spark core之BlockManagerMaser

• BlockManagerMaster运行在driver上
• BlockManagerMaster使用BlockManagerMasterEndpoint允许executors发送块状态更新消息并且能够跟踪这些消息。说穿了，就是负责对各个节点上的BlockManager内部管理的数据的元数据，进行维护。比如block增删改等操作，都会在这里维护数据的变更。

1. SparkEnv实例化一个BlockManagerMaster对象

    val blockManagerMaster = new BlockManagerMaster(
         registerOrLookupEndpoint(
              BlockManagerMaster.DRIVER_ENDPOINT_NAME,
              new BlockManagerMasterEndpoint(rpcEnv, isLocal, conf, listenerBus)),
         conf, 
         isDriver)

进入registerOrLookupEndpoint方法

    def registerOrLookupEndpoint(
        name: String, endpointCreator: => RpcEndpoint):
      RpcEndpointRef = {
      if (isDriver) {
        logInfo("Registering " + name)
        rpcEnv.setupEndpoint(name, endpointCreator)
      } else {
        RpcUtils.makeDriverRef(name, conf, rpcEnv)
      }
    }

如果是river端，就在BlockManagerMaster内部，创建终端点BlockManagerMasterEndpoint，并进行注册，最终调用代码如下：

  def registerRpcEndpoint(name: String, endpoint: RpcEndpoint): NettyRpcEndpointRef = {
    val addr = RpcEndpointAddress(nettyEnv.address, name)
    val endpointRef = new NettyRpcEndpointRef(nettyEnv.conf, addr, nettyEnv)
    synchronized {
      if (stopped) {
        throw new IllegalStateException("RpcEnv has been stopped")
      }
      if (endpoints.putIfAbsent(name, new EndpointData(name, endpoint, endpointRef)) != null) {
        throw new IllegalArgumentException(s"There is already an RpcEndpoint called $name")
      }
      val data = endpoints.get(name)
      endpointRefs.put(data.endpoint, data.ref)
      receivers.offer(data)  // for the OnStart message
    }
    endpointRef
  }

如果是executor，则创建BlockManagerMasterEndpoint的引用