Github user gatorsmile commented on a diff in the pull request:
https://github.com/apache/spark/pull/15541#discussion_r84590773
--- Diff: core/src/main/scala/org/apache/spark/scheduler/TaskAssigner.scala
---
@@ -0,0 +1,218 @@
+/*
+ * 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)
+}
+
+/**
+ * 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 a number of 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()/getNext() is
used by TaskScheduler
+ * to check the worker availability and retrieve current offering from
TaskAssigner.
+ *
+ * Fourth, then offerAccepted is used by TaskScheduler 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 tasks()
to
--- End diff --
`After` -> `after`
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