Github user mengxr commented on a diff in the pull request:
https://github.com/apache/spark/pull/21898#discussion_r207444459
--- Diff: core/src/main/scala/org/apache/spark/BarrierCoordinator.scala ---
@@ -0,0 +1,229 @@
+/*
+ * 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
+
+import java.util.{Timer, TimerTask}
+import java.util.concurrent.ConcurrentHashMap
+import java.util.concurrent.atomic.AtomicInteger
+
+import scala.collection.mutable.ArrayBuffer
+
+import org.apache.spark.internal.Logging
+import org.apache.spark.rpc.{RpcCallContext, RpcEnv, ThreadSafeRpcEndpoint}
+import org.apache.spark.scheduler.{LiveListenerBus, SparkListener,
SparkListenerStageCompleted}
+
+/**
+ * A coordinator that handles all global sync requests from
BarrierTaskContext. Each global sync
+ * request is generated by `BarrierTaskContext.barrier()`, and identified
by
+ * stageId + stageAttemptId + barrierEpoch. Reply all the blocking global
sync requests upon
+ * received all the requests for a group of `barrier()` calls. If the
coordinator doesn't collect
+ * enough global sync requests within a configured time, fail all the
requests due to timeout.
+ */
+private[spark] class BarrierCoordinator(
+ timeout: Int,
+ listenerBus: LiveListenerBus,
+ override val rpcEnv: RpcEnv) extends ThreadSafeRpcEndpoint with
Logging {
+
+ private val timer = new Timer("BarrierCoordinator barrier epoch
increment timer")
+
+ private val listener = new SparkListener {
+ override def onStageCompleted(stageCompleted:
SparkListenerStageCompleted): Unit = {
+ val stageInfo = stageCompleted.stageInfo
+ // Remove internal data from a finished stage attempt.
+ cleanupSyncRequests(stageInfo.stageId, stageInfo.attemptNumber)
+ barrierEpochByStageIdAndAttempt.remove((stageInfo.stageId,
stageInfo.attemptNumber))
+ cancelTimerTask(stageInfo.stageId, stageInfo.attemptNumber)
+ }
+ }
+
+ // Epoch counter for each barrier (stage, attempt).
+ private val barrierEpochByStageIdAndAttempt = new
ConcurrentHashMap[(Int, Int), Int]
+
+ // Remember all the blocking global sync requests for each barrier
(stage, attempt).
+ private val syncRequestsByStageIdAndAttempt =
+ new ConcurrentHashMap[(Int, Int), ArrayBuffer[RpcCallContext]]
+
+ // Remember all the TimerTasks for each barrier (stage, attempt).
+ private val timerTaskByStageIdAndAttempt = new ConcurrentHashMap[(Int,
Int), TimerTask]
+
+ // Number of tasks for each stage.
+ private val numTasksByStage = new ConcurrentHashMap[Int, Int]
+
+ override def onStart(): Unit = {
+ super.onStart()
+ listenerBus.addToStatusQueue(listener)
+ }
+
+ /**
+ * Get the array of [[RpcCallContext]]s that correspond to a barrier
sync request from a stage
+ * attempt.
+ */
+ private def getOrInitSyncRequests(
+ stageId: Int,
+ stageAttemptId: Int,
+ numTasks: Int): ArrayBuffer[RpcCallContext] = {
+ syncRequestsByStageIdAndAttempt.putIfAbsent((stageId, stageAttemptId),
+ new ArrayBuffer[RpcCallContext](numTasks))
+ syncRequestsByStageIdAndAttempt.get((stageId, stageAttemptId))
+ }
+
+ /**
+ * Clean up the array of [[RpcCallContext]]s that correspond to a
barrier sync request from a
+ * stage attempt.
+ */
+ private def cleanupSyncRequests(stageId: Int, stageAttemptId: Int): Unit
= {
+ val requests = syncRequestsByStageIdAndAttempt.remove((stageId,
stageAttemptId))
+ if (requests != null) {
+ requests.clear()
+ }
+ logInfo(s"Removed all the pending barrier sync requests from Stage
$stageId (Attempt " +
+ s"$stageAttemptId).")
+ }
+
+ /**
+ * Get the barrier epoch that correspond to a barrier sync request from
a stage attempt.
+ */
+ private def getOrInitBarrierEpoch(stageId: Int, stageAttemptId: Int):
Int = {
+ barrierEpochByStageIdAndAttempt.putIfAbsent((stageId, stageAttemptId),
0)
+ barrierEpochByStageIdAndAttempt.get((stageId, stageAttemptId))
+ }
+
+ /**
+ * Increase the barrier epoch that correspond to a barrier sync request
from a stage attempt.
+ */
+ private def increaseBarrierEpoch(stageId: Int, stageAttemptId: Int):
Unit = {
+ val barrierEpoch =
barrierEpochByStageIdAndAttempt.getOrDefault((stageId, stageAttemptId), -1)
+ if (barrierEpoch >= 0) {
+ barrierEpochByStageIdAndAttempt.put((stageId, stageAttemptId),
barrierEpoch + 1)
+ } else {
+ // The stage attempt already finished, don't update barrier epoch.
+ }
+ }
+
+ /**
+ * Cancel TimerTask for a stage attempt.
+ */
+ private def cancelTimerTask(stageId: Int, stageAttemptId: Int): Unit = {
+ val timerTask = timerTaskByStageIdAndAttempt.get((stageId,
stageAttemptId))
+ if (timerTask != null) {
+ timerTask.cancel()
+ timerTaskByStageIdAndAttempt.remove((stageId, stageAttemptId))
+ }
+ }
+
+ /**
+ * Send failure to all the blocking barrier sync requests from a stage
attempt with proper
+ * failure message.
+ */
+ private def failAllSyncRequests(
+ syncRequests: ArrayBuffer[RpcCallContext],
+ message: String): Unit = {
+ syncRequests.foreach(_.sendFailure(new SparkException(message)))
+ }
+
+ /**
+ * Finish all the blocking barrier sync requests from a stage attempt
successfully if we
+ * have received all the sync requests.
+ */
+ private def maybeFinishAllSyncRequests(
+ syncRequests: ArrayBuffer[RpcCallContext],
+ numTasks: Int): Boolean = {
+ if (syncRequests.size == numTasks) {
+ syncRequests.foreach(_.reply(()))
+ true
+ } else {
+ false
+ }
+ }
+
+
+ override def receiveAndReply(context: RpcCallContext):
PartialFunction[Any, Unit] = {
+ case RequestToSync(numTasks, stageId, stageAttemptId, taskAttemptId,
barrierEpoch) =>
+ // Require the number of tasks is correctly set from the
BarrierTaskContext.
+ val currentNumTasks: Any = numTasksByStage.putIfAbsent(stageId,
numTasks)
+ require(currentNumTasks == null || currentNumTasks == numTasks,
"Number of tasks of " +
+ s"Stage $stageId is $numTasks from Task $taskAttemptId, previously
it was " +
+ s"$currentNumTasks.")
+
+ // Check the barrier epoch, to see which barrier() call we are
processing.
+ val currentBarrierEpoch = getOrInitBarrierEpoch(stageId,
stageAttemptId)
+ logInfo(s"Current barrier epoch for Stage $stageId (Attempt
$stageAttemptId) is" +
+ s"$currentBarrierEpoch.")
+ if (currentBarrierEpoch != barrierEpoch) {
+ context.sendFailure(new SparkException(s"The request to sync of
Stage $stageId (Attempt " +
+ s"$stageAttemptId) with barrier epoch $barrierEpoch has already
finished. Maybe task " +
+ s"$taskAttemptId is not properly killed."))
+ } else {
+ val syncRequests = getOrInitSyncRequests(stageId, stageAttemptId,
numTasks)
+ // If this is the first sync message received for a barrier()
call, init a timer to ensure
+ // we may timeout for the sync.
+ if (syncRequests.isEmpty) {
+ val timerTask = new TimerTask {
+ override def run(): Unit = {
+ // Timeout for current barrier() call, fail all the sync
requests.
+ val requests = getOrInitSyncRequests(stageId,
stageAttemptId, numTasks)
+ failAllSyncRequests(requests, "The coordinator didn't get
all barrier sync " +
+ s"requests for barrier epoch $barrierEpoch from Stage
$stageId (Attempt " +
+ s"$stageAttemptId) within ${timeout}s.")
+ cleanupSyncRequests(stageId, stageAttemptId)
+ // The global sync fails so the stage is expected to retry
another attempt, all sync
+ // messages come from current stage attempt shall fail.
+ barrierEpochByStageIdAndAttempt.put((stageId,
stageAttemptId), -1)
+ }
+ }
+ timer.schedule(timerTask, timeout * 1000)
+ timerTaskByStageIdAndAttempt.putIfAbsent((stageId,
stageAttemptId), timerTask)
+ }
+
+ syncRequests += context
--- End diff --
Is it thread safe?
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