Github user jiangxb1987 commented on a diff in the pull request: https://github.com/apache/spark/pull/21898#discussion_r207736706 --- Diff: core/src/main/scala/org/apache/spark/BarrierCoordinator.scala --- @@ -0,0 +1,225 @@ +/* + * 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.{Timer, TimerTask} +import java.util.concurrent.ConcurrentHashMap +import java.util.function.Consumer + +import scala.collection.mutable.ArrayBuffer + +import org.apache.spark.internal.Logging +import org.apache.spark.rpc.{RpcCallContext, RpcEnv, ThreadSafeRpcEndpoint} +import org.apache.spark.scheduler.{LiveListenerBus, SparkListener, SparkListenerStageCompleted} + +/** + * Only one barrier() call shall happen on a barrier stage attempt at each time, we can use + * (stageId, stageAttemptId) to identify the stage attempt where the barrier() call is from. --- End diff -- Actually, a barrier stage attempt can trigger multiple barrier() calls, but only one call can be active at any time.
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