Github user mengxr commented on a diff in the pull request:
https://github.com/apache/spark/pull/21898#discussion_r207442439
--- Diff: core/src/main/scala/org/apache/spark/BarrierCoordinator.scala ---
@@ -0,0 +1,199 @@
+/*
+ * 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.concurrent.atomic.AtomicInteger
+
+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}
+
+/**
+ * A coordinator that handles all global sync requests from
BarrierTaskContext. Each global sync
+ * request is generated by `BarrierTaskContext.barrier()`, and identified
by
+ * stageId + stageAttemptId + barrierEpoch. Reply all the blocking global
sync requests upon
+ * received all the requests for a group of `barrier()` calls. If the
coordinator doesn't collect
+ * enough global sync requests within a configured time, fail all the
requests due to timeout.
+ */
+private[spark] class BarrierCoordinator(
+ timeout: Int,
+ listenerBus: LiveListenerBus,
+ override val rpcEnv: RpcEnv) extends ThreadSafeRpcEndpoint with
Logging {
+
+ private val timer = new Timer("BarrierCoordinator barrier epoch
increment timer")
+
+ private val listener = new SparkListener {
+ override def onStageCompleted(stageCompleted:
SparkListenerStageCompleted): Unit = {
+ val stageInfo = stageCompleted.stageInfo
+ // Remove internal data from a finished stage attempt.
+ cleanupSyncRequests(stageInfo.stageId, stageInfo.attemptNumber)
+ barrierEpochByStageIdAndAttempt.remove((stageInfo.stageId,
stageInfo.attemptNumber))
+ }
+ }
+
+ // Epoch counter for each barrier (stage, attempt).
+ private val barrierEpochByStageIdAndAttempt = new
ConcurrentHashMap[(Int, Int), AtomicInteger]
+
+ // Remember all the blocking global sync requests for each barrier
(stage, attempt).
+ private val syncRequestsByStageIdAndAttempt =
+ new ConcurrentHashMap[(Int, Int), ArrayBuffer[RpcCallContext]]
+
+ override def onStart(): Unit = {
+ super.onStart()
+ listenerBus.addToStatusQueue(listener)
+ }
+
+ /**
+ * Get the array of [[RpcCallContext]]s that correspond to a barrier
sync request from a stage
+ * attempt.
+ */
+ private def getOrInitSyncRequests(
+ stageId: Int,
+ stageAttemptId: Int,
+ numTasks: Int = 0): ArrayBuffer[RpcCallContext] = {
+ val requests = syncRequestsByStageIdAndAttempt.putIfAbsent((stageId,
stageAttemptId),
+ new ArrayBuffer[RpcCallContext](numTasks))
+ if (requests == null) {
+ syncRequestsByStageIdAndAttempt.get((stageId, stageAttemptId))
+ } else {
+ requests
+ }
+ }
+
+ /**
+ * Clean up the array of [[RpcCallContext]]s that correspond to a
barrier sync request from a
+ * stage attempt.
+ */
+ private def cleanupSyncRequests(stageId: Int, stageAttemptId: Int): Unit
= {
+ val requests = syncRequestsByStageIdAndAttempt.remove((stageId,
stageAttemptId))
+ if (requests != null) {
+ requests.clear()
--- End diff --
Agree with @cloud-fan that this is not necessary. It only explicitly clears
the ArrayBuffer object instead of the contexts.
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