| 'use strict'; |
| const pTry = require('p-try'); |
| |
| module.exports = concurrency => { |
| if (concurrency < 1) { |
| throw 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()(); |
| } |
| }; |
| |
| return fn => new Promise((resolve, reject) => { |
| const run = () => { |
| activeCount++; |
| |
| pTry(fn).then( |
| val => { |
| resolve(val); |
| next(); |
| }, |
| err => { |
| reject(err); |
| next(); |
| } |
| ); |
| }; |
| |
| if (activeCount < concurrency) { |
| run(); |
| } else { |
| queue.push(run); |
| } |
| }); |
| }; |