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Merge pull request #211 from optimizely/ll/cache-abstraction
Caching Abstraction
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,221 @@ | ||
| import { List, Map, OrderedSet, Record } from 'immutable' | ||
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| export const CacheEntry = Record({ | ||
| value: null, | ||
| storeStates: Map(), | ||
| dispatchId: null, | ||
| }) | ||
|
|
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| /******************************************************************************* | ||
| * interface PersistentCache { | ||
| * has(item) | ||
| * lookup(item, notFoundValue) | ||
| * hit(item) | ||
| * miss(item, entry) | ||
| * evict(item) | ||
| * asMap() | ||
| * } | ||
| * | ||
| * Inspired by clojure.core.cache/CacheProtocol | ||
| *******************************************************************************/ | ||
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| /** | ||
| * Plain map-based cache | ||
| */ | ||
| export class BasicCache { | ||
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| /** | ||
| * @param {Immutable.Map} cache | ||
| */ | ||
| constructor(cache = Map()) { | ||
| this.cache = cache; | ||
| } | ||
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|
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| /** | ||
| * Retrieve the associated value, if it exists in this cache, otherwise | ||
| * returns notFoundValue (or undefined if not provided) | ||
| * @param {Object} item | ||
| * @param {Object?} notFoundValue | ||
| * @return {CacheEntry?} | ||
| */ | ||
| lookup(item, notFoundValue) { | ||
| return this.cache.get(item, notFoundValue) | ||
| } | ||
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|
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| /** | ||
| * Checks if this cache contains an associated value | ||
| * @param {Object} item | ||
| * @return {boolean} | ||
| */ | ||
| has(item) { | ||
| return this.cache.has(item) | ||
| } | ||
|
|
||
| /** | ||
| * Return cached items as map | ||
| * @return {Immutable.Map} | ||
| */ | ||
| asMap() { | ||
| return this.cache | ||
| } | ||
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|
||
| /** | ||
| * Updates this cache when it is determined to contain the associated value | ||
| * @param {Object} item | ||
| * @return {BasicCache} | ||
| */ | ||
| hit(item) { | ||
| return this; | ||
| } | ||
|
|
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| /** | ||
| * Updates this cache when it is determined to **not** contain the associated value | ||
| * @param {Object} item | ||
| * @param {CacheEntry} entry | ||
| * @return {BasicCache} | ||
| */ | ||
| miss(item, entry) { | ||
| return new BasicCache( | ||
| this.cache.update(item, existingEntry => { | ||
| if (existingEntry && existingEntry.dispatchId > entry.dispatchId) { | ||
| throw new Error("Refusing to cache older value") | ||
| } | ||
| return entry | ||
| }) | ||
| ) | ||
| } | ||
|
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| /** | ||
| * Removes entry from cache | ||
| * @param {Object} item | ||
| * @return {BasicCache} | ||
| */ | ||
| evict(item) { | ||
| return new BasicCache(this.cache.remove(item)) | ||
| } | ||
| } | ||
|
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| const DEFAULT_LRU_LIMIT = 1000 | ||
| const DEFAULT_LRU_EVICT_COUNT = 1 | ||
|
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| /** | ||
| * Implements caching strategy that evicts least-recently-used items in cache | ||
| * when an item is being added to a cache that has reached a configured size | ||
| * limit. | ||
| */ | ||
| export class LRUCache { | ||
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| constructor(limit = DEFAULT_LRU_LIMIT, evictCount = DEFAULT_LRU_EVICT_COUNT, cache = new BasicCache(), lru = OrderedSet()) { | ||
| this.limit = limit; | ||
| this.evictCount = evictCount | ||
| this.cache = cache; | ||
| this.lru = lru; | ||
| } | ||
|
|
||
| /** | ||
| * Retrieve the associated value, if it exists in this cache, otherwise | ||
| * returns notFoundValue (or undefined if not provided) | ||
| * @param {Object} item | ||
| * @param {Object?} notFoundValue | ||
| * @return {CacheEntry} | ||
| */ | ||
| lookup(item, notFoundValue) { | ||
| return this.cache.lookup(item, notFoundValue) | ||
| } | ||
|
|
||
| /** | ||
| * Checks if this cache contains an associated value | ||
| * @param {Object} item | ||
| * @return {boolean} | ||
| */ | ||
| has(item) { | ||
| return this.cache.has(item) | ||
| } | ||
|
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| /** | ||
| * Return cached items as map | ||
| * @return {Immutable.Map} | ||
| */ | ||
| asMap() { | ||
| return this.cache.asMap() | ||
| } | ||
|
|
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| /** | ||
| * Updates this cache when it is determined to contain the associated value | ||
| * @param {Object} item | ||
| * @return {LRUCache} | ||
| */ | ||
| hit(item) { | ||
| if (!this.cache.has(item)) { | ||
| return this; | ||
| } | ||
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| // remove it first to reorder in lru OrderedSet | ||
| return new LRUCache(this.limit, this.evictCount, this.cache, this.lru.remove(item).add(item)) | ||
| } | ||
|
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| /** | ||
| * Updates this cache when it is determined to **not** contain the associated value | ||
| * If cache has reached size limit, the LRU item is evicted. | ||
| * @param {Object} item | ||
| * @param {CacheEntry} entry | ||
| * @return {LRUCache} | ||
| */ | ||
| miss(item, entry) { | ||
| if (this.lru.size >= this.limit) { | ||
| if (this.has(item)) { | ||
| return new LRUCache( | ||
| this.limit, | ||
| this.evictCount, | ||
| this.cache.miss(item, entry), | ||
| this.lru.remove(item).add(item) | ||
| ) | ||
| } | ||
|
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| const cache = (this.lru | ||
| .take(this.evictCount) | ||
| .reduce((c, evictItem) => c.evict(evictItem), this.cache) | ||
| .miss(item, entry)); | ||
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| return new LRUCache( | ||
| this.limit, | ||
| this.evictCount, | ||
| cache, | ||
| this.lru.skip(this.evictCount).add(item) | ||
| ) | ||
| } else { | ||
| return new LRUCache( | ||
| this.limit, | ||
| this.evictCount, | ||
| this.cache.miss(item, entry), | ||
| this.lru.add(item) | ||
| ) | ||
| } | ||
| } | ||
|
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| /** | ||
| * Removes entry from cache | ||
| * @param {Object} item | ||
| * @return {LRUCache} | ||
| */ | ||
| evict(item) { | ||
| if (!this.cache.has(item)) { | ||
| return this; | ||
| } | ||
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| return new LRUCache( | ||
| this.limit, | ||
| this.evictCount, | ||
| this.cache.evict(item), | ||
| this.lru.remove(item) | ||
| ) | ||
| } | ||
| } | ||
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| /** | ||
| * Returns default cache strategy | ||
| * @return {BasicCache} | ||
| */ | ||
| export function DefaultCache() { | ||
| return new BasicCache() | ||
| } |
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