1
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'use strict';
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2
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const pTry = require('p-try');
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3
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4
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const pLimit = concurrency => {
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5
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if (!((Number.isInteger(concurrency) || concurrency === Infinity) && concurrency > 0)) {
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6
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return Promise.reject(new TypeError('Expected `concurrency` to be a number from 1 and up'));
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7
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}
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8
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9
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const queue = [];
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10
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let activeCount = 0;
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11
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12
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const next = () => {
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activeCount--;
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14
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15
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if (queue.length > 0) {
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queue.shift()();
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}
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};
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19
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const run = (fn, resolve, ...args) => {
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activeCount++;
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22
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23
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const result = pTry(fn, ...args);
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24
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resolve(result);
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26
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27
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result.then(next, next);
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28
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};
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29
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30
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const enqueue = (fn, resolve, ...args) => {
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31
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if (activeCount < concurrency) {
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32
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run(fn, resolve, ...args);
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33
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} else {
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queue.push(run.bind(null, fn, resolve, ...args));
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35
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}
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};
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37
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38
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const generator = (fn, ...args) => new Promise(resolve => enqueue(fn, resolve, ...args));
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39
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Object.defineProperties(generator, {
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40
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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.length
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45
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},
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46
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clearQueue: {
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47
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value: () => {
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48
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queue.length = 0;
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49
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}
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50
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}
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51
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});
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52
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53
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return generator;
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54
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};
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55
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56
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module.exports = pLimit;
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57
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module.exports.default = pLimit;
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