private[scheduler] class DAGSchedulerEventProcessLoop(dagScheduler: DAGScheduler)
extends EventLoop[DAGSchedulerEvent]("dag-scheduler-event-loop") with Logging {
private[this] val timer = dagScheduler.metricsSource.messageProcessingTimer
/**
* The main event loop of the DAG scheduler.
*/
override def onReceive(event: DAGSchedulerEvent): Unit = {
val timerContext = timer.time()
try {
doOnReceive(event)
} finally {
timerContext.stop()
}
}
private def doOnReceive(event: DAGSchedulerEvent): Unit = event match {
case JobSubmitted(jobId, rdd, func, partitions, callSite, listener, properties) =>
dagScheduler.handleJobSubmitted(jobId, rdd, func, partitions, callSite, listener, properties)
case MapStageSubmitted(jobId, dependency, callSite, listener, properties) =>
dagScheduler.handleMapStageSubmitted(jobId, dependency, callSite, listener, properties)
case StageCancelled(stageId) =>
dagScheduler.handleStageCancellation(stageId)
case JobCancelled(jobId) =>
dagScheduler.handleJobCancellation(jobId)
case JobGroupCancelled(groupId) =>
dagScheduler.handleJobGroupCancelled(groupId)
case AllJobsCancelled =>
dagScheduler.doCancelAllJobs()
case ExecutorAdded(execId, host) =>
dagScheduler.handleExecutorAdded(execId, host)
case ExecutorLost(execId) =>
dagScheduler.handleExecutorLost(execId, fetchFailed = false)
case BeginEvent(task, taskInfo) =>
dagScheduler.handleBeginEvent(task, taskInfo)
case GettingResultEvent(taskInfo) =>
dagScheduler.handleGetTaskResult(taskInfo)
case completion @ CompletionEvent(task, reason, _, _, taskInfo, taskMetrics) =>
dagScheduler.handleTaskCompletion(completion)
case TaskSetFailed(taskSet, reason, exception) =>
dagScheduler.handleTaskSetFailed(taskSet, reason, exception)
case ResubmitFailedStages =>
dagScheduler.resubmitFailedStages()
}
override def onError(e: Throwable): Unit = {
logError("DAGSchedulerEventProcessLoop failed; shutting down SparkContext", e)
try {
dagScheduler.doCancelAllJobs()
} catch {
case t: Throwable => logError("DAGScheduler failed to cancel all jobs.", t)
}
dagScheduler.sc.stop()
}
override def onStop(): Unit = {
// Cancel any active jobs in postStop hook
dagScheduler.cleanUpAfterSchedulerStop()
}
}
EventLoop.scala
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.spark.util
import java.util.concurrent.atomic.AtomicBoolean
import java.util.concurrent.{BlockingQueue, LinkedBlockingDeque}
import scala.util.control.NonFatal
import org.apache.spark.Logging
/**
* An event loop to receive events from the caller and process all events in the event thread. It
* will start an exclusive event thread to process all events.
*
* Note: The event queue will grow indefinitely. So subclasses should make sure `onReceive` can
* handle events in time to avoid the potential OOM.
*/
private[spark] abstract class EventLoop[E](name: String) extends Logging {
private val eventQueue: BlockingQueue[E] = new LinkedBlockingDeque[E]()
private val stopped = new AtomicBoolean(false)
private val eventThread = new Thread(name) {
setDaemon(true)
override def run(): Unit = {
try {
while (!stopped.get) {
val event = eventQueue.take()
try {
onReceive(event)
} catch {
case NonFatal(e) => {
try {
onError(e)
} catch {
case NonFatal(e) => logError("Unexpected error in " + name, e)
}
}
}
}
} catch {
case ie: InterruptedException => // exit even if eventQueue is not empty
case NonFatal(e) => logError("Unexpected error in " + name, e)
}
}
}
def start(): Unit = {
if (stopped.get) {
throw new IllegalStateException(name + " has already been stopped")
}
// Call onStart before starting the event thread to make sure it happens before onReceive
onStart()
eventThread.start()
}
def stop(): Unit = {
if (stopped.compareAndSet(false, true)) {
eventThread.interrupt()
var onStopCalled = false
try {
eventThread.join()
// Call onStop after the event thread exits to make sure onReceive happens before onStop
onStopCalled = true
onStop()
} catch {
case ie: InterruptedException =>
Thread.currentThread().interrupt()
if (!onStopCalled) {
// ie is thrown from `eventThread.join()`. Otherwise, we should not call `onStop` since
// it's already called.
onStop()
}
}
} else {
// Keep quiet to allow calling `stop` multiple times.
}
}
/**
* Put the event into the event queue. The event thread will process it later.
*/
def post(event: E): Unit = {
eventQueue.put(event)
}
/**
* Return if the event thread has already been started but not yet stopped.
*/
def isActive: Boolean = eventThread.isAlive
/**
* Invoked when `start()` is called but before the event thread starts.
*/
protected def onStart(): Unit = {}
/**
* Invoked when `stop()` is called and the event thread exits.
*/
protected def onStop(): Unit = {}
/**
* Invoked in the event thread when polling events from the event queue.
*
* Note: Should avoid calling blocking actions in `onReceive`, or the event thread will be blocked
* and cannot process events in time. If you want to call some blocking actions, run them in
* another thread.
*/
protected def onReceive(event: E): Unit
/**
* Invoked if `onReceive` throws any non fatal error. Any non fatal error thrown from `onError`
* will be ignored.
*/
protected def onError(e: Throwable): Unit
}
