wehub-resource-sync
51 lines
1.7 KiB
TypeScript
51 lines
1.7 KiB
TypeScript
/**
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* Tiny in-process bounded TTL cache shared by the realtime feeds: entries expire after `ttlMs` (evicted on read),
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* and at-capacity writes sweep expired entries then drop the oldest. A stored `undefined` is indistinguishable from a miss (use `null` for absence).
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*/
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export class BoundedTtlCache<V> {
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readonly #entries = new Map<string, { value: V; expiresAt: number }>();
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constructor(
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private readonly ttlMs: number,
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private readonly maxEntries: number
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) {}
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get(key: string): V | undefined {
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const entry = this.#entries.get(key);
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if (!entry) {
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return undefined;
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}
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if (entry.expiresAt > Date.now()) {
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return entry.value;
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}
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// Evict on read so expired entries don't linger until the next at-capacity
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// sweep — important for read-heavy / low-churn caches (per-handle working sets).
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this.#entries.delete(key);
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return undefined;
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}
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set(key: string, value: V): void {
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// Only run capacity eviction when inserting a NEW key — updating an existing key
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// doesn't grow the map, so it must never drop an unrelated live entry.
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if (!this.#entries.has(key) && this.#entries.size >= this.maxEntries) {
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const now = Date.now();
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for (const [key, entry] of this.#entries) {
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if (entry.expiresAt <= now) {
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this.#entries.delete(key);
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}
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}
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if (this.#entries.size >= this.maxEntries) {
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const oldest = this.#entries.keys().next().value;
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if (oldest !== undefined) {
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this.#entries.delete(oldest);
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}
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}
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}
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this.#entries.set(key, { value, expiresAt: Date.now() + this.ttlMs });
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}
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get size(): number {
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return this.#entries.size;
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}
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}
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