1 | 'use strict';
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2 |
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3 | module.exports = parallelLimit;
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4 |
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5 |
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6 |
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7 |
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8 |
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9 | function parallelLimit(fns, limit, callback) {
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10 | let numInProgress = 0;
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11 | let numFinished = 0;
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12 | let error = null;
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13 |
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14 | if (limit <= 0) {
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15 | throw new Error('Limit must be positive');
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16 | }
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17 |
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18 | if (fns.length === 0) {
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19 | return callback(null, []);
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20 | }
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21 |
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22 | for (let i = 0; i < fns.length && i < limit; ++i) {
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23 | _start();
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24 | }
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25 |
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26 | function _start() {
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27 | fns[numFinished + numInProgress](_done(numFinished + numInProgress));
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28 | ++numInProgress;
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29 | }
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30 |
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31 | const results = [];
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32 |
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33 | function _done(index) {
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34 | return (err, res) => {
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35 | --numInProgress;
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36 | ++numFinished;
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37 |
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38 | if (error != null) {
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39 | return;
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40 | }
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41 | if (err != null) {
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42 | error = err;
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43 | return callback(error);
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44 | }
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45 |
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46 | results[index] = res;
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47 |
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48 | if (numFinished === fns.length) {
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49 | return callback(null, results);
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50 | } else if (numFinished + numInProgress < fns.length) {
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51 | _start();
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52 | }
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53 | };
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54 | }
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55 | }
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