Github user brad-kaiser commented on a diff in the pull request:

    https://github.com/apache/spark/pull/19041#discussion_r179551630
  
    --- Diff: core/src/main/scala/org/apache/spark/CacheRecoveryManager.scala 
---
    @@ -0,0 +1,201 @@
    +/*
    + * 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.concurrent.TimeUnit
    +
    +import scala.collection.JavaConverters._
    +import scala.concurrent.{ExecutionContext, Future, Promise}
    +import scala.util.Failure
    +
    +import com.google.common.cache.CacheBuilder
    +
    +import org.apache.spark.CacheRecoveryManager.{DoneRecovering, KillReason, 
Timeout}
    +import org.apache.spark.internal.Logging
    +import 
org.apache.spark.internal.config.DYN_ALLOCATION_CACHE_RECOVERY_TIMEOUT
    +import org.apache.spark.rpc.RpcEndpointRef
    +import org.apache.spark.storage.BlockManagerId
    +import org.apache.spark.storage.BlockManagerMessages._
    +import org.apache.spark.util.ThreadUtils
    +
    +/**
    + * Responsible for asynchronously replicating all of an executor's cached 
blocks, and then shutting
    + * it down.
    + */
    +private class CacheRecoveryManager(
    +    blockManagerMasterEndpoint: RpcEndpointRef,
    +    executorAllocationManager: ExecutorAllocationManager,
    +    conf: SparkConf)
    +  extends Logging {
    +
    +  private val forceKillAfterS = 
conf.get(DYN_ALLOCATION_CACHE_RECOVERY_TIMEOUT)
    +  private val threadPool = 
ThreadUtils.newDaemonCachedThreadPool("cache-recovery-manager-pool")
    +  private implicit val asyncExecutionContext = 
ExecutionContext.fromExecutorService(threadPool)
    +  private val scheduler =
    +    
ThreadUtils.newDaemonSingleThreadScheduledExecutor("cache-recovery-shutdown-timers")
    +  private val recoveringExecutors = CacheBuilder.newBuilder()
    +    .expireAfterWrite(forceKillAfterS * 2, TimeUnit.SECONDS)
    +    .build[String, String]()
    +
    +  /**
    +   * Start the recover cache shutdown process for these executors
    +   *
    +   * @param execIds the executors to start shutting down
    +   * @return a sequence of futures of Unit that will complete once the 
executor has been killed.
    +   */
    +  def startCacheRecovery(execIds: Seq[String]): Future[Seq[KillReason]] = {
    +    logDebug(s"Recover cached data before shutting down executors 
${execIds.mkString(", ")}.")
    +    val canBeRecovered: Future[Seq[String]] = checkMem(execIds)
    +
    +    canBeRecovered.flatMap { execIds =>
    +      execIds.foreach { execId => recoveringExecutors.put(execId, execId) }
    +      Future.sequence(execIds.map { replicateUntilTimeoutThenKill })
    +    }
    +  }
    +
    +  def replicateUntilTimeoutThenKill(execId: String): Future[KillReason] = {
    +    val timeoutFuture = returnAfterTimeout(Timeout, forceKillAfterS)
    +    val replicationFuture = replicateUntilDone(execId)
    +
    +    Future.firstCompletedOf(List(timeoutFuture, 
replicationFuture)).andThen {
    --- End diff --
    
    Ah, so my original thought was that whatever future finished first, the 
replication future or the timeout future, the other would complete harmlessly 
in the background. I didn't realize that the future returned by 
firstCompletedOf wouldn't complete until both were done. I will fix this. Thanks


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