Github user nongli commented on a diff in the pull request: https://github.com/apache/spark/pull/11748#discussion_r56576152 --- Diff: core/src/main/scala/org/apache/spark/util/io/ChunkedByteBuffer.scala --- @@ -0,0 +1,218 @@ +/* + * 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.io + +import java.io.InputStream +import java.nio.ByteBuffer +import java.nio.channels.WritableByteChannel + +import com.google.common.primitives.UnsignedBytes +import io.netty.buffer.{ByteBuf, Unpooled} + +import org.apache.spark.network.util.ByteArrayWritableChannel +import org.apache.spark.storage.StorageUtils + +/** + * Read-only byte buffer which is physically stored as multiple chunks rather than a single + * contiguous array. + * + * @param chunks an array of [[ByteBuffer]]s. Each buffer in this array must be non-empty and have + * position == 0. Ownership of these buffers is transferred to the ChunkedByteBuffer, + * so if these buffers may also be used elsewhere then the caller is responsible for + * copying them as needed. + */ +private[spark] class ChunkedByteBuffer(var chunks: Array[ByteBuffer]) { + require(chunks != null, "chunks must not be null") + require(chunks.forall(_.limit() > 0), "chunks must be non-empty") + require(chunks.forall(_.position() == 0), "chunks' positions must be 0") + + /** + * This size of this buffer, in bytes. + */ + val size: Long = chunks.map(_.limit().asInstanceOf[Long]).sum + + def this(byteBuffer: ByteBuffer) = { + this(Array(byteBuffer)) + } + + /** + * Write this buffer to a channel. + */ + def writeFully(channel: WritableByteChannel): Unit = { + for (bytes <- getChunks()) { + while (bytes.remaining > 0) { + channel.write(bytes) + } + } + } + + /** + * Wrap this buffer to view it as a Netty ByteBuf. + */ + def toNetty: ByteBuf = { + Unpooled.wrappedBuffer(getChunks(): _*) + } + + /** + * Copy this buffer into a new byte array. + * + * @throws UnsupportedOperationException if this buffer's size exceeds the maximum array size. + */ + def toArray: Array[Byte] = { + if (size >= Integer.MAX_VALUE) { + throw new UnsupportedOperationException( + s"cannot call toArray because buffer size ($size bytes) exceeds maximum array size") + } + val byteChannel = new ByteArrayWritableChannel(size.toInt) + writeFully(byteChannel) + byteChannel.close() + byteChannel.getData + } + + /** + * Copy this buffer into a new ByteBuffer. + * + * @throws UnsupportedOperationException if this buffer's size exceeds the max ByteBuffer size. + */ + def toByteBuffer: ByteBuffer = { + if (chunks.length == 1) { + chunks.head.duplicate() + } else { + ByteBuffer.wrap(toArray) + } + } + + /** + * Creates an input stream to read data from this ChunkedByteBuffer. + * + * @param dispose if true, [[dispose()]] will be called at the end of the stream + * in order to close any memory-mapped files which back this buffer. + */ + def toInputStream(dispose: Boolean = false): InputStream = { + new ChunkedByteBufferInputStream(this, dispose) + } + + /** + * Get duplicates of the ByteBuffers backing this ChunkedByteBuffer. + */ + def getChunks(): Array[ByteBuffer] = { + chunks.map(_.duplicate()) + } + + /** + * Make a copy of this ChunkedByteBuffer, copying all of the backing data into new buffers. + * The new buffer will share no resources with the original buffer. + */ + def copy(): ChunkedByteBuffer = { + val copiedChunks = getChunks().map { chunk => + // TODO: accept an allocator in this copy method to integrate with mem. accounting systems + val newChunk = ByteBuffer.allocate(chunk.limit()) + newChunk.put(chunk) + newChunk.flip() + newChunk + } + new ChunkedByteBuffer(copiedChunks) + } + + /** + * Attempt to clean up a ByteBuffer if it is memory-mapped. This uses an *unsafe* Sun API that + * might cause errors if one attempts to read from the unmapped buffer, but it's better than + * waiting for the GC to find it because that could lead to huge numbers of open files. There's + * unfortunately no standard API to do this. + */ + def dispose(): Unit = { + chunks.foreach(StorageUtils.dispose) + } +} + +/** + * Reads data from a ChunkedByteBuffer. + * + * @param dispose if true, [[ChunkedByteBuffer.dispose()]] will be called at the end of the stream --- End diff -- This seems to be weird. When is it only checked on close() but not read?
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