Github user pwendell commented on a diff in the pull request:
https://github.com/apache/spark/pull/4450#discussion_r29113605
--- Diff:
core/src/main/scala/org/apache/spark/util/collection/ChainedBuffer.scala ---
@@ -0,0 +1,134 @@
+/*
+ * 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.util.collection
+
+import java.io.OutputStream
+
+import scala.collection.mutable.ArrayBuffer
+
+import org.apache.spark.storage.BlockObjectWriter
+
+/**
+ * A logical byte buffer that wraps a list of byte arrays. All the byte
arrays have equal size. The
+ * advantage of this over a standard ArrayBuffer is that it can grow
without claiming large amounts
+ * of memory and needing to copy the full contents.
+ */
+private[spark] class ChainedBuffer(chunkSize: Int) {
+ private val chunkSizeLog2 = (math.log(chunkSize) / math.log(2)).toInt
+ assert(math.pow(2, chunkSizeLog2).toInt == chunkSize)
+ private val chunks: ArrayBuffer[Array[Byte]] = new
ArrayBuffer[Array[Byte]]()
+ private var _size: Int = _
+
+ /**
+ * Feed bytes from this buffer into a BlockObjectWriter.
+ *
+ * @param pos Offset in the buffer to read from.
+ * @param writer BlockObjectWriter to read into.
+ * @param len Number of bytes to read.
+ */
+ def read(pos: Int, writer: BlockObjectWriter, len: Int): Unit = {
+ var chunkIndex = pos >> chunkSizeLog2
+ var posInChunk = pos - (chunkIndex << chunkSizeLog2)
+ var moved = 0
+ while (moved < len) {
+ val toRead = math.min(len - moved, chunkSize - posInChunk)
+ writer.writeBytes(chunks(chunkIndex), posInChunk, toRead)
+ moved += toRead
+ chunkIndex += 1
+ posInChunk = 0
+ }
+ }
+
+ /**
+ * Read bytes from this buffer into a byte array.
+ *
+ * @param pos Offset in the buffer to read from.
+ * @param bytes Byte array to read into.
+ * @param offs Offset in the byte array to read to.
+ * @param len Number of bytes to read.
+ */
+ def read(pos: Int, bytes: Array[Byte], offs: Int, len: Int): Unit = {
+ var chunkIndex = pos >> chunkSizeLog2
+ var posInChunk = pos - (chunkIndex << chunkSizeLog2)
+ var moved = 0
+ while (moved < len) {
+ val toRead = math.min(len - moved, chunkSize - posInChunk)
+ System.arraycopy(chunks(chunkIndex), posInChunk, bytes, offs +
moved, toRead)
+ moved += toRead
+ chunkIndex += 1
+ posInChunk = 0
+ }
+ }
+
+ /**
+ * Write bytes from a byte array into this buffer.
+ *
+ * @param pos Offset in the buffer to write to.
+ * @param bytes Byte array to write from.
+ * @param offs Offset in the byte array to write from.
+ * @param len Number of bytes to write.
+ */
+ def write(pos: Int, bytes: Array[Byte], offs: Int, len: Int): Unit = {
+ // Grow if needed
+ val endChunkIndex = (pos + len - 1) >> chunkSizeLog2
+ while (endChunkIndex >= chunks.length) {
+ chunks += new Array[Byte](chunkSize)
+ }
+
+ var chunkIndex = pos >> chunkSizeLog2
+ var posInChunk = pos - (chunkIndex << chunkSizeLog2)
+ var moved = 0
--- End diff --
also feel like this should be written (minor)
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