1 | 'use strict';
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2 | const pTry = require('p-try');
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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 | return Promise.reject(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 = [];
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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.length > 0) {
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16 | queue.shift()();
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17 | }
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18 | };
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19 |
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20 | const run = (fn, resolve, ...args) => {
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21 | activeCount++;
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22 |
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23 | const result = pTry(fn, ...args);
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24 |
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25 | resolve(result);
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26 |
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27 | result.then(next, next);
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28 | };
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29 |
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30 | const enqueue = (fn, resolve, ...args) => {
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31 | if (activeCount < concurrency) {
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32 | run(fn, resolve, ...args);
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33 | } else {
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34 | queue.push(run.bind(null, fn, resolve, ...args));
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35 | }
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36 | };
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37 |
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38 | const generator = (fn, ...args) => new Promise(resolve => enqueue(fn, resolve, ...args));
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39 | Object.defineProperties(generator, {
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40 | activeCount: {
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41 | get: () => activeCount
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42 | },
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43 | pendingCount: {
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44 | get: () => queue.length
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45 | },
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46 | clearQueue: {
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47 | value: () => {
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48 | queue.length = 0;
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49 | }
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50 | }
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51 | });
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52 |
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53 | return generator;
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54 | };
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55 |
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56 | module.exports = pLimit;
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57 | module.exports.default = pLimit;
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