Github user tdas commented on a diff in the pull request:
https://github.com/apache/spark/pull/20828#discussion_r179603916
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/continuous/ContinuousMemoryStream.scala
---
@@ -0,0 +1,212 @@
+/*
+ * 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 => ju}
+import java.util.Optional
+import java.util.concurrent.ArrayBlockingQueue
+import javax.annotation.concurrent.GuardedBy
+
+import scala.collection.JavaConverters._
+import scala.collection.mutable.ListBuffer
+import scala.reflect.ClassTag
+
+import org.json4s.NoTypeHints
+import org.json4s.jackson.Serialization
+
+import org.apache.spark.SparkEnv
+import org.apache.spark.internal.Logging
+import org.apache.spark.rpc.{RpcCallContext, RpcEndpointRef, RpcEnv,
ThreadSafeRpcEndpoint}
+import org.apache.spark.sql.{Dataset, Encoder, Row, SQLContext}
+import org.apache.spark.sql.catalyst.encoders.encoderFor
+import org.apache.spark.sql.catalyst.expressions.UnsafeRow
+import org.apache.spark.sql.execution.streaming._
+import org.apache.spark.sql.sources.v2.{ContinuousReadSupport,
DataSourceOptions}
+import org.apache.spark.sql.sources.v2.reader.{DataReader,
DataReaderFactory, SupportsScanUnsafeRow}
+import
org.apache.spark.sql.sources.v2.reader.streaming.{ContinuousDataReader,
ContinuousReader, Offset, PartitionOffset}
+import org.apache.spark.sql.types.StructType
+import org.apache.spark.util.RpcUtils
+
+/**
+ * The overall strategy here is:
+ * * ContinuousMemoryStream maintains a list of records for each
partition. addData() will
+ * distribute records evenly-ish across partitions.
+ * * ContinuousMemoryStreamRecordBuffer is set up as an endpoint for
partition-level
+ * ContinuousMemoryStreamDataReader instances to poll. It returns the
record at the specified
+ * offset within the list, or null if that offset doesn't yet have a
record.
+ */
+
+private case class GetRecord(offset: ContinuousMemoryStreamPartitionOffset)
--- End diff --
nit: I generally put such small-use generically-named classes inside a
relevant object to avoid cluttering of the general class namespace. Example:
this can be inside a object ContinuousMemoryStreamRecordBuffer as that is the
only one using it. Then when someone searches for a different GetRecord-ish
named class, then it would be less confusing.
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