Kafka基础组件和辅助类库简介

• 在正式开始扒代码之前, 先来个开胃菜,简单介绍一下kafka的基础组件和一些代码实现中用到的基础类库

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Kafka基础组件概述

• KafkaServer是整个Kafka的核心组件，里面包含了kafka对外提供功能的所有角色；
• 一图顶千言:

kafkaserver1.png

Kafka辅助类库简介

KafkaScheduler

• 所在文件: core/src/main/scala/kafka/utils/KafkaScheduler.scala
• 功能: 接收需周期性执行的任务和延迟作务的添加, 使用一组thread pool来执行具体的任务;
• 实现: 封装了 java.util.concurrent.ScheduledThreadPoolExecutor;
• 接口(原有注释已经很清晰):

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/**
   * Initialize this scheduler so it is ready to accept scheduling of tasks
   */
  def startup()
  
  /**
   * Shutdown this scheduler. When this method is complete no more executions of background tasks will occur. 
   * This includes tasks scheduled with a delayed execution.
   */
  def shutdown()
  
  /**
   * Check if the scheduler has been started
   */
  def isStarted: Boolean
  
  /**
   * Schedule a task
   * @param name The name of this task
   * @param delay The amount of time to wait before the first execution
   * @param period The period with which to execute the task. If < 0 the task will execute only once.
   * @param unit The unit for the preceding times.
   */
  def schedule(name: String, fun: ()=>Unit, delay: Long = 0, period: Long = -1, unit: TimeUnit = TimeUnit.MILLISECONDS)

ZkUtils

• 所在文件: core/scr/main/scala/kafka/utils/ZkUtils.scala
• 功能: 封装了可能用到的对zk上节点的创建,读,写,解析(主要是json)操作;
• 实现: 使用了一个小众的类库 I0Itec 来操作zk;
• 涉及到以下zk节点:

代码语言：javascript复制

  val ConsumersPath = "/consumers"
  val BrokerIdsPath = "/brokers/ids"
  val BrokerTopicsPath = "/brokers/topics"
  val ControllerPath = "/controller"
  val ControllerEpochPath = "/controller_epoch"
  val ReassignPartitionsPath = "/admin/reassign_partitions"
  val DeleteTopicsPath = "/admin/delete_topics"
  val PreferredReplicaLeaderElectionPath = "/admin/preferred_replica_election"
  val BrokerSequenceIdPath = "/brokers/seqid"
  val IsrChangeNotificationPath = "/isr_change_notification"
  val EntityConfigPath = "/config"
  val EntityConfigChangesPath = "/config/changes"

Pool

• 所在文件: core/src/main/scala/kafka/utils/Pool.scala
• 功能: 简单的并发对象池;
• 实现: 对ConcurrentHashMap的封裝;
• getAndMaybePut实现小技巧, 使用了double check技术, 在有值的情况下降低锁的开销;

代码语言：javascript复制

def getAndMaybePut(key: K) = {
    if (valueFactory.isEmpty)
      throw new KafkaException("Empty value factory in pool.")
    val curr = pool.get(key)
    if (curr == null) {
      createLock synchronized {
        val curr = pool.get(key)
        if (curr == null)
          pool.put(key, valueFactory.get(key))
        pool.get(key)
      }
    }
    else
      curr
  }

Logging

• 所在文件: core/src/main/scala/kafka/utils/Logging.scala
• 功能: 定义了trait Logging 供其他类继承,方便写日志;
• 实现: 对org.apache.log4j.Logger的封装;

FileLock

• 所在文件: core/src/main/scala/kafka/utils/FileLock.scala
• 功能: 文件锁, 相当于linux的/usr/bin/lockf;
• 实现: 使用java.nio.channels.FileLock实现;

ByteBounderBlockingQueue

• 所在文件: core/src/main/scala/kafkak/utils/ByteBoundedBlockingQueue.scala;
• 功能: 阻塞队列, 队列满的衡量标准有两条: 队列内元素个数达到了上限, 队列内所有元素的size之各达到了上限;
• 实现: 使用java.util.concurrent.LinkedBlockingQueue实现, 加上了对队列内已有元素size大小的check;
• 接口:

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def offer(e: E, timeout: Long, unit: TimeUnit = TimeUnit.MICROSECONDS): Boolean
def offer(e: E): Boolean
def put(e: E): Boolean
def poll(timeout: Long, unit: TimeUnit)
def poll()
def take(): E
...

DelayedItem

• 所在文件: core/src/main/scala/kafaka/utils/DelayedItem.scala
• 功能: 定义了可以放入到DelayQueue队列的对象;
• 实现: 实现了Delayed接口;

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