Spark源码分析之Akka的启动

Akka是Actor编程模型的库，用于提供高并发的Actor编程模型，Spark即利用ActorSystem实现分布式消息的发送和并发编程。下面将通过源码分析来观察Spark中ActorSystem的创建与启动。

首先在SparkEnv.scala中

// Create a ActorSystem for legacy codes，即通过AkkaUtils.createActorSystem方法创建ActorSystem
        AkkaUtils.createActorSystem(
          actorSystemName + "ActorSystem",
          hostname,
          actorSystemPort,
          conf,
          securityManager
        )._1

在AkkaUtils.scala中可以发现createActorSystem的源码

  def createActorSystem(
 //传入name、host、port、conf等信息，返回值即startServiceOnPort的返回值
 name: String, host: String, port: Int, conf: SparkConf, securityManager: SecurityManager): (ActorSystem, Int) = { 
 //对doCreateActorSystem函数进行柯里化，实际通过doCreateActorSystem启动Akka
 val startService: Int => (ActorSystem, Int) = { actualPort => doCreateActorSystem(name, host, actualPort, conf, securityManager) }
 //返回值是（T,int）在这里是(ActorSystem,int)
 Utils.startServiceOnPort(port, startService, conf, name)}

在Utils.scala中可以看到在startServiceOnPort中调用柯里化后的doCreateActorSystem启动Akka的代码

  def startServiceOnPort[T](
      startPort: Int,
      startService: Int => (T, Int),
      conf: SparkConf,
      serviceName: String = ""): (T, Int) = {

    require(startPort == 0 || (1024 <= startPort && startPort < 65536),
      "startPort should be between 1024 and 65535 (inclusive), or 0 for a random free port.")

    val serviceString = if (serviceName.isEmpty) "" else s" '$serviceName'"
    val maxRetries = portMaxRetries(conf)
    for (offset <- 0 to maxRetries) {
      // Do not increment port if startPort is 0, which is treated as a special port
      val tryPort = if (startPort == 0) {
        startPort
      } else {
        // If the new port wraps around, do not try a privilege port
        ((startPort + offset - 1024) % (65536 - 1024)) + 1024
      }
      try {
//startServiceOnPort中调用startService,在本例中传入的startService就是柯里化后的doCreateActorSystem用于启动Akka

val (service, port) = startService(tryPort) logInfo(s"Successfully started service$serviceString on port $port.") return (service, port) } catch { case e: Exception if isBindCollision(e) => if (offset >= maxRetries) { val exceptionMessage = s"${e.getMessage}: Service$serviceString failed after " + s"$maxRetries retries! Consider explicitly setting the appropriate port for the " + s"service$serviceString (for example spark.ui.port for SparkUI) to an available " + "port or increasing spark.port.maxRetries." val exception = new BindException(exceptionMessage) // restore original stack trace exception.setStackTrace(e.getStackTrace) throw exception } logWarning(s"Service$serviceString could not bind on port $tryPort. " + s"Attempting port ${tryPort + 1}.") } } // Should never happen throw new SparkException(s"Failed to start service$serviceString on port $startPort") }

现在我们可以分析一下用于启动Akka的函数doCreateActorSystem的源码，该源码同样在AkkaUtils.scala中

 private def doCreateActorSystem(
      name: String,
      host: String,
      port: Int,
      conf: SparkConf,
      securityManager: SecurityManager): (ActorSystem, Int) = {
//对conf中的一些参数进行设置
    val akkaThreads = conf.getInt("spark.akka.threads", 4)
    val akkaBatchSize = conf.getInt("spark.akka.batchSize", 15)
    val akkaTimeoutS = conf.getTimeAsSeconds("spark.akka.timeout",
      conf.get("spark.network.timeout", "120s"))
    val akkaFrameSize = maxFrameSizeBytes(conf)
    val akkaLogLifecycleEvents = conf.getBoolean("spark.akka.logLifecycleEvents", false)
    val lifecycleEvents = if (akkaLogLifecycleEvents) "on" else "off"
    if (!akkaLogLifecycleEvents) {
      // As a workaround for Akka issue #3787, we coerce the "EndpointWriter" log to be silent.
      // See: https://www.assembla.com/spaces/akka/tickets/3787#/
      Option(Logger.getLogger("akka.remote.EndpointWriter")).map(l => l.setLevel(Level.FATAL))
    }

    val logAkkaConfig = if (conf.getBoolean("spark.akka.logAkkaConfig", false)) "on" else "off"

    val akkaHeartBeatPausesS = conf.getTimeAsSeconds("spark.akka.heartbeat.pauses", "6000s")
    val akkaHeartBeatIntervalS = conf.getTimeAsSeconds("spark.akka.heartbeat.interval", "1000s")

    val secretKey = securityManager.getSecretKey()
    val isAuthOn = securityManager.isAuthenticationEnabled()
    if (isAuthOn && secretKey == null) {
      throw new Exception("Secret key is null with authentication on")
    }
    val requireCookie = if (isAuthOn) "on" else "off"
    val secureCookie = if (isAuthOn) secretKey else ""
    logDebug(s"In createActorSystem, requireCookie is: $requireCookie")

    val akkaSslConfig = securityManager.akkaSSLOptions.createAkkaConfig
        .getOrElse(ConfigFactory.empty())

    val akkaConf = ConfigFactory.parseMap(conf.getAkkaConf.toMap.asJava)
      .withFallback(akkaSslConfig).withFallback(ConfigFactory.parseString(
      s"""
      |akka.daemonic = on
      |akka.loggers = [""akka.event.slf4j.Slf4jLogger""]
      |akka.stdout-loglevel = "ERROR"
      |akka.jvm-exit-on-fatal-error = off
      |akka.remote.require-cookie = "$requireCookie"
      |akka.remote.secure-cookie = "$secureCookie"
      |akka.remote.transport-failure-detector.heartbeat-interval = $akkaHeartBeatIntervalS s
      |akka.remote.transport-failure-detector.acceptable-heartbeat-pause = $akkaHeartBeatPausesS s
      |akka.actor.provider = "akka.remote.RemoteActorRefProvider"
      |akka.remote.netty.tcp.transport-class = "akka.remote.transport.netty.NettyTransport"
      |akka.remote.netty.tcp.hostname = "$host"
      |akka.remote.netty.tcp.port = $port
      |akka.remote.netty.tcp.tcp-nodelay = on
      |akka.remote.netty.tcp.connection-timeout = $akkaTimeoutS s
      |akka.remote.netty.tcp.maximum-frame-size = ${akkaFrameSize}B
      |akka.remote.netty.tcp.execution-pool-size = $akkaThreads
      |akka.actor.default-dispatcher.throughput = $akkaBatchSize
      |akka.log-config-on-start = $logAkkaConfig
      |akka.remote.log-remote-lifecycle-events = $lifecycleEvents
      |akka.log-dead-letters = $lifecycleEvents
      |akka.log-dead-letters-during-shutdown = $lifecycleEvents
      """.stripMargin))
//创建ActorSystem对象
 val actorSystem = ActorSystem(name, akkaConf) val provider = actorSystem.asInstanceOf[ExtendedActorSystem].provider val boundPort = provider.getDefaultAddress.port.get
//返回（ActorSystem，int）元组
 (actorSystem, boundPort) }

以上，我们通过源码分析追踪了Spark通过ActorSystem的构造器创建ActorSystem对象的整个过程。