Github user vanzin commented on a diff in the pull request:
https://github.com/apache/spark/pull/5400#discussion_r27925549
--- 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())
--- End diff --
nit: add braces
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