@uwdata/mosaic-core/dist/src/util/cache.js

Scalable and extensible linked data views.

const requestIdle = typeof requestIdleCallback !== 'undefined'
    ? requestIdleCallback
    : setTimeout;
/**
 * Create a new cache that ignores all values.
 * @returns A void cache implementation.
 */
export function voidCache() {
    return {
        get: () => undefined,
        set: (key, value) => value,
        clear: () => { }
    };
}
/**
 * Create a new cache that uses an LRU eviction policy.
 * @param options Cache options.
 * @param options.max Maximum number of cache entries.
 * @param options.ttl Time-to-live for cache entries.
 * @returns An LRU cache implementation.
 */
export function lruCache({ max = 1000, // max entries
ttl = 3 * 60 * 60 * 1000 // time-to-live, default 3 hours
 } = {}) {
    let cache = new Map();
    function evict() {
        const expire = performance.now() - ttl;
        let lruKey = null;
        let lruLast = Infinity;
        for (const [key, value] of cache) {
            const { last } = value;
            // least recently used entry seen so far
            if (last < lruLast) {
                lruKey = key;
                lruLast = last;
            }
            // remove if time since last access exceeds ttl
            if (expire > last) {
                cache.delete(key);
            }
        }
        // remove lru entry
        if (lruKey) {
            cache.delete(lruKey);
        }
    }
    return {
        get(key) {
            const entry = cache.get(key);
            if (entry) {
                entry.last = performance.now();
                return entry.value;
            }
        },
        set(key, value) {
            cache.set(key, { last: performance.now(), value });
            if (cache.size > max)
                requestIdle(evict);
            return value;
        },
        clear() {
            cache = new Map();
        }
    };
}
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