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50 lines
1.6 KiB
TypeScript
50 lines
1.6 KiB
TypeScript
// Loaded from https://deno.land/std@0.73.0/async/pool.ts
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// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
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/**
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* pooledMap transforms values from an (async) iterable into another async
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* iterable. The transforms are done concurrently, with a max concurrency
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* defined by the poolLimit.
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*
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* @param poolLimit The maximum count of items being processed concurrently.
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* @param array The input array for mapping.
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* @param iteratorFn The function to call for every item of the array.
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*/
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export function pooledMap<T, R>(
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poolLimit: number,
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array: Iterable<T> | AsyncIterable<T>,
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iteratorFn: (data: T) => Promise<R>,
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): AsyncIterableIterator<R> {
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// Create the async iterable that is returned from this function.
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const res = new TransformStream<Promise<R>, R>({
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async transform(
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p: Promise<R>,
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controller: TransformStreamDefaultController<R>,
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): Promise<void> {
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controller.enqueue(await p);
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},
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});
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// Start processing items from the iterator
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(async (): Promise<void> => {
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const writer = res.writable.getWriter();
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const executing: Array<Promise<unknown>> = [];
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for await (const item of array) {
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const p = Promise.resolve().then(() => iteratorFn(item));
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writer.write(p);
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const e: Promise<unknown> = p.then(() =>
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executing.splice(executing.indexOf(e), 1)
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);
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executing.push(e);
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if (executing.length >= poolLimit) {
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await Promise.race(executing);
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}
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}
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// Wait until all ongoing events have processed, then close the writer.
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await Promise.all(executing);
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writer.close();
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})();
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return res.readable.getIterator();
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}
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