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/*
 * 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 spark.scheduler

import spark.scheduler.cluster.Pool
import spark.scheduler.cluster.SchedulingMode.SchedulingMode
/**
 * Low-level task scheduler interface, implemented by both ClusterScheduler and LocalScheduler.
 * These schedulers get sets of tasks submitted to them from the DAGScheduler for each stage,
 * and are responsible for sending the tasks to the cluster, running them, retrying if there
 * are failures, and mitigating stragglers. They return events to the DAGScheduler through
 * the TaskSchedulerListener interface.
 */
private[spark] trait TaskScheduler {

  def rootPool: Pool

  def schedulingMode: SchedulingMode

  def start(): Unit

  // Invoked after system has successfully initialized (typically in spark context).
  // Yarn uses this to bootstrap allocation of resources based on preferred locations, wait for slave registerations, etc.
  def postStartHook() { }

  // Disconnect from the cluster.
  def stop(): Unit

  // Submit a sequence of tasks to run.
  def submitTasks(taskSet: TaskSet): Unit

  // Set a listener for upcalls. This is guaranteed to be set before submitTasks is called.
  def setListener(listener: TaskSchedulerListener): Unit

  // Get the default level of parallelism to use in the cluster, as a hint for sizing jobs.
  def defaultParallelism(): Int
}