Last change
on this file since 6a80231 was 6a3a178, checked in by Ema <ema_spirova@…>, 3 years ago |
initial commit
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100644
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File size:
1.5 KB
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[6a3a178] | 1 | 'use strict';
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| 2 | const Queue = require('yocto-queue');
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| 3 |
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| 4 | const pLimit = concurrency => {
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| 5 | if (!((Number.isInteger(concurrency) || concurrency === Infinity) && concurrency > 0)) {
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| 6 | throw new TypeError('Expected `concurrency` to be a number from 1 and up');
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| 7 | }
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| 8 |
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| 9 | const queue = new Queue();
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| 10 | let activeCount = 0;
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| 11 |
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| 12 | const next = () => {
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| 13 | activeCount--;
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| 14 |
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| 15 | if (queue.size > 0) {
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| 16 | queue.dequeue()();
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| 17 | }
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| 18 | };
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| 19 |
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| 20 | const run = async (fn, resolve, ...args) => {
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| 21 | activeCount++;
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| 22 |
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| 23 | const result = (async () => fn(...args))();
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| 24 |
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| 25 | resolve(result);
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| 26 |
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| 27 | try {
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| 28 | await result;
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| 29 | } catch {}
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| 30 |
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| 31 | next();
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| 32 | };
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| 33 |
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| 34 | const enqueue = (fn, resolve, ...args) => {
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| 35 | queue.enqueue(run.bind(null, fn, resolve, ...args));
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| 36 |
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| 37 | (async () => {
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| 38 | // This function needs to wait until the next microtask before comparing
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| 39 | // `activeCount` to `concurrency`, because `activeCount` is updated asynchronously
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| 40 | // when the run function is dequeued and called. The comparison in the if-statement
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| 41 | // needs to happen asynchronously as well to get an up-to-date value for `activeCount`.
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| 42 | await Promise.resolve();
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| 43 |
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| 44 | if (activeCount < concurrency && queue.size > 0) {
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| 45 | queue.dequeue()();
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| 46 | }
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| 47 | })();
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| 48 | };
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| 49 |
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| 50 | const generator = (fn, ...args) => new Promise(resolve => {
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| 51 | enqueue(fn, resolve, ...args);
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| 52 | });
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| 53 |
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| 54 | Object.defineProperties(generator, {
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| 55 | activeCount: {
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| 56 | get: () => activeCount
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| 57 | },
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| 58 | pendingCount: {
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| 59 | get: () => queue.size
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| 60 | },
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| 61 | clearQueue: {
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| 62 | value: () => {
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| 63 | queue.clear();
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| 64 | }
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| 65 | }
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| 66 | });
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| 67 |
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| 68 | return generator;
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| 69 | };
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| 70 |
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| 71 | module.exports = pLimit;
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