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/*
* 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
import org.apache.spark.annotation.DeveloperApi
/**
* :: DeveloperApi ::
* A fast hash map implementation for nullable keys. This hash map supports insertions and updates,
* but not deletions. This map is about 5X faster than java.util.HashMap, while using much less
* space overhead.
*
* Under the hood, it uses our OpenHashSet implementation.
*/
@DeveloperApi
private[spark]
class OpenHashMap[K : ClassTag, @specialized(Long, Int, Double) V: ClassTag](
initialCapacity: Int)
extends Iterable[(K, V)]
with Serializable {
def this() = this(64)
protected var _keySet = new OpenHashSet[K](initialCapacity)
// Init in constructor (instead of in declaration) to work around a Scala compiler specialization
// bug that would generate two arrays (one for Object and one for specialized T).
private var _values: Array[V] = _
_values = new Array[V](_keySet.capacity)
@transient private var _oldValues: Array[V] = null
// Treat the null key differently so we can use nulls in "data" to represent empty items.
private var haveNullValue = false
private var nullValue: V = null.asInstanceOf[V]
override def size: Int = if (haveNullValue) _keySet.size + 1 else _keySet.size
/** Get the value for a given key */
def apply(k: K): V = {
if (k == null) {
nullValue
} else {
val pos = _keySet.getPos(k)
if (pos < 0) {
null.asInstanceOf[V]
} else {
_values(pos)
}
}
}
/** Set the value for a key */
def update(k: K, v: V) {
if (k == null) {
haveNullValue = true
nullValue = v
} else {
val pos = _keySet.addWithoutResize(k) & OpenHashSet.POSITION_MASK
_values(pos) = v
_keySet.rehashIfNeeded(k, grow, move)
_oldValues = null
}
}
/**
* If the key doesn't exist yet in the hash map, set its value to defaultValue; otherwise,
* set its value to mergeValue(oldValue).
*
* @return the newly updated value.
*/
def changeValue(k: K, defaultValue: => V, mergeValue: (V) => V): V = {
if (k == null) {
if (haveNullValue) {
nullValue = mergeValue(nullValue)
} else {
haveNullValue = true
nullValue = defaultValue
}
nullValue
} else {
val pos = _keySet.addWithoutResize(k)
if ((pos & OpenHashSet.NONEXISTENCE_MASK) != 0) {
val newValue = defaultValue
_values(pos & OpenHashSet.POSITION_MASK) = newValue
_keySet.rehashIfNeeded(k, grow, move)
newValue
} else {
_values(pos) = mergeValue(_values(pos))
_values(pos)
}
}
}
override def iterator = new Iterator[(K, V)] {
var pos = -1
var nextPair: (K, V) = computeNextPair()
/** Get the next value we should return from next(), or null if we're finished iterating */
def computeNextPair(): (K, V) = {
if (pos == -1) { // Treat position -1 as looking at the null value
if (haveNullValue) {
pos += 1
return (null.asInstanceOf[K], nullValue)
}
pos += 1
}
pos = _keySet.nextPos(pos)
if (pos >= 0) {
val ret = (_keySet.getValue(pos), _values(pos))
pos += 1
ret
} else {
null
}
}
def hasNext = nextPair != null
def next() = {
val pair = nextPair
nextPair = computeNextPair()
pair
}
}
// The following member variables are declared as protected instead of private for the
// specialization to work (specialized class extends the non-specialized one and needs access
// to the "private" variables).
// They also should have been val's. We use var's because there is a Scala compiler bug that
// would throw illegal access error at runtime if they are declared as val's.
protected var grow = (newCapacity: Int) => {
_oldValues = _values
_values = new Array[V](newCapacity)
}
protected var move = (oldPos: Int, newPos: Int) => {
_values(newPos) = _oldValues(oldPos)
}
}
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