Github user mengxr commented on a diff in the pull request:
https://github.com/apache/spark/pull/21898#discussion_r206707800
--- Diff: core/src/main/scala/org/apache/spark/BarrierCoordinator.scala ---
@@ -0,0 +1,184 @@
+/*
+ * 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 scala.collection.mutable.{ArrayBuffer, HashMap}
+
+import org.apache.spark.internal.Logging
+import org.apache.spark.rpc.{RpcCallContext, RpcEnv, ThreadSafeRpcEndpoint}
+
+class BarrierCoordinator(
+ timeout: Long,
+ override val rpcEnv: RpcEnv) extends ThreadSafeRpcEndpoint with
Logging {
+
+ private val timer = new Timer("BarrierCoordinator barrier epoch
increment timer")
+
+ // Barrier epoch for each stage attempt, fail a sync request if the
barrier epoch in the request
+ // mismatches the barrier epoch in the coordinator.
+ private val barrierEpochByStageIdAndAttempt = new HashMap[Int,
HashMap[Int, Int]]
+
+ // Any access to this should be synchronized.
+ private val syncRequestsByStageIdAndAttempt =
+ new HashMap[Int, HashMap[Int, ArrayBuffer[RpcCallContext]]]
+
+ /**
+ * 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] = synchronized {
+ val syncRequestsByStage = syncRequestsByStageIdAndAttempt
+ .getOrElseUpdate(stageId, new HashMap[Int,
ArrayBuffer[RpcCallContext]])
+ syncRequestsByStage.getOrElseUpdate(stageAttemptId, new
ArrayBuffer[RpcCallContext](numTasks))
+ }
+
+ /**
+ * 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
= synchronized {
+ syncRequestsByStageIdAndAttempt.get(stageId).foreach {
syncRequestByStage =>
+ syncRequestByStage.get(stageAttemptId).foreach { syncRequests =>
+ syncRequests.clear()
+ }
+ syncRequestByStage -= stageAttemptId
+ if (syncRequestByStage.isEmpty) {
+ syncRequestsByStageIdAndAttempt -= stageId
+ }
+ logInfo(s"Removed all the pending barrier sync requests from Stage
$stageId(Attempt " +
+ s"$stageAttemptId).")
+ }
+ }
+
+ /**
+ * Get the barrier epoch that correspond to a barrier sync request from
a stage attempt.
+ */
+ private def getOrInitBarrierEpoch(stageId: Int, stageAttemptId: Int):
Int = synchronized {
--- End diff --
Ditto: one-liner with logging.
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