Github user vanzin commented on a diff in the pull request:
https://github.com/apache/spark/pull/5400#discussion_r31566932
--- Diff:
network/common/src/main/java/org/apache/spark/network/buffer/WrappedLargeByteBuffer.java
---
@@ -0,0 +1,280 @@
+/*
+* 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 java.io.IOException;
+import java.nio.BufferUnderflowException;
+import java.nio.ByteBuffer;
+import java.nio.channels.WritableByteChannel;
+import java.util.Arrays;
+import java.util.List;
+
+import com.google.common.annotations.VisibleForTesting;
+import sun.nio.ch.DirectBuffer;
+
+/**
+ * A {@link org.apache.spark.network.buffer.LargeByteBuffer} which may
contain multiple
+ * {@link java.nio.ByteBuffer}s. In order to support
<code>asByteBuffer</code>, all
+ * of the underlying ByteBuffers must have size equal to
+ * {@link
org.apache.spark.network.buffer.LargeByteBufferHelper#MAX_CHUNK_SIZE} (except
that last
+ * one). The underlying ByteBuffers may be on-heap, direct, or
memory-mapped.
+ */
+public class WrappedLargeByteBuffer implements LargeByteBuffer {
+
+ @VisibleForTesting
+ final ByteBuffer[] underlying;
+
+ private final long size;
+ /**
+ * each sub-ByteBuffer (except for the last one) must be exactly this
size. Note that this
+ * class *really* expects this to be
LargeByteBufferHelper.MAX_CHUNK_SIZE. The only reason it isn't
+ * is so that we can do tests without creating ginormous buffers.
Public methods force it to
+ * be LargeByteBufferHelper.MAX_CHUNK_SIZE
+ */
+ private final int subBufferSize;
+ private long _pos;
+ @VisibleForTesting
+ int currentBufferIdx;
+ @VisibleForTesting
+ ByteBuffer currentBuffer;
+
+ /**
+ * Construct a WrappedLargeByteBuffer from the given ByteBuffers. Each
of the ByteBuffers must
+ * have size equal to {@link
org.apache.spark.network.buffer.LargeByteBufferHelper#MAX_CHUNK_SIZE}
+ * except for the final one. The buffers are <code>duplicate</code>d,
so the position of the
+ * given buffers and the returned buffer will be independent, though the
underlying data will be
+ * shared. The constructed buffer will always have position == 0.
+ */
+ public WrappedLargeByteBuffer(ByteBuffer[] underlying) {
+ this(underlying, LargeByteBufferHelper.MAX_CHUNK_SIZE);
+ }
+
+ /**
+ * you do **not** want to call this version. It leads to a buffer which
doesn't properly
+ * support {@link #asByteBuffer}. The only reason it exists is to we
can have tests which
+ * don't require 2GB of memory
+ *
+ * @param underlying
+ * @param subBufferSize
+ */
+ @VisibleForTesting
+ WrappedLargeByteBuffer(ByteBuffer[] underlying, int subBufferSize) {
--- End diff --
I think I understand. But a better comment explaining why the check exists
would help a lot.
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