3.10　创建和启动ExecutorAllocationManager

ExecutorAllocationManager用于对已分配的Executor进行管理，创建和启动Executor-AllocationManager的代码如下。

private[spark] val executorAllocationManager: Option[ExecutorAllocationManager] =

    if (conf.getBoolean("spark.dynamicAllocation.enabled", false)) {

        Some(new ExecutorAllocationManager(this, listenerBus, conf))

    } else {

        None

    }

executorAllocationManager.foreach(_.start())

默认情况下不会创建ExecutorAllocationManager，可以修改属性spark.dynamicAllocation.enabled为true来创建。ExecutorAllocationManager可以设置动态分配最小Executor数量、动态分配最大Executor数量、每个Executor可以运行的Task数量等配置信息，并对配置信息进行校验。start方法将ExecutorAllocationListener加入listenerBus中，ExecutorAllocationListener通过监听listenerBus里的事件，动态添加、删除Executor。并且通过Thread不断添加Executor，遍历Executor，将超时的Executor杀掉并移除。ExecutorAllocationListener的实现与其他SparkListener类似，不再赘述。ExecutorAllocationManager的关键代码见代码清单3-47。

代码清单3-47　ExecutorAllocationManager的关键代码

private val intervalMillis: Long = 100

private var clock: Clock = new RealClock

private val listener = new ExecutorAllocationListener

def start(): Unit = {

    listenerBus.addListener(listener)

    startPolling()

}

 

private def startPolling(): Unit = {

    val t = new Thread {

        override def run(): Unit = {

            while (true) {

                try {

                    schedule()

                } catch {

                    case e: Exception => logError("Exception in dynamic executor allocation thread!", e)

                }

                Thread.sleep(intervalMillis)

            }

        }

    }

    t.setName("spark-dynamic-executor-allocation")

    t.setDaemon(true)

    t.start()

}

根据3.4.1节的内容，我们知道listenerBus内置了线程listenerThread，此线程不断从eventQueue中拉出事件对象，调用监听器的监听方法。要启动此线程，需要调用listenerBus的start方法，代码如下。

  listenerBus.start()