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feat(cache): Implement simple LRU cache
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,93 @@ | ||
| package com.grohden.repotagger.cache | ||
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| private data class Node<K, V>( | ||
| val key: K, | ||
| val value: V, | ||
| var next: Node<K, V>? = null, | ||
| var prev: Node<K, V>? = null | ||
| ) | ||
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| /** | ||
| * Simple LRU cache (I think) | ||
| * | ||
| * This is basically a linked list with a replacement | ||
| * and get algorithm that reposition it's head and tail | ||
| */ | ||
| class LRUCache<K, V>( | ||
| private val capacity: Int | ||
| ) { | ||
| val size get() = cache.size | ||
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| private var head: Node<K, V>? = null | ||
| private var tail: Node<K, V>? = null | ||
| private val cache: HashMap<K, Node<K, V>> = hashMapOf() | ||
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| private fun replaceWithNewHead(node: Node<K, V>) { | ||
| if (head == null) { | ||
| node.prev = tail | ||
| node.next = null | ||
| head = node | ||
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| return | ||
| } | ||
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| head?.takeIf { node.key != it.key }?.let { oldHead -> | ||
| oldHead.next = node | ||
| node.prev = oldHead | ||
| node.next = null | ||
| head = node | ||
| } | ||
| } | ||
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| private fun replaceWithNewTail(node: Node<K, V>) { | ||
| if (tail == null) { | ||
| node.next = head | ||
| node.prev = null | ||
| tail = node | ||
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| return | ||
| } | ||
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| tail?.takeIf { node.key != it.key }?.let { oldTail -> | ||
| oldTail.prev = node | ||
| node.next = oldTail | ||
| node.prev = null | ||
| tail = node | ||
| } | ||
| } | ||
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| fun get(key: K): V? { | ||
| val node = cache[key] ?: return null | ||
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| replaceWithNewHead(node) | ||
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| return node.value | ||
| } | ||
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| /** | ||
| * Similar to [get] but uses a default provider | ||
| * in case the value is not found in cache, and also | ||
| * puts this new value in cache | ||
| * | ||
| * TODO: review the suspend usage | ||
| */ | ||
| suspend fun getOrDefaultAndPut(key: K, orElse: suspend () -> V): V { | ||
| return get(key) ?: orElse().also { put(key, it) } | ||
| } | ||
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| fun put(key: K, value: V) { | ||
| val node = Node(key, value).also { | ||
| cache[key] = it | ||
| } | ||
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| replaceWithNewHead(node) | ||
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| if (cache.size >= capacity) { | ||
| cache.remove(tail!!.key) | ||
| } | ||
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| (tail ?: node).let(this::replaceWithNewTail) | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,67 @@ | ||
| package com.grohden.repotagger.cache | ||
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| import org.amshove.kluent.shouldBe | ||
| import org.amshove.kluent.shouldBeEqualTo | ||
| import kotlin.test.Test | ||
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| class LRUCacheTest { | ||
| @Test | ||
| fun `should not grow with duplicated keys`() { | ||
| val instance = LRUCache<String, String>(4) | ||
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| instance.apply { | ||
| put("bazz", "1") | ||
| put("bar", "1") | ||
| put("bar", "2") | ||
| put("bar", "3") | ||
| } | ||
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| instance.size shouldBe 2 | ||
| } | ||
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| @Test | ||
| fun `should respect capacity`() { | ||
| val instance = LRUCache<String, String>(4) | ||
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| instance.apply { | ||
| put("1", "1") | ||
| put("2", "1") | ||
| put("3", "1") | ||
| put("4", "1") | ||
| put("5", "1") | ||
| } | ||
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| instance.size shouldBe 4 | ||
| } | ||
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| @Test | ||
| fun `should update cache contents for same key`() { | ||
| val instance = LRUCache<String, String>(4) | ||
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| instance.apply { | ||
| put("bar", "1") | ||
| put("bar", "2") | ||
| put("bar", "3") | ||
| } | ||
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| instance.get("bar") shouldBeEqualTo "3" | ||
| } | ||
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| @Test | ||
| fun `should evict last updated when at limit`() { | ||
| val instance = LRUCache<String, String>(4) | ||
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| instance.apply { | ||
| put("1", "1") | ||
| put("2", "2") | ||
| put("3", "3") | ||
| put("4", "4") | ||
| put("5", "5") | ||
| } | ||
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| instance.get("1") shouldBe null | ||
| instance.get("2") shouldBe "2" | ||
| instance.get("5") shouldBe "5" | ||
| } | ||
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| } |