40 lines
597 B
JavaScript
40 lines
597 B
JavaScript
'use strict';
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module.exports = concurrency => {
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if (concurrency < 1) {
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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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const queue = [];
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let activeCount = 0;
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const next = () => {
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activeCount--;
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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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return fn => new Promise((resolve, reject) => {
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const run = () => {
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activeCount++;
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fn().then(
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val => {
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resolve(val);
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next();
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},
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err => {
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reject(err);
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next();
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}
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);
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};
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if (activeCount < concurrency) {
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run();
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} else {
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queue.push(run);
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}
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});
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};
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