Github user zhzhan commented on a diff in the pull request: https://github.com/apache/spark/pull/15541#discussion_r84619023 --- Diff: core/src/main/scala/org/apache/spark/scheduler/TaskAssigner.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 + +import scala.collection.mutable.ArrayBuffer +import scala.collection.mutable.PriorityQueue +import scala.util.Random + +import org.apache.spark.internal.{config, Logging} +import org.apache.spark.SparkConf +import org.apache.spark.util.Utils + +/** Tracks the current state of the workers with available cores and assigned task list. */ +private[scheduler] class OfferState(val workOffer: WorkerOffer) { + /** The current remaining cores that can be allocated to tasks. */ + var coresAvailable: Int = workOffer.cores + /** The list of tasks that are assigned to this WorkerOffer. */ + val tasks = new ArrayBuffer[TaskDescription](coresAvailable) + + def assignTask(task: TaskDescription, cpu: Int): Unit = { + tasks += task + coresAvailable -= cpu + assert(coresAvailable >= 0) + } +} + +/** + * TaskAssigner is the base class for all task assigner implementations, and can be + * extended to implement different task scheduling algorithms. + * Together with [[org.apache.spark.scheduler.TaskScheduler TaskScheduler]], TaskAssigner + * is used to assign tasks to workers with available cores. Internally, when TaskScheduler + * performs task assignment given available workers, it first sorts the candidate tasksets, + * and then for each taskset, it takes multiple rounds to request TaskAssigner for task + * assignment with different locality restrictions until there is either no qualified + * workers or no valid tasks to be assigned. + * + * TaskAssigner is responsible to maintain the worker availability state and task assignment + * information. The contract between [[org.apache.spark.scheduler.TaskScheduler TaskScheduler]] + * and TaskAssigner is as follows. + * + * First, TaskScheduler invokes construct() of TaskAssigner to initialize the its internal + * worker states at the beginning of resource offering. + * + * Second, before each round of task assignment for a taskset, TaskScheduler invokes the init() + * of TaskAssigner to initialize the data structure for the round. + * + * Third, when performing real task assignment, hasNext/next() is used by TaskScheduler + * to check the worker availability and retrieve current offering from TaskAssigner. + * + * Fourth, TaskScheduler calls offerAccepted() to notify the TaskAssigner so that + * TaskAssigner can decide whether the current offer is valid or not for the next request. + * + * Fifth, after task assignment is done, TaskScheduler invokes the function tasks to + * retrieve all the task assignment information. + */ + +private[scheduler] sealed abstract class TaskAssigner { + protected var offer: Seq[OfferState] = _ + protected var cpuPerTask = 1 + + protected def withCpuPerTask(cpuPerTask: Int): TaskAssigner = { + this.cpuPerTask = cpuPerTask --- End diff -- You mean cpuPerTask >= 1? I don't think we need this check.
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