spark 2.0 spark Inbox消息类型

Inbox定义了所有的消息类型。

首先所有的消息都必须有InbosMessage特质。

在注册的时候，向 receivers放置一个看似没有内容的EndpointData对象。然而，这个对象非常重要，因为以后向该endpoint放置的任何消息都放到这个对象的inbox里的messages队列里。

 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
  }

放置了空的EndpointData对象，那么是怎么从该对象的inbox里取数据处理的呢，原来是初始化EndpointData的inbox时，自动放置了一个OnStart消息，所以空的Endpoint对象对应于OnStart。

 // OnStart should be the first message to process
  inbox.synchronized {
    messages.add(OnStart)
  }

  private def postMessage(
      endpointName: String,
      message: InboxMessage,
      callbackIfStopped: (Exception) => Unit): Unit = {
    val error = synchronized {
      val data = endpoints.get(endpointName)
      if (stopped) {
        Some(new RpcEnvStoppedException())
      } else if (data == null) {
        Some(new SparkException(s"Could not find $endpointName."))
      } else {
        data.inbox.post(message)
        receivers.offer(data)
        None
      }
    }
    // We don't need to call `onStop` in the `synchronized` block
    error.foreach(callbackIfStopped)
  }

private[netty] sealed trait InboxMessage

private[netty] case class OneWayMessage(
    senderAddress: RpcAddress,
    content: Any) extends InboxMessage

private[netty] case class RpcMessage(
    senderAddress: RpcAddress,
    content: Any,
    context: NettyRpcCallContext) extends InboxMessage

private[netty] case object OnStart extends InboxMessage

private[netty] case object OnStop extends InboxMessage

/** A message to tell all endpoints that a remote process has connected. */
private[netty] case class RemoteProcessConnected(remoteAddress: RpcAddress) extends InboxMessage

/** A message to tell all endpoints that a remote process has disconnected. */
private[netty] case class RemoteProcessDisconnected(remoteAddress: RpcAddress) extends InboxMessage

/** A message to tell all endpoints that a network error has happened. */
private[netty] case class RemoteProcessConnectionError(cause: Throwable, remoteAddress: RpcAddress)
  extends InboxMessage

/**
 * An inbox that stores messages for an [[RpcEndpoint]] and posts messages to it thread-safely.
 */
private[netty] class Inbox(
    val endpointRef: NettyRpcEndpointRef,
    val endpoint: RpcEndpoint)
  extends Logging {

  inbox =>  // Give this an alias so we can use it more clearly in closures.

  @GuardedBy("this")
  protected val messages = new java.util.LinkedList[InboxMessage]()

  /** True if the inbox (and its associated endpoint) is stopped. */
  @GuardedBy("this")
  private var stopped = false

  /** Allow multiple threads to process messages at the same time. */
  @GuardedBy("this")
  private var enableConcurrent = false

  /** The number of threads processing messages for this inbox. */
  @GuardedBy("this")
  private var numActiveThreads = 0

  // OnStart should be the first message to process
  inbox.synchronized {
    messages.add(OnStart)
  }

  /**
   * Process stored messages.
   */
  def process(dispatcher: Dispatcher): Unit = {
    var message: InboxMessage = null
    inbox.synchronized {
      if (!enableConcurrent && numActiveThreads != 0) {
        return
      }
      message = messages.poll()
      if (message != null) {
        numActiveThreads += 1
      } else {
        return
      }
    }
    while (true) {
      safelyCall(endpoint) {
        message match {
          case RpcMessage(_sender, content, context) =>
            try {
              endpoint.receiveAndReply(context).applyOrElse[Any, Unit](content, { msg =>
                throw new SparkException(s"Unsupported message $message from ${_sender}")
              })
            } catch {
              case NonFatal(e) =>
                context.sendFailure(e)
                // Throw the exception -- this exception will be caught by the safelyCall function.
                // The endpoint's onError function will be called.
                throw e
            }

          case OneWayMessage(_sender, content) =>
            endpoint.receive.applyOrElse[Any, Unit](content, { msg =>
              throw new SparkException(s"Unsupported message $message from ${_sender}")
            })

          case OnStart =>
            endpoint.onStart()
            if (!endpoint.isInstanceOf[ThreadSafeRpcEndpoint]) {
              inbox.synchronized {
                if (!stopped) {
                  enableConcurrent = true
                }
              }
            }

          case OnStop =>
            val activeThreads = inbox.synchronized { inbox.numActiveThreads }
            assert(activeThreads == 1,
              s"There should be only a single active thread but found $activeThreads threads.")
            dispatcher.removeRpcEndpointRef(endpoint)
            endpoint.onStop()
            assert(isEmpty, "OnStop should be the last message")

          case RemoteProcessConnected(remoteAddress) =>
            endpoint.onConnected(remoteAddress)

          case RemoteProcessDisconnected(remoteAddress) =>
            endpoint.onDisconnected(remoteAddress)

          case RemoteProcessConnectionError(cause, remoteAddress) =>
            endpoint.onNetworkError(cause, remoteAddress)
        }
      }

      inbox.synchronized {
        // "enableConcurrent" will be set to false after `onStop` is called, so we should check it
        // every time.
        if (!enableConcurrent && numActiveThreads != 1) {
          // If we are not the only one worker, exit
          numActiveThreads -= 1
          return
        }
        message = messages.poll()
        if (message == null) {
          numActiveThreads -= 1
          return
        }
      }
    }
  }

  def post(message: InboxMessage): Unit = inbox.synchronized {
    if (stopped) {
      // We already put "OnStop" into "messages", so we should drop further messages
      onDrop(message)
    } else {
      messages.add(message)
      false
    }
  }

  def stop(): Unit = inbox.synchronized {
    // The following codes should be in `synchronized` so that we can make sure "OnStop" is the last
    // message
    if (!stopped) {
      // We should disable concurrent here. Then when RpcEndpoint.onStop is called, it's the only
      // thread that is processing messages. So `RpcEndpoint.onStop` can release its resources
      // safely.
      enableConcurrent = false
      stopped = true
      messages.add(OnStop)
      // Note: The concurrent events in messages will be processed one by one.
    }
  }

  def isEmpty: Boolean = inbox.synchronized { messages.isEmpty }

  /**
   * Called when we are dropping a message. Test cases override this to test message dropping.
   * Exposed for testing.
   */
  protected def onDrop(message: InboxMessage): Unit = {
    logWarning(s"Drop $message because $endpointRef is stopped")
  }

  /**
   * Calls action closure, and calls the endpoint's onError function in the case of exceptions.
   */
  private def safelyCall(endpoint: RpcEndpoint)(action: => Unit): Unit = {
    try action catch {
      case NonFatal(e) =>
        try endpoint.onError(e) catch {
          case NonFatal(ee) => logError(s"Ignoring error", ee)
        }
    }
  }

}