Github user concretevitamin commented on a diff in the pull request:
https://github.com/apache/spark/pull/1297#discussion_r14578164
--- Diff:
core/src/main/scala/org/apache/spark/util/collection/ImmutableVector.scala ---
@@ -0,0 +1,219 @@
+/*
+ * 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.collection
+
+import scala.reflect.ClassTag
+
+/**
+ * An immutable vector that supports efficient point updates. Similarly to
+ * scala.collection.immutable.Vector, it is implemented using a 32-ary
tree with 32-element arrays
+ * at the leaves. Unlike Scala's Vector, it is specialized on the value
type, making it much more
+ * memory-efficient for primitive values.
+ */
+private[spark] class ImmutableVector[@specialized(Long, Int) A](val size:
Int, root: VectorNode[A])
+ extends Serializable {
+
+ def iterator: Iterator[A] = new VectorIterator[A](root)
+ def apply(index: Int): A = root(index)
+ def updated(index: Int, elem: A): ImmutableVector[A] =
+ new ImmutableVector(size, root.updated(index, elem))
+}
+
+private[spark] object ImmutableVector {
+ def empty[A: ClassTag]: ImmutableVector[A] = new ImmutableVector(0,
emptyNode)
+
+ def fromArray[A: ClassTag](array: Array[A]): ImmutableVector[A] = {
+ fromArray(array, 0, array.length)
+ }
+
+ def fromArray[A: ClassTag](array: Array[A], start: Int, end: Int):
ImmutableVector[A] = {
+ new ImmutableVector(end - start, nodeFromArray(array, start, end))
+ }
+
+ def fill[A: ClassTag](n: Int)(a: A): ImmutableVector[A] = {
+ // TODO: Implement this without allocating an extra array
+ fromArray(Array.fill(n)(a), 0, n)
+ }
+
+ /** Returns the root of a 32-ary tree representing the specified
interval into the array. */
+ private def nodeFromArray[A: ClassTag](array: Array[A], start: Int, end:
Int): VectorNode[A] = {
+ val length = end - start
+ if (length == 0) {
+ emptyNode
+ } else {
+ val depth = depthOf(length)
+ if (depth == 0) {
+ new LeafNode(array.slice(start, end))
+ } else {
+ val shift = 5 * depth
+ val numChildren = ((length - 1) >> shift) + 1
+ val children = new Array[VectorNode[A]](numChildren)
+ var i = 0
+ while (i < numChildren) {
+ val childStart = start + (i << shift)
+ var childEnd = start + ((i + 1) << shift)
+ if (end < childEnd) {
+ childEnd = end
+ }
+ children(i) = nodeFromArray(array, childStart, childEnd)
+ i += 1
+ }
+ new InternalNode(children, depth)
+ }
+ }
+ }
+
+ private def emptyNode[A: ClassTag] = new LeafNode(Array.empty)
+
+ /** Returns the required tree depth for an ImmutableVector of the given
size. */
+ private def depthOf(size: Int): Int = {
+ var depth = 0
+ var sizeLeft = (size - 1) >> 5
+ while (sizeLeft > 0) {
+ sizeLeft >>= 5
+ depth += 1
+ }
+ depth
+ }
+}
+
+/** Trait representing nodes in the vector tree. */
+private sealed trait VectorNode[@specialized(Long, Int) A] extends
Serializable {
+ def apply(index: Int): A
+ def updated(index: Int, elem: A): VectorNode[A]
+ def numChildren: Int
+}
+
+/** An internal node in the vector tree (one containing other nodes rather
than vector elements). */
+private class InternalNode[@specialized(Long, Int) A: ClassTag](
+ children: Array[VectorNode[A]],
+ val depth: Int)
+ extends VectorNode[A] {
+
+ require(children.length > 0, "InternalNode must have children")
+ require(children.length <= 32, "nodes cannot have more than 32 children
(got ${children.length})")
+ require(depth >= 1, "InternalNode must have depth >= 1 (got $depth)")
--- End diff --
minor nit: add "s", same for the line above
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