.call('zrange', KEYS[2], 0, 0); "
              + "if v[1] == value then "
                 + "redis.call('publish', KEYS[4], ARGV[1]); "
              + "end;"
                 ,
              Arrays.<Object>asList(getName(), timeoutSetName, queueName, channelName), 
              timeout, randomId, encode(e));
    }

    public ByteBuf encode(Object value) {
        if (commandExecutor.isRedissonReferenceSupportEnabled()) {
            RedissonReference reference = RedissonObjectFactory.toReference(commandExecutor.getConnectionManager().getCfg(), value);
            if (reference != null) {
                value = reference;
            }
        }
        
        try {
            return codec.getValueEncoder().encode(value);
        } catch (IOException e) {
            throw new IllegalArgumentException(e);
        }
    }

    public static String prefixName(String prefix, String name) {
        if (name.contains("{")) {
            return prefix + ":" + name;
        }
        return prefix + ":{" + name + "}";
    }

    //......
}

• 这里使用的是一段lua脚本，其中keys参数数组有四个值，KEYS[1]为getName(), KEYS[2]为timeoutSetName, KEYS[3]为queueName, KEYS[4]为channelName
• 变量有三个，ARGV[1]为timeout，ARGV[2]为randomId，ARGV[3]为encode(e)
• 这段lua脚本对timeoutSetName的zset添加一个结构体，其score为timeout值；对queueName的list的表尾添加结构体；然后判断timeoutSetName的zset的第一个元素是否是当前的结构体，如果是则对channel发布timeout消息

queueTransferService.schedule

redisson-3.8.1-sources.jar!/org/redisson/RedissonDelayedQueue.java

        QueueTransferTask task = new QueueTransferTask(commandExecutor.getConnectionManager()) {
            
            @Override
            protected RFuture<Long> pushTaskAsync() {
                return commandExecutor.evalWriteAsync(getName(), LongCodec.INSTANCE, RedisCommands.EVAL_LONG,
                        "local expiredValues = redis.call('zrangebyscore', KEYS[2], 0, ARGV[1], 'limit', 0, ARGV[2]); "
                      + "if #expiredValues > 0 then "
                          + "for i, v in ipairs(expiredValues) do "
                              + "local randomId, value = struct.unpack('dLc0', v);"
                              + "redis.call('rpush', KEYS[1], value);"
                              + "redis.call('lrem', KEYS[3], 1, v);"
                          + "end; "
                          + "redis.call('zrem', KEYS[2], unpack(expiredValues));"
                      + "end; "
                        // get startTime from scheduler queue head task
                      + "local v = redis.call('zrange', KEYS[2], 0, 0, 'WITHSCORES'); "
                      + "if v[1] ~= nil then "
                         + "return v[2]; "
                      + "end "
                      + "return nil;",
                      Arrays.<Object>asList(getName(), timeoutSetName, queueName), 
                      System.currentTimeMillis(), 100);
            }
            
            @Override
            protected RTopic<Long> getTopic() {
                return new RedissonTopic<Long>(LongCodec.INSTANCE, commandExecutor, channelName);
            }
        };
        
        queueTransferService.schedule(queueName, task);

• RedissonDelayedQueue构造器里头对QueueTransferTask进行调度
• 调度执行的是pushTaskAsync方法，主要就是将到期的元素从元素队列移到目标队列
• 这里使用一段lua脚本，KEYS[1]为getName()，KEYS[2]为timeoutSetName，KEYS[3]为queueName；ARGV[1]为当前时间戳，ARGV[2]为100
• 这里调用zrangebyscore，对timeoutSetName的zset使用timeout参数进行排序，取得分介于0和当前时间戳的元素，取前200条
• 如果有值表示该元素需要移交到目标队列，然后调用rpush移交到目标队列，再调用lrem从元素队列移除，最后在从timeoutSetName的zset中删除掉已经处理的这些元素
• 处理完过元素转移之后，再取timeoutSetName的zset的第一个元素的得分返回，如果没有返回nil

QueueTransferService.schedule

redisson-3.8.1-sources.jar!/org/redisson/QueueTransferService.java

public class QueueTransferService {

    private final ConcurrentMap<String, QueueTransferTask> tasks = PlatformDependent.newConcurrentHashMap();
    
    public synchronized void schedule(String name, QueueTransferTask task) {
        QueueTransferTask oldTask = tasks.putIfAbsent(name, task);
        if (oldTask == null) {
            task.start();
        } else {
            oldTask.incUsage();
        }
    }
    
    public synchronized void remove(String name) {
        QueueTransferTask task = tasks.get(name);
        if (task != null) {
            if (task.decUsage() == 0) {
                tasks.remove(name, task);
                task.stop();
            }
        }
    }
}

• 这里的schedule方法首先添加到ConcurrentMap中，如果该任务已经存在，则调用oldTask.incUsage()，不存在则启动该任务

QueueTransferTask.start

redisson-3.8.1-sources.jar!/org/redisson/QueueTransferTask.java

    public void start() {
        RTopic<Long> schedulerTopic = getTopic();
        statusListenerId = schedulerTopic.addListener(new BaseStatusListener() {
            @Override
            public void onSubscribe(String channel) {
                pushTask();
            }
        });
        
        messageListenerId = schedulerTopic.addListener(new MessageListener<Long>() {
            @Override
            public void onMessage(CharSequence channel, Long startTime) {
                scheduleTask(startTime);
            }
        });
    }

    private void scheduleTask(final Long startTime) {
        TimeoutTask oldTimeout = lastTimeout.get();
        if (startTime == null) {
            return;
        }
        
        if (oldTimeout != null) {
            oldTimeout.getTask().cancel();
        }
        
        long delay = startTime - System.currentTimeMillis();
        if (delay > 10) {
            Timeout timeout = connectionManager.newTimeout(new TimerTask() {                    
                @Override
                public void run(Timeout timeout) throws Exception {
                    pushTask();
                    
                    TimeoutTask currentTimeout = lastTimeout.get();
                    if (currentTimeout.getTask() == timeout) {
                        lastTimeout.compareAndSet(currentTimeout, null);
                    }
                }
            }, delay, TimeUnit.MILLISECONDS);
            if (!lastTimeout.compareAndSet(oldTimeout, new TimeoutTask(startTime, timeout))) {
                timeout.cancel();
            }
        } else {
            pushTask();
        }
    }

    private void pushTask() {
        RFuture<Long> startTimeFuture = pushTaskAsync();
        startTimeFuture.addListener(new FutureListener<Long>() {
            @Override
            public void operationComplete(io.netty.util.concurrent.Future<Long> future) throws Exception {
                if (!future.isSuccess()) {
                    if (future.cause() instanceof RedissonShutdownException) {
                        return;
                    }
                    log.error(future.cause().getMessage(), future.cause());
                    scheduleTask(System.currentTimeMillis() + 5 * 1000L);
                    return;
                }
                
                if (future.getNow() != null) {
                    scheduleTask(future.getNow());
                }
            }
        });
    }

• 这里用到了RTopic，添加了StatusListener以及MessageListener
• StatusListener在订阅的时候触发pushTask，MessageListener主要是调用scheduleTask
• pushTaskAsync在RedissonDelayedQueue的实现就是上面讲的实现元素在原始队列及目标队列的转移
• scheduleTask方法会重新计算delay，对于大于10的延时触发pushTask，小于等于10的则立刻触发pushTask
• pushTask会对pushTaskAsync操作进行回调，如果执行不成功则重新触发scheduleTask，如果执行成功但是返回值(timeoutSetName的zset的第一个元素的得分)不为null的话，则以该值触发scheduleTask

小结

• redisson的DelayedQueue使用上是将元素及延时信息入队，之后定时任务将到期的元素转移到目标队列
• 这里使用了三个结构来存储，一个是目标队列list；一个是原生队列list，添加的是带有延时信息的结构体；一个是timeoutSetName的zset，元素是结构体，其score为timeout值
• redisson使用了很多异步回调来操作，整体代码阅读上会相对费劲些

doc

• delayed-queue