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| import type { SchedulerFn } from './scheduler' | |
| import { DetachedPromise } from './detached-promise' | |
| type CacheKeyFn<K, C extends string | number | null> = ( | |
| key: K | |
| ) => PromiseLike<C> | C | |
| type BatcherOptions<K, C extends string | number | null> = { | |
| cacheKeyFn?: CacheKeyFn<K, C> | |
| schedulerFn?: SchedulerFn<void> | |
| } | |
| type WorkFn<V, C> = ( | |
| key: C, | |
| resolve: (value: V | PromiseLike<V>) => void | |
| ) => Promise<V> | |
| /** | |
| * A wrapper for a function that will only allow one call to the function to | |
| * execute at a time. | |
| */ | |
| export class Batcher<K, V, C extends string | number | null> { | |
| private readonly pending = new Map<C, Promise<V>>() | |
| protected constructor( | |
| private readonly cacheKeyFn?: CacheKeyFn<K, C>, | |
| /** | |
| * A function that will be called to schedule the wrapped function to be | |
| * executed. This defaults to a function that will execute the function | |
| * immediately. | |
| */ | |
| private readonly schedulerFn: SchedulerFn<void> = (fn) => fn() | |
| ) {} | |
| /** | |
| * Creates a new instance of PendingWrapper. If the key extends a string or | |
| * number, the key will be used as the cache key. If the key is an object, a | |
| * cache key function must be provided. | |
| */ | |
| public static create<K extends string | number | null, V>( | |
| options?: BatcherOptions<K, K> | |
| ): Batcher<K, V, K> | |
| public static create<K, V, C extends string | number | null>( | |
| options: BatcherOptions<K, C> & | |
| Required<Pick<BatcherOptions<K, C>, 'cacheKeyFn'>> | |
| ): Batcher<K, V, C> | |
| public static create<K, V, C extends string | number | null>( | |
| options?: BatcherOptions<K, C> | |
| ): Batcher<K, V, C> { | |
| return new Batcher<K, V, C>(options?.cacheKeyFn, options?.schedulerFn) | |
| } | |
| /** | |
| * Wraps a function in a promise that will be resolved or rejected only once | |
| * for a given key. This will allow multiple calls to the function to be | |
| * made, but only one will be executed at a time. The result of the first | |
| * call will be returned to all callers. | |
| * | |
| * @param key the key to use for the cache | |
| * @param fn the function to wrap | |
| * @returns a promise that resolves to the result of the function | |
| */ | |
| public async batch(key: K, fn: WorkFn<V, C>): Promise<V> { | |
| const cacheKey = (this.cacheKeyFn ? await this.cacheKeyFn(key) : key) as C | |
| if (cacheKey === null) { | |
| return fn(cacheKey, Promise.resolve) | |
| } | |
| const pending = this.pending.get(cacheKey) | |
| if (pending) return pending | |
| const { promise, resolve, reject } = new DetachedPromise<V>() | |
| this.pending.set(cacheKey, promise) | |
| this.schedulerFn(async () => { | |
| try { | |
| const result = await fn(cacheKey, resolve) | |
| // Resolving a promise multiple times is a no-op, so we can safely | |
| // resolve all pending promises with the same result. | |
| resolve(result) | |
| } catch (err) { | |
| reject(err) | |
| } finally { | |
| this.pending.delete(cacheKey) | |
| } | |
| }) | |
| return promise | |
| } | |
| } | |