SpringData-Redis发布订阅自动重连分析

RedisMessageListenerContainer

配置

@Bean
@Autowired
RedisMessageListenerContainer redisContainer(JedisConnectionFactory redisConnectionFactory, RedisMessageListener a) {
    RedisMessageListenerContainer container
            = new RedisMessageListenerContainer();
    container.setConnectionFactory(redisConnectionFactory);
    List<Topic> topics = Lists.newArrayList(new ChannelTopic(
                    CHANNEL),
            new ChannelTopic(CHANNEL)
    );
    container.addMessageListener(new MessageListenerAdapter(a), topics);
    return container;
}

启动分析

添加频道监听java

//RedisMessageListenerContainer.java

public void addMessageListener(MessageListener listener, Collection<? extends Topic> topics) {
	addListener(listener, topics);
	lazyListen();
}

这个AddListener会对Topic作一些记录，patternMapping, channelMapping，去重等等，而后最关键的一步：redis

//RedisMessageListenerContainer.java
//addListener
// check the current listening state
	if (listening) {
		subscriptionTask.subscribeChannel(channels.toArray(new byte[channels.size()][]));
		subscriptionTask.subscribePattern(patterns.toArray(new byte[patterns.size()][]));
	}

//RedisMessageListenerContainer.java

void subscribeChannel(byte[]... channels) {
	if (channels != null && channels.length > 0) {
		if (connection != null) {
			synchronized (localMonitor) {
				Subscription sub = connection.getSubscription();
				if (sub != null) {
					sub.subscribe(channels);
				}
			}
		}
	}
}

//JedisSubscription.java
	protected void doSubscribe(byte[]... channels) {
		jedisPubSub.subscribe(channels);
	}

可是启动以前这个listening=false。故该代码不生效。再看lazyListen方法：服务器

//RedisMessageListenerContainer.java
private void lazyListen() {
		boolean debug = logger.isDebugEnabled();
		boolean started = false;

		if (isRunning()) {
			if (!listening) {
				synchronized (monitor) {
					if (!listening) {
						if (channelMapping.size() > 0 || patternMapping.size() > 0) {
							subscriptionExecutor.execute(subscriptionTask);
							listening = true;
							started = true;
						}
					}
				}
				if (debug) {
					if (started) {
						logger.debug("Started listening for Redis messages");
					} else {
						logger.debug("Postpone listening for Redis messages until actual listeners are added");
					}
				}
			}
		}
	}

调用addMessageListener的时候，isRunning()=false 也不生效。app

最后：当@Bean构造完成的时候，LifeCycle进入start的时候，该Container启动。框架

//RedisMessageListenerContainer.java

    public void start() {
		if (!running) {
			running = true;
			// wait for the subscription to start before returning
			// technically speaking we can only be notified right before the subscription starts
			synchronized (monitor) {
				lazyListen();
				if (listening) {
					try {
						// wait up to 5 seconds for Subscription thread
						monitor.wait(initWait);
					} catch (InterruptedException e) {
						// stop waiting
					}
				}
			}

			if (logger.isDebugEnabled()) {
				logger.debug("Started RedisMessageListenerContainer");
			}
		}
	}

这个时候，running=true了。而后调用 lazyListen()，确实比较Lazy。这个时候，启动子线程来执行订阅和监听。async

subscriptionExecutor.execute(subscriptionTask);

这个subscriptionTask的构造以下：this

//RedisMessageListenerContainer.java
public void run() {
	synchronized (localMonitor) {
		subscriptionTaskRunning = true;
	}
	try {
		connection = connectionFactory.getConnection();
		if (connection.isSubscribed()) {
			throw new IllegalStateException("Retrieved connection is already subscribed; aborting listening");
		}

		boolean asyncConnection = ConnectionUtils.isAsync(connectionFactory);

		// NB: async drivers' Xsubscribe calls block, so we notify the RDMLC before performing the actual subscription.
		if (!asyncConnection) {
			synchronized (monitor) {
				monitor.notify();
			}
		}

		SubscriptionPresentCondition subscriptionPresent = eventuallyPerformSubscription();

		if (asyncConnection) {
			SpinBarrier.waitFor(subscriptionPresent, getMaxSubscriptionRegistrationWaitingTime());

			synchronized (monitor) {
				monitor.notify();
			}
		}
	} catch (Throwable t) {
		handleSubscriptionException(t);
	} finally {
		// this block is executed once the subscription thread has ended, this may or may not mean
		// the connection has been unsubscribed, depending on driver
		synchronized (localMonitor) {
			subscriptionTaskRunning = false;
			localMonitor.notify();
		}
	}
}

这里connection 确定不是subscribed。而后他根据Redis的客户端类型来判断是不是阻塞的若是是阻塞的类型，则唤醒一下被阻塞的Container线程。（？？？）spa

而后，最关键的是：eventuallyPerformSubscription()，最终发起订阅的，并轮询订阅的是方法。线程

//RDMLC

private SubscriptionPresentCondition eventuallyPerformSubscription() {

	SubscriptionPresentCondition condition = null;

	if (channelMapping.isEmpty()) {

		condition = new PatternSubscriptionPresentCondition();
		connection.pSubscribe(new DispatchMessageListener(), unwrap(patternMapping.keySet()));
	} else {

		if (patternMapping.isEmpty()) {
			condition = new SubscriptionPresentCondition();
		} else {
			// schedule the rest of the subscription
			subscriptionExecutor.execute(new PatternSubscriptionTask());
			condition = new PatternSubscriptionPresentCondition();
		}

		connection.subscribe(new DispatchMessageListener(), unwrap(channelMapping.keySet()));
	}

	return condition;
}

以connection.subscribe()为例：即将发起订阅，注意这里是利用DispatchMessageListener作的事件分发监听器。debug

//JedisConnection.java

public void subscribe(MessageListener listener, byte[]... channels) {
	if (isSubscribed()) {
		throw new RedisSubscribedConnectionException(
				"Connection already subscribed; use the connection Subscription to cancel or add new channels");
	}

	if (isQueueing()) {
		throw new UnsupportedOperationException();
	}
	if (isPipelined()) {
		throw new UnsupportedOperationException();
	}

	try {
		BinaryJedisPubSub jedisPubSub = new JedisMessageListener(listener);

		subscription = new JedisSubscription(listener, jedisPubSub, channels, null);
		jedis.subscribe(jedisPubSub, channels);

	} catch (Exception ex) {
		throw convertJedisAccessException(ex);
	}
}

//BinaryJedis.java

public void subscribe(BinaryJedisPubSub jedisPubSub, byte[]... channels) {
    client.setTimeoutInfinite();
    try {
      jedisPubSub.proceed(client, channels);
    } finally {
      client.rollbackTimeout();
    }
}

这里调用了BinaryJedisPubSub的proceed()。

这里先提出两个问题？ 要订阅是否是要发起subscribe命令给Redis？发起 subscribe channel命令，而后Listener怎么办？

这里调用是jedis.subscribe(jedisPubSub, channels);而一开始 subscibeChannels的实现却不太同样？

下面看jedisPubSub：

public void proceed(Client client, byte[]... channels) {
    this.client = client;
    client.subscribe(channels);
    client.flush();
    process(client);
  }

这里subscribe是再次发起订阅请求，而后process轮询检查消息。

异常处理

再看看JedisConnection类subscribe方法的异常的处理：

protected DataAccessException convertJedisAccessException(Exception ex) {

	if (ex instanceof NullPointerException) {
		// An NPE before flush will leave data in the OutputStream of a pooled connection
		broken = true;
	}

	DataAccessException exception = EXCEPTION_TRANSLATION.translate(ex);
	if (exception instanceof RedisConnectionFailureException) {
		broken = true;
	}

	return exception;
}

EXCEPTION_TRANSLATION.translate(ex); 会调用：PassThroughExceptionTranslationStrategy的Convert。

public class JedisExceptionConverter implements Converter<Exception, DataAccessException> {

	public DataAccessException convert(Exception ex) {

		if (ex instanceof DataAccessException) {
			return (DataAccessException) ex;
		}
		if (ex instanceof JedisDataException) {
			return new InvalidDataAccessApiUsageException(ex.getMessage(), ex);
		}
		if (ex instanceof JedisConnectionException) {
			return new RedisConnectionFailureException(ex.getMessage(), ex);
		}
		if (ex instanceof JedisException) {
			return new InvalidDataAccessApiUsageException(ex.getMessage(), ex);
		}
		if (ex instanceof UnknownHostException) {
			return new RedisConnectionFailureException("Unknown host " + ex.getMessage(), ex);
		}
		if (ex instanceof IOException) {
			return new RedisConnectionFailureException("Could not connect to Redis server", ex);
		}

		return null;
	}
}

那么，当Jedis抛错：JedisConnectionException 服务器彷佛断开了链接这个时候，subscribe 从而抛出RedisConnectionFailureException。

最后，再看RedisMessageListenerContainerd的run方法内的异常处理：这个时候，

protected void handleSubscriptionException(Throwable ex) {
	listening = false;
	subscriptionTask.closeConnection();
	if (ex instanceof RedisConnectionFailureException) {
		if (isRunning()) {
			logger.error("Connection failure occurred. Restarting subscription task after " + recoveryInterval + " ms");
			sleepBeforeRecoveryAttempt();
			lazyListen();
		}
	} else {
		logger.error("SubscriptionTask aborted with exception:", ex);
	}
}

到这个时候，isRunning仍是true的（当且仅当LifeCycle进入close的时候，才会变成false），结果就会在 recoveryInterval ms以后，重启调用lazyListen()，再次启动订阅和监听。

实际效果

实际上，我在服务器上的错误日志中，我确实看到了

Connection failure occurred. Restarting subscription task after 5000 ms

总结

SpringData-Redis，可以解决手动处理Redis pub/sub的订阅被意外断开，致使监听失败的问题。他能确保，服务持续监听，出现异常时，可以从新订阅并监听给定的频道。因此，仍是用框架吧，比本身手写的发布订阅更可靠。