105 lines
2.5 KiB
JavaScript
105 lines
2.5 KiB
JavaScript
import Queue from 'yocto-queue';
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export default function pLimit(concurrency) {
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validateConcurrency(concurrency);
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const queue = new Queue();
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let activeCount = 0;
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const resumeNext = () => {
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if (activeCount < concurrency && queue.size > 0) {
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queue.dequeue()();
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// Since `pendingCount` has been decreased by one, increase `activeCount` by one.
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activeCount++;
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}
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};
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const next = () => {
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activeCount--;
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resumeNext();
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};
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const run = async (function_, resolve, arguments_) => {
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const result = (async () => function_(...arguments_))();
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resolve(result);
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try {
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await result;
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} catch {}
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next();
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};
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const enqueue = (function_, resolve, arguments_) => {
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// Queue `internalResolve` instead of the `run` function
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// to preserve asynchronous context.
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new Promise(internalResolve => {
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queue.enqueue(internalResolve);
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}).then(
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run.bind(undefined, function_, resolve, arguments_),
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);
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(async () => {
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// This function needs to wait until the next microtask before comparing
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// `activeCount` to `concurrency`, because `activeCount` is updated asynchronously
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// after the `internalResolve` function is dequeued and called. The comparison in the if-statement
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// needs to happen asynchronously as well to get an up-to-date value for `activeCount`.
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await Promise.resolve();
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if (activeCount < concurrency) {
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resumeNext();
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}
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})();
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};
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const generator = (function_, ...arguments_) => new Promise(resolve => {
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enqueue(function_, resolve, arguments_);
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});
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Object.defineProperties(generator, {
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activeCount: {
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get: () => activeCount,
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},
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pendingCount: {
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get: () => queue.size,
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},
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clearQueue: {
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value() {
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queue.clear();
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},
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},
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concurrency: {
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get: () => concurrency,
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set(newConcurrency) {
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validateConcurrency(newConcurrency);
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concurrency = newConcurrency;
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queueMicrotask(() => {
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// eslint-disable-next-line no-unmodified-loop-condition
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while (activeCount < concurrency && queue.size > 0) {
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resumeNext();
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}
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});
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},
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},
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});
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return generator;
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}
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export function limitFunction(function_, option) {
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const {concurrency} = option;
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const limit = pLimit(concurrency);
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return (...arguments_) => limit(() => function_(...arguments_));
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}
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function validateConcurrency(concurrency) {
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if (!((Number.isInteger(concurrency) || concurrency === Number.POSITIVE_INFINITY) && concurrency > 0)) {
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throw new TypeError('Expected `concurrency` to be a number from 1 and up');
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}
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}
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