Github user joseph-torres commented on a diff in the pull request:
https://github.com/apache/spark/pull/19925#discussion_r156540689
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/continuous/ContinuousRateStreamSource.scala
---
@@ -0,0 +1,155 @@
+/*
+ * 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 scala.collection.JavaConverters._
+
+import org.json4s.DefaultFormats
+import org.json4s.jackson.Serialization
+
+import org.apache.spark.sql.Row
+import org.apache.spark.sql.catalyst.expressions.UnsafeRow
+import org.apache.spark.sql.catalyst.util.DateTimeUtils
+import org.apache.spark.sql.execution.streaming._
+import org.apache.spark.sql.sources.v2.{ContinuousReadSupport,
DataSourceV2, DataSourceV2Options}
+import org.apache.spark.sql.sources.v2.reader._
+import org.apache.spark.sql.types.{LongType, StructField, StructType,
TimestampType}
+
+object ContinuousRateStreamSource {
+ val NUM_PARTITIONS = "numPartitions"
+ val ROWS_PER_SECOND = "rowsPerSecond"
+}
+
+case class ContinuousRateStreamOffset(partitionToStartValue: Map[Int,
Long]) extends Offset {
+ implicit val defaultFormats: DefaultFormats = DefaultFormats
+ override val json = Serialization.write(partitionToStartValue)
+}
+
+case class ContinuousRateStreamPartitionOffset(partition: Int, start:
Long) extends PartitionOffset
+
+class ContinuousRateStreamReader(options: DataSourceV2Options)
+ extends ContinuousReader {
+ implicit val defaultFormats: DefaultFormats = DefaultFormats
+
+ val numPartitions =
options.get(ContinuousRateStreamSource.NUM_PARTITIONS).orElse("5").toInt
+ val rowsPerSecond =
options.get(ContinuousRateStreamSource.ROWS_PER_SECOND).orElse("6").toLong
+
+ override def mergeOffsets(offsets: Array[PartitionOffset]): Offset = {
+ assert(offsets.length == numPartitions)
+ val tuples = offsets.map {
+ case ContinuousRateStreamPartitionOffset(p, s) => p -> s
+ }
+ ContinuousRateStreamOffset(Map(tuples: _*))
+ }
+
+ override def deserializeOffset(json: String): Offset = {
+ ContinuousRateStreamOffset(Serialization.read[Map[Int, Long]](json))
+ }
+
+ override def readSchema(): StructType = {
+ StructType(
+ StructField("timestamp", TimestampType, false) ::
+ StructField("value", LongType, false) :: Nil)
+ }
+
+ private var offset: java.util.Optional[Offset] = _
+
+ override def setOffset(offset: java.util.Optional[Offset]): Unit = {
+ this.offset = offset
+ }
+
+ override def getStartOffset(): Offset = offset.get()
+
+ override def createReadTasks(): java.util.List[ReadTask[Row]] = {
+ val partitionStartMap = Option(offset.orElse(null)).map {
+ case o: ContinuousRateStreamOffset => o.partitionToStartValue
+ case s: SerializedOffset => Serialization.read[Map[Int,
Long]](s.json)
+ case _ => throw new IllegalArgumentException("invalid offset type
for ContinuousRateSource")
+ }
+ if (partitionStartMap.exists(_.keySet.size > numPartitions)) {
+ throw new IllegalArgumentException("Start offset contained too many
partitions.")
+ }
+ val perPartitionRate = rowsPerSecond.toDouble / numPartitions.toDouble
+
+ Range(0, numPartitions).map { n =>
+ // If the offset doesn't have a value for this partition, start from
the beginning.
+ val start = partitionStartMap.flatMap(_.get(n)).getOrElse(0L + n)
+ // Have each partition advance by numPartitions each row, with
starting points staggered
+ // by their partition index.
+ RateStreamReadTask(start, n, numPartitions, perPartitionRate)
+ .asInstanceOf[ReadTask[Row]]
+ }.asJava
+ }
+
+ override def commit(end: Offset): Unit = {}
+ override def stop(): Unit = {}
+
+}
+
+case class RateStreamReadTask(
+ startValue: Long, partitionIndex: Int, increment: Long, rowsPerSecond:
Double)
+ extends ReadTask[Row] {
+ override def createDataReader(): DataReader[Row] =
+ new RateStreamDataReader(startValue, partitionIndex, increment,
rowsPerSecond.toLong)
+}
+
+class RateStreamDataReader(
+ startValue: Long, partitionIndex: Int, increment: Long, rowsPerSecond:
Long)
+ extends ContinuousDataReader[Row] {
+ private var nextReadTime = 0L
+ private var numReadRows = 0L
+
+ private var currentValue = startValue
+ private var currentRow: Row = null
+
+ override def next(): Boolean = {
+ // Set the timestamp for the first time.
+ if (currentRow == null) nextReadTime = System.currentTimeMillis() +
1000
+
+ if (numReadRows == rowsPerSecond) {
+ // Sleep until we reach the next second.
+
+ try {
+ while (System.currentTimeMillis < nextReadTime) {
+ Thread.sleep(nextReadTime - System.currentTimeMillis)
+ }
+ } catch {
+ case _: InterruptedException =>
+ // Someone's trying to end the task; just let them.
+ return false
+ }
+ numReadRows = 0
+ nextReadTime += 1000
+ }
+
+ currentRow = Row(
+
DateTimeUtils.toJavaTimestamp(DateTimeUtils.fromMillis(System.currentTimeMillis)),
+ currentValue)
+ currentValue += increment
+ numReadRows += 1
+
+ true
+ }
+
+ override def get: Row = currentRow
+
+ override def close(): Unit = {}
+
+ override def getOffset(): PartitionOffset =
+ ContinuousRateStreamPartitionOffset(partitionIndex, currentValue -
increment)
--- End diff --
(Your comment made me relalize there was a fencepost error here, which I'll
swap some things around to fix.)
getOffset(), like get(), is supposed to be paired with next() in a
pseudo-iterator and non-thread-safe manner. It'd be incorrect for a caller to
look for getOffset() to be correct after a failed next() call.
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