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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

    @Testpublic 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()) {@Overrideprotected 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);}@Overrideprotected 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() {@Overridepublic void onSubscribe(String channel) {pushTask();}});messageListenerId = schedulerTopic.addListener(new MessageListener<Long>() {@Overridepublic 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() {                    @Overridepublic 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>() {@Overridepublic 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