com.johnsnowlabs.nlp.util.LfuCache.scala Maven / Gradle / Ivy
/*
* Copyright 2017-2022 John Snow Labs
*
* Licensed 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 com.johnsnowlabs.nlp.util
import scala.collection.mutable
@specialized
class LfuCache[TKey, TValue](maxSize: Int) {
private val entries = mutable.HashMap.empty[TKey, CachedItem]
private val frequencyList = new FrequencyList(0)
def getSize: Int = entries.size
def getOrElseUpdate(key: TKey, value: => TValue): TValue = {
if (entries.contains(key)) get(key).get
else {
val content = value
append(key, content)
content
}
}
def get(itemId: TKey): Option[TValue] = {
entries.get(itemId).map { cachedItem =>
{
cachedItem.bump()
cachedItem.value
}
}
}
def removeLast(): Option[TValue] = {
if (entries.isEmpty) return None
val last = frequencyList.next.removeLast()
entries.remove(last.key)
Some(last.value)
}
private def append(key: TKey, item: => TValue): Unit = {
if (getSize == maxSize) removeLast()
val cachedItem = new CachedItem(key, item)
frequencyList.add(cachedItem)
cachedItem.bump()
entries.put(key, cachedItem)
}
class FrequencyList(val frequency: Int) extends DoubleLinked[FrequencyList] {
var previous: FrequencyList = this
var next: FrequencyList = this
var items: CachedItem = _
def bump(item: CachedItem): Unit = {
val bumpedFrequency = frequency + 1
val linked =
if (next.frequency == bumpedFrequency) next
else link(new FrequencyList(bumpedFrequency))
remove(item)
linked.add(item)
}
def link(link: FrequencyList): FrequencyList = {
link.next = next
link.previous = this
next.previous = link
next = link
link
}
def unlink(link: FrequencyList): FrequencyList = {
link.previous.next = link.next
link.next.previous = link.previous
link
}
def add(item: CachedItem): Unit = {
item.list = this
if (items == null) item.reset()
else items.addBefore(item)
items = item
}
def remove(item: CachedItem): Unit = {
if (frequency == 0) items = null
else if (item.isSingle) unlink(this)
else item.remove()
if (items == item) items = item.next
}
def removeLast(): CachedItem = {
if (items.isSingle) unlink(this).items
else items.last.remove()
}
}
class CachedItem(val key: TKey, val value: TValue) extends DoubleLinked[CachedItem] {
var list: FrequencyList = _
var previous: CachedItem = this
var next: CachedItem = this
def isSingle: Boolean =
next == this
def addBefore(item: CachedItem): Unit = {
item.previous = previous
item.next = this
previous.next = item
previous = item
}
def remove(): CachedItem = {
previous.next = next
next.previous = previous
this
}
def reset(): Unit = {
previous = this
next = this
}
def bump(): Unit = {
list.bump(this)
}
def last: CachedItem =
previous
}
trait DoubleLinked[Type <: DoubleLinked[Type]] { self: Type =>
def next: Type
def previous: Type
def iterate(f: Type => Unit): Unit = {
var tail = this
do {
f(tail)
tail = tail.next
} while (tail != this)
}
}
}