Notification service for every node of a cluster

In cluster mode, it might be useful, for every node to be able to register to a notification channel, in order to be able to broadcast messages.

Connect cluster has implemented a Redis Pub/Sub channel, for such notification, see GitCacheServiceCluster class.
It is based on:

• Nuxeo RedisExecutor class, to benefit from Nuxeo interface to the Redis server.
• Subscription to the channel:

      protected void subscribeToRedis(RedisExecutor redisExecutor) {
          try {
              log.info("Subscribing to Redis channel: " + CHANNEL);
              redisExecutor.execute(new RedisCallable<Object>() {
                  @Override
                  public Object call(Jedis jedis) throws Exception {
                      jedis.subscribe(new JedisPubSub() {
  
                          @Override
                          public void onSubscribe(String channel, int subscribedChannels) {
                              super.onSubscribe(channel, subscribedChannels);
                              if (subscribtionLatch != null) {
                                  subscribtionLatch.countDown();
                              }
                          }
  
                          @Override
                          public void onMessage(String channel, String message) {
                              if (CHANNEL.equals(channel)) {
                                  log.debug("Receive message: " + message);
                                  GitCacheServiceClusterEvent event;
                                  try {
                                      event = GitCacheServiceClusterEvent.fromJSON(message);
                                      log.debug("Event read: " + event);
                                      handleRedisEvent(event);
                                  } catch (IOException e) {
                                      log.error("Error while parsing the message", e);
                                  }
                              }
                          }
  
                      }, CHANNEL);
                      return null;
                  }
              });
  

• Publishing a message

  RedisExecutor redisExecutor = Framework.getService(RedisExecutor.class);
              redisExecutor.execute(new RedisCallable<Object>() {
                  @Override
                  public Object call(Jedis jedis) throws Exception {
                      String json = event.toJSON();
                      return jedis.publish(CHANNEL, json);
                  }
              });