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From cloud-fan <...@git.apache.org>
Subject [GitHub] spark pull request #21898: [SPARK-24817][Core] Implement BarrierTaskContext....
Date Thu, 02 Aug 2018 04:16:22 GMT
Github user cloud-fan commented on a diff in the pull request:

    https://github.com/apache/spark/pull/21898#discussion_r207097401
  
    --- Diff: core/src/main/scala/org/apache/spark/BarrierCoordinator.scala ---
    @@ -0,0 +1,199 @@
    +/*
    + * 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))
    +    }
    +  }
    +
    +  // Epoch counter for each barrier (stage, attempt).
    +  private val barrierEpochByStageIdAndAttempt = new ConcurrentHashMap[(Int, Int), AtomicInteger]
    +
    +  // Remember all the blocking global sync requests for each barrier (stage, attempt).
    +  private val syncRequestsByStageIdAndAttempt =
    +    new ConcurrentHashMap[(Int, Int), ArrayBuffer[RpcCallContext]]
    +
    +  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 = 0): ArrayBuffer[RpcCallContext] = {
    +    val requests = syncRequestsByStageIdAndAttempt.putIfAbsent((stageId, stageAttemptId),
    +      new ArrayBuffer[RpcCallContext](numTasks))
    +    if (requests == null) {
    +      syncRequestsByStageIdAndAttempt.get((stageId, stageAttemptId))
    +    } else {
    +      requests
    +    }
    +  }
    +
    +  /**
    +   * 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): AtomicInteger
= {
    +    val barrierEpoch = barrierEpochByStageIdAndAttempt.putIfAbsent((stageId, stageAttemptId),
    +      new AtomicInteger(0))
    +    if (barrierEpoch == null) {
    +      barrierEpochByStageIdAndAttempt.get((stageId, stageAttemptId))
    +    } else {
    +      barrierEpoch
    +    }
    +  }
    +
    +  /**
    +   * 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(()))
    +      return true
    +    }
    +
    +    false
    +  }
    +
    +
    +  override def receiveAndReply(context: RpcCallContext): PartialFunction[Any, Unit] =
{
    +    case RequestToSync(numTasks, stageId, stageAttemptId, taskAttemptId, barrierEpoch)
=>
    +      // 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.get() != 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)
    +        // 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) {
    +          timer.schedule(new TimerTask {
    +            override def run(): Unit = {
    +              // Timeout for current barrier() call, fail all the sync requests.
    +              val requests = getOrInitSyncRequests(stageId, stageAttemptId)
    +              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.
    +              currentBarrierEpoch.set(-1)
    --- End diff --
    
    do we need to do this? if the barrier sync successes before timeout, the epoch data will
be removed from `barrierEpochByStageIdAndAttempt` and get GCed.


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