kafka源码解析之十四TopicConfigManager

当Kakfka的topic创建之后，需要中途修改该topic的属性的时候，可以通过在/brokers/config_changes上传配置信息，触发TopicConfigManager内部的监听函数来更改topic的属性。

class TopicConfigManager(private val zkClient: ZkClient,
                         private val logManager: LogManager,
                         private val changeExpirationMs: Long = 15*60*1000,
                         private val time: Time = SystemTime) extends Logging {
  private var lastExecutedChange = -1L
  def startup() {//在/brokers/config_changes目录下注册监听函数ConfigChangeListener
    ZkUtils.makeSurePersistentPathExists(zkClient, ZkUtils.TopicConfigChangesPath)
    zkClient.subscribeChildChanges(ZkUtils.TopicConfigChangesPath, ConfigChangeListener)
    processAllConfigChanges()
  }
  private def processAllConfigChanges() {
    val configChanges = zkClient.getChildren(ZkUtils.TopicConfigChangesPath)
    import JavaConversions._
    processConfigChanges((configChanges: mutable.Buffer[String]).sorted)
  }
  private def processConfigChanges(notifications: Seq[String]) {
    if (notifications.size > 0) {
      info("Processing config change notification(s)...")
      val now = time.milliseconds
      val logs = logManager.logsByTopicPartition.toBuffer
      val logsByTopic = logs.groupBy(_._1.topic).mapValues(_.map(_._2))
      for (notification <- notifications) {
        val changeId = changeNumber(notification)
        if (changeId > lastExecutedChange) {//标识更改的时间戳，不能利用旧的时间戳的config来覆盖新的时间戳的config
          val changeZnode = ZkUtils.TopicConfigChangesPath + "/" + notification
          val (jsonOpt, stat) = ZkUtils.readDataMaybeNull(zkClient, changeZnode)
          if(jsonOpt.isDefined) {
            val json = jsonOpt.get
            val topic = json.substring(1, json.length - 1) // hacky way to dequote
            if (logsByTopic.contains(topic)) {
              //合并zk上被更改的属性至topic里面
              val props = new Properties(logManager.defaultConfig.toProps)
              props.putAll(AdminUtils.fetchTopicConfig(zkClient, topic))
              val logConfig = LogConfig.fromProps(props)
              for (log <- logsByTopic(topic))
                log.config = logConfig
              info("Processed topic config change %d for topic %s, setting new config to %s.".format(changeId, topic, props))
              purgeObsoleteNotifications(now, notifications)
            }
          }
          lastExecutedChange = changed//更改时间戳
        }
      }
    }
  }
  private def purgeObsoleteNotifications(now: Long, notifications: Seq[String]) {
    for(notification <- notifications.sorted) {
      val (jsonOpt, stat) = ZkUtils.readDataMaybeNull(zkClient, ZkUtils.TopicConfigChangesPath + "/" + notification)
      if(jsonOpt.isDefined) {//删除过期的通知
        val changeZnode = ZkUtils.TopicConfigChangesPath + "/" + notification
        if (now - stat.getCtime > changeExpirationMs) {//删除过期的通知
          debug("Purging config change notification " + notification)
          ZkUtils.deletePath(zkClient, changeZnode)
        } else {
          return
        }
      }
    }
  }
  private def changeNumber(name: String): Long = name.substring(AdminUtils.TopicConfigChangeZnodePrefix.length).toLong
  object ConfigChangeListener extends IZkChildListener {
    override def handleChildChange(path: String, chillins: java.util.List[String]) {
      try {
        import JavaConversions._
        processConfigChanges(chillins: mutable.Buffer[String])
      } catch {
        case e: Exception => error("Error processing config change:", e)
      }
    }
  }
}