Github user liyinan926 commented on a diff in the pull request:

    https://github.com/apache/spark/pull/21366#discussion_r190398282
  
    --- Diff: 
resource-managers/kubernetes/core/src/main/scala/org/apache/spark/scheduler/cluster/k8s/ExecutorPodsEventHandler.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.scheduler.cluster.k8s
    +
    +import java.util.concurrent.{Future, LinkedBlockingQueue, 
ScheduledExecutorService, TimeUnit}
    +import java.util.concurrent.atomic.{AtomicInteger, AtomicLong}
    +
    +import io.fabric8.kubernetes.api.model.{Pod, PodBuilder}
    +import io.fabric8.kubernetes.client.KubernetesClient
    +import scala.collection.JavaConverters._
    +import scala.collection.mutable
    +
    +import org.apache.spark.{SparkConf, SparkException}
    +import org.apache.spark.deploy.k8s.Config._
    +import org.apache.spark.deploy.k8s.Constants._
    +import org.apache.spark.deploy.k8s.KubernetesConf
    +import org.apache.spark.internal.Logging
    +import org.apache.spark.scheduler.ExecutorExited
    +import org.apache.spark.util.Utils
    +
    +private[spark] class ExecutorPodsEventHandler(
    +    conf: SparkConf,
    +    executorBuilder: KubernetesExecutorBuilder,
    +    kubernetesClient: KubernetesClient,
    +    eventProcessorExecutor: ScheduledExecutorService) extends Logging {
    +
    +  import ExecutorPodsEventHandler._
    +
    +  private val EXECUTOR_ID_COUNTER = new AtomicLong(0L)
    +
    +  private val totalExpectedExecutors = new AtomicInteger(0)
    +
    +  private val eventQueue = new LinkedBlockingQueue[Seq[Pod]]()
    +
    +  private val podAllocationSize = 
conf.get(KUBERNETES_ALLOCATION_BATCH_SIZE)
    +
    +  private val podAllocationDelay = 
conf.get(KUBERNETES_ALLOCATION_BATCH_DELAY)
    +
    +  private val kubernetesDriverPodName = conf
    +    .get(KUBERNETES_DRIVER_POD_NAME)
    +    .getOrElse(throw new SparkException("Must specify the driver pod 
name"))
    +
    +  private val driverPod = kubernetesClient.pods()
    +    .withName(kubernetesDriverPodName)
    +    .get()
    +
    +  // Use sets of ids instead of counters to be able to handle duplicate 
events.
    +
    +  // Executor IDs that have been requested from Kubernetes but are not 
running yet.
    +  private val pendingExecutors = mutable.Set.empty[Long]
    +
    +  // We could use CoarseGrainedSchedulerBackend#totalRegisteredExecutors 
here for tallying the
    +  // executors that are running. But, here we choose instead to maintain 
all state within this
    +  // class from the persecptive of the k8s API. Therefore whether or not 
this scheduler loop
    +  // believes an executor is running is dictated by the K8s API rather 
than Spark's RPC events.
    +  // We may need to consider where these perspectives may differ and which 
perspective should
    +  // take precedence.
    +  private val runningExecutors = mutable.Set.empty[Long]
    +
    +  private var eventProcessorFuture: Future[_] = _
    +
    +  def start(applicationId: String, schedulerBackend: 
KubernetesClusterSchedulerBackend): Unit = {
    +    require(eventProcessorFuture == null, "Cannot start event processing 
twice.")
    +    logInfo(s"Starting Kubernetes executor pods event handler for 
application with" +
    +      s" id $applicationId.")
    +    val eventProcessor = new Runnable {
    +      override def run(): Unit = {
    +        Utils.tryLogNonFatalError {
    +          processEvents(applicationId, schedulerBackend)
    +        }
    +      }
    +    }
    +    eventProcessorFuture = eventProcessorExecutor.scheduleWithFixedDelay(
    +      eventProcessor, 0L, podAllocationDelay, TimeUnit.MILLISECONDS)
    +  }
    +
    +  def stop(): Unit = {
    +    if (eventProcessorFuture != null) {
    +      eventProcessorFuture.cancel(true)
    +      eventProcessorFuture = null
    +    }
    +  }
    +
    +  private def processEvents(
    +      applicationId: String, schedulerBackend: 
KubernetesClusterSchedulerBackend) {
    +    val currentEvents = new 
java.util.ArrayList[Seq[Pod]](eventQueue.size())
    +    eventQueue.drainTo(currentEvents)
    +    currentEvents.asScala.flatten.foreach { updatedPod =>
    +      val execId = 
updatedPod.getMetadata.getLabels.get(SPARK_EXECUTOR_ID_LABEL).toLong
    +      val podPhase = updatedPod.getStatus.getPhase.toLowerCase
    +      if (isDeleted(updatedPod)) {
    +        removeExecutorFromSpark(schedulerBackend, updatedPod, execId)
    +      } else {
    +        updatedPod.getStatus.getPhase.toLowerCase match {
    +          case "running" =>
    +            // If clause is for resililence to out of order operations - 
executor must be
    +            // pending and first reach running. Without this check you may 
e.g. process a
    +            // deletion event followed by some arbitrary modification 
event - we want the
    +            // deletion event to "stick".
    +            if (pendingExecutors.contains(execId)) {
    +              pendingExecutors.remove(execId)
    +              runningExecutors.add(execId)
    +            }
    +          // TODO (SPARK-24135) - handle more classes of errors
    +          case "error" | "failed" | "succeeded" =>
    +            // If deletion failed on a previous try, we can try again if 
resync informs us the pod
    +            // is still around.
    +            // Delete as best attempt - duplicate deletes will throw an 
exception but the end state
    +            // of getting rid of the pod is what matters.
    +            if (!isDeleted(updatedPod)) {
    +              Utils.tryLogNonFatalError {
    +                kubernetesClient
    +                  .pods()
    +                  .withName(updatedPod.getMetadata.getName)
    +                  .delete()
    +              }
    +            }
    +            removeExecutorFromSpark(schedulerBackend, updatedPod, execId)
    +        }
    +      }
    +    }
    +
    +    val currentRunningExecutors = runningExecutors.size
    --- End diff --
    
    Sounds good to me.


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