Github user srowen commented on a diff in the pull request:
https://github.com/apache/spark/pull/397#discussion_r11559113
--- Diff:
core/src/main/scala/org/apache/spark/util/io/FastByteArrayOutputStream.scala ---
@@ -0,0 +1,104 @@
+/*
+ * 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.OutputStream
+
+/**
+ * A simple, fast byte-array output stream that exposes the backing array,
+ * inspired by fastutil's FastByteArrayOutputStream.
+ *
+ * [[java.io.ByteArrayOutputStream]] is nice, but to get its content you
+ * must generate each time a new object. This doesn't happen here.
+ *
+ * This class will automatically enlarge the backing array, doubling its
+ * size whenever new space is needed.
+ */
+private[spark] class FastByteArrayOutputStream(initialCapacity: Int = 16)
extends OutputStream {
+
+ private[this] var _array = new Array[Byte](initialCapacity)
+
+ /** The current writing position. */
+ private[this] var _position: Int = 0
+
+ /** The array backing the output stream. */
+ def array: Array[Byte] = _array
+
+ /** The number of valid bytes in array. */
+ def length: Int = _position
+
+ override def write(b: Int): Unit = {
+ if (_position >= _array.length ) {
+ _array = FastByteArrayOutputStream.growArray(_array, _position + 1,
_position)
+ }
+ _array(_position) = b.toByte
+ _position += 1
+ }
+
+ override def write(b: Array[Byte], off: Int, len: Int) {
+ if (off < 0) {
+ throw new ArrayIndexOutOfBoundsException(s"Offset ($off) is
negative" )
+ }
+ if (len < 0) {
+ throw new IllegalArgumentException(s"Length ($len) is negative" )
+ }
+ if (off + len > b.length) {
+ throw new ArrayIndexOutOfBoundsException(
+ s"Last index (${off+len}) is greater than array length
(${b.length})")
+ }
+ if ( _position + len > _array.length ) {
+ _array = FastByteArrayOutputStream.growArray(_array, _position +
len, _position)
+ }
+ System.arraycopy(b, off, _array, _position, len)
+ _position += len
+ }
+
+ /** Ensures that the length of the backing array is equal to [[length]].
*/
+ def trim(): this.type = {
+ if (_position < _array.length) {
+ val newArr = new Array[Byte](_position)
--- End diff --
This still entails a copy, right? I don't see that this improves the
situation by itself.
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