| 'use strict'; |
| const pTry = require('p-try'); |
| |
| const pLimit = concurrency => { |
| if (!((Number.isInteger(concurrency) || concurrency === Infinity) && concurrency > 0)) { |
| return Promise.reject(new TypeError('Expected `concurrency` to be a number from 1 and up')); |
| } |
| |
| const queue = []; |
| let activeCount = 0; |
| |
| const next = () => { |
| activeCount--; |
| |
| if (queue.length > 0) { |
| queue.shift()(); |
| } |
| }; |
| |
| const run = (fn, resolve, ...args) => { |
| activeCount++; |
| |
| const result = pTry(fn, ...args); |
| |
| resolve(result); |
| |
| result.then(next, next); |
| }; |
| |
| const enqueue = (fn, resolve, ...args) => { |
| if (activeCount < concurrency) { |
| run(fn, resolve, ...args); |
| } else { |
| queue.push(run.bind(null, fn, resolve, ...args)); |
| } |
| }; |
| |
| const generator = (fn, ...args) => new Promise(resolve => enqueue(fn, resolve, ...args)); |
| Object.defineProperties(generator, { |
| activeCount: { |
| get: () => activeCount |
| }, |
| pendingCount: { |
| get: () => queue.length |
| } |
| }); |
| |
| return generator; |
| }; |
| |
| module.exports = pLimit; |
| module.exports.default = pLimit; |