Github user vanzin commented on a diff in the pull request:
https://github.com/apache/spark/pull/5400#discussion_r27926259
--- Diff:
network/common/src/main/java/org/apache/spark/network/buffer/WrappedLargeByteBuffer.java
---
@@ -0,0 +1,252 @@
+/*
+* 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.network.buffer;
+
+import sun.nio.ch.DirectBuffer;
+
+import java.io.IOException;
+import java.nio.BufferUnderflowException;
+import java.nio.ByteBuffer;
+import java.nio.MappedByteBuffer;
+import java.nio.channels.WritableByteChannel;
+import java.util.Arrays;
+import java.util.List;
+
+public class WrappedLargeByteBuffer implements LargeByteBuffer {
+
+ //only public for tests
+ public final ByteBuffer[] underlying;
+
+ private final long size;
+ private long _pos;
+ private int currentBufferIdx;
+ private ByteBuffer currentBuffer;
+
+
+ public WrappedLargeByteBuffer(ByteBuffer[] underlying) {
+ this(underlying, findExpectedInitialPosition(underlying));
+ }
+
+ private static long findExpectedInitialPosition(ByteBuffer[] bufs) {
+ long sum = 0L;
+ for (ByteBuffer b: bufs) {
+ if (b.position() > 0) {
+ // this could still lead to a mix of positions half-way through
buffers that
+ // would be inconsistent -- but we'll discover that in the
constructor checks
+ sum += b.position();
+ } else {
+ break;
+ }
+ }
+ return sum;
+ }
+
+ private WrappedLargeByteBuffer(ByteBuffer[] underlying, long
initialPosition) {
+ this.underlying = underlying;
+ long sum = 0L;
+ for (int i = 0; i < underlying.length; i++) {
+ ByteBuffer b = underlying[i];
+ long nextSum = sum + b.capacity();
+ int expectedPosition;
+ if (nextSum < initialPosition) {
+ expectedPosition = b.capacity();
+ } else if (sum > initialPosition) {
+ expectedPosition = 0;
+ } else {
+ expectedPosition = (int) (initialPosition - sum);
+ }
+ if (b.position() != expectedPosition) {
+ throw new IllegalArgumentException("ByteBuffer[" + i + "]:" + b +
" was expected to have" +
+ " position = " + expectedPosition + " to be consistent with the
overall " +
+ "initialPosition = " + initialPosition);
+ }
+ sum = nextSum;
+ }
+ _pos = initialPosition;
+ currentBufferIdx = 0;
+ currentBuffer = underlying[0];
+ size = sum;
+ }
+
+ @Override
+ public void get(byte[] dest, int offset, int length) {
+ if (length > remaining())
+ throw new BufferUnderflowException();
+ int moved = 0;
+ while (moved < length) {
+ int toRead = Math.min(length - moved, currentBuffer.remaining());
+ currentBuffer.get(dest, offset + moved, toRead);
+ moved += toRead;
+ updateCurrentBuffer();
+ }
+ _pos += moved;
+ }
+
+ @Override
+ public LargeByteBuffer rewind() {
+ while (currentBufferIdx > 0) {
+ if (currentBuffer != null) {
+ currentBuffer.rewind();
+ }
+ currentBufferIdx -= 1;
+ currentBuffer = underlying[currentBufferIdx];
+ }
+ currentBuffer.rewind();
+ _pos = 0;
+ return this;
+ }
+
+ @Override
+ public WrappedLargeByteBuffer deepCopy() {
+ ByteBuffer[] dataCopy = new ByteBuffer[underlying.length];
+ for (int i = 0; i < underlying.length; i++) {
+ ByteBuffer b = underlying[i];
+ dataCopy[i] = ByteBuffer.allocate(b.capacity());
+ int originalPosition = b.position();
+ b.position(0);
+ dataCopy[i].put(b);
+ dataCopy[i].position(0);
+ b.position(originalPosition);
+ }
+ return new WrappedLargeByteBuffer(dataCopy);
+ }
+
+ @Override
+ public byte get() {
+ byte r = currentBuffer.get();
+ _pos += 1;
+ updateCurrentBuffer();
+ return r;
+ }
+
+ private void updateCurrentBuffer() {
+ while (currentBuffer != null && !currentBuffer.hasRemaining()) {
+ currentBufferIdx += 1;
+ currentBuffer = currentBufferIdx < underlying.length ?
underlying[currentBufferIdx] : null;
+ }
+ }
+
+ @Override
+ public long position() {
+ return _pos;
+ }
+
+ @Override
+ public long skip(long n) {
+ if (n < 0) {
+ final long moveTotal = Math.min(-n, _pos);
+ long toMove = moveTotal;
+ // move backwards -- set the position to 0 of every buffer's we go
back
+ if (currentBuffer != null) {
+ currentBufferIdx += 1;
+ }
+ while (toMove > 0) {
+ currentBufferIdx -= 1;
+ currentBuffer = underlying[currentBufferIdx];
+ int thisMove = (int) Math.min(toMove, currentBuffer.position());
+ currentBuffer.position(currentBuffer.position() - thisMove);
+ toMove -= thisMove;
+ }
+ _pos -= moveTotal;
+ return -moveTotal;
+ } else if (n > 0) {
+ final long moveTotal = Math.min(n, remaining());
+ long toMove = moveTotal;
+ // move forwards-- set the position to the end of every buffer as we
go forwards
+ currentBufferIdx -= 1;
+ while (toMove > 0) {
+ currentBufferIdx += 1;
+ currentBuffer = underlying[currentBufferIdx];
+ int thisMove = (int) Math.min(toMove, currentBuffer.remaining());
+ currentBuffer.position(currentBuffer.position() + thisMove);
+ toMove -= thisMove;
+ }
+ _pos += moveTotal;
+ return moveTotal;
+ } else {
+ return 0;
+ }
+ }
+
+ @Override
+ public long remaining() {
+ return size - _pos;
+ }
+
+ @Override
+ public WrappedLargeByteBuffer duplicate() {
+ ByteBuffer[] duplicates = new ByteBuffer[underlying.length];
+ for (int i = 0; i < underlying.length; i++) {
+ duplicates[i] = underlying[i].duplicate();
+ }
+ return new WrappedLargeByteBuffer(duplicates, _pos);
+ }
+
+ @Override
+ public long size() {
+ return size;
+ }
+
+ @Override
+ public long writeTo(WritableByteChannel channel) throws IOException {
+ long written = 0l;
+ for (; currentBufferIdx < underlying.length; currentBufferIdx++) {
+ currentBuffer = underlying[currentBufferIdx];
+ written += currentBuffer.remaining();
+ while (currentBuffer.hasRemaining())
+ channel.write(currentBuffer);
+ }
+ _pos = size();
+ return written;
+ }
+
+ @Override
+ public ByteBuffer asByteBuffer() throws BufferTooLargeException {
+ if (underlying.length > 1) {
+ throw new BufferTooLargeException(size());
+ }
+ return underlying[0];
+ }
+
+ // only needed for tests
+ public List<ByteBuffer> nioBuffers() {
+ return Arrays.asList(underlying);
+ }
+
+ /**
+ * 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.
+ */
+ private static void dispose(ByteBuffer buffer) {
+ if (buffer != null && buffer instanceof MappedByteBuffer) {
--- End diff --
Isn't it safer to check for `DirectBuffer` here?
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