93 lines
2.6 KiB
JavaScript
93 lines
2.6 KiB
JavaScript
// Cache any data with a timestamp,
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// remove only the oldest data.
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var typeEnum = {
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unit: 0,
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heap: 1,
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};
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function Cache(size, type) {
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if (!this instanceof Cache) { return new Cache(size, type); }
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this.size = size;
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this.type = typeEnum[type];
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// `cache` contains {content, index}.
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// - content: the actual data that is cached.
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// - index: the position in `order` of the data.
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this.cache = Object.create(null);
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this.order = []; // list of cache keys from oldest to newest.
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}
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Cache.prototype = {
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set: function addToCache(cacheIndex, cached) {
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if (this.cache[cacheIndex] !== undefined) {
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this.order.splice(this.cache[cacheIndex].index, 1);
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// Put the new element at the end of `order`.
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this.cache[cacheIndex].index = this.order.length;
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this.cache[cacheIndex].content = cached;
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this.order.push(cacheIndex);
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} else {
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// If the cache is full, remove the oldest data
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// (ie, the data requested longest ago.)
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var numberToRemove = this.limitReached();
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for (var i = 0; i < numberToRemove; i++) {
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// Remove `order`'s oldest element, the first.
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delete this.cache[this.order[0]];
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this.order.shift();
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}
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this.cache[cacheIndex] = {
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index: this.order.length,
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content: cached,
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}
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this.order.push(cacheIndex);
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}
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},
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get: function getFromCache(cacheIndex) {
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if (this.cache[cacheIndex] !== undefined) {
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this.order.splice(this.cache[cacheIndex].index, 1);
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// Put the new element at the end of `order`.
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this.cache[cacheIndex].index = this.order.length;
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this.order.push(cacheIndex);
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return this.cache[cacheIndex].content;
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} else { return; }
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},
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has: function hasInCache(cacheIndex) {
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return this.cache[cacheIndex] !== undefined;
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},
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// Returns true if we're past the limit.
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limitReached: function heuristic() {
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if (this.type === typeEnum.unit) {
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return Math.max(0, (this.order.length - this.size));
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} else if (this.type === typeEnum.heap) {
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if (getHeapSize() >= this.size) {
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// Remove a quarter of them.
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return (this.order.length >> 2);
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} else { return 0; }
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} else {
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console.error("Unknown heuristic for LRU cache.");
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return 1;
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}
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},
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};
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// In bytes.
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var heapSize;
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var heapSizeTimeout;
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function getHeapSize() {
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if (heapSizeTimeout == null) {
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// Compute the heap size every 60 seconds.
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heapSizeTimeout = setInterval(computeHeapSize, 60 * 1000);
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return computeHeapSize();
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} else {
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return heapSize;
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}
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}
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function computeHeapSize() {
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return heapSize = process.memoryUsage().heapTotal;
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}
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module.exports = Cache;
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