Github user tdas commented on a diff in the pull request:
https://github.com/apache/spark/pull/21200#discussion_r185369742
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/continuous/EpochPollRunnable.scala
---
@@ -0,0 +1,61 @@
+/*
+ * 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.sql.execution.streaming.continuous
+
+import java.util.concurrent.BlockingQueue
+import java.util.concurrent.atomic.AtomicBoolean
+
+import org.apache.spark.{SparkEnv, TaskContext}
+import org.apache.spark.internal.Logging
+import org.apache.spark.sql.catalyst.expressions.UnsafeRow
+import org.apache.spark.sql.sources.v2.reader.streaming.PartitionOffset
+
+/**
+ * The epoch marker component of [[ContinuousQueuedDataReader]]. Populates
the queue with
+ * (null, null) when a new epoch marker arrives.
+ */
+class EpochPollRunnable(
+ queue: BlockingQueue[(UnsafeRow, PartitionOffset)],
+ context: TaskContext,
+ failedFlag: AtomicBoolean)
+ extends Thread with Logging {
+ private[continuous] var failureReason: Throwable = _
+
+ private val epochEndpoint = EpochCoordinatorRef.get(
+
context.getLocalProperty(ContinuousExecution.EPOCH_COORDINATOR_ID_KEY),
SparkEnv.get)
+ // Note that this is *not* the same as the currentEpoch in
[[ContinuousDataQueuedReader]]! That
+ // field represents the epoch wrt the data being processed. The
currentEpoch here is just a
+ // counter to ensure we send the appropriate number of markers if we
fall behind the driver.
+ private var currentEpoch =
context.getLocalProperty(ContinuousExecution.START_EPOCH_KEY).toLong
+
+ override def run(): Unit = {
+ try {
+ val newEpoch = epochEndpoint.askSync[Long](GetCurrentEpoch)
+ for (i <- currentEpoch to newEpoch - 1) {
--- End diff --
I strongly suggest adding more docs here to explain this logic.
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