Github user squito commented on a diff in the pull request:
https://github.com/apache/spark/pull/1297#discussion_r17791303
--- Diff:
core/src/main/scala/org/apache/spark/util/collection/ImmutableLongOpenHashSet.scala
---
@@ -0,0 +1,228 @@
+/*
+ * 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._
+import com.google.common.hash.Hashing
+
+/**
+ * A fast, immutable hash set optimized for insertions and lookups (but
not deletions) of `Long`
+ * elements. Because it exposes the position of a key in the underlying
array, this is useful as a
+ * building block for higher level data structures such as a hash map (for
example,
+ * IndexedRDDPartition).
+ *
+ * It uses quadratic probing with a power-of-2 hash table size, which is
guaranteed to explore all
+ * spaces for each key (see
http://en.wikipedia.org/wiki/Quadratic_probing).
+ */
+private[spark] class ImmutableLongOpenHashSet(
+ /** Underlying array of elements used as a hash table. */
+ val data: ImmutableVector[Long],
+ /** Whether or not there is an element at the corresponding position
in `data`. */
+ val bitset: ImmutableBitSet,
+ /**
+ * Position of a focused element. This is useful when returning a
modified set along with a
+ * pointer to the location of modification.
+ */
+ val focus: Int,
+ /** Load threshold at which to grow the underlying vectors. */
+ loadFactor: Double
+ ) extends Serializable {
+
+ require(loadFactor < 1.0, "Load factor must be less than 1.0")
+ require(loadFactor > 0.0, "Load factor must be greater than 0.0")
+ require(capacity == nextPowerOf2(capacity), "data capacity must be a
power of 2")
+
+ import OpenHashSet.{INVALID_POS, NONEXISTENCE_MASK, POSITION_MASK,
Hasher, LongHasher}
+
+ private val hasher: Hasher[Long] = new LongHasher
+
+ private def mask = capacity - 1
+ private def growThreshold = (loadFactor * capacity).toInt
+
+ def withFocus(focus: Int): ImmutableLongOpenHashSet =
+ new ImmutableLongOpenHashSet(data, bitset, focus, loadFactor)
+
+ /** The number of elements in the set. */
+ def size: Int = bitset.cardinality
+
+ /** The capacity of the set (i.e. size of the underlying vector). */
+ def capacity: Int = data.size
+
+ /** Return true if this set contains the specified element. */
+ def contains(k: Long): Boolean = getPos(k) != INVALID_POS
+
+ /**
+ * Nondestructively add an element to the set, returning a new set. If
the set is over capacity
+ * after the insertion, grows the set and rehashes all elements.
+ */
+ def add(k: Long): ImmutableLongOpenHashSet = {
+ addWithoutResize(k).rehashIfNeeded(ImmutableLongOpenHashSet.grow,
ImmutableLongOpenHashSet.move)
+ }
+
+ /**
+ * Add an element to the set. This one differs from add in that it
doesn't trigger rehashing.
+ * The caller is responsible for calling rehashIfNeeded.
+ *
+ * Use (retval.focus & POSITION_MASK) to get the actual position, and
+ * (retval.focus & NONEXISTENCE_MASK) == 0 for prior existence.
+ */
+ def addWithoutResize(k: Long): ImmutableLongOpenHashSet = {
+ var pos = hashcode(hasher.hash(k)) & mask
+ var i = 1
+ var result: ImmutableLongOpenHashSet = null
+ while (result == null) {
+ if (!bitset.get(pos)) {
+ // This is a new key.
+ result = new ImmutableLongOpenHashSet(
+ data.updated(pos, k), bitset.set(pos), pos | NONEXISTENCE_MASK,
loadFactor)
+ } else if (data(pos) == k) {
+ // Found an existing key.
+ result = this.withFocus(pos)
+ } else {
+ val delta = i
+ pos = (pos + delta) & mask
+ i += 1
+ }
+ }
+ result
+ }
+
+ /**
+ * Rehash the set if it is overloaded.
+ * @param allocateFunc Callback invoked when we are allocating a new,
larger array.
+ * @param moveFunc Callback invoked when we move the key from one
position (in the old data array)
+ * to a new position (in the new data array).
+ */
+ def rehashIfNeeded(
+ allocateFunc: (Int) => Unit, moveFunc: (Int, Int) => Unit):
ImmutableLongOpenHashSet = {
+ if (size > growThreshold) {
+ rehash(allocateFunc, moveFunc)
+ } else {
+ this
+ }
+ }
+
+ /**
+ * Return the position of the element in the underlying array, or
INVALID_POS if it is not found.
+ */
+ def getPos(k: Long): Int = {
+ var pos = hashcode(hasher.hash(k)) & mask
+ var i = 1
+ val maxProbe = capacity
+ while (i < maxProbe) {
+ if (!bitset.get(pos)) {
+ return INVALID_POS
+ } else if (k == data(pos)) {
+ return pos
+ } else {
+ val delta = i
+ pos = (pos + delta) & mask
+ i += 1
+ }
+ }
+ // Never reached here
+ INVALID_POS
--- End diff --
would it be better to throw an exception here? Just in case something goes
wrong and you end up here, you get a stack trace which will pinpoint the
problem.
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