80 lines
1.7 KiB
Kotlin
80 lines
1.7 KiB
Kotlin
/*
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* LRUCache.kt
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* Copyright (C) 2009-2021 Ultrasonic developers
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*
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* Distributed under terms of the GNU GPLv3 license.
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*/
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package org.moire.ultrasonic.util
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import java.lang.ref.SoftReference
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import java.util.HashMap
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/**
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* A cache that deletes the least-recently-used items.
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*/
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class LRUCache<K, V>(capacity: Int) {
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private val capacity: Int
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private val map: MutableMap<K, TimestampedValue>
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@Synchronized
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operator fun get(key: K): V? {
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val value = map[key]
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var result: V? = null
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if (value != null) {
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value.updateTimestamp()
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result = value.getValue()
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}
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return result
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}
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@Synchronized
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fun put(key: K, value: V) {
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if (map.size >= capacity) {
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removeOldest()
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}
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map[key] = TimestampedValue(value)
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}
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fun clear() {
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map.clear()
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}
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private fun removeOldest() {
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var oldestKey: K? = null
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var oldestTimestamp = Long.MAX_VALUE
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for ((key, value) in map) {
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if (value.timestamp < oldestTimestamp) {
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oldestTimestamp = value.timestamp
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oldestKey = key
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}
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}
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if (oldestKey != null) {
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map.remove(oldestKey)
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}
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}
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private inner class TimestampedValue(value: V) {
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private val value: SoftReference<V> = SoftReference(value)
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var timestamp: Long = 0
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private set
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fun getValue(): V? {
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return value.get()
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}
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fun updateTimestamp() {
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timestamp = System.currentTimeMillis()
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}
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init {
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updateTimestamp()
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}
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}
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init {
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map = HashMap(capacity)
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this.capacity = capacity
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}
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}
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